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Objective: To determine the frequency of mismatch repair deficiency in colorectal carcinoma determined by immunohistochemistry. Study Design: Cross-sectional study. Place and Duration of Study: Department of Histopathology, Armed Forces Institute of Pathology, Rawalpindi, from Aug 2018 to Jan 2019. Methodology: A total of 101 patients of adenocarcinoma of colorectum who underwent surgical resections and their characteristic and clinical data were recorded. Immunohistochemical stains were performed using antibodies MLH1, MSH2, PMS2 and MSH6. Results were interpreted and mismatch repair deficiency status of all patients was determined. Patients with loss of expression for MLH1, MSH2, PMS2 and MSH6 antibodies were observed and noted. Results: In this study, out of 101 patients with CRC, 71 (70.3%) were male and 30 (29.7%) female. The mean age was (54 years ± 15.9). Amongst the 101 cases loss of immunohistochemical staining for MMR proteins was noted in 19 patients (18.8%). The combined loss of all four antibodies was seen in one case, loss of MLH1 and PMS2 in 7, MSH2 and MSH6 in 5 and MLH1 only in 6 patients. However, no mismatch repair deficiency was detected in remaining 82 cases. According to statistical analysis no significant association between mismatch repair deficiency and variables was found. Conclusion: The frequency of mismatch repair deficiency in colorectal carcinoma patients was found to be 18.8% in our population.

Neoadjuvant chemotherapy (NACT) before radical gastrectomy is preferred for locally advanced gastric cancer (GC). However, clinical practices demonstrate that a considerable proportion of GC patients do not benefit from NACT, largely due to the lack of biomarkers for patient selection and prognosis prediction. A recent study revealed that patients with microsatellite instability-high (MSI-H) may be resistant to NACT, however, most tumors in Chinese GC patients (~ 95%) are characterized by microsatellite stability (MSS). Here, we aimed to discover new molecular biomarkers for this larger population. We performed whole-exome sequencing on 46 clinical samples (pre- and post-treatment) from 30 stage II/III MSS GC patients whose response to NACT was rigorously defined. Serum tumor markers (TMs), including AFP, CEA, CA199, CA724 and CA242 were measured during the course. High tumor mutation burden (TMB-H) and 19q12 amplification (19q12 +) were positively associated with the NACT response. When TMB and 19q12 amplification were jointly analyzed, those with TMB-H or 19q12 + showed favorable response to NACT (p = 0.035). Further, TMB-H was negatively correlated with ypN stage, lymph node metastasis, and macrophage infiltration. Patients with TMB-H showed better disease-free survival (DFS) than those with TMB-L (P = 0.025, HR = 0.1331), and this was further validated using two larger GC datasets: TCGA-STAD (p = 0.004) and ICGC-CN (p = 0.045). The combination of TMB-H and 19q12 + can serve as an early indicator of response to NACT. Superior to traditional clinical indicators, TMB-H is a robust and easily accessible candidate biomarker associated with better DFS, and can be evaluated at the time of diagnosis.

BACKGROUND Rectal cancer in adolescents and young adults (age ≤39) is increasing. Early diagnosis is a challenge in this subset of patients. OBJECTIVE This study aims to analyze the presentation pattern and outcomes of sporadic rectal cancer in adolescents and young adults. DESIGN This is a retrospective study. SETTING This study was conducted at 3 European tertiary centers. PATIENTS Data on adolescents and young adults operated on for sporadic rectal cancer (January 2008 through October 2019) were analyzed. To compare outcomes, adolescents and young adults were matched to a group of patients aged ≥40 operated on during the same period. MAIN OUTCOME MEASURES The primary outcomes measured were clinical presentation and long-term outcomes. RESULTS Sporadic rectal cancers occurred in 101 adolescents and young adults (2.4%; mean age, 33.5; range, 18-39); 51.5% were male, and a smoking habit was reported by 17.8% of patients. The rate of a family history for colorectal cancer was 25.7%, and of these patients, 24.7% were obese. Diagnosis based on symptoms was reported in 92.1% patients, and the mean time from first symptoms to diagnosis was 13.7 months. The most common symptom at diagnosis was rectal bleeding (68.8%), and 12% and 34% of the adolescents and young adults presented with locally advanced or metastatic disease at diagnosis. Consequently, 68.3% and 62.4% adolescents and young adults received neoadjuvant and adjuvant treatments. The rate of complete pathological response was 24.1%; whereas 38.6% patients had stage IV disease, and 93.1% were microsatellite stable. At a mean follow-up of 5 years, no difference in cancer-specific survival, but a lower disease-free survival was reported in adolescents and young adults (p < 0.0001) vs the matched group. Adolescents and young adults with stages I to II disease had shorter cancer-specific survival and disease-free survival (p = 0.006; p < 0.0001); with stage III disease, they had a shorter disease-free survival (p = 0.01). LIMITATIONS This study was limited by its observational, retrospective design. CONCLUSIONS The significantly delayed diagnosis in adolescents and young adults may have contributed to the advanced disease at presentation and lower disease-free survival, even at earlier stages, suggesting a higher metastatic potential than in older patients. See Video Abstract at http://links.lww.com/DCR/B537. CNCER DE RECTO EN PACIENTES ADOLESCENTES Y ADULTOS JVENES CUADRO DE PRESENTACIN CLNICA Y COMPARACIN DE DESENLACES POR CASOS EMPAREJADOS ANTECEDENTES:El cancer de recto en adolescentes y adultos jovenes (edad ≤ 39) esta aumentando. El diagnostico temprano es un desafio en este subgrupo de pacientes.OBJETIVO:Analizar el cuadro de presentacion y los desenlaces en adolescentes y adultos jovenes con cancer de recto esporadico.DISENO:Estudio retrospectivo.AMBITO:Tres centros europeos de tercer nivel.PACIENTES:Se analizaron los datos de adolescentes y adultos jovenes operados de cancer de recto esporadico (enero de 2008 - octubre de 2019). Para comparar los desenlaces se emparejo a adolescentes y adultos jovenes con un grupo de pacientes mayores de 40 anos operados en el mismo periodo de tiempo.PRINCIPALES VARIABLES ANALIZADAS:Cuadro clinico, resultados a largo plazo.RESULTADOS:Los canceres de recto esporadicos en adolescentes y adultos jovenes fueron 101 (2,4%, edad media: 33,5, rango 18-39). El 51,5% eran hombres, el 17,8% de los pacientes fumaba. El 25,7% tentia antecedentes familiares de cancer colorrectal. El 24,7% eran obesos. El diagnostico con base en los sintomas se informo en el 92,1% de los pacientes, el tiempo promedio desde los primeros sintomas hasta el diagnostico fue de 13,7 meses. El sintoma mas comun en el momento del diagnostico fue el sangrado rectal (68,8%). 12% y 34% de adolescentes y adultos jovenes presentaron enfermedad localmente avanzada o metastasica en el momento del diagnostico. Por lo tanto, el 68,3% y el 62,4% de adolescentes y adultos jovenes recibieron neoadyuvancia y adyuvancia. La tasa de respuesta patologica completa fue del 24,1%; mientras que el 38,6% estaban en estadio IV. El 93,1% eran microsatelite estable. Con una media de seguimiento de 5 anos, no se observaron diferencias en la sobrevida especifica del cancer, pero se informo una menor sobrevida libre de enfermedad en adolescentes y adultos jovenes (p

Colorectal cancer represents the second leading cause of cancer-related death worldwide. The therapeutic field of immuno-oncology has rapidly gained momentum, with strikingly promising results observed in clinical practice. Increasing emphasis has been placed on the role of the immune response in tumorigenesis, therapy and predicting prognosis. Enhanced understanding of the dynamic and complex tumour-immune microenvironment has enabled the development of molecularly directed, individualised treatment. Analysis of intra-tumoural lymphocyte infiltration and the dichotomisation of colorectal cancer into microsatellite stable and unstable disease has important therapeutic and prognostic implications, with potential to capitalise further on this data. This review discusses the latest evidence surrounding the tumour biology and immune landscape of colorectal cancer, novel immunotherapies and the interaction of the immune system with each apex of the tripartite of cancer management (oncotherapeutics, radiotherapy and surgery). By utilising the synergy of chemotherapeutic agents and immunotherapies, and identifying prognostic and predictive immunological biomarkers, we may enter an era of unprecedented disease control, survivorship and cure rates.

CASE SUMMARY A 65-year-old man presents with new liver lesions on surveillance imaging 2 years after a right hemicolectomy for cecal adenocarcinoma. The primary tumor was pT3N1, microsatellite stable, and KRAS wild type. He completed adjuvant FOLFOX. His CEA level is 22 ng/mL. There are two 1.5-cm lesions in the right lobe near the dome of the liver and a 4-cm lesion in segment II. No luminal recurrence is detected endoscopically, and there is no evidence of peritoneal or pulmonary disease.

Aya Alsayed,1 Salem E Salem,1 Mostafa M El Serafi,1 Mona S Abdellateif,2 Abdel-Rahman N Zekri,3 Marwa Mohanad,4 Abeer A Bahnassy5 1Department of Medical Oncology, National Cancer Institute, Cairo University, Cairo, 11976, Egypt; 2Medical Biochemistry and Molecular Biology, Cancer Biology Department, National Cancer Institute, Cairo University, Cairo, 11976, Egypt; 3Molecular Virology and Immunology Unit, Cancer Biology Department, National Cancer Institute, Cairo University, Cairo, 11976, Egypt; 4Biochemistry Department, College of Pharmaceutical Sciences and Drug Manufacturing, Misr University for Science and Technology, Giza, 12945, Egypt; 5Pathology Department, National Cancer Institute, Cairo University, Cairo, 11976, EgyptCorrespondence: Abeer A BahnassyPathology Department, National Cancer Institute, Cairo University, Cairo, EgyptFax +20 223644720Email chaya2000@hotmail.ComBackground: Microsatellite instability (MSI) and circulating tumor cells (CTCs) play important roles in the diagnosis, prognosis and management of colorectal cancer (CRC) patients.Methods: CTCs and MSI were assessed in the blood and representative tumor tissues of 100 CRC patients by flow cytometry (FCM) and PCR amplification. The data were correlated to relevant clinicopathological features of the patients, progression-free survival (PFS) and overall survival (OS) rates.Results: MSI-high was detected in 44 (44.0%) patients, MSI-low in 37 (37%), and microsatellite stable (MSS) in 19 (19.0%) patients (P=0.007). The baseline CTCs count (< 4 cells/7mL blood) was reported in 39% of the patients, and CTCs ≥ 4 cells/7mL blood in 61% of the patients (P=0.028). Improved PFS and OS rates were associated significantly with MSI-high (P< 0.001), decreased CTC levels during the course of treatment (P< 0.001) and post-treatment CTCs (P=0.008). There was no significant association between MSI-high and PFS or OS in early-stage patients (P=0.187 and P=0.187; respectively); however, it was associated significantly with better PFS and OS in late-stage patients (P< 0.001). Multivariate analysis showed that only a change in serial CTC levels is considered an independent prognostic factor for OS (P< 0.012). Post-treatment CTCs level, serial CTCs level changes during the course of treatment, lymph nodes and distant metastasis were independent prognostic factors for PFS (P< 0.001, P= 0.047, P=0.001 and P< 0.001; respectively).Conclusion: MSI and CTCs could be used as accurate, reliable and sensitive diagnostic and prognostic biomarkers for CRC patients’ survival rates and outcomes.Keywords: circulating tumor cells, microsatellite instability, colorectal cancer, response to treatment, survival rates

Immune checkpoint inhibitors changed treatment paradigms across several malignancies. With the exception of tumors with microsatellite instability (MSI-H), gastrointestinal cancers have been largely resistant to these agents. Herein, we review the data supporting the use of immunotherapy for patients with (MSI-H) colorectal tumors. We discuss ongoing research and answered questions regarding resistance and sequence of use of these agents for this disease. We discuss ongoing research efforts to augment activity of these agents in microsatellite stable colorectal cancer. We also provide an overview of the data and ongoing studies immune checkpoint inhibitors in the treatment of anal cancer.

Supplemental Digital Content is available in the text., Grade 3 (G3, poorly differentiated) is an important treatment-decision factor in stage II colon cancer, but no unified diagnostic criteria are established. According to previous studies, an intratumoural poorly differentiated area with no glandular formation (POR) that fills the microscopic field of a ×40 objective lens was an essential factor that defined G3. We aimed to prospectively validate this in a randomized controlled study of adjuvant chemotherapy (SACURA trial). We enrolled 991 patients with stage II colon cancer. POR was graded according to the ×40 objective lens rule and the intensity of poorly differentiated clusters (GradePOR), and its prognostic power was compared with that of the conventional tumor grade on the basis of predominant histology rule (Gradeconv). According to GradePOR, 313, 526, and 152 tumors were classified as G1POR, G2POR, and G3POR, respectively, and the 5-year relapse-free survival (RFS) rates were 91.1%, 82.9%, and 74.7%, respectively (P

BackgroundFor a majority of patients with metastatic colorectal cancer (mCRC) with MS stable (MSS) or mismatch repair proficient (pMMR), the role of immunotherapy is undetermined. This study investigated the efficacy and safety of camrelizumab when added to XELOX chemotherapy plus bevacizumab or regorafenib as first-line therapy for mCRC.Materials and MethodsMedical records of mCRC patients who received camrelizumab and XELOX plus bevacizumab or regorafenib at the First Hospital of Quanzhou Affiliated to Fujian Medical University between June 1, 2019, and April 30, 2021, were retrospectively collected. The objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and side effects of the drug were recorded and reviewed.ResultsTwenty-five eligible patients received combination therapy, including bevacizumab in 19 patients and regorafenib in 6. Twenty-one patients had pMMR/MSS and one MSI-H. Of the 25 patients who could be evaluated for efficacy, 18 (72%) achieved PR, 6 (24%) achieved SD, and 1 (4%) achieved PD. The ORR and DCR were 72% (18/25) and 96% (24/25), respectively. The median progression-free survival (PFS) was 11.2 months (95% CI 8.9–13.9), and OS had not yet been reached. The combination regimen of regorafenib in six (24%) patients was unassociated with treatment outcomes. Most AEs were either grade 1 or 2, and treatment-related grade 3 toxicities were observed in 8/25 (32%) patients.ConclusionCamrelizumab combined with XELOX plus bevacizumab or regorafenib was feasible, producing high rates of responses as first-line therapy in unselected Chinese patients with MSS mCRC. The toxicities were generally tolerable and manageable. Prospective randomized trials with large sample sizes are needed to evaluate these findings.

BackgroundMicrosatellite stability (MSS) or mismatch repair proficient (pMMR) metastatic colorectal cancer (mCRC) is resistant to immune checkpoint inhibitors. Studies have shown that antiangiogenic drugs combined with programmed death receptor-1 (PD-1) inhibitors can improve immunosuppression. The purpose of this study was to compare the efficacy of fruquintinib combined with PD-1 inhibitor (FP) and regorafenib combined with PD-1 inhibitor (RP) in the treatment of advanced mCRC with MSS or pMMR.Materials and MethodsWe retrospectively collected advanced MSS or pMMR mCRC patient data from The Second Affiliated Hospital of Nanchang, China, from June 2019 to March 2021. Then, we analyzed and compared the efficacy and safety of FP and RP.ResultsA total of 51 patients who met the criteria were divided into FP (n = 28) and RP groups (n = 23). The overall response rate of the FP and RP groups was 7.1% and 8.7% and the disease control rate was 89.3% and 56.5%, respectively. The median progression-free survival (PFS) time was higher in the FP group than in the RP group (6.4 vs. 3.9 months, respectively; P = 0.0209). Patients with no liver metastasis, KRAS wild type, and left colon tumor may benefit from FP. Eight patients (15.7%) had grade 3 toxicity related to treatment. Cox multivariate regression analysis showed that the treatment method was an independent risk factor for median PFS time.ConclusionOur study indicates that FP could improve PFS time of patients with advanced mCRC compared with RP.

Purpose:To analytically and clinically validate microsatellite instability (MSI) detection using cell-free DNA (cfDNA) sequencing.Experimental Design:Pan-cancer MSI detection using Guardant360 was analytically validated according to established guidelines and clinically validated using 1,145 cfDNA samples for which tissue MSI status based on standard-of-care tissue testing was available. The landscape of cfDNA-based MSI across solid tumor types was investigated in a cohort of 28,459 clinical plasma samples. Clinical outcomes for 16 patients with cfDNA MSI-H gastric cancer treated with immunotherapy were evaluated.Results:cfDNA MSI evaluation was shown to have high specificity, precision, and sensitivity, with a limit of detection of 0.1% tumor content. In evaluable patients, cfDNA testing accurately detected 87% (71/82) of tissue MSI-H and 99.5% of tissue microsatellite stable (863/867) for an overall accuracy of 98.4% (934/949) and a positive predictive value of 95% (71/75). Concordance of cfDNA MSI with tissue PCR and next-generation sequencing was significantly higher than IHC. Prevalence of cfDNA MSI for major cancer types was consistent with those reported for tissue. Finally, robust clinical activity of immunotherapy treatment was seen in patients with advanced gastric cancer positive for MSI by cfDNA, with 63% (10/16) of patients achieving complete or partial remission with sustained clinical benefit.Conclusions:cfDNA-based MSI detection using Guardant360 is highly concordant with tissue-based testing, enabling highly accurate detection of MSI status concurrent with comprehensive genomic profiling and expanding access to immunotherapy for patients with advanced cancer for whom current testing practices are inadequate.See related commentary by Wang and Ajani, p. 6887

RATIONALE: Loss of DNA mismatch repair function has long been known in various malignancies, particularly colorectal cancer. However, microsatellite instability (MSI) testing was rarely requested in Thailand. Recently, the US Food and Drug Administration (FDA) has approved pembrolizumab, an antibody to PD-1 receptor, as an alternative treatment for high MSI (MSI-H) and/or MMR (mismatch repair)-deficient solid tumors. We report our recent observation on MSI testing in Thailand. MATERIALS AND METHODS: Data was collected from Chulalongkorn GenePRO Center, Faculty of Medicine, Chulalongkorn University, during July 2013 and July 2017. MSI testing was performed, using 5 microsatellite markers (BAT-25, BAT-26, D2S123, D5S346 and D17S250). The number, source, and result of samples underwent MSI assay were analyzed. RESULTS: Requests for MSI testing have increased significantly in recent years. The shift started in 2015 when the MMR status was found to predict clinical benefit with the immune checkpoint blockade. There were 118 (75.2%) colorectal, 11 (7%) gastric, and 28 (17.8%) other cancers tested. MSI-H, MSI-L, and microsatellite stable (MSS) tumors were detected in 18 (11.5%), 11 (7%), and 128 (81.5%) patients, respectively. Of the 18 MSI-H cancers; 13 (72.2%), 4 (22.2%), and 1 (5.6%) were colorectal, gastric, and gynecologic malignancy, respectively. BAT25 and BAT26 markers were unstable in all MSI-H tumors. CONCLUSION: We have experienced increasing demand for MSI testing in Thai patients at Chulalongkorn GenePRO Center. Colorectal cancers were most frequently tested, and accounted for the highest percentage among the MSI-H cancers. Keywords: microsatellite instability, mismatch repair, immunotherapy, cancers Address Correspondence to author: Chinachote Teerapakpinyo, PhD Chulalongkorn GenePRO Center,Faculty of Medicine, Chulalongkorn University 1873, Rama 4 Rd., Pathumwan, Bangkok 10330, Thailand. email: Chinachote.T@chula.ac.th Received: May 28, 2018 Revision received: June 1, 2018 Accepted after revision: July 17, 2018 BKK Med J 2018;14(2): 1-5. DOI: 10.31524/bkkmedj.2018.09.001

Immune checkpoint blockade has emerged as an effective therapeutic strategy for patients with advanced cancer. Identification of biomarkers associated with treatment efficacy will help to select patients more likely to respond to this approach. High levels of microsatellite instability, tumor expression of PD-L1, high tumor mutation burden, and increased tumor-infiltrating lymphocytes have all been associated with response to checkpoint inhibitor blockade. The purpose of this study was to determine if a subset of microsatellite-stable endometrioid endometrial carcinomas have higher immune cell infiltrates and/or expression of PD-L1. PD-L1 expression and characterization of immune cell infiltrates were analyzed in 132 microsatellite stable, FIGO grade 2 endometrioid carcinomas. PD-L1 was positive in 48% (63/132) of the tumors. Tumor cell expression of PD-L1 was significantly associated with lymphatic/vascular invasion and deep myometrial invasion. PD-L1 expression was especially prominent at the invasive front and in foci of tumor-associated squamous metaplasia. Twenty-one cases (16% of the total) with more diffuse and/or especially strong PD-L1 expression were identified. This PD-L1 high subset was associated with significantly higher numbers of tumor-associated CD3+ and CD8+ lymphocytes. Only one tumor in the PD-L1 high subset harbored a POLE mutation. PTEN immunohistochemical loss, a common event in endometrioid-type endometrial carcinoma and associated with local immune suppression in melanoma, was not associated with PD-L1 expression or lymphocyte/macrophage infiltration of the tumor. These results suggest that a subset of microsatellite-stable endometrial cancers has higher expression of PD-L1 and increased tumor-associated CD3+ and CD8+ lymphocytes, characteristics more commonly associated with endometrial cancers with high levels of microsatellite instability. These results suggest that screening strategies to select only microsatellite instability-high advanced endometrial cancers for checkpoint inhibitor therapy might exclude patients who could potentially benefit from this therapeutic approach.

AimsAnalysis of microsatellite instability (MSI) is strongly recommended in endometrial cancer (EC) and colorectal cancer to screen for Lynch syndrome, to predict prognosis and to determine optimal treatment and follow-up. In a large monoinstitutional series of ECs, we evaluated the reliability and accuracy of Idylla assay, a rapid, fully automated system to detect MSI, and we compared its performance with two routine reference methods.MethodsWe evaluated MSI status in 174 formalin-fixed, paraffin-embedded EC tissue samples using immunohistochemistry (IHC) for mismatch repair (MMR) proteins and Idylla assay. Samples with discordant or equivocal results were analysed with a third technique, the Promega MSI kit.ResultsIdylla MSI assay and IHC were highly concordant (overall agreement: 154/170=90.59%, 95% CI 85.26% to 94.12%). However, in four samples, MMR-IHC staining was equivocal; moreover, 16 cases showed discordant results, that is, MMR deficient using IHC and microsatellite stable using Idylla. These 20 samples were reanalysed using the MSI-Promega kit, which showed the same results of Idylla assay in 18/20 cases (overall agreement: 90%, 95% CI 69.90% to 97.21%).ConclusionsOur results suggest that IHC is an efficient method to determine MMR status in ECs. However, the Idylla MSI assay is a rapid and reliable tool to define MSI status, and it could represent a valuable alternative to conventional MSI-PCR methods.

Objective To determine the cost-effectiveness of lenvatinib plus pembrolizumab (LP) in patients with microsatellite stable (MSS), recurrent, pretreated endometrial cancer (EC). Methods A decision analysis model was created to evaluate the cost-effectiveness of LP relative to doxorubicin, pegylated liposomal doxorubicin (PLD), and bevacizumab in patients with recurrent pretreated MSS EC. Published data was used to estimate quality adjusted life years (QALYs) and drug cost estimates were obtained using average wholesale prices. A health state utility (HSU) penalty of −0.10 was applied to the LP group to account for treatment toxicity. Incremental cost-effectiveness ratios (ICERs) were calculated to determine cost/QALY. The willingness to pay threshold (WTP) was set at $100,000 per QALY saved. Sensitivity analyses were performed on cost, effectiveness, and HSU penalty for LP. Results Costs of treatment with doxorubicin, PLD, and bevacizumab are $23.7 million (M), $56.9 M, and $250.8 M respectively. Cost of treatment with LP is $1.8 billion. Relative to doxorubicin, the ICERs for PLD, bevacizumab, and LP are $56,808, $345,824, and $1.6 M respectively. A sensitivity analysis varying the cost of LP shows that if the combined drug cost decreases from over $58,000 to less than $11,000 per cycle, this strategy would be cost-effective. Eliminating the HSU penalty for LP decreased the ICER $1.0 M while increasing the penalty to −0.20 increased the ICER to $3.7 M. Conclusions LP is not cost-effective in patients with recurrent pretreated, MSS EC. A dramatic reduction in cost of LP is required for this novel strategy to be cost-effective.

BackgroundTumor sidedness as a prognostic factor in advanced stage colon cancer (CC) is well established. The impact of tumor sidedness on the clinical outcomes of stage II and III CC has not been well studied.MethodsThe National Cancer Database (NCDB) was utilized to identify patients with pathological stage II and III primary adenocarcinoma of the colon from 2010 to 2015 using ICD-O-3 morphology and topography codes: 8140-47, 8210-11, 8220-21, 8260-63, 8480-81, 8490 and C18.0, 18.2,18.3, 18.5,18.6, 18.7. Univariate (UVA) and multivariable (MVA) survival analyses and Kaplan–Meier Curves with Log-rank test were utilized to compare overall survival (OS) based on tumor location and treatment received.ResultsA total of 35,071 patients with stage II (n = 17,629) and III (n = 17,442) CC were identified. 51.3% female; 81.5% Caucasian; median age 66 (range, 18–90). Majority of stage II and III tumors were right sided, 61.2% (n = 10,794) and 56.0% (n = 9,763). Microsatellite instability high (MSI-H) was more common in stage II compared to III, 23.3% (n = 4,115) vs 18.2% (n = 3,171) (p < 0.0001). In stage II MSI-H CC right was more common than left, 78.3% (n = 3223) vs 21.7% (n = 892). There was no significant difference in survival between stage II MSI-H left vs right (5-year OS 76.2 vs 74.7%, p = 0.1578). Stage II MSS CC right was more common than left, 56.0% (n = 7571) vs 44.0% (n = 5943), and survival was better in the left vs right (5-year OS 73.2 vs 70.8%, p = 0.0029). Stage III MSI-H CC was more common in the right than in the left, 75.6% (n = 2,397) vs 24.4% (n = 774) and survival was better in the left (5-year OS 62.5 vs 56.5%, p = 0.0026). Stage III MSS CC was more common in the right than in the left, 51.6% (n = 7,366) vs 48.4% (n = 6,905), and survival was better in the left vs right (5-year OS 67.0 vs 54.4%, p < 0.001).ConclusionSurvival was better in left sided tumors compared to right in stage II MSS, stage III MSS, and stage III MSI-H CC.

Background: In patients with synchronous colorectal cancer (SCRC), understanding the underlying molecular behavior of such cases is mandatory for designing individualized therapy. The aim of this paper is to highlight the importance of transdisciplinary evaluation of the pre- and post-operative assessment of patients with SCRCs, from imaging to molecular investigations. Methods: Six patients with SCRCs presented with two carcinomas each. In addition to the microsatellite status (MSS), the epithelial mesenchymal transition was checked in each tumor using the biomarkers β-catenin and E-cadherin, same as KRAS and BRAF mutations. Results: In two of the patients, the second tumor was missed at endoscopy, but diagnosed by a subsequent computed-tomography-scan (CT-scan). From the six patients, a total of 11 adenocarcinomas (ADKs) and one squamous cell carcinoma (SCC) were analyzed. All the examined carcinomas were BRAF-wildtype microsatellite stable tumors with an epithelial histological subtype. In two of the six cases, KRAS gene status showed discordance between the two synchronous tumors, with mutations in the index tumors and wildtype status in the companion ones. Conclusions: Preoperative CT-scans can be useful for detection of synchronous tumors which may be missed by colonoscopy. Where synchronous tumors are identified, therapy should be based on the molecular profile of the indexed tumors.

Immune-checkpoint inhibitors (ICIs) play a key role in the treatment of advanced stage colorectal cancer (CRC) patients featuring a deficient DNA mismatch repair (dMMR) system or a high microsatellite instability (MSI-H) profile. However, beyond the established role in CRC patients, ICIs have highly proven efficacy in other solid tumors featuring MSI-H/dMMR status represented by endometrial, gastric, ovarian, prostatic, and pancreatic carcinomas (EC, GC, OC, PrC, and PaC). Our aim was to compare the concordance rates among the Idylla™ MSI test, TapeStation 4200, and immunohistochemical (IHC) analysis in assessing MSI-H/dMMR status in EC, GC, OC, PrC, and PaC patients. The Sanger sequencing-based Titano MSI test was used in discordant cases. One hundred and eighty-five cases (n = 40 PrC, n = 39 GC, n = 38 OC, n = 35 PaC, and n = 33 EC) were retrospectively selected. MMR protein expression was evaluated by IHC. After DNA quality and quantity evaluations, the IdyllaTM and TapeStation 4200 platforms were adopted for the evaluation of MSI status. Remarkably, compared to IHC, the Idylla™ platform achieved a global concordance rate of 94.5% (154/163) for the microsatellite stable (MSS)/proficient MMR (pMMR) cases and 77.3% (17/22) for the MSI-H/dMMR cases. Similarly, a global concordance rate of 91.4% (149/163) and 68.2% (15/22) for MSS/pMMR and MSI-H/dMMR cases was also identified between IHC and the TapeStation 4200 microfluidic system. In addition, a global concordance of 93.1% (148/159) and 69.2% (18/26) for MSS/pMMR and MSI-H/dMMR cases was observed between the Idylla™ and TapeStation 4200 platforms. Discordant cases were analyzed using the Titano MSI kit. Overall, our data pinpointed a central role for molecular techniques in the diagnostic evaluation of dMMR/MSI-H status not only in CRC patients but also in other types of solid tumors.

Background Microsatellite stable (MSS) or mismatch repair proficient (pMMR) metastatic colorectal cancer (mCRC) is resistant to immune checkpoint inhibitors. However, a recent Japanese trial showed that regorafenib plus nivolumab had encouraging anti-cancer activity in MSS or pMMR mCRCs. Materials and methods We retrospectively reviewed the efficacy and safety data of combination therapy with regorafenib plus anti-PD-1 antibody in patients with refractory MSS or pMMR mCRC in the medical centers of Shandong Province in China. Results Twenty-three patients with MSS or pMMR mCRC received regorafenib plus anti-PD-1 antibody. Eighteen (78.3%) patients experienced stable disease as best response, five (21.7%) patients had progressive disease, and no partial response was observed. The disease control rate (DCR) was 78.3% (18/23), and the median progression-free survival (PFS) was 3.1 months (95% CI, 2.32-3.89). Four of five (80.0%) patients with progressive disease had baseline liver metastasis, while nine of 18 (50.0%) patients with stable disease displayed no liver metastasis. One patient receiving radiofrequency ablation treatment for liver and abdominal wall metastases prior to combination treatment experienced a remarkably prolonged PFS of 9.2 months with SD. Neither liver metastasis status nor previous exposure to regorafenib was associated with treatment outcome. Treatment-related grade 3 toxicities were observed in 5/23 (21.7%) patients. Conclusion No objective response was observed with the combination of regorafenib plus anti-PD-1 antibody, suggesting its little clinical activity in unselected Chinese patients with pMMR/MSS mCRC. Meanwhile, it exhibited some potential benefit in this cohort in terms of DCR and PFS. Adverse events were generally tolerable and manageable. Prospective studies with large sample sizes are needed to verify the findings. This combination strategy plus local ablative therapy might be worthy of further exploration.

Purpose: Colorectal cancer (CRC) incidence is increasing in adults younger than 50 years. This study evaluated clinicopathological characteristics and outcome of adolescent and young adult (AYA)-on...

Most colorectal cancers are microsatellite-stable with no response to anti-PD-1 therapy, necessitating the development of new immunomodulatory treatment strategies. Coinhibition of anti-PD-1 and STAT3 can elicit an effective antitumor response in a small subset of patients with microsatellite-stable colorectal cancer, and biomarkers predictive of response are under investigation. See related article by Kawazoe et al., p. 5887

In an integrated genomic and clinical analysis, we evaluate the effects of Wnt and DNA damage response pathway alterations on metastatic colorectal cancer.

Summary Purpose This study aims to analyze sensitivities and polymorphisms of the Bethesda panel markers (BAT25, BAT26, D2S123, D5S346 and D17S250) for microsatellite instability testing in Chinese from Jiangsu Province and their clinical implication. Methods MSI, sensitivity and polymorphism analysis in 541 colorectal cancer (CRC) patients were detected by fragment analysis. Results Five hundred and twenty-five tissue samples and 541 blood samples of the 541 sample pairs were successfully amplified. Thirty-four (6.5%) cases were MSI-high (MSI-H) while 33 (6.3%) and 458 (87.2%) were MSI-low (MSI-L) and microsatellite stable (MSS), respectively. BAT26 (85.3%) exhibited the highest instability followed by BAT25 (82.4%), D2S123 (67.6%), D17S250 (64.7%) and D5S346 (50.0%) in MSI-H cases. The median ages of CRC patients with LS, MSI-H, MSI-L and MSS status were 38–43, 48, 60 and 63, respectively. 75.0%, 44.1%, 12.1% and 7.0% CRC cases were mucinous carcinomas in LS, MSI-H, MSI-L and MSS group, respectively. For D2S123, D17S250 and D5S346, heterozygosity was 80.8%, 74.1% and 57.7% and sizes of polymorphic variation range (PVR) were 207 bp to 234 bp, 140 bp to 169 bp and 109 bp to 137 bp, respectively. For D2S123 and D5S346, there was a bimodal distribution distinguishing the D17S250 from an indistinct trimodal or tetramodal distribution. Conclusion MSI-H cases showed earlier onset and higher proportion of mucinous carcinomas. Mononucleotide BAT26 and BAT25 exhibited higher sensitivity than dinucleotides D2S123, D17S250 and D5S346 in the Chinese population. The dinucleotide markers were highly polymorphic with high percent of heterozygosity, great variation in repeat length and non-normal distribution in Chinese population from Jiangsu Province.

Approximately 20% early-stage (I/II) colorectal cancer (CRC) patients develop metastases despite curative surgery. We aim to develop a formalin-fixed and paraffin-embedded (FFPE)-based predictor of metastases in early-stage, clinically-defined low risk, microsatellite-stable (MSS) CRC patients. We considered genome-wide mRNA and miRNA expression and mutation status of 20 genes assayed in 150 fresh-frozen tumours with known metastasis status. We selected 193 genes for further analysis using NanoString nCounter arrays on corresponding FFPE tumours. Neither mutation status nor miRNA expression improved the estimated prediction. The final predictor, ColoMet19, based on the top 19 genes' mRNA levels trained by Random Forest machine-learning strategy, had an estimated positive-predictive-value (PPV) of 0.66. We tested ColoMet19 on an independent test-set of 131 tumours and obtained a population-adjusted PPV of 0.67 indicating that early-stage CRC patients who tested positive have a 67% risk of developing metastases, substantially higher than the metastasis risk of 40% for node-positive (Stage III) patients who are generally treated with chemotherapy. Predicted-positive patients also had poorer metastasis-free survival (hazard ratios [HR] = 1.92, design-set; HR = 2.05, test-set). Thus, early-stage CRC patients who test positive may be considered for adjuvant therapy after surgery.

ZusammenfassungEine Meningeosis neoplastica ist eine seltene, aber schwerwiegende Komplikation solider Neopasien (Melanome, Mamma-, Bronchial- oder gastrointestinale Karzinome). Die klinische Manifestation der Meningeosis ist äußerst variabel. Sie äußert sich z. B. in radikulären Schmerzen mit oder ohne neurologischen Ausfällen sowie in Kopfschmerzen bis hin zu halluzinatorischen Reizsymptomen. Ob dieses unspezifischen Symptomcharakters wird eine Meningeosis neoplastica häufig zu spät diagnostiziert und behandelt. Wir berichten hier über den seltenen Fall einer Patientin mit einem lymphatisch und ossär metastasierten BRAF-mutierten Mikrosatelliten-stabilen Kolonkarzinom, welche einen Monat nach der Diagnosestellung neurologische Reiz- und Ausfallsymptome entwickelte. Durch den zytologischen Nachweis von Tumorzellen im Liquorsediment konnte – trotz einer unauffälligen MRT-Diagnostik – eine Meningeosis carcinomatosa gesichert werden. Unter einer intrathekalen Therapie mit Methotrexat, kombiniert mit einer intensiven systemischen Antikörperchemotherapie, wurde passager eine gute partielle Remission der Tumorerkrankung erreicht. Ca. 8 Monate nach Therapiebeginn entwickelte jedoch die Patientin eine progrediente Meningeosis und verstarb wenige Wochen später.

The prognostic value of CpG island methylator phenotype (CIMP) in colorectal cancer remains unsettled. We aimed to assess the prognostic value of this phenotype analyzing a total of 1126 tumor samples obtained from two Norwegian consecutive colorectal cancer series. CIMP status was determined by analyzing the 5-markers CAGNA1G, IGF2, NEUROG1, RUNX3 and SOCS1 by quantitative methylation specific PCR (qMSP). The effect of CIMP on time to recurrence (TTR) and overall survival (OS) were determined by uni- and multivariate analyses. Subgroup analyses were conducted according to MSI and BRAF mutation status, disease stage, and also age at time of diagnosis (

Background: Grade 3 (G3, poorly differentiated) is an important treatment-decision factor in stage II colon cancer, but no unified diagnostic criteria are established. According to previous studies, an intra-tumoural poorly differentiated area with no glandular formation (POR) that fills the microscopic field of a 40× objective lens was an essential factor that defined G3. We aimed to prospectively validate this in a randomised controlled study of adjuvant chemotherapy (SACURA trial). Methods: Between 2006 and 2010, we enrolled 991 patients with stage II colon cancer from 123 institutions. POR was quantitatively graded according to the 40× objective lens rule and the intensity of poorly differentiated clusters (GradePOR). The prognostic power of GradePOR was compared with that of the conventional tumour grade based on the predominant histology rule (Gradeconv). Findings: According to GradePOR, 313, 526 and 152 tumours were classified as G1POR, G2POR and G3POR, respectively, and the 5-year relapse-free survival (RFS) rates were 91·1%, 82·9%, and 74·7%, respectively (P < 0·0001). When G3POR and G3conv were alternatively added to the standard prognostic model consisting of eight conventional factors, only G3POR was a significant factor for RFS (P = 0·040, Wald test). The adverse impact of G3POR on RFS was greater in the microsatellite stable (MSS)/microsatellite instability (MSI)-low subset (hazard ratio [HR], 2·61; 95% confidence interval [CI], 1·81–3·77) compared with that in the full analysis set (HR, 1·93; 95% CI, 1·34–2·77). In the MSS/MSI-low subset, the 5-year RFS rate of patients with G3POR tumours in the adjuvant chemotherapy group achieved greater improvement (9·1%) than the surgery-alone group (HR, 0·65; 95% CI, 0·34–1·24). Interpretation: The validated prognostic value of the least differentiation policy with the 40× objective lens rule may be highlighted as the diagnostic criterion for G3 in the adjuvant treatment setting for stage II colon cancer, particularly for MSS/MSI-low tumours. Trial Registration: ClinicalTrials.gov NCT00392899 Funding: This study was supported by the Foundation for Biomedical Research and Innovation at Kobe, Translational Research Center for Medical Innovation (TRI), under the funding contract with Taiho Pharmaceutical Co. Ltd., Japan. Declaration of Interests: MI has received consulting fees from Taiho Pharmaceutical Co. Ltd., BristolMyers Squibb and Merck Serono Co. Ltd; honoraria from Taiho, Chugai Pharmaceutical Co. Ltd., and Yakult Honsha Co. Ltd. HM has received consulting fees from Otsuka Pharmaceutical Factory, Inc. and Sysmex Co.; honoraria from Taiho, Chugai, Yakult Honsha, Daiichi Sankyo Co. Ltd., Astellas Pharma Inc. NT has received research funding from Taiho, Chugai, and Yakult Honsha; honoraria from Taiho, Chugai, Takeda Pharmaceutical Co. Ltd., Merck Serono. YS has received honoraria from Taiho, Chugai and Yakult Honsha. KT has received honoraria from Taiho and Takeda. KK has received consulting fees from Taiho and Chugai; honoraria from Taiho, Chugai, Bristol-Myers, Merck Serono and Otsuka. MW has received research funding from Taiho, Chugai, Yakult Honsha, Johnson and Johnson K. K. and Covidien Japan Co. Ltd. YK has received honoraria from Taiho and Chugai. H. Ueno has received honoraria from Taiho, Chugai, Yakult Honsha, BristolMyers and Daiichi Sankyo. TI has received research funding from Taiho; honoraria from Chugai. H. Uetake has received consulting fees, research funding, and honoraria from Taiho, Chugai, Takeda, Bristol-Myers and Merck Serono. SM has no competing interest. ST has received consulting fees from Taiho, Daiichi Sankyo and Solasia Pharma K. K.; research funding from Daiichi Sankyo, Yakult Honsha and Kureha Co. Ltd.; honoraria from Daiichi Sankyo. KS has received consultant fees, research funding and honoraria from Taiho, Chugai, Takeda, Yakult Honsha, Daiichi Sankyo, Bristol-Myers, Merck Serono, and Pfizer Co. Ltd. Ethics Approval Statement: The study protocol was approved by the Institutional Review Boards of each participating institution and was conducted in accordance with the tenets of the Declaration of Helsinki and comparable Japanese ethical standards. Furthermore, written informed consent was obtained from all study participants.

PURPOSE:To predict microsatellite instability (MSI) status of colon cancer on preoperative CT imaging using radiomic analysis. METHODS:This retrospective study involved radiomic analysis of preoperative CT imaging of patients who underwent resection of stage II-III colon cancer from 2004 to 2012. A radiologist blinded to MSI status manually segmented the tumor region on CT images.254 Intensity-based radiomic features were extracted from the tumor region. Three prediction models were developed with (1) only clinical features, (2) only radiomic features, and (3) "combined" clinical and radiomic features. Patients were randomly separated into training (n = 139) and test (n = 59) sets. The model was constructed from training data only; the test set was reserved for validation only. Model performance was evaluated using AUC, sensitivity, specificity, PPV, and NPV. RESULTS:Of the total 198 patients, 134 (68%) patients had microsatellite stable tumors and 64 (32%) patients had MSI tumors. The combined model performed slightly better than the other models, predicting MSI with an AUC of 0.80 for the training set and 0.79 for the test set (specificity = 96.8% and 92.5%, respectively), whereas the model with only clinical features achieved an AUC of 0.74 and the model with only radiomic features achieved an AUC of 0.76. The model with clinical features alone had the lowest specificity (70%) compared with the model with radiomic features alone (95%) and the combined model (92.5%). CONCLUSIONS:Preoperative prediction of MSI status via radiomic analysis of preoperative CT adds specificity to clinical assessment and could contribute to personalized treatment selection.

Recent research has established tumor budding as a prognostic factor and a possible histomorphologic reflection of epithelial-mesenchymal transition in colorectal cancer, highlighting the ability of cancer cells exhibiting epithelial-mesenchymal transition to resist chemotherapy.This study aimed to investigate the clinical benefits of adjuvant chemotherapy according to the tumor budding status in microsatellite-stable stage III colorectal cancer.This was a retrospective study of 2 cohorts.The study was conducted at the National Defense Medical College in Japan.We reviewed 2 data sets of patients with microsatellite-stable stage III colorectal cancer with curatively intended surgery (R0) from 1999 to 2005 (first cohort; n = 203) and 2006 to 2012 (second cohort; n = 346). In both cohorts, 128 and 203 patients received 5-fluorouracil-based adjuvant chemotherapy and 75 and 143 patients did not.We assessed the benefits of adjuvant chemotherapy according to the grades of tumor budding based on the cancer-specific survival.In low-budding tumors, the chemotherapy group exhibited better cancer-specific survival than the surgery-alone group (first cohort, 93.1% vs 65.5%, p = 0.001; second cohort, 94.0% vs 76.0%, p0.0001). Conversely, the prognostic difference between the chemotherapy and surgery-alone groups was statistically insignificant in high-budding tumors (first cohort, 59.7% vs 52.4%, p = 0.57; second cohort, 83.1% vs 75.6%, p = 0.19). The multivariate analysis corroborated the benefits of adjuvant chemotherapy in low-budding tumors (first cohort, p = 0.002, HR = 0.28; second cohort, p0.0001, HR = 0.23) but not in high-budding tumors.Postoperative adjuvant chemotherapy and treatments for recurrence were not homogeneous, and the patient backgrounds differed between the chemotherapy and surgery alone groups.The high-budding group demonstrated resistance to 5-fluorouracil-based chemotherapy, whereas the low-budding group exhibited significant survival benefits from adjuvant chemotherapy in stage III colorectal cancer. See Video Abstract at http://links.lww.com/DCR/B14. BENEFICIOS DE SUPERVIVENCIA DIFERENCIAL DE LA QUIMIOTERAPIA ADYUVANTE BASADA EN 5-FLUOROURACILO PARA PACIENTES CON CÁNCER COLORRECTAL EN ESTADIO III ESTABLE CON MICROSATÉLITE SEGÚN EL ESTADO DE BROTACIÓN DEL TUMOR: UN ANÁLISIS RETROSPECTIVO:: Investigaciones recientes han establecido la aparición de tumores como un factor pronóstico y una posible reflexión histomorfológica de la transición epitelial-mesenquimatosa en el cáncer colorrectal, destacando la capacidad de las células cancerosas que presentan una transición epitelio-mesenquimática para resistir la quimioterapia.El objetivo de este estudio es investigar los beneficios clínicos de la quimioterapia adyuvante según el estado de brotación del tumor en el cáncer colorrectal en estadio III estable con microsatélite.Este fue un estudio retrospectivo de dos cohortes.El estudio se realizó en la Escuela de Medicina de la Defensa Nacional de Japón.Revisamos dos conjuntos de datos de pacientes con cáncer colorrectal en estadio III estable con microsatélite con cirugía de intención curativa (R0) de 1999 a 2005 (primera cohorte; n = 203) y 2006 a 2012 (segunda cohorte; n = 346). En ambas cohortes, 128 y 203 pacientes recibieron quimioterapia adyuvante basada en 5-fluorouracilo y 75 y 143 pacientes no, respectivamente.Evaluamos los beneficios de la quimioterapia adyuvante de acuerdo con los grados de brotación del tumor en función de la supervivencia específica del cáncer.n los tumores con brotes bajos, el grupo de quimioterapia mostró una mejor supervivencia específica al cáncer que el grupo con cirugía sola (primera cohorte, 93.1% vs. 65.5%, p = 0.001; segunda cohorte, 94.0% vs. 76.0%, p0.0001). A la inversa, la diferencia pronóstica entre los grupos de quimioterapia y cirugía sola fue estadísticamente insignificante en los tumores de brotes elevados (primera cohorte, 59.7% vs. 52.4%, p = 0.57; segunda cohorte, 83.1% vs. 75.6%, p = 0.19). El análisis multivariado corroboró los beneficios de la quimioterapia adyuvante en los tumores de brotes bajos (primera cohorte, p = 0,002, índice de riesgo: 0,28; segundo cohorte, p0,0001, índice de riesgo: 0,23) pero no en los tumores de alto brote.a quimioterapia adyuvante postoperatoria y los tratamientos para la recurrencia no fueron homogéneos, y los antecedentes de los pacientes difirieron entre los grupos de quimioterapia y cirugía sola.El grupo de alto brote demostró resistencia a la quimioterapia basada en 5-fluorouracilo, mientras que el grupo de bajo brote mostró beneficios significativos de supervivencia de la quimioterapia adyuvante en el cáncer colorrectal en estadio III. Vea el Resumen del Video en http://links.lww.com/DCR/B14.

Immunotherapy using checkpoint inhibitor targeting PD-1 and PD-L1 revolutionized the treatment of microsatellite instable metastatic colon cancer. Such treatment is now a standard of care for these patients. However, when used as monotherapy checkpoint inhibitors targeting PD-1 and PD-L1 are not effective in metastatic colorectal cancer patients with microsatellite stable tumors. Recent advances in biology provide a rationale for this intrinsic resistance and support the evaluation of combination therapy to reverse resistance. This article will highlight recent findings on the mechanism of intrinsic resistance and recent advances in clinical trials for combination therapy.

3584 Background: Patients (pts) with microsatellite stable (MSS) metastatic colorectal cancer (mCRC) that progressed on ≥2 prior therapies have limited treatment options, with median OS ranging from 6-9 months (mo). In the dose-escalation phase of this first-in-human multicohort study (NCT02720068), the anti-lymphocyte activation gene (LAG)-3 antibody favezelimab (fave) was well tolerated alone and with pembrolizumab (pembro) across all dose levels (Lakhani, SITC, 2018, abstract O26). Here, we evaluate the safety and efficacy of fave alone or in combination with pembro in pts with advanced MSS CRC from the dose confirmation phase. Methods: Eligible pts with MSS PD-1/PD-L1-treatment-naïve mCRC that progressed on prior standard-of-care (3L+) were enrolled (cohort A) to receive the RP2D of 800 mg fave alone (Arm 1), 800 mg fave + 200 mg pembro (Arm 2C), or 800 mg fave + 200 mg pembro (MK-4280A) co-formulation (Arm 5), all Q3W. Treatment continued for 35 cycles or until progression, unacceptable toxicity, or investigator/pt decision. Pts with confirmed progression per irRECIST v1.1 on fave alone could crossover to 800 mg fave + pembro. Safety was assessed in all treated pts; efficacy in the full analysis set (FAS) of all treated pts with baseline scan. Objectives included safety (primary), ORR (RECIST v1.1 by investigator [secondary]), and DOR, PFS, and OS (exploratory). Interim analysis data cut-off was: Oct. 23, 2020. Results: A total of 20 pts received fave (Arm 1); 89 pts (including 9 crossover) received fave + pembro (Arms 2C+5); 12 pts (Arm 1) and 36 pts (Arms 2C+5), had PD-L1 CPS ≥1 tumors. At data cut-off, median follow-up was 5.8 months (mo) in Arm 1 and 6.2 mo in Arms 2C+5. Treatment-related adverse events (TRAEs) were 65% with fave (Arm 1) and 65.2% with fave + pembro (Arms 2C+5). Grade ≥3 TRAEs were 15% (Arm 1), and 20% [Arms 2C+5]). No grade 5 TRAEs were reported. Common TRAEs (≥15%) included fatigue (20.0%), nausea (15%) with fave, and fatigue (16.9%) with fave + pembro. Confirmed ORR was 6.3% (4PR, 1CR) with fave + pembro (Arms 2C+5). No pt receiving fave alone responded. In Arms 2C+5, median DOR was 10.6 mo (range, 5.6-12.7). ORR, OS and PFS by PD-L1 status are reported in the Table. Conclusions: Favezelimab alone or in combination with pembrolizumab had a manageable safety profile, with no treatment-related deaths. Promising antitumor activity was observed with combination therapy, including with MK-4280A, compared with monotherapy most notably in pts with PD-L1 CPS ≥1 tumors. Clinical trial information: NCT02720068. [Table: see text]

e15560 Background: PD-1 blockade is particularly ineffective in patients with microsatellite stable (MSS) or mismatch repair (MMR)-proficient colorectal cancer (CRC). Regorafenib (R) has been shown to modulate anti-tumor immunity through different mechanisms, including the reduction of tumor-associated macrophages (TAMs) and lymphocyte activation or immunosuppressive cells, such as forkhead box P3 (Foxp3)+ CD25+ regulatory T cells (Tregs). Synergy between R and anti–PD-1/PD-L1 antibodies has been demonstrated in pre-clinical models compared to that of either treatment alone. Accordingly, this study attempted to evaluate the combined activity of regorafenib with an immune checkpoint inhibitor. Methods: This trial was a prospective, open-label, monocentric, nonrandomized, single arm study. This study included patients with non MSI-H mCRC who received R (80 mg QD 3weeks/4) and sintilimab (S)(200 mg every 3 weeks).The primary endpoint was the confirmed objective response rate (ORR).The secondary endpoints were progression free survival (PFS),overall survival (OS),disease control rate (DCR) and safety. Results: As of January 8, 2021, 24 patients (median age 59 years) with mCRC were enrolled and received treatment with R+S. RAS wild type was 50% of all patients. In addition, 83.3% of patients received two prior lines of treatment, while 58.3% had liver metastases at enrollment. Of the 24 patients, the best response was observed to be stable disease(SD) in six patients (25%) and progressive disease (PD)in four patients (16.7%). Another nine (37.5%) patients have yet to be evaluated. In the 15 evaluated patients, the ORR(RECIST version 1.1) was 33.3% , the DCR was 73.3%. Additionally, among the 10 evaluated patients with liver metastases, the ORR was 30% , the DCR was 80%. Among the nine evaluated patients with wild-type populations of k-ras, the ORR and DCR was found to be 44.4% and 66.7%, which was higher than the mutation patients. The median PFS was 4.2 (95% CI, 2.5, NA) months, the median OS was not reached. The most common grade 3/4 adverse events were palmar-plantar erythro-dysesthesia syndrome (4.2%), erythra (4.2%). No death was related to the treatment. Moreover, four (16.7%) patients were subject to at least 1 dose modification or treatment interruption. Conclusions: In this study, the combination of R+S achieved a similar ORR with REGONIVO. Furthermore, this combination was well tolerated and had a manageable safety profile. However, due to the limited sample size, some biases may be present. As a result, we will continue to expand the sample size for future verification. Clinical trial information: NCT04745130.

5581 Background: Traditional platinum-based systemic chemotherapy continue to be the SOC for aEC in the first line. Phase 2 clinical trials of chemotherapy (GOG 129 series) and some targeted therapies (229 series) for second line advanced endometrial cancer (aEC) have proved disappointing. Recently the treatment landscape for aEC patients has significantly changed with newer targeted therapies focusing on the microsatellite instability (MSI) status of endometrial tumors. The objective of the ECHO study was to describe real-world treatment patterns and outcomes in non-MSI-high or DNA mismatch repair proficient (pMMR) aEC patients in clinical practice in the United States (US) prior to 2019. Methods: The ECHO study is a multicenter, retrospective chart review study in women diagnosed with aEC in the US. Data were obtained from medical records of adult women (≥18 years) diagnosed with advanced or inoperable aEC (stages III or IV) with known MSI status, who had received at least one prior systemic therapy and progressed between July 1, 2016 – June 30, 2019. De-identified patient data extracted by treating oncologists included patient demographics, clinical and treatment characteristics, and clinical outcomes. Kaplan-Meier analyses were performed to estimate real-world progression-free survival (rwPFS) and overall survival (OS). Results: A total of 124 non-MSI-high or pMMR aEC patients who had progression following first line therapy were included in this interim analysis. Average age was 63 years, 62.9% White/Caucasian, 16.9% Hispanic/Latino, and 86% had ECOG ≤1. Metastases were observed in 70% of patients at diagnosis, with the most common metastatic sites being lung (47.6%), liver (32.3%), and distant lymph nodes (29%). As 2nd line therapy, 69% of patients received mono or combination chemotherapy (primarily with doxorubicin), 13% hormonal therapy, and 18% targeted therapy ± chemotherapy. Median duration of 2nd line therapy was 4 months. The majority (86.3%) discontinued 2nd line therapy, with disease progression the most common reason (66.4%). A quarter (26.6%) of patients initiated an additional line of therapy. Median rwPFS from initiation of 2nd line therapy was 5 months (95% confidence interval [CI]: 4-9). Median OS from initiation of 2nd line therapy was 12 months (95%CI: 9-18). Estimated OS rates from initiation of 2nd line therapy at 6, 12, and 24 months were 66%, 47%, and 30%, respectively. Conclusions: In this retrospective, chart review study, patients with non-MSI-high/pMMR aEC in the US who failed at least one systemic therapy had poor prognosis on subsequent therapies. There continues to be a significant unmet need in this group of women. Novel therapies are needed that delay progression and/or improve overall survival and further research is indicated to explore this.

e15585 Background: A previous phase 1b trial has shown encouraging efficacy of regorafenib plus nivolumab in patients with microsatellite stable/mismatch repair proficient (MSS/pMMR) metastatic colorectal cancer (mCRC). We aimed to evaluate the efficacy and safety of this regimen in Chinese patients in the real world. Methods: We retrospectively identified patients with MSS/pMMR mCRC who received at least one dose of programmed cell death-1 (PD-1) inhibitors plus regorafenib from 5/2019 to 2/2021 in 10 Chinese medical centers. The primary endpoint was overall survival (OS). Secondary endpoints included progression-free survival (PFS), objective response rate (ORR), disease control rate (DCR) and the safety. Results: Fifty-two patients were identified. Liver metastases were presented in 35 patients (67%). A total of 48 patients (92%) received regorafenib plus a PD-1 inhibitor as the third or later line treatment. At the data cut-off, 11 patients (21%) were still on treatment. Other patients terminated treatment because of progressive disease (45%), treatment-related adverse events (TRAEs) (14%) or treatment-unrelated deaths (6%). The median treatment cycle was 3 (range, 1-18). At a median follow-up of 4.9 months, the median OS was 17.3 months (95% CI, 10.2-NR) and the median PFS was 3.1 months (95%CI, 2.5-6.0). Baseline liver metastases were associated with inferior PFS (2.7 versus 6.3 months, p

3573 Background: Microsatellite stable metastatic colorectal cancer (MSS mCRC) represents a high unmet need since there are currently no approved immunotherapy options. Since the inhibition of the transforming growth factor-β (TGF-β) pathway is known to contribute to the enhancement of immunotherapy efficacy, here, we report the results of vactosertib, a potent and selective TGF-β receptor I kinase inhibitor, combined with pembrolizumab in patients with MSS mCRC. Methods: In this phase 2, open label trial, patients have received vactosertib (300 mg BID, 5 days on / 2 days off) and pembrolizumab (200 mg, every 3 weeks) until confirmed progressive disease (PD), unacceptable toxicity or consent withdrawal. Patients with histologically confirmed mCRC who had disease progression after treatment with all available therapies including fluoropyrimidine and oxaliplatin or irinotecan were enrolled. Eligible patients were ≥19 years old, had ECOG status ≤1, and had no prior exposure to immunotherapy. The objectives were to evaluate the safety and efficacy (objective response rate (ORR) per RECIST v1.1). Results: Thirty-three patients with MSS mCRC were enrolled. Median age was 60 (range 33-72), 55% were male, median number of previous lines of chemotherapy was 3 (range 1-7), and 82% were consensus molecular subtype (CMS) 4. The ORR was 15.2% including 5 partial responses (PRs), 7 stable diseases, and 17 PDs as best overall responses; 12 patients remain on treatment. Among 5 patients with PR, 3 patients had confirmed PR and median duration of response was not reached yet. As of 04 Jan 2021, the most common treatment related adverse events (AEs) were increased amylase (21.2%), pruritus (21.2%), rash (21.2%), and increased lipase (18.2%). There were 3 treatment-related SAEs reported; drug induced pneumonitis (3%), nausea (3%), and vomiting (3%). Conclusions: The combination treatment with vactosertib and pembrolizumab showed favorable safety profile with promising efficacy in patients with MSS mCRC. Updated data including pharmacodynamic markers will be presented at the meeting. Clinical trial information: NCT03724851.

3561 Background: BRAF V600E+, MSS mCRC patients comprise up to 10% of advanced CRC. They have a poor prognosis with median survivals typically

3559 Background: The MORPHEUS platform consists of multiple, global, open-label, randomized Phase Ib/II trials designed to identify early efficacy and safety signals of treatment (tx) combinations across cancers. Here, atezo (anti-PD-L1) was tested with Imprime and bev (anti-VEGF) for MSS mCRC, a poorly immunogenic cancer generally resistant to checkpoint inhibitors. Imprime acts as a pathogen-associated molecular pattern that, when bound to anti-β glucan antibodies (ABA), activates the innate immune system with the potential to 1) promote priming and expansion of tumor-specific T cells, 2) promote M2-M1 macrophage polarization and 3) enhance the immunomodulatory effects of atezo and bev. Therefore, we hypothesized that atezo + Imprime + bev would induce an antitumor response beyond that of rego, a standard-of-care multikinase inhibitor, in patients (pts) with MSS mCRC. Methods: Pts with MSS mCRC unselected for the Imprime-specific biomarker (ABA) and refractory to 1-2 prior lines of standard therapy received atezo (1200 mg IV every 3 weeks [q3w]) + Imprime (4 mg/kg IV on Days 1, 8, 15) + bev (7.5 mg/kg IV q3w) or control tx with rego (160 mg orally days 1-21; dose escalation to 160 mg during Cycle 1 allowed per institutional guidelines). The primary endpoint was objective response rate (ORR; investigator-assessed RECIST 1.1); secondary endpoints included disease control rate (DCR; response or stable disease ≥ 12 weeks), progression-free survival (PFS), overall survival (OS) and safety. Results: Pts were followed-up for ≥18 wk. 15 pts received atezo + Imprime + bev and 13 received rego. Grade (Gr) 3/4 tx-related adverse events (TRAEs) were seen in 13% of atezo + Imprime + bev and 62% of rego pts. No Gr 5 AEs occurred in atezo + Imprime + bev pts and 1 (8%) was reported in a rego pt. One pt in each arm (7% vs 8%, respectively) withdrew from tx due to a TRAE. No radiological responses were seen in either arm. Five pts (33%) receiving atezo + Imprime + bev and 8 (62%) receiving rego had stable disease as best response. DCR was 13% with atezo + Imprime + bev and 23% with rego. Median PFS was 1.5 mo (95% CI: 1.4, 2.8) and 2.8 mo (95% CI: 1.6, 3.1), and median OS was 5.7 mo (95% CI: 4.4, 10.5) and 10.2 mo (95% CI: 4.8, NE) with atezo + Imprime + bev and rego, respectively. There was no apparent correlation between baseline PD-L1 expression or CD8+ lymphocyte tumor infiltration and clinical benefit. Further, the systemic exposure of atezo, Imprime and bev and immunogenicity of atezo and bev are in line with previous clinical experience. Additional biomarker, pharmacokinetics and anti-drug antibody data will be shown. Conclusions: Atezo + Imprime + bev was well tolerated; toxicities were consistent with the safety profiles of the individual agents. No efficacy signal was identified with atezo + Imprime + bev in pts with MSS refractory mCRC. Clinical trial information: NCT03555149.

3560 Background: The role of immunotherapy in the treatment of pMMR/MSS metastatic CRC is not established. A Japanese phase 1b trial in this setting showed the combination of regorafenib (multikinase inhibitor with immunomodulatory activity) plus nivolumab (anti PD-1) had encouraging activity and manageable safety (Fukuoka, 2020). This study further assessed the safety and efficacy of this combination. Methods: Patients (pts) from the US aged ≥18 years who progressed on/were intolerant to standard chemotherapy were enrolled. Regorafenib was given orally, once daily in 28-day (D) cycles (21D on/7D off) plus IV nivolumab 480 mg on D1. Regorafenib starting dose was 80 mg; if well tolerated, it could be escalated to 120 mg in Cycle 2. Primary endpoint was overall response rate (ORR; RECIST 1.1); secondary aims included disease control rate (DCR), overall survival (OS), progression-free survival (PFS), and safety (NCI-CTCAE v5.0 grade). Biomarker analysis was exploratory. Results: 70 pts (59% male) started treatment. At baseline, median age was 57 years (range 34–85), ECOG PS 0/1 was 51%/49%, 67% had liver metastases (mets), and the primary tumor site was right-sided colon in 36% and rectum in 17%. Median number of cycles was 3.0 (range 1–13); 41% of pts escalated regorafenib to 120 mg. Five pts (7.1%) had a partial response (PR) lasting ≥16 weeks (wks) and 22 (31.4%) had stable disease (SD); pts without liver mets had a higher ORR (21.7%). In pts with tumor samples (n = 40), higher baseline expression (IHC) of cytotoxic T cells (CD3+/CD8+/GranzymeB+), Tregs (FoxP3+), and macrophages (CD68+) trended with clinical benefit (PR/SD ≥16 wks/PFS); pts with liver mets had lower expression. Lower plasma levels of biomarkers of vascular biology (e.g. VEGF-D, Ang-2, VWF) trended with longer PFS. Grade (Gr) 3 treatment-emergent adverse events (TEAEs) occurred in 53% of pts and Gr 4 in 10%. Three pts had a Gr 5 TEAE: n = 1 related to the combination (sepsis); n = 1 related to nivolumab only by investigator (sepsis); n = 1 unrelated to treatment (respiratory failure). Most common Gr 3/4 TEAEs: maculopapular rash (14%), fatigue (7%), pneumonia (6%), increased bilirubin (6%). Conclusions: Combination treatment with regorafenib (up to 120 mg/day) and nivolumab (480 mg every 28D) has manageable safety. Efficacy of this combination in the North American population did not emulate results in the Japanese population. Absence of liver mets and expression of specific biomarkers indicate a better response and may warrant further analysis. Clinical trial information: NCT04126733. [Table: see text]

124 Background: Microsatellite stable (MSS) colorectal cancer and CRCLM are highly resistant to current immunotherapeutic approaches. Understanding the TME and the impact of standard chemotherapeutics is of utmost importance in developing optimal therapeutic strategies. Data is limited on the impact of NACT in the TME. In this study, we sought to explore the effects of chemotherapy on the proportions of different immune cell populations [Total leukohematopoetic cells, CD45+, T cell markers, CD3+, CD8+, and macrophage (M) markers, CD163+, CD68+)], as well as to assess their prognostic capacity. Methods: CRCLM pts who underwent liver resection were divided in 2 groups: pts who had NACT within 4 months of liver resection [NACT (+)] and no NACT [NACT (-)]. Whole slide staining of metastatectomy specimen for CD3, CD8, CD68, CD163, and CD45 was done. Cellular density within representative tumor core sections was analyzed. Retrospective chart review was done to obtain clinical data. Disease free (DFS), relapse free (RFS), and overall survival (OS) were analyzed using Kaplan Meir methods. Association between markers and outcomes was evaluated using Cox Regression Models. Results: A total of 43 pts were studied [NACT (+), n= 14; NACT (-), n=29). There were no significant differences in baseline characteristics between the two groups, including age, primary site, T stage, N stage, and grade. Median OS was 48 months. Outcomes were not significantly different with use of NACT. Within the NACT (+) CRCLM significant increases were seen in densities of CD3, CD8, CD45 and CD163 cells. Densities of CD8 cells were strongly correlated to CD163 cell densities ([r] 0.77, p < .0001). The NACT (+) cohort saw significantly increased ratios of T-cells/macrophages as compared to NACT (-) (CD3/CD68, CD3/CD163, CD8/CD163). High CD45 density was associated with improved OS (HR = 0.28, p = 0.006). CD3, CD8, CD68, and CD163 were not independently associated with OS. However, both the ratio of CD3/CD68 and CD3/163 were associated with improved OS (HR 0.44, p=0.03 and HR 0.27, p=0.03 respectively). Conversely, CD68/45 and CD163/CD45 ratios were associated with a worse OS (HR 1.42, p=0.05 and HR 1.43, p=0.03 respectively). No difference was seen in cellular populations based on the type of NACT received: oxaliplatin vs irinotecan. Conclusions: Our study highlights that the administration of NACT is associated with favorable changes in LM TME. While there is a general increase in leukocytes (CD45), the density of CD3+ and CD8+ T cells is particularly increased. Further, this increase is proportionately greater than the concurrent increases on monocytoid populations, reflected by increased CD3/CD163 and CD8/CD163 ratios. Ratios of T-cells/ macrophages are predictive of survival. This study was partly supported by the American Cancer Society Grant, 126771-IRG-14-194-11-IRG.

72 Background: Microsatellite stable (MSS) metastatic colorectal cancer (mCRC) has been associated with immunotherapy resistance. However, the impact of metastatic diseases sites on clinical outcome with checkpoint inhibition has not be adequately investigated. Methods: Following IRB approval (14361), we performed a retrospective study to assess the response and progression-free survival (PFS) to PD-1 or PD-L1 based therapy in patients with MSS mCRC who progressed following standard chemotherapy and targeted therapy. Patients were included if they received an FDA approved anti-PD1 or anti-PD-L1 agent, alone or in combination with other investigational agents. Exclusion criteria included concurrent cytotoxic therapy. Response and PFS were determined by RECIST guidelines. Results: 97 patients with refractory MSS mCRC satisfied the inclusion criteria were evaluable for analysis. 57, 17, 13, and 10 received nivolumab, atezolizumab, pembrolizumab, and durvalumab, respectively. 47, 8, 10, 10, 17 received concurrent VEGFR, MEK, CTLA-4, radiation, or other targeted therapies. Among tested variables, including age, gender, primary tumor location, ECOG status, RAS, BRAF, APC, TP53, TMB, and sites of metastasis, only ECOG status (0 vs. 1) and metastatic disease to the liver were associated with disease control (partial response and stable disease; p = 0.005 and < 0.001 respectively). Disease control rates in patients without liver metastases (n = 43) was 56% (95% CI: 40-71%), compared with 2% (95% CI: 0.1-10%) in patients with liver metastases (n = 54) (p < 0.001). Also, liver involvement was predictive for PFS based on multivariate Cox regression model (p < 0.001). The median PFS in patients with liver involvement was 1.5 vs 4.5 months for no liver involvement (HR = 4.41, p = < 0.001). Amongst patients without liver metastases, 35% (15/43) remained without progression at 6 months. These patients were characterized by lung metastases (n = 8) and/or lymph node metastases (n = 4). Conclusions: The presence of liver metastases is MSS mCRC is predictive for lack of benefit from PD-1/PD-L1 inhibitors. Patients without liver metastases can derive a meaningful clinical benefit, with 35% being progression-free at 6 months. Future PD-1/PD-L1 drug development should consider metastatic sites of disease in study design and development.

77 Background: MSS mCRC rarely responds to pembrolizumab monotherapy, but capecitabine and bevacizumab may induce immune-stimulatory effects. This study evaluates the safety, tolerability and preliminary efficacy of pembrolizumab in combination with capecitabine and bevacizumab in MSS mCRC. We present results at the planned interim analysis. Methods: Design:single-arm, open-label, single-site phase 2 trial with a safety lead-in to confirm the recommended phase 2 dose (RP2D) for capecitabine and expansion cohorts. Per the Simon’s 2-stage design, ≤1 response in 29 patients (pts) requires trial suspension. Key eligibility criteria: MSS mCRC with stable disease (SD) or progressive disease (PD) on prior fluoropyrimidine-based therapy. Treatment: RP2D PO capecitabine on days 1-14 plus 200 mg IV pembrolizumab and 7.5 mg/kg IV bevacizumab on day 1 in 21-day cycles. Pts are followed for toxicity and radiographic response. Results: From 04/2018-09/2020, 29 pts were enrolled, of whom 15 (52%) were female; 21 (72%) white; and median age was 55 years (range 36-77 years). Prior therapies: 2 (7%) pts had SD and 27 (93%) pts had PD on fluoropyrimidine-containing regimens; 24 (83%) pts had prior exposure to bevacizumab. The RP2D for capecitabine was 1000 mg/m2 PO BID, with no dose limiting toxicities observed. Complete toxicity data are available for 25 off-treatment pts. The most common related adverse events (AEs) were palmar-plantar erythrodysesthesia (PPE) (64%) and fatigue (68%). Grade ≥3 related AEs occurred in 9 (36%) pts, including immune-related AEs of Grade 3 dyspnea, hypophosphatemia, and pancreatitis in 1 pt each. Treatment related AEs leading to dose interruptions, reductions, or delays occurred in 15 (60%) pts, most commonly PPE in 13 (52%) pts. No pt had a related AE leading to treatment discontinuation or death. Disposition: of 29 pts enrolled, 24 were removed for PD and 1 was removed for an unrelated AE. Best response by RECIST 1.1 in 23 evaluable pts: partial response (PR) in 2 (9%); SD in 14 (61%); PD in 7 (30%). Median time on treatment was 6 months (range 2-26 months). Conclusions: Combination of pembrolizumab with capecitabine and bevacizumab was found to be tolerable with an expected toxicity profile in MSS mCRC pts. With 2 responses, the study met interim analysis criteria to continue accrual. Tissue and blood-based immune correlatives are planned. Clinical trial information: NCT03396926.

Introduction/Objective Microsatellite stable (MSS) and Instable colorectal cancer (CRC) as primary colon cancers differ in their pathological features and biological behavior including response to treatment. In general, MSI-high CRC has a better prognosis and a more favorable response to treatment. To our knowledge, the co-occurrence of the microsatellite stable and unstable CRCs in the same person has not been reported in the literature. Herein, we present the case report of 78 year African American female who presented to us with this condition. Methods A literature search of publication up to March 2020 in PubMed was conducted on the occurrence of microsatellite stable and unstable CRCs in the same individual. The literature search was limited to English language only. The following words were used in the search engine of PubMed: “Microsatellite stable colorectal cancer + unstable colorectal cancer and colorectal cancer + same patient”. No articles were identified. Results A search using the terms “coexistence of MSS and MSI CRC in the same individual” identified 45 articles. No case report or article discussing the presence of coexisting MSS and MSI CRC in the same individual was identified Conclusion Identification of MSI CRC is important, as MSI may serve as a screening tool for detecting Lynch Syndrome, a prognostic marker for patient outcome, and as a predictive marker for response to chemotherapy and to immunotherapy. Whether coexistence of MSI and MSS favorably affects the prognosis of the disease is unknown.

Microsatellite instability (MSI) assays are used to screen cancer patients with mismatch repair deficiency (dMMR) for immune checkpoint inhibitor therapy. However, short mononucleotide repeat (SMR) markers in current MSI assays may sometimes display subtle shifts that are difficult to interpret in certain dMMR cancers, particular non-colorectal cancers. Long mononucleotide repeat (LMR) markers that are more prone to replication errors may improve the sensitivity of MSI assays. In this study, we compared the performance of SMR and LMR markers using two panels: (1) MSI Analysis System Version 1.2 (Promega) consisting of five SMR markers (21-27 bases in length) and (2) MSI LMR System (Promega) consisting of four SMR markers from the Version 1.2 panel and four LMR markers (52-60 bases in length). We studied 20 MMR proficient (pMMR) and 18 dMMR colorectal cancers (CRC) defined by concordant immunohistochemical staining (IHC) and the Version 1.2 MSI panel, 12 pMMR and 9 dMMR endometrial cancers (EC) defined by IHC alone, and 9 dMMR prostate cancers (PC) defined by loss of MSH2 IHC staining, loss of function MSH2 mutations, and increased mutation frequency. A marker was defined as unstable if a shift of 2 or more bases was observed in the tumor sample when compared to the normal sample. When using the Version 1.2 panel, we defined MSI high (MSI-H) as 2 or more unstable markers, MSI low (MSI-L) as 1 unstable marker, and microsatellite stable (MSS) as no shifts. With the LMR panel, we defined MSI-H as 3 or more unstable markers, MSI-L as 1 or 2 unstable markers, and MSS as no shifts. In dMMR CRC, the clinical sensitivity of the LMR and Version 1.2 panels for MSI were both 100%. In pMMR CRC, MSI-H was not observed in any cases using either panel, but MSI-L was observed in 2 and 0 cases using the LMR and Version 1.2 panels, respectively. In dMMR CRC, the average size of allelic shifts in the four LMR and SMR markers from the LMR panel were 8.7 and 22.1 bases, respectively. Germline polymorphisms were observed in 47% and 1% of LMR and SMR markers, respectively. In dMMR EC, the LMR panel showed greater sensitivity than the Version 1.2 panel (100% vs 89%). In pMMR EC, MSI-H was not observed in any cases using either panel, but MSI-L was observed more often using the LMR panel when compared to the Version 1.2 panel (2 vs 0 cases). In addition, LMR markers displayed larger shifts than SMR markers (12.1 vs 4.9 bases). Polymorphisms were also more frequent in LMR markers relative to SMR markers (60% vs 2%). Likewise, in dMMR PC, the sensitivity of the LMR panel was greater than that of the Version 1.2 panel (89% vs 44%). Furthermore, shifts in LMR markers were larger than those in SMR markers (10.3 vs 3.1 bases), and polymorphisms in LMR markers were more frequent than in SMR markers (33% vs 0%). Overall, LMR markers display greater clinical sensitivity and larger shifts, indicating that LMR markers can improve MSI detection in non-colorectal cancer. Citation Format: John H. Lin, Suping Chen, Liana B. Guedes, Emmanuel S. Antonarakis, Colin C. Pritchard, Tamara L. Lotan, James R. Eshleman. Improved microsatellite instability detection in endometrial and prostate cancers using long mononucleotide repeat markers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 740.

4100 Background: Chemoradiotherapy (CRT) followed by radical surgery (S) is standard therapy for patients (pts) with locally advanced rectal cancer (LARC). Sequential use of an anti-PD-1 antibody after radiation demonstrates synergistic effects in in vivo models, and an anti-PD-1 antibody is effective in pts with microsatellite instability-high (MSI-H) metastatic colorectal cancer (mCRC). We studied nivolumab (nivo) and radical S following CRT (50.4 Gy with capecitabine 1,650 mg/m2) in T3–4 NanyM0 LARC. Methods: After the quality-assured CRT, 240 mg q2 weeks x 5 cycles of nivo and radical S were investigated. In cohort A-1, for pts with microsatellite stable (MSS) LARC, the primary endpoint was a centrally confirmed pathological complete response (pCR) rate using AJCC tumor regression grading. The estimated required sample size assuming null and alternative hypotheses pCR = 10% and 30% was 37 pts, with a 1-sided alpha of 5% and power of 90%. In Cohort A-2, 5 pts with MSI-H LARC were included in an exploratory manner. Results: From Jan/2017 to Oct/2019, a targeted number of pts was included and assessed. In cohort A-1, 30% (11/37; 90% CI 18-44%) of pCR (AJCC grade (gr) 0) rate and 38% (14/37) of major pathological response (MPR) (AJCC gr 0+1) rate were observed. Clinical CR was observed in one additional pt (3%) refusing S after nivo. In cohort A-2, 60% (3/5) of pCR rate and 60% (3/5) of MPR rate were observed. As of Jan/2020, only 2 pts (1 local and 1 metastatic) in cohort A-1 and none in cohort A-2 recurred. Immune-related severe adverse events were observed in 3 pts (gr 3 myasthenia, gr 3 interstitial nephritis, and gr 2 peripheral motor neuropathy); all fully recovered and received radical S. During the follow-up period, one additional pt with gr 2 colitis was observed. No treatment-related deaths were observed. Conclusions: Promising pCR rates of 30% and 60%, with mild toxicities, were shown in MSS and MSI-H LARC pts treated with nivo plus radical S after CRT, suggesting the candidate therapy for the future non-surgical approach. Clinical trial information: NCT02948348 .

3006 Background: Single agent PD-1/L1 inhibition are not effective in metastatic colorectal cancer (MCRC) with microsatellite stable tumors. However, signal of efficacy was shown using combo therapy of anti-PD-L1 and anti CTLA-4 in multitreated patients. FOLFOX regimen could induced immunogenic cell death and elimination of myeloid derived suppressor cells (MDSCs) thus leading to a potential positive effect on antitumor immune response. Methods: This is a single arm exploratory investigator-initiated trial planned to include 57 pts to receive mFOLFOX6 (6cycles) in combination with durvalumab (150mg/q2W) and tremelimumab (75mg/q4W). After 6 cycles of chemotherapy, patients are treated with durvalumab untils progression. Primary endpoint is 6 months’ progression-free survival rate. Secondary endpoints are response rate, tolerability and translational research evaluating tissue and blood immune parameter. Upon Simon’s design an efficacy intermediate analysis was planned after the 16th patient has passed 6 months. Results: As of 1st of January 2020 the 55/57 pts were enrolled and treated with the MEDETREME regimen at 8 French sites. The intermediate efficacy analysis was conducted on the 1st of January after a median of 13.4 months of treatment. The following adverse events were noted: asthenia (81.25%), neuropathy (87.5%), diarrhea (56.25%) and neutropenia (62.5%). Notable grade 3/4 (CTC AE 4.03) include asthenia (18.75%) diarrhea (12.5%) neutropenia (50%) and elevated blood pressure (25%). Most of adverse events were related to chemotherapy. It has been noted one cytolysis grade 3, one thyroid dysfunction grade 3 and one hypophysitis grade 3 related to immunotherapy. Median PFS was not reached. Progression free survival at 6 months was observed in 10/16 pts (62,5%) given 5 CR, 5 PR and 4 SD. Updated translational data will be presented at the meeting. Conclusions: The interim safety analysis has supported safety and efficacy of the MEDITREME regimen in first- line MCRC. Finally, results will be presented after maturation of follow up. Clinical trial information: NCT03202758 .

3010 Background: Checkpoint inhibition using PD-1/PD-L1 inhibitors does not show clinically relevant activity in MSS/pMMR (Mismatch Repair Proficient) colorectal cancer. Previous work showed that inhibition of CCR5 (C-C chemokine receptor type 5) leads to a macrophage re-polarization towards M1 macrophages within the tumor microenvironment which directly affects immune cell infiltrates. The current phase I trial explores a combined modification of the innate immune system (by CCR 5 blockade) and the adaptive immune system (by PD-1 inhibition) in the treatment of MSS CRC. Methods: 20 patients with metastatic MSS/pMMR colorectal cancer with failure of fluoropyrimidines, oxaliplatin, irinotecan, VEGF antibodies and EGFR antibodies (in ras WT patients) received pembrolizumab 200 mg q21d and maraviroc 300 mg bid cont. for 8 cycles, followed by pembrolizumab monotherapy for a maximum of 24 additional cycles. Imaging was performed every nine weeks (RECIST and irRECIST criteria). Primary endpoint was the feasibility rate (rate of patients receiving the protocol treatment during the core treatment without special event: treatment-related Grade ≥ 3 immune-related abnormalities, treatment-related Grade ≥ 4 AEs or any toxicity-related premature withdrawal of treatment). Secondary endpoints included safety/toxicity, ORR, PFS and OS. Results: 20 patients were enrolled. The median number of applied cycles was 3.5 for pembrolizumab and 3.5 for maraviroc. Two patients completed the core treatment period with pembrolizumab and started maintenance treatment. The feasibility rate was 94.7% (90% CI 77.4 to 99.7%), with one patient experiencing a special event. Except this grade 4 event (hyperglycemia) no ≥ 3 treatment-related toxicities were observed. According to irRECIST criteria one patient showed a partial response and one a stable disease as best response, resulting in an irDCR of 10.5%. Median PFS according to irRECIST was 2 months (CI 95%, 2 to 3), median OS 9 months (CI 95%, 6 to 20). Conclusions: Therapy with pembrolizumab and maraviroc was feasible and showed a beneficial toxicity pattern. Clinical activity in MSS CRC patients was limited, however prolonged disease stabilizations were observed in single patients and overall survival was higher than expected in this heavily pretreated population. Clinical trial information: NCT03274804 .