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Colorectal cancer (CRC) remains a significant cause of cancer-related mortality worldwide. Despite advancements in surgery, chemotherapy, and radiotherapy, the effectiveness of these conventional treatments is limited, particularly in advanced cases. Therefore, transition to novel treatment is urgently needed. Immunotherapy, especially immune checkpoint inhibitors (ICIs), has shown promise in improving outcomes for CRC patients. Notably, patients with deficient mismatch repair (dMMR) or microsatellite instability-high (MSI-H) tumors often benefit from ICIs, while the majority of CRC cases, which exhibit proficient mismatch repair (pMMR) or microsatellite-stable (MSS) status, generally show resistance to this approach. It is assumed that the MSI phenotype cause some changes in the tumor microenvironment (TME), thus triggering antitumor immunity and leading to response to immunotherapy. Understanding these differences in the TME relative to MSI status is essential for developing more effective therapeutic strategies. This review provides an overview of the TME components in CRC and explores current approaches aimed at enhancing ICI efficacy in MSS CRC. [ABSTRACT FROM AUTHOR]

Objective To evaluate the efficacy and safety of fruquintinib alone or in combination with immune checkpoint inhibitor (ICI) in patients with microsatellite stable (MSS) metastatic colorectal cancer (mCRC)in third⁃line or above treatment. Methods Patients with pMMR/MSS type mCRC admitted to the Department of Oncology, Renmin Hospital of Wuhan University, from January 2020 to April 2024 were selected as the research objects. The prognoses, efficacies and safeties of fruquintinib alone and in combination with ICI were compared in the unadjusted model and the propensity score matching. Results A total of 104 patients were included in the analysis, 33 in the fruquintinib group and 71 in the fruquintinib combined with ICI group. Compared to the fruquintinib group, the median progression⁃free survival was longer in the fruquintinib combined ICI group (3.0 months vs 4.5 months; HR=0.55, 95%CI: 0.33-0.89）. However, there were no significant differences in the median overall survival (10.1 months vs 13.1 months）, the objective response rate (9.1% vs 11.3%) and the disease control rate (51.5% vs 66.2%)between the two groups (all P>0. 05）. Similar results were obtained in the analysis of the propensity score matching. The adverse events of grade 3 or above in both groups mainly included hand⁃foot⁃skin reaction, thrombocytopeniaandleukopenia. The incidence of grade 3 or above adverse events was 30. 3% in the fruquintinib group and 36.6% in the fruquintinib combined with ICI group (P=0.529）. Conclusions Compared with fruquintinib, fruquintinib combined with ICI provides benefits in the progression ⁃free survival for pMMR/MSS type mCRC patients in third ⁃line or above treatment with controllable safety, which is worthy of further study. [ABSTRACT FROM AUTHOR]

Purpose of Review: This review will explore various strategies to rendering MSS mCRCs susceptible to ICI. Moreover, we will provide an overview of potential biomarkers that may aid to better patient selection, and discuss ongoing efforts in this area of research. Recent Findings: Colorectal cancer (CRC) ranks among the top three most common cancers worldwide. While significant advances in treatment strategies have improved the prognosis for patients in the early stages of the disease, treatment options for metastatic CRC (mCRC) remain limited. Although immune checkpoint inhibitors (ICI) have revolutionized the treatment of several malignancies, its efficacy in mCRC is largely confined to patients exhibiting a high microsatellite instability status (MSI-H). However, the vast majority of mCRC patients do not exhibit a MSI-H, but are microsatellite stable (MSS). In these patients ICIs are largely ineffective. Summary: So far, ICIs do not play a crucial role in patients with MSS mCRC, despite the promising data for inducing long-term remissions in other tumour entities. For this reason, novel treatment strategies are needed to overcome the primary resistance upon ICI in patients with MSS. [ABSTRACT FROM AUTHOR]

Immunotherapy based on the PD-1/PD-L1 axis blockade has no benefit for patients diagnosed with colon cancer liver metastasis (CCLM) for the microsatellite stable/proficient mismatch repair (MSS/pMMR)) subtype, which is known as an immune-desert cancer featuring poor immunogenicity and insufficient CD8+ T cell infiltration in the tumor microenvironment. Here, a multifunctional nanodrug carrying a cyclin-dependent kinase (CDK)1/2/5/9 inhibitor and PD-L1 antibody is prepared to boost the immune checkpoint blockade (ICB)-based immunotherapy against MSS/pMMR CCLM via reversing the immunosuppressive tumor microenvironment. To enhance the MSS/pMMR CCLM-targeting efficacy, we modify the nanodrug with PD-L1 knockout cell membrane of this colon cancer subtype. First, CDKs inhibitor delivered by nanodrug down-regulates phosphorylated retinoblastoma and phosphorylated RNA polymerase II and meanwhile arrests the G2/M cell cycle in CCLM to promote immunogenic signal release, stimulate dendritic cell maturation, and enhance CD8+ T cell infiltration. Moreover, CDKi suppresses the secretion of immunosuppressive cytokines in tumor-associated myeloid cells sensitizing ICB therapy in CCLM. Notably, the great efficacy to activate immune responses is demonstrated in the patient-derived xenograft model and the patient-derived organoid model as well, revealing a clinical application potential. Overall, our study represents a promising therapeutic approach for targeting liver metastasis, remolding the tumor immune microenvironment (TIME), and enhancing the response of MSS/pMMR CCLM to boost ICB immunotherapy. Schematic illustration of preparation and CCLM-targeted therapy of engineered cell membrane-camouflaged nanodrug. (A) Preparation of engineered cell membrane-camouflaged nanoparticles co-delivered with CDK inhibitor (CDKi) and anti-mouse/human programmed death ligand 1 antibody (aPD-L1) in response to extracellular acidity of tumor microenvironment. (B) Multifunctional nanodrug targets CDKs in colon cancer cell and tumor-associated myeloid cell (TAMC) to activate aPD-L1 immunotherapy against liver metastasis of immune-desert colon cancer. [Display omitted] [ABSTRACT FROM AUTHOR]

The use of immune checkpoint inhibitors (ICIs) has revolutionized cancer care, particularly in immune-inflamed tumors and tumors with a high mutational burden, like microsatellite instable colorectal cancer (CRC). However, their effectiveness in microsatellite stable (MSS) CRC is limited. This systematic review aims to evaluate the efficacy of ICIs in MSS CRC and explore promising combination strategies. A comprehensive search from the Web of Science, Medline, and Embase databases, for studies published until 14 November 2022, identified 53 clinical trials included in the review. ICI monotherapy or ICI-ICI combinations demonstrated limited clinical activity for patients with MSS CRC, with overall response rates below (ORR) 10% in most studies. The ICI and tyrosine kinase inhibitor (TKI) garnered ORRs ranging from 10% to 40% and indicated a higher benefit for patients, particularly those without active liver metastases. The combination of ICIs with anti-VEGF agents showed modest ORRs, especially in the earlier treatment lines and in combination with chemotherapy. While these combinations could lead to modest improvements, well-defined biomarkers for long-term benefit are yet to be delineated. Combinations involving BRAF inhibitors with ICIs were studied, showing promising responses with combination approaches in molecularly defined subgroups. In conclusion, while ICI monotherapy has limited efficacy in MSS CRC, combination strategies hold promise to enhance survival outcomes. Further research is necessary to identify optimal combination approaches, predictive biomarkers for treatment response, as well as enrollment according to tumor molecular characteristics. [ABSTRACT FROM AUTHOR]

Purpose: Clinical practice guidelines recommend that all patients with metastatic colorectal cancer (mCRC) should be tested for mismatch repair deficiency (dMMR) or microsatellite instability-high (MSI-H). We aimed to describe the dMMR/MSI-H testing practice in patients with mCRC in Spanish centers. Methods: Multicenter, observational retrospective study that included patients newly diagnosed with mCRC or who progressed to a metastatic stage from early/localized stages. Results: Three hundred patients were included in the study from May 2020 through May 2021, with a median age of 68 years, and two hundred twenty-five (75%) had stage IV disease at initial diagnosis; two hundred eighty-four patients received first-line treatment, and dMMR/MSI-H testing was performed in two hundred fifty-one (84%) patients. The results of the dMMR/MSI-H tests were available in 61 (24%) of 251 patients before the diagnosis of metastatic disease and in 191 (81%) of 236 evaluable patients for this outcome before the initiation of first-line treatment. Among the 244 patients who were tested for dMMR/MSI-H with IHC or PCR, 14 (6%) were MMR deficient. The most frequent type of first-line treatment was the combination of chemotherapy and biological agent, that was received by 71% and 50% of patients with MMR proficient and deficient tumors, respectively, followed by chemotherapy alone, received in over 20% of patients in each subgroup. Only 29% of dMMR/MSI-H tumors received first-line immunotherapy. Conclusion: Our study suggests that a high proportion of patients with mCRC are currently tested for dMMR/MSI-H in tertiary hospitals across Spain. However, there is still room for improvement until universal testing is achieved. Trial registration: Not applicable. [ABSTRACT FROM AUTHOR]

Opinion statement: Neoadjuvant chemotherapy is safe for patients with locally advanced colon cancer (LACC). The FOxTROT trial demonstrated a reduction in residual and recurrent cancer at 2 years with neoadjuvant chemotherapy for patients with cT3-4 LACC. Preoperative chemotherapy should be avoided, if possible, for patients with dMMR LACC, as over 50% of dMMR cancers have no pathologic response. Early universal testing of MMR status is critical to selecting the appropriate neoadjuvant therapy. Concerns about CT staging of LACC have limited uptake of neoadjuvant chemotherapy, as approximately 25% of patients with cT3-T4 cancer on CT have low-risk stage II disease. Development of CT criteria for malignant nodes should reduce the risk of over-staging. A multidisciplinary approach is needed to identify patients for neoadjuvant therapy. Neoadjuvant immunotherapy is safe and results in dramatic pathologic responses in patients with dMMR LACC. Longer follow-up is needed to determine if the exceptionally high pathologic response rates observed will translate into long-term remission. Remarkably, neoadjuvant immunotherapy has been found to cause major pathologic responses in a subset of patients with pMMR LACC, indicating the potential to cure more patients with this common cancer. Patients with cT4 LACC, whether stage II or III, have a substantial risk of recurrence despite adjuvant fluoropyrimidine plus oxaliplatin chemotherapy. We recommend neoadjuvant systemic therapy for all patients with cT4b LACC (dMMR and pMMR). Features of T4b disease are routinely reported by radiology. We use three cycles of FOLFOX chemotherapy for patients with cT4b pMMR LACC, due to the high rate of compliance and improvement in residual and recurrent disease. Patients with cT4b dMMR LACC should receive neoadjuvant immunotherapy, if there are no contraindications. Clinical trials of neoadjuvant therapy for LACC are of great interest and should provide training for radiologists to identify eligible patients. Results are anticipated from multiple ongoing trials of neoadjuvant chemotherapy, immunotherapy, and targeted therapy for pMMR LACC and immunotherapy for dMMR LACC. [ABSTRACT FROM AUTHOR]

Objective To investigate the clinical efficacy and safety of fruquintinib combined with sintilimab in the treatment of advanced microsatellite stable (MSS) colorectal cancer. Methods A retrospective study of 44 patients with MSS colorectal cancer treated with fruquintinib and sintilimab was conducted.The patients were divided into the fruquintinib alone (n=22) and fruquintinib combined with sintilimab (n=22) groups.The treatment regimen was as follows: The patients in the fruquintinib alone group consumed oral fruquintinib capsules at 5 mg/d once for three consecutive weeks with a one week stop in 28 day cycles.The patients in the fruquintinib combined sintilimab group were injected intravenously with sintilimab (200 mg) once per three weeks, and fruquintinib was used in the same manner as the fruquintinib alone group. Results The objective response rate (ORR) of the fruquintinib alone group was 9.09%, the disease control rate (DCR) of the fruquintinib alone group was 45.45%.The ORR of the fruquintinib combined with sintilimab group was 18.18%, and the DCR was 63.64%.The median PFS of the fruquintinib alone and fruquintinib combined with sintilimab groups were 4.4 months (IQR: 2.1-8.2) and 6.7 months (IQR: 3.9-12.6), respectively (χ2=4.372, P=0.037).Most of the adverse reactions during the treatment of the two groups were grades 1-2.In addition, no significant difference in the incidence of adverse reactions was found between two groups (P > 0.05). Conclusion Compared with fruquintinib alone, fruquintinib combined with sintilimab in the treatment of patients with MSS colorectal cancer after the failure of standard treatment has better clinical efficacy, and adverse drug reactions can be controlled.

Circulating tumor DNA (ctDNA) is increasingly being investigated as a tool to detect minimal residual disease in resected, stage I-III colorectal cancer. Recent ctDNA studies have indicated that detection of ctDNA following surgery for resectable colorectal cancer confers a significantly higher risk of recurrence than those with negative ctDNA postoperatively. In those with postoperative ctDNA positivity, clearance of minimal residual disease with adjuvant chemotherapy is a positive prognostic indicator. Lastly, ctDNA has demonstrated superior sensitivity to the conventional blood tumor marker carcinoembryonic antigen (CEA) and can offer median lead times of up to 11 months for radiographic detection of recurrence during the surveillance of resected, stage I-III colorectal cancer. In metastatic colorectal cancer (mCRC), there is growing evidence to suggest that plasma ctDNA can be used to monitor tumor response to conventional chemotherapy as well. The present case series demonstrated that plasma ctDNA is a predictor of tumor response to immunotherapy in patients with mCRC that are microsatellite stable or microsatellite instability high. Plasma ctDNA could serve as a dynamic marker of immunotherapy response even in colorectal tumors that were CEA non-producers. Overall, these findings add to ongoing efforts to establish the role of plasma ctDNA in monitoring response to immunotherapy in CRC.

Purpose: Several studies have demonstrated the effectiveness of anti-angiogenic drugs in combination with immune checkpoint inhibitors (ICIs) in patients with microsatellite stable (MSS) or mismatch repair proficient (pMMR) metastatic colorectal cancer (mCRC). However, whether combination radiotherapy (RT) can further improve the prognosis of mCRC patients after second-line treatment remains to be explored. Methods: Retrospective analysis of data from mCRC patients who received antiangiogenic targeted therapy (TT) and immunotherapy (IT) with or without RT after the failure of standard therapy. Progression-free survival (PFS), overall survival (OS), objective response rate (ORR), disease control rate (DCR), and safety were evaluated. Results: A total of 82 patients who received TT + IT were analyzed. For RT group (n = 42) versus NRT group (n = 40), ORR was 21.4% (9/42) versus 5.0% (2/40); DCR was 83.8% (35/42) versus 65.0% (26/40). Compared with NRT group, RT improved PFS (median: 5.0 vs. 3.6 months; p = 0.04) and OS (median: 15.2 vs. 7.2 months; p = 0.01). In addition, in the population receiving RT, the PFS of RT sequential/simultaneous TT + IT was superior to TT + IT sequential RT (median: 7.1 vs. 6.2 vs. 3.5 months, p = 0.004). Multivariate analysis suggested RT was an independent prognostic factor for PFS and OS. No treatment-related deaths were reported.Conclusions: Compared with TT + IT, RT combined with TT + IT improved survival outcomes in MSS/pMMR mCRC patients, with manageable toxicity. RT sequential/simultaneous TT + IT treatment is expected to be the optimal strategy for MSS/PMMR mCRC. [ABSTRACT FROM AUTHOR]

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Summary: Background: Immunotherapy has revolutionized the treatment of cancer. However, microsatellite stable (MSS) metastatic colorectal cancer (mCRC) shows a low response to PD-1 inhibitors. Antiangiogenic therapy can enhance anti-PD-1 efficacy, but it still cannot meet clinical needs. Increasing evidence supported a close relationship between gut microbiome and anti-PD-1 efficacy. This study aimed to explore the efficacy and safety of the combination of fecal microbiota transplantation (FMT) and tislelizumab and fruquintinib in refractory MSS mCRC. Methods: In the phase II trial, MSS mCRC patients were administered FMT plus tislelizumab and fruquintinib as a third-line or above treatment. The primary endpoint was progression-free survival (PFS). Secondary endpoints were overall survival (OS), objective response rate (ORR), disease control rate (DCR), duration of response (DoR), clinical benefit rate (CBR), safety and quality of life. Feces and peripheral blood were collected for exploratory biomarker analysis. This study is registered with Chictr.org.cn, identifier ChiCTR2100046768. Findings: From May 10, 2021 to January 17, 2022, 20 patients were enrolled. Median follow-up was 13.7 months. Median PFS was 9.6 months (95% CI 4.1–15.1). Median OS was 13.7 months (95% CI 9.3–17.7). Median DoR was 8.1 months (95% CI 1.7–10.6). ORR was 20% (95% CI 5.7–43.7). DCR was 95% (95% CI 75.1–99.9). CBR was 60% (95% CI 36.1–80.9). Nineteen patients (95%) experienced at least one treatment-related adverse event (TRAE). Six patients (30%) had grade 3–4 TRAEs, with the most common being albuminuria (10%), urine occult blood (10%), fecal occult blood (10%), hypertension (5%), hyperglycemia (5%), liver dysfunction (5%), hand-foot skin reaction (5%), and hypothyroidism (5%). No treatment-related deaths occurred. Responders had a high-abundance of Proteobacteria and Lachnospiraceae family and a low-abundance of Actinobacteriota and Bifidobacterium. The treatment did not change the structure of peripheral blood TCR repertoire. However, the expanded TCRs exhibited the characteristics of antigen-driven responses in responders. Interpretation: FMT plus tislelizumab and fruquintinib as third-line or above treatment showed improved survival and manageable safety in refractory MSS mCRC, suggesting a valuable new treatment option for this patient population. Funding: This study was supported by the National Natural Science Foundation of China (82102954 to Wensi Zhao) and the Special Project of Central Government for Local Science and Technology Development of Hubei Province (ZYYD2020000169 to Yongshun Chen).

For colorectal cancer (CRC), surgical resection remains essential for achieving good prognoses. Unfortunately, numerous patients with locally advanced CRC and metastatic CRC failed to meet surgical indications or achieve pathological complete response after surgery. Perioperative therapy has been proven to effectively lower tumor staging and reduce recurrence and metastasis. Immune checkpoint inhibitors (ICIs) have shown unprecedented prolongation of survival time and satisfactory safety in patients with high microsatellite instability/deficient mismatch repair (MSI-H/dMMR), while the therapeutic effect obtained by patients with mismatch repair-proficient or microsatellite stable (pMMR/MSS) was considered minimal. However, recent studies found that certain CRC patients with dMMR/MSI-H presented intrinsic or acquired immune resistance, and pMMR/MSS CRC patients can also achieve better efficacy. Therefore, more predictors are required for screening patients with potential clinical benefits. Since the discovery of synergistic effects between immunotherapy, chemotherapy, and radiotherapy, different immunotherapy-based therapies have been applied to the perioperative therapy of CRC in an increasing number of research. This review comprehensively summarized the past and current progress of different combinations of immunotherapy in perioperative clinical trials for CRC, focusing on the efficacy and safety, and points out the direction for future development. [ABSTRACT FROM AUTHOR]

Rectal cancer is a heterogeneous disease with complex genetic and molecular subtypes. Emerging progress of neoadjuvant therapy has led to increased pathological and clinical complete response (cCR) rates for microsatellite stable (MSS) rectal cancer, which responds poorly to immune checkpoint inhibitor alone. As a result, organ preservation of MSS rectal cancer as an alternative to radical surgery has gradually become a feasible option. For patients with cCR or near-cCR after neoadjuvant treatment, organ preservation can be implemented safely with less morbidity. Patient selection can be done either before the neoadjuvant treatment for higher probability or after with careful assessment for a favorable outcome. Those patients who achieved a good clinical response are managed with nonoperative management, organ preservation surgery, or radiation therapy alone followed by strict surveillance. The oncological outcomes of patients with careful selection and organ preservation seem to be noninferior compared with those of radical surgery, with lower postoperative morbidity. However, more studies should be done to seek better regression of tumor and maximize the possibility of organ preservation in MSS rectal cancer. [ABSTRACT FROM AUTHOR]

Objective: To assess the clinical efficacy of neoadjuvant chemoradiotherapy combined with immunotherapy for patients with microsatellite stable (MSS) locally advanced rectal cancer and provide evidence to support clinical decision-making. Methods: A systematic search was conducted on the PubMed, Embase, Cochrane Collaboration databases, conference summaries, and Chinese databases for clinical studies that investigated neoadjuvant chemoradiotherapy combined with immunotherapy for the treatment of locally advanced rectal cancer with MSS status. The search spanned from the inception of each database through July 2023. Data from the identified studies were extracted using a predesigned table, and efficacy outcomes were analyzed. An integrated analysis was conducted using Stata 12.0 software. Results: Eight studies were included, comprising 204 patients with locally advanced MSS rectal cancer who received chemoradiotherapy combined with immunotherapy. The integrated analysis revealed a pathologic complete remission rate of 0.33, a sphincter preservation rate of 0.86, an R0 resection rate of 0.83, a major pathologic remission rate of 0.33, and a clinical complete remission rate of 0.30. Conclusion: Neoadjuvant chemoradiotherapy combined with immunotherapy demonstrates significant short-term efficacy in MSS-type locally advanced rectal cancer, notably enhancing the pathologic complete remission and sphincter preservation rates. This combination is a recommended treatment for patients with MSS-type rectal cancer. [ABSTRACT FROM AUTHOR]

Background: Microsatellite stable (MSS) colorectal cancer (CRC) has been referred to as the "cold tumor" because of almost no response to anti-- programmed death-1 (PD-1) antibody. A recent REGONIVO trial showed that regorafenib plus nivolumab had an encouraging efficacy in MSS metastatic CRC (mCRC). However, only a small subset of patients may benefit from the combination therapy. We aim to evaluate the efficacy and safety data of immune checkpoint inhibitors combined with regorafenib in refractory MSS mCRC and to discover biomarkers that can effectively stratify the beneficial patient population. Methods: We retrospectively analyzed patients with MSS mCRC who received regorafenib combined with anti--PD-1 antibody therapy. The objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and status of gene mutation were reviewed and evaluated. Results: Twenty-one patients received combination treatment. At a median treatment duration of 4 months, one patient achieved complete response, three patients achieved partial response, and two patients achieved stable disease as the best response. The ORR and DCR were 19% and 28.5% in the overall population, respectively. The median PFS was 4 months, and the median OS was 25 months. Only erbb2 receptor tyrosine kinase 2/erbb3 receptor tyrosine kinase 3 (ERBB2/ ERBB3) mutation status was confirmed to be a potential predictive factor for effective treatment. In patients with ERBB2/ERBB3 mutation, ORR, DCR, and PFS exhibited significant improvements in comparison with that in wild-type patients. Grade 3 or higher treatment-related adverse events occurred in three patients (14.3%). Conclusions: Regorafenib in combination with PD-1 inhibitor provides a feasible treatment regimen for refractory MSS mCRC with tolerated toxicity. Patients with ERBB2/ERBB3 mutation may be the preferred population for this combination regimen. [ABSTRACT FROM AUTHOR]

Abstract Background Although the use of regorafenib plus nivolumab demonstrates promising outcomes in patients with refractory microsatellite stable (MSS) metastatic colorectal cancer (mCRC), this effect has not been substantiated in other studies. Moreover, a comparison between the outcomes of regorafenib and programmed cell death protein 1 (PD‐1) antibody combination therapy and regorafenib monotherapy remains unexplored. In this study, we aimed to assess whether regorafenib and PD‐1 antibody combination therapy is superior to regorafenib monotherapy as a third‐line treatment for MSS mCRC. Methods Patients with MSS mCRC who received regorafenib and PD‐1 antibody or regorafenib monotherapy as third‐line treatment were eligible for inclusion. Results In total, 179 patients were enrolled, of which 84 were administered regorafenib combined with a PD‐1 antibody and 95 were administered regorafenib monotherapy. Patients administered regorafenib combined with a PD‐1 antibody had similar progression‐free survival (PFS) as those on regorafenib monotherapy (median PFS was 2.4 months and 1.9 months, respectively, p = 0.086). The administration of regorafenib combined with a PD‐1 antibody resulted in significantly longer PFS than that seen with regorafenib monotherapy in both male (5.2 months vs. 2.4 months, p = 0.001) and female (3.9 months vs. 1.8 months, p = 0.037) patients without liver metastasis. Female patients with liver metastasis who were administered regorafenib combined with a PD‐1 antibody had shorter PFS than those administered regorafenib monotherapy (1.8 months vs. 2.0 months, p = 0.030). Conclusion Liver metastasis and sex are predictors of survival benefit following the addition of a PD‐1 antibody to regorafenib in patients with MSS mCRC.

The exploration of biomarkers predicting response to immune checkpoint inhibitors in microsatellite stability colorectal cancer can enable more patients to benefit from immunotherapy. Tumor mutational burden (TMB), POLE/POLD1 mutation, CMS classifications, MGMT methylation, and other indicators own the potential and value of predicting response to immune checkpoint inhibitors in microsatellite stability colorectal cancer. In this paper, we reviewed the related research on predictive biomarkers of immune checkpoint inhibitors in microsatellite stability colorectal cancer, provide a reference for the best treatment strategy for microsatellite stability colorectal cancer.

Background & Aims: In contrast to mismatch repair deficient colorectal carcinoma (CRC), MMR proficient (pMMR) CRC does not respond to immune checkpoint blockade. We studied immune checkpoint stimulation via glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) on ex vivo functionality of human tumor-infiltrating lymphocytes (TIL) isolated from pMMR primary CRC and liver metastases (CRLM). Methods: Using lymphocytes from resected tumor, adjacent tissues, and peripheral blood mononuclear cells (PBMC) of 132 pMMR primary CRC or CRLM patients, we determined GITR expression and the in vitro T-cell agonistic activity of recombinant GITR ligation. Results: Here, we show that GITR was overexpressed on TIL when compared with other stimulatory immune checkpoints (4-1BB, OX40). Its expression was enhanced in TIL compared with PBMC and adjacent tissues. Among CD4+ TIL, GITR expression was primarily expressed by CD45RA- FoxP3hi activated regulatory T cells. Within CD8+ TIL, GITR was predominantly expressed on functionally exhausted and putative tumor-reactive CD103+ CD39+ TIL. Strikingly, recombinant GITRL reinvigorated ex vivo TIL responses by significantly enhancing CD4+ and CD8+ TIL numbers. Dual treatment with GITRL and nivolumab (anti-PD1) enhanced CD8+ TIL expansion compared with GITRL monotherapy. Moreover, GITRL/anti-PD1 dual therapy further improved anti-PD1-mediated reinvigoration of interferon gamma secretion by exhausted CD8 TIL from primary CRC. Conclusions: GITR is overexpressed on CD4+ and CD8+ TIL from pMMR CRC and CRLM. Agonistic targeting of GITR enhances ex vivo human TIL functionality and may therefore be a promising approach for novel monotherapy or combined immunotherapies in primary pMRR CRC and CRLM.

Abstract Introduction A large proportion of indigenous African (IA) colorectal cancer (CRC) patients in South Africa are young (

Summary: Background: Microsatellite stable (MSS) and RAS-mutant metastatic colorectal cancer (mCRC) patients are characterized by an immunosuppressive microenvironment and a low response rate to immunotherapy. Chemotherapy and anti-angiogenesis therapy have been reported to potentially promote immunotherapy response. This study aims to assess the preliminary anti-tumor activity and safety of sintilimab plus bevacizumab, oxaliplatin and capecitabine as a treatment option for patients with RAS-mutant MSS mCRC. Methods: This study was an open-label, single-arm, phase II trial in China. Patients with unresectable, RAS-mutant and MSS metastatic colorectal adenocarcinoma received treatment by intravenous sintilimab (200 mg, day 1) plus bevacizumab (7.5 mg/kg, day 1), oxaliplatin (135 mg/m2, day 1) and oral capecitabine (1 g/m2, day 1–14) in each 21-day cycle. The primary endpoints included objective response rate (ORR) and adverse events. Biomarker analysis was performed to identify potential predictors of good response to treatment. This study is registered with ClinicalTrials.gov, number NCT04194359. Findings: Between April 2021 and December 2021, 25 patients were enrolled. Two (8%) patients showed complete response (CR), 19 (76%) had partial response (PR) and 4 (16%) presented with stable disease. ORR reached 84% (95% CI, 63.9–95.5) and the disease control rate was 100% (95% CI, 86.3–100). The median progression-free survival (PFS) was 18.2 months for the full analysis set. The most common treatment-related adverse events (TRAEs) in all grades were anemia (21/25, 84%), neutropenia (20/25, 80%), and hand-foot syndrome (14/25, 56%). The most frequent grade 3 or 4 TRAEs were neutropenia (3/25, 12%) and increased alanine transaminase (2/25, 8%). No grade 5 adverse events occurred. In the exploration of biomarkers, 5 patients could be characterized as TTN/OBSCN “double-hit” after treatment, and the copy number variants burden was significantly decreased in tumor tissues after treatment compared with the baseline. Nanostring panel RNA sequencing analysis indicated a better tumor immune microenvironment cell infiltration in CR/PR patients compared with non-CR/PR patients as well as the PFS-long (≥12.5 months) group compared with the PFS-short group. Interpretation: Combination treatment with sintilimab plus bevacizumab, oxaliplatin and capecitabine as first-line treatment demonstrated a promising antitumor activity and a manageable safety profile in RAS-mutant, MSS and unresectable mCRC. Exploratory biomarker assessment analysis showed that some RAS-mutant and MSS patients changed into “immune-hot” subtype after the treatment. Funding: This study was supported by the Key R&D Program of Zhejiang Province (2021C03125 to Ying Yuan), the National Natural Science Foundation of China (81872481 to Ying Yuan, 82072624 to Kefeng Ding), the Fundamental Research Funds for the Central Universities (No. 226-2022-00009 to Kefeng Ding), and the Zhejiang Provincial Natural Science Foundation of China (No. LY22H160024 to Hanguang Hu).

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths worldwide, despite several advances has been achieved in last decades. Few prognostic and predictive biomarkers guide therapeutic choice in metastatic CRC (mCRC), among which DNA mismatch repair deficiency and/or microsatellite instability (dMMR/MSI) holds a crucial role. Tumors characterized by dMMR/MSI benefit from immune checkpoint inhibitors. However, most of the mCRC patients (around 95%) are microsatellite stable (MSS), thereby intrinsically resistant to immunotherapy. This represents a clear unmet need for more effective treatments in this population of patients. In this review, we aim to analyze immune-resistance mechanisms and therapeutic strategies to overcome them, such as combinations of immunotherapy and chemotherapy, radiotherapy or target therapies specifically in MSS mCRC. We also explored both available and potential biomarkers that may better select MSS mCRC patients for immunotherapy. Lastly, we provide a brief overview on future perspectives in this field, such as the gut microbiome and its potential role as immunomodulator. [ABSTRACT FROM AUTHOR]

Background: Although the use of regorafenib plus nivolumab demonstrates promising outcomes in patients with refractory microsatellite stable (MSS) metastatic colorectal cancer (mCRC), this effect has not been substantiated in other studies. Moreover, a comparison between the outcomes of regorafenib and programmed cell death protein 1 (PD‐1) antibody combination therapy and regorafenib monotherapy remains unexplored. In this study, we aimed to assess whether regorafenib and PD‐1 antibody combination therapy is superior to regorafenib monotherapy as a third‐line treatment for MSS mCRC. Methods: Patients with MSS mCRC who received regorafenib and PD‐1 antibody or regorafenib monotherapy as third‐line treatment were eligible for inclusion. Results: In total, 179 patients were enrolled, of which 84 were administered regorafenib combined with a PD‐1 antibody and 95 were administered regorafenib monotherapy. Patients administered regorafenib combined with a PD‐1 antibody had similar progression‐free survival (PFS) as those on regorafenib monotherapy (median PFS was 2.4 months and 1.9 months, respectively, p = 0.086). The administration of regorafenib combined with a PD‐1 antibody resulted in significantly longer PFS than that seen with regorafenib monotherapy in both male (5.2 months vs. 2.4 months, p = 0.001) and female (3.9 months vs. 1.8 months, p = 0.037) patients without liver metastasis. Female patients with liver metastasis who were administered regorafenib combined with a PD‐1 antibody had shorter PFS than those administered regorafenib monotherapy (1.8 months vs. 2.0 months, p = 0.030). Conclusion: Liver metastasis and sex are predictors of survival benefit following the addition of a PD‐1 antibody to regorafenib in patients with MSS mCRC. [ABSTRACT FROM AUTHOR]

Objective: Immune checkpoint inhibitors have been widely used in the treatment of endometrial cancer (EC) with microsatellite instability-hypermutated (MSI-H). However, there is an unmet need for microsatellite stable (MSS) EC because of their modest activity. This study aimed to identify potential immune-related biomarkers in MSS EC. Methods: One hundred and twenty-three patients with EC who underwent hysterectomy were enrolled. MSI status was determined using MSI analysis and/or immunohistochemical staining for mismatch repair proteins. Immunohistochemical analysis of programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), PD-L2, cytotoxic T-lymphocyteassociated protein 4 (CTLA-4), cluster of differentiation 3 (CD3), CD8, lymphocyte activation gene-3 (LAG-3), indoleamine 2,3-dioxygenase 1 (IDO1), phosphatase and tensin homolog (PTEN), p53, AT-rich interactive domain-containing protein 1A (ARID1A), and ß-catenin was performed using tissue microarray blocks. Results: Among 123 patients, 95 (77.2%) were classified as having MSS. Within EC with MSS, PD-L1 positivity was significantly associated with positive PD-1 (p<0.001), CTLA-4 (p<0.001), CD3 (p=0.002), CD8 (p<0.001), and LAG-3 (p<0.001). In the univariate analysis, positive PD-1 (odds ratio [OR]=9.281; 95% confidence interval [CI]=2.560-33.653; p<0.001), CTLA-4 (OR=5.33; 95% CI=1.418-19.307; p=0.005), CD3 (OR=5.571; 95% CI=1.746-17.775; p=0.004), CD8 (OR=6.909; 95% CI=2.647-18.037; p<0.001), and LAG-3 (OR=9.75; 95% CI=1.947-48.828; p=0.005) were significantly associated with PD-L1 positivity in MSS EC. In the multivariate analysis, LAG-3 demonstrated a significant association with positive PD-L1 expression in MSS EC (OR=5.061; 95% CI=1.534-16.693; p=0.023). Conclusion: In patients with MSS EC harboring PD-L1, LAG-3 may be a potential immunotherapeutic target. Clinical trials investigating the role of anti-LAG-3 antibodies, alone or in combination with other immunotherapies, are warranted. [ABSTRACT FROM AUTHOR]

Combination regorafenib, ipilimumab, and nivolumab (RIN) was evaluated in a phase 1 nonrandomized study (NCT04362839) of refractory microsatellite stable (MSS) metastatic colorectal cancer. Promising antitumor activity was previously reported in the non-liver metastatic (NLM) population. This updated analysis describes long-term survival outcomes in the NLM cohort and highlights durable remissions with potential cure following completion of RIN therapy. Between May 2020 and January 2022, 39 patients with refractory MSS metastatic colorectal cancer were enrolled. Patients received RIN until progression, unacceptable toxicity, or completion at two years. The primary endpoint was recommended phase 2 dose (RP2D) selection. Secondary endpoints were safety, overall response rate (ORR), progression-free survival (PFS) and overall survival (OS) at the RP2D level. 22 patients with refractory non-liver metastatic MSS colorectal cancer were treated at the RP2D of RIN. ORR was 36.4 % (8/22 patients), and median PFS was 5.0 months (95 % CI: 3–9). After a median follow-up of 42 months, the 1-, 2-, and 3-year PFS rates were 24.1 %, 24.1 %, and 19.3 % by RECIST. The median OS was 27.5 months (95 % CI: 14.0 to NE). At data cutoff, 6 patients had ongoing clinical benefit, including 3 responders who remain disease-free > 18 months after treatment completion. With extended follow-up, RIN combination therapy demonstrated durable clinical benefit in a subset of patients with NLM MSS metastatic colorectal cancer, including potential cure in 3 responders who remain disease-free > 18 months after treatment completion. • Regorafenib, ipilimumab, and nivolumab was potentially curative in microsatellite stable tumors. • Long-term efficacy was observed only in the non-liver metastatic colorectal cancer cohort. • 3-year progression-free survival was 19.3 %. • 3-year overall survival was 40.9 %. • 3 responders remain disease-free for > 18 months after completing RIN therapy. [ABSTRACT FROM AUTHOR]

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths worldwide, despite several advances has been achieved in last decades. Few prognostic and predictive biomarkers guide therapeutic choice in metastatic CRC (mCRC), among which DNA mismatch repair deficiency and/or microsatellite instability (dMMR/MSI) holds a crucial role. Tumors characterized by dMMR/MSI benefit from immune checkpoint inhibitors. However, most of the mCRC patients (around 95%) are microsatellite stable (MSS), thereby intrinsically resistant to immunotherapy. This represents a clear unmet need for more effective treatments in this population of patients. In this review, we aim to analyze immune-resistance mechanisms and therapeutic strategies to overcome them, such as combinations of immunotherapy and chemotherapy, radiotherapy or target therapies specifically in MSS mCRC. We also explored both available and potential biomarkers that may better select MSS mCRC patients for immunotherapy. Lastly, we provide a brief overview on future perspectives in this field, such as the gut microbiome and its potential role as immunomodulator.

Summary: Background: Anti-programmed cell death protein 1 antibodies plus multikinase inhibitors have shown encouraging activity in several tumour types, including colorectal cancer. This study assessed regorafenib plus nivolumab in patients with microsatellite stable/mismatch repair-proficient metastatic colorectal cancer. Methods: This single-arm, open-label, multicentre phase 2 study enrolled adults from 13 sites in the USA with previously treated advanced microsatellite stable/mismatch repair-proficient metastatic colorectal cancer. Eligible patients had known extended RAS and BRAF status, progression or intolerance to no more than two (for extended RAS mutant) or three (for extended RAS wild type) lines of systemic chemotherapy and an Eastern Cooperative Oncology Group performance status of 0 or 1. Regorafenib 80 mg/day was administered orally for 3 weeks on/1 week off (increased to 120 mg/day if 80 mg/day was well tolerated) with intravenous nivolumab 480 mg every 4 weeks. Primary endpoint was objective response rate. Secondary endpoints included safety, overall survival, and progression-free survival. Exploratory endpoints included biomarkers associated with antitumour activity. Patients who received at least one dose of study intervention were included in the efficacy and safety analyses. Tumour assessments were carried out every 8 weeks for the first year, and every 12 weeks thereafter until progressive disease/end of the study, and objective response rate was analysed after all patients had met the criteria for primary completion of five post-baseline scans and either 10-months’ follow-up or drop out. This trial is registered with ClinicalTrials.gov, number NCT04126733. Findings: Between 14 October 2019 and 14 January 2020, 94 patients were enrolled, 70 received treatment. Five patients had a partial response, yielding an objective response rate of 7% (95% CI 2.4–15.9; p = 0.27). All responders had no liver metastases at baseline. Median overall survival (data immature) and progression-free survival were 11.9 months (95% CI 7.0–not evaluable) and 1.8 months (95% CI 1.8–2.4), respectively. Most patients (97%, 68/70) experienced a treatment-related adverse event; 51% were grade 1 or 2, 40% were grade 3, 3% were grade 4, and 3% were grade 5. The most common (≥20%) events were fatigue (26/70), palmar-plantar erythrodysesthesia syndrome (19/70), maculopapular rash (17/70), increased blood bilirubin (14/70), and decreased appetite (14/70). Higher baseline expression of tumour biomarkers of immune sensitivity correlated with antitumour activity. Interpretation: Further studies are warranted to identify subgroups of patients with clinical characteristics or biomarkers that would benefit most from treatment with regorafenib plus nivolumab. Funding: Bayer/Bristol Myers Squibb.

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Colorectal cancer (CRC) is one of the most prevalent and lethal cancers worldwide, ranking third in incidence and second in mortality. While immunotherapy has shown promise in patients with deficient mismatch repair (dMMR) or high microsatellite instability (MSI-H), its effectiveness in proficient mismatch repair (pMMR) or microsatellite stable (MSS) CRC remains limited. Recent advances highlight the gut microbiota as a potential modulator of anti-tumor immunity. The gut microbiome can significantly influence the efficacy of immune checkpoint inhibitors (ICIs), especially in pMMR/MSS CRC, by modulating immune responses and systemic inflammation. This review explores the role of the gut microbiota in pMMR/MSS CRC, the mechanisms by which it may enhance immunotherapy, and current strategies for microbiota modulation. We discuss the potential benefits of combining microbiota-targeting interventions with immunotherapy to improve treatment outcomes for pMMR/MSS CRC patients., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2025 Elsevier B.V. All rights reserved.)

Introduction: A large proportion of indigenous African (IA) colorectal cancer (CRC) patients in South Africa are young (< 50 years), with no unique histopathological or molecular characteristics. Anatomical site as well as microsatellite instability (MSI) status have shown to be associated with different clinicopathological and molecular features. This study aimed to ascertain key histopathological features in microsatellite stable (MSS) and low-frequency MSI (MSI-L) patients, to provide insight into the mechanism of the disease.Methods: A retrospective cohort (2011-2015) of MSS/MSI-L CRC patient samples diagnosed at Charlotte Maxeke Johannesburg Academic Hospital was analyzed. Samples were categorized by site [right colon cancer (RCC) versus left (LCC)], ethnicity [IA versus other ethnic groups (OEG)] and MSI status (MSI-L vs MSS). T-test, Fischer's exact and Chi-square tests were conducted.Results: IA patients with LCC demonstrated an increased prevalence in males, sigmoid colon, signet-ring-cell morphology, MSI-L with BAT25/26 marker instability and advanced disease association.Conclusion: This study revealed distinct histopathological features for LCC, and suggests BAT25 and BAT26 as negative prognostic markers in African CRC patients. Larger confirmatory studies are recommended. [ABSTRACT FROM AUTHOR]

Objective To evaluate the efficacy and safety of Regorafenib combined with PD ⁃ 1 inhibitors for the third ⁃line or above treatment of advanced microsatellite stable (MSS) colorectal cancer (CRC). Methods A total of 22 patients with advanced MSS CRC, who received Regorafenib combined with PD ⁃1 inhibitors or Regorafenib monotherapy for third ⁃line or above treatment in Renmin Hospital of Wuhan University from January 2019 to March 2022, were selected as the research objects, including 10 patients in the combination therapy group and 12 patients in the Regorafenib monotherapy group. The progression⁃free survival (PFS), overall survival (OS), objective response rate (ORR), disease control rate (DCR) and incidence of adverse events (AEs) were compared between the two groups. Results Kaplan⁃Meier survival analysis showed that there was no significant difference in median OS between the combination therapy group and the monotherapy group (6.10 months vs 6.13 months, P=0.827). However, the combination therapy group had better median PFS than the monotherapy group (4.00 months vs 1.63 months, P=0.025), and the DCR in combination therapy group were also better than the monotherapy group, though there was no statistical significance (70.0% vs 25.0%, P=0.084). No grade 4 or higher AEs were observed in either group. The overall incidence of AEs (100.0% vs 91.7%) and the incidence of grade ≥3 AEs (30.0% vs 25.0%) were not statistically different between the combination therapy group and the monotherapy group (all P>0.05). Conclusions Compared with Regorafenib monotherapy, Regorafenib combined with PD ⁃1 inhibitors as the third ⁃line or above treatment regimen for advanced MSS CRC may bring benefits for PFS, and it is worthy of further clinical trials. [ABSTRACT FROM AUTHOR]

Objectives: The antitumor activity of nivolumab plus regorafenib in colorectal cancer from a phase Ib REGONIVO study is encouraging. The present study was conducted to evaluate the efficacy and safety of regorafenib or fruquintinib plus sintilimab as third-line or above therapy in patients with microsatellite stable (MSS) metastatic colorectal cancer. Methods: Patients with MSS metastatic colorectal cancer who have failed from prior treatment and received regorafenib or fruquintinib plus sintilimab as thirdline or above therapy from January 2019 to December 2020 were prospectively analyzed based on real-world clinical practice. The primary end point was progression free survival (PFS). Secondary end points included objective response rate (ORR), disease control rate (DCR), overall survival (OS), and safety. Results: 42 patients received regorafenib plus sintilimab(RS), and the other 30 patients received fruquintinib plus sintilimab(FS). In the general population, the ORR and DCR were 13.9% and 70.8%, and the median PFS and OS was 4.2(95% CI=2.9-5.5) and 10.5 (95% CI=8.6-12.4) months, respectively. There were no statistically significant differences between RS and FS group in PFS (3.5(2.2-4.8) vs. 5.5(3.5-7.5) months, P=0.434) and OS (11.0(7.0-15.0) vs. 10.5(3.8-17.2) months, P=0.486). Subgroup analysis suggested that patients without liver metastasis responded well to this combination regimen (ORR: 21.4% vs. 9.1%) and obtained better OS (26(8.8-43.2) vs. 10.0(7.4-12.6) months, P=0.016). The incidence of Grade 3-4 adverse events (AEs) was 15.3% and the toxicities were generally tolerable and manageable. Conclusions: Regorafenib or fruquintinib plus sintilimab as third-line or above therapy provide a feasible treatment regimen for MSS metastatic colorectal cancer with tolerated toxicity. Patients without liver metastasis may be the preferred population for this combination regimen. [ABSTRACT FROM AUTHOR]

ObjectivesThe antitumor activity of nivolumab plus regorafenib in colorectal cancer from a phase Ib REGONIVO study is encouraging. The present study was conducted to evaluate the efficacy and safety of regorafenib or fruquintinib plus sintilimab as third-line or above therapy in patients with microsatellite stable (MSS) metastatic colorectal cancer.MethodsPatients with MSS metastatic colorectal cancer who have failed from prior treatment and received regorafenib or fruquintinib plus sintilimab as third-line or above therapy from January 2019 to December 2020 were prospectively analyzed based on real-world clinical practice. The primary end point was progression free survival (PFS). Secondary end points included objective response rate (ORR), disease control rate (DCR), overall survival (OS), and safety.Results42 patients received regorafenib plus sintilimab(RS), and the other 30 patients received fruquintinib plus sintilimab(FS). In the general population, the ORR and DCR were 13.9% and 70.8%, and the median PFS and OS was 4.2(95% CI=2.9-5.5) and 10.5 (95% CI=8.6-12.4) months, respectively. There were no statistically significant differences between RS and FS group in PFS (3.5(2.2-4.8) vs. 5.5(3.5-7.5) months, P=0.434) and OS (11.0(7.0-15.0) vs. 10.5(3.8-17.2) months, P=0.486). Subgroup analysis suggested that patients without liver metastasis responded well to this combination regimen (ORR: 21.4% vs. 9.1%) and obtained better OS (26(8.8-43.2) vs. 10.0(7.4-12.6) months, P=0.016). The incidence of Grade 3-4 adverse events (AEs) was 15.3% and the toxicities were generally tolerable and manageable.ConclusionsRegorafenib or fruquintinib plus sintilimab as third-line or above therapy provide a feasible treatment regimen for MSS metastatic colorectal cancer with tolerated toxicity. Patients without liver metastasis may be the preferred population for this combination regimen.

Simple Summary: There is a crucial need to improve treatment regimens in patients with recurrent endometrial cancer. Although immunotherapy treatments have shown impressive benefit in microsatellite instability-high endometrial cancer, they have been less predictable in the majority of endometrial cancers, which are microsatellite stable. Our aim was to characterize clinical outcomes in patients with recurrent microsatellite stable endometrial cancer treated in early-phase immunotherapy clinical trials in order unravel treatment regimens that would improve response and survival. Our findings suggest that utilizing immunotherapy in combination with other non-immunotherapy agents resulted in greater duration of disease control and improved survival outcomes compared to immunotherapy only (monotherapy) or in combination with other immunotherapy agents. Future studies are needed to validate these findings. Recurrent microsatellite stable (MSS) endometrial cancer has poor response to conventional therapy and limited efficacy with immune checkpoint monotherapy. We conducted a retrospective study of recurrent MSS endometrial cancer patients enrolled in immunotherapy-based clinical trials at MD Anderson Cancer Center between 1 January 2010 and 31 December 2019. Patients were evaluated for radiologic response using RECIST 1.1 criteria, progression-free survival (PFS), and overall survival (OS). Thirty-five patients were treated with immune checkpoint inhibitors: 8 with monotherapy, 17 with immunotherapy (IO) in combination with another IO-only, and 10 with IO in combination with non-IO therapy. Among those treated with combination IO plus non-IO therapy, one had a partial response but 50% had clinical benefit. Patients who received combination IO plus non-IO therapy had improved PFS compared to those who received monotherapy (HR 0.56, 95% CI 0.33–0.97; p = 0.037) or combination IO-only therapy (HR 0.36, 95% CI 0.15–0.90; p = 0.028) and had improved OS when compared to monotherapy after adjusting for prior lines of therapy (HR 0.50, 95% CI 0.27–0.95; p = 0.036). The potential beneficial clinical outcomes of combination IO plus non-IO therapy in MSS endometrial cancer should be validated in a larger study. [ABSTRACT FROM AUTHOR]

DNA transposons are exposed to a molecular domestication process, which results in the formation of neogenes, which may play a role in human genetic instability. TIGD3 (Tigger-derived [TIGD] family of proteins) is one of these Neogene, and its role in the human genome is unknown. Aim: The expression of Neogene TIGD3 in colorectal cancer cell lines and its putative function in carcinogenesis are being investigated. Method: The protein expression of the TIGD3 gene was investigated using the western blot method in twelve colorectal cancer cell lines (HCT116, SW48, LOVO, DLD1) that are microsatellite instable MSI, (SW480, SW620, HT29, LS123, COLO205, T84, SW403, SW1463) that are microsatellite stable MSS, and in healthy colon tissue as a control in our study. Results: The expression of the TIGD3 protein was found in all twelve colorectal cancer cell lines, with varying degrees of expression and numerous isoforms, which was not found in healthy colon tissue. Conclusion: There may be a link between colorectal cancer evolution or progression and TIGD3 gene expression. [ABSTRACT FROM AUTHOR]

Colon adenocarcinoma (COAD) is one of the leading causes of cancer-associated deaths worldwide. Patients with microsatellite instability-high (MSI-H) tumors were shown to highly benefit from immune checkpoint inhibitors (ICIs) than patients with microsatellite stable (MSS) tumors. Furthermore, the infiltration of immune cells and the expression of cancer stem cells (CSCs) in COAD were associated with the anti-tumor immune response. However, the potential mechanisms showing the relationship between microsatellite instability and CSCs or tumor-infiltrating immune cells (TIICs) have not been elucidated. Accumulating evidence reveals that achaete-scute family bHLH transcription factor 2 (ASCL2) plays a crucial role in the initiation and progression of COAD and drug resistance. However, the specific biological functions of ASCL2 in COAD remain unknown. In this study, we performed weighted gene co-expression network analysis (WGCNA) between MSS and MSI-H subsets of COAD. The results revealed that ASCL2 was a potential key candidate in COAD. Subsequently, the single-cell RNA-seq revealed that ASCL2 was positively associated with CSCs. Further, ASCL2 was shown to indirectly affect tumor immune cell infiltration by negatively regulating the expression of DUSP4. Finally, we inferred that the immunotherapy-sensitive role of ASCL2/DUSP4 axis on COAD is partly attributed to the activation of WNT/β-catenin pathway. In conclusion, this study revealed that ASCL2 was positively correlated to CSCs and tumor immune infiltration in COAD. Therefore, ASCL2 is a promising predictor of clinical responsiveness to anti-PD-1/PD-L1 therapy in COAD. [ABSTRACT FROM AUTHOR]

Colorectal carcinoma (CRC) is the second leading cause of cancer mortality worldwide. CRC is stratified into two major groups: microsatellite stable (MSS) and microsatellite instability‐high (MSI‐H). MSS CRC constitutes the majority of cases, has worse overall prognosis, and thus far has failed to respond to immunotherapies targeting the immune checkpoint receptors PD‐1, PD‐L1, and CTLA‐4. Here we examined the alternate immunotherapy targets Tim‐3 and Lag‐3, as well as PD‐1, on immune cells in a cohort of MSS CRC using immunohistochemistry and flow cytometry together with mutational analysis and clinical data. We found that PD‐1 was variably expressed across CD4+ tumor‐infiltrating lymphocyte (TIL) subtypes, and Tim‐3 was mostly restricted to CD4+ regulatory T cells. Lag‐3, when detected by flow cytometry, was largely coexpressed with Tim‐3 and PD‐1 in CD4+ TILs. Furthermore, Tim‐3+PD‐1+ CD8+ TILs accumulated in the tumor and exhibited a dysfunctional or 'exhausted' phenotype. Notably, we observed a subset of patients with a high proportion of Tim‐3−PD‐1− CD8+ TILs and, conversely, a low proportion of Tim‐3+PD‐1+ CD8+ TILs, thus stratifying MSS CRC patients based on a feature of immune exhaustion (MSS‐ImmEx). MSS‐ImmExhi patients had abundant Tim‐3+PD‐1+ CD8+ TILs, PD‐1+ CD4+ effector, and regulatory T cells, and were enriched for left‐sided colon tumors and mutations in the APC tumor‐suppressor gene. We further investigated the spatial organization of Tim‐3, Lag‐3, PD‐1, and PD‐L1 by immunohistochemistry and found higher levels in the tumor margin; however, MSS‐ImmExhi tumors exhibited a higher density of Tim‐3+ cells in the tumor center over MSS‐ImmExlow tumors. Immunofluorescence revealed a higher density of PD‐1+/CD8+ cells in the tumor center in this group. Our findings identify a subset of MSS CRC that exhibits evidence of higher prior immune activation (MSS‐ImmExhi) in which therapies targeting Tim‐3 in conjunction with anti‐PD‐1 or other immunotherapies may provide clinical benefit. © 2022 The Pathological Society of Great Britain and Ireland. [ABSTRACT FROM AUTHOR]

Objective: Microsatellite instability (MSI) due to defective DNA mismatch repair has emerged as an actionable biomarker in advanced endometrial cancer (aEC). Currently, there are no treatment patterns and outcomes data in non-MSI-high (non-MSI-H) or mismatch repair proficient (pMMR) aEC patients following prior systemic therapy (FPST). Our goal was to describe real-world data in this population in the US in 2019 and prior years. Methods: Endometrial Cancer Health Outcomes (ECHO) is a retrospective patient chart review study conducted in the US. Patients with non-MSI-H/pMMR aEC and progression between 06/01/2016–06/30/2019 FPST were eligible. Data collected included patient demographics, clinical and treatment characteristics, and clinical outcomes. Kaplan-Meier analyses were performed to estimate time to treatment discontinuation, real-world progression-free survival (rwPFS), and overall survival (OS), separately by treatment category. Results: A total of 165 eligible patients initiated second-line therapy with chemotherapy ± bevacizumab (n = 140) or hormonal therapy (n = 25). Median age was 66.0 years at aEC diagnosis, 70.2% were Stage IIIB-IV, 40.0% had ECOG ≥ 2 at second-line therapy initiation. Median rwPFS was 5.0 months (95% CI: 4.0–6.0) for patients receiving chemotherapy ± bevacizumab and 5.5 months (95% CI: 3.0–29.0) for those receiving hormonal therapy. Median OS was 10.0 months (95% CI: 8.0–13.0) and 9.0 months (95% CI: 6.0-NA) in these groups, respectively. Conclusions: Non-MSI-H/pMMR patients who initiated second-line therapy with chemotherapy ± bevacizumab or hormonal therapy had poor clinical outcomes with a median survival less than 1 year and rwPFS less than 6 months. This was the first study to define the clinical unmet need in patients with non-MSI-H/pMMR aEC with conventional therapy.

Colon adenocarcinoma (COAD) is one of the leading causes of cancer-associated deaths worldwide. Patients with microsatellite instability-high (MSI-H) tumors were shown to highly benefit from immune checkpoint inhibitors (ICIs) than patients with microsatellite stable (MSS) tumors. Furthermore, the infiltration of immune cells and the expression of cancer stem cells (CSCs) in COAD were associated with the anti-tumor immune response. However, the potential mechanisms showing the relationship between microsatellite instability and CSCs or tumor-infiltrating immune cells (TIICs) have not been elucidated. Accumulating evidence reveals that achaete-scute family bHLH transcription factor 2 (ASCL2) plays a crucial role in the initiation and progression of COAD and drug resistance. However, the specific biological functions of ASCL2 in COAD remain unknown. In this study, we performed weighted gene co-expression network analysis (WGCNA) between MSS and MSI-H subsets of COAD. The results revealed that ASCL2 was a potential key candidate in COAD. Subsequently, the single-cell RNA-seq revealed that ASCL2 was positively associated with CSCs. Further, ASCL2 was shown to indirectly affect tumor immune cell infiltration by negatively regulating the expression of DUSP4. Finally, we inferred that the immunotherapy-sensitive role of ASCL2/DUSP4 axis on COAD is partly attributed to the activation of WNT/β-catenin pathway. In conclusion, this study revealed that ASCL2 was positively correlated to CSCs and tumor immune infiltration in COAD. Therefore, ASCL2 is a promising predictor of clinical responsiveness to anti-PD-1/PD-L1 therapy in COAD.

Background/Aim: Better stratification of the risk of relapse will help select the right patients for adjuvant treatment and improve targeted therapies for patients with colon cancer. Materials and Methods: To understand why a subset of tumors relapse, we compared the proteome of two groups of patients with colon cancer with similar stage, stratified based on the presence or absence of recurrence. Results: Using tumor biopsies from the primary operation, we identified dissimilarity between recurrent and nonrecurrent mismatch satellite stable colon cancer and found that signaling related to immune activation and inflammation was associated with relapse. Conclusion: Immune modulation may have an effect on mismatch satellite stable colon cancer. At present, immune therapy is offered primarily to microsatellite instable colon cancer. Hopefully, immune therapy in mismatch satellite stable colon cancer beyond PD-1 and PD-L1 inhibitors can be implemented. [ABSTRACT FROM AUTHOR]

Primary analysis of the open-label, single-arm, phase II RENMIN-215 trial (primary data cutoff date: July 10, 2023) showed promising efficacy and tolerable safety with tislelizumab plus fruquintinib and fecal microbiota transplantation (FMT) in patients with refractory microsatellite stable (MSS) metastatic colorectal cancer (mCRC). Here, we reported updated survival and safety results with a median follow-up of 34.0 months (data cut-off May 20, 2024), as well as patient-reported outcomes and laboratory analysis. Twenty patients with MSS mCRC resistant or refractory to at least second-line therapy were enrolled and received tislelizumab plus fruquintinib and FMT. The primary endpoint was progression-free survival. Secondary endpoints included overall survival (OS), objective response rate (ORR), disease control rate, safety, health-related quality of life questionnaire and exploratory laboratory tests. In addition, 94 mCRC patients who received third-line or above immunotherapy in real world were screened for propensity score matching (PSM) analysis to compare efficacy. Our results showed that the median OS was 13.7 months (95% CI, 9.3-17.7), and the ORR was 20.0% (95% CI, 5.7-43.7). After PSM, the median OS benefit of the study regimen remained statistically significant (HR = 0.26; 95% CI, 0.07-0.95; P = 0.042). Patients with primary tumor surgery had better clinical outcomes. No new safety concerns were detected. Seven (35.0%) patients had one or more grade 3 treatment-related adverse events. The majority of patients had improved or stable global health status (GHS). Median time to deterioration for GHS was 7.7 months. Peripheral blood lymphocyte analysis showed that increased gamma-delta 2 T cells were positively associated with improved response and survival. To conclude, the updated results provide further evidence of sustained antitumor activity of tislelizumab plus fruquintinib and FMT in heavily pretreated MSS mCRC patients with a consistent safety profile., Competing Interests: None., (AJCR Copyright © 2024.)

Immune checkpoint inhibitor (ICI) has changed the situation of anti-tumor therapy. Several phase I/II clinical trials explored ICI-based combinations in microsatellite stable (MSS) metastatic colorectal cancer (mCRC) with mixed outcomes. However, real-world data regarding ICI-based combinations in this population is lacking. This retrospective study aimed to evaluate the efficacy and safety of ICI in MSS mCRC patients in third-line or above setting. A total of 143 eligible patients who received third-line or above ICI monotherapy or ICI-based combinations at the Cancer Center of Renmin Hospital of Wuhan University from June 2019 to April 2024 were included in this study. The primary endpoints were real-world median progression-free survival (PFS) and overall survival (OS), and the secondary endpoints included objective response rate (ORR), disease control rate (DCR), safety and prognostic analyses. Results showed that the median PFS was 4.6 months, and the median OS was 11.8 months, with an ORR of 11.2% and a DCR of 72.7%. ICI plus small molecule tyrosine kinase inhibitors have become the most popular combination for MSS mCRC patients at third-line or above setting with a median PFS of 4.4 months and OS of 10.1 months. The subgroup of patients with liver metastasis had worse clinical outcomes and liver metastasis was an independent prognostic factor for PFS (HR = 2.35, 95% CI, 1.54-3.59; P = 0.000) and OS (HR = 1.77, 95% CI, 1.06-2.96; P = 0.030). Forty-eight patients received cross-line ICI and obtained significantly improved OS (15.8 months vs 10.2 months; HR = 0.59, 95% CI, 0.38-0.89; P = 0.017). No new safety concerns were detected. Grade 3/4 treatment-related adverse events were generally controllable, with an incidence of 39.9%. To conclude, ICI-based combinations provide survival benefits for these heavily pretreated MSS mCRC patients with manageable safety, which is worthy of further study., Competing Interests: None., (AJCR Copyright © 2024.)

Background: Microsatellite stable (MSS) metastatic colorectal cancer (CRC) remains predominantly managed with chemotherapy. The use of immunotherapy, whether alone or in combination with other systemic or local treatments, displays limited success, especially in the context of active liver metastases (LM). The mechanisms responsible for this resistance are not fully understood., Methods: We conducted a comprehensive search across electronic databases such as Medline, PubMed, Google Scholar and ScienceDirect. This search targeted translational studies evaluating the liver tumour immune microenvironment and immune tolerance mechanisms in CRC with LM and prospective studies that assessed immunotherapy either as a standalone treatment or in combination with other systemic or local therapies for patients diagnosed with MSS CRC. Our primary objectives included elucidating the mechanisms of resistance originating from LM in a non-systematic literature review and presenting a summary of the outcomes observed in prospective trials utilising immune checkpoint inhibitors (ICIs), with a focus on the presence of LM., Findings: There were 16 prospective trials evaluating immunotherapy for metastatic CRC comprising 1,713 patients. Response rates to immunotherapy inpatients with colorectal liver metastases (CRLM) varied from 0% to 23%. Overall, reduced or null responses to immunotherapy in the presence of liver metastasis in comparison to patients without liver involvement were observed., Conclusion: Studies consistently show the resistance derived from classical ICI, both alone and in combination with other systemic treatments in patients with CRLM. The design of upcoming trials using immunotherapy should consider LM as a stratification factor or contemplate excluding patients with liver involvement., Competing Interests: The authors declare no conflict of interest with the present manuscript., (© the authors; licensee ecancermedicalscience.)

Background: Cohorts A, C, and E of the phase Ib KEYNOTE-651 study evaluated pembrolizumab + binimetinib ± chemotherapy in microsatellite stable/mismatch repair-proficient metastatic colorectal cancer., Patients and Methods: Patients received pembrolizumab 200 mg every 3 weeks plus binimetinib 30 mg twice daily alone (cohort A; previously treated with any chemotherapy) or with 5-fluorouracil, leucovorin, oxaliplatin (cohort C; previously untreated) or 5-fluorouracil, leucovorin, irinotecan (cohort E; previously treated with 1 line of therapy including fluoropyrimidine + oxaliplatin-based regimen) every 2 weeks. Binimetinib dose-escalation to 45 mg twice daily was planned in all cohorts using a modified toxicity probability interval design (target dose-limiting toxicity [DLT], 30%). The primary endpoint was safety; investigator-assessed objective response rate was secondary., Results: In cohort A, 1/6 patients (17%) had DLTs with binimetinib 30 mg; none occurred in 14 patients with 45 mg. In cohort C, 3/9 patients (33%) had DLTs with binimetinib 30 mg; dose was not escalated to 45 mg. In cohort E, 1/5 patients (20%) had DLTs with binimetinib 30 mg; 5/10 patients (50%) had DLTs with 45 mg. Enrollment was stopped in cohort E binimetinib 45 mg and deescalated to 30 mg; 2/4 additional patients (50%) had DLTs with binimetinib 30 mg (total 3/9 [33%] had DLTs with binimetinib 30 mg). Objective response rate was 0% in cohort A, 9% in cohort C, and 15% in cohort E., Conclusion: Per DLT criteria, binimetinib + pembrolizumab (cohort A) was tolerable, binimetinib + pembrolizumab + 5-fluorouracil, leucovorin, oxaliplatin (cohort C) did not qualify for binimetinib dose escalation to 45 mg, and binimetinib + pembrolizumab + 5-fluorouracil, leucovorin, irinotecan (cohort E) required binimetinib dose reduction from 45 to 30 mg. No new safety findings were observed across cohorts. There was no apparent additive efficacy when binimetinib + pembrolizumab was added to chemotherapy. Data did not support continued enrollment in cohorts C and E., Competing Interests: Disclosure E. X. Chen reports advisory/consultancy roles from AstraZeneca, Eisai, and GSK; research funding to their institution from AstraZeneca, Merck & Co., Inc., Rahway, NJ, USA, BMS, Novartis, Roche, Zymeworks, and 1Globe. P. Kavan reports advisory/consultancy role with Merck; Expert Testimony for Merck & Co., Inc., Rahway, NJ, USA; and an institutional educational grant to their institution. M. Tehfe reports advisory/consultancy roles with Merck & Co., Inc., Rahway, NJ, USA, BMS, Taiho, and Pfizer; and speaker bureau for BMS and Taiho. J. S. Kortmansky reports research funding to their institution from Merck & Co., Inc., Rahway, NJ, USA and Genentech. M. B. Sawyer reports honoraria from Ipsen, BMS, Mylan, Amgen, AstraZeneca, Eisai, Sandoz, Celgene, Servier, Novartis, Leo, Taiho, and Shire; advisory/consultancy roles with AstraZeneca, Leo, and Immuneering; expert testimony for AstraZeneca; research funding to their institution from AstraZeneca and BMS; and travel/accommodation expenses from Ipsen. E. G. Chiorean reports advisory/consultancy roles with Astellas, Bayer, Cardiff, Foundation, G1 Therapeutics, Ipsen, Noxxon, Novartis, Merck & Co., Inc., Rahway, NJ, USA, Pfizer, and Stemline; research funding to their institution from Aadi, Biosplice, BioMed Valley, Boehringer-Ingelheim, Clovis, Corcept, Erasca, Fibrogen, Lona, Merck & Co., Inc., Rahway, NJ, USA, Novartis, Rafael, and Stemline; and travel/accommodation from G1 Therapeutics. C. H. Lieu reports research funding to their institution from Merck & Co., Inc., Rahway, NJ, USA. M. Fakih reports advisory/consultancy roles with AstraZeneca, Bayer, Bristol Myers Squibb, GlaxoSmithKline, Incyte, Mirati, Nouscom, PsiOxus, Roche/Genentech, and Taiho. K. Spencer reports advisory/consultancy roles from QED Therapeutics, Helsinn, Lynx Group, and Caris. C. Li, P. Leconte, and D. Adelberg report employment with Merck & Co., Inc., Rahway, NJ, USA; P. Leconte and D. Adelberg report stock ownership at Merck & Co., Inc., Rahway, NJ, USA. R. Kim reports honoraria from Taiho; advisory/consultancy roles with Bayer Servier, Ipsen and Roche; and speaker bureau for Eisai, Pfizer, and Incyte. B. Polite, L. Wong, and J. Chaves report no conflicts of interest., (Copyright © 2024. Published by Elsevier Inc.)

Background: The phase 1b KEYNOTE-651 study evaluated pembrolizumab plus chemotherapy in microsatellite stable or mismatch repair-proficient metastatic colorectal cancer., Patients and Methods: Patients with microsatellite stable or mismatch repair-proficient metastatic colorectal cancer received pembrolizumab 200 mg every 3 weeks plus 5-fluorouracil, leucovorin, oxaliplatin (previously untreated; cohort B) or 5-fluorouracil, leucovorin, irinotecan (previously treated with fluoropyrimidine plus oxaliplatin; cohort D) every 2 weeks. Primary end point was safety; investigator-assessed objective response rate per RECIST v1.1 was secondary and biomarker analysis was exploratory., Results: Thirty-one patients were enrolled in cohort B and 32 in cohort D; median follow-up was 30.2 and 33.5 months, respectively. One dose-limiting toxicity (grade 3 small intestine obstruction) occurred in cohort D. In cohort B, grade 3 or 4 treatment-related adverse events (AEs) occurred in 18 patients (58%), most commonly neutropenia and decreased neutrophil count (n = 5 each). In cohort D, grade 3 or 4 treatment-related AEs occurred in 17 patients (53%), most commonly neutropenia (n = 7). No grade 5 treatment-related AEs occurred. Objective response rate was 61% in cohort B (KRAS wildtype: 71%; KRAS mutant: 53%) and 25% in cohort D (KRAS wildtype: 47%; KRAS mutant: 6%). In both cohorts, PD-L1 combined positive score and T-cell-inflamed gene expression profiles were higher and HER2 expression was lower in responders than nonresponders. No association between tumor mutational burden and response was observed., Conclusion: Pembrolizumab plus 5-fluorouracil, leucovorin, oxaliplatin/5-fluorouracil, leucovorin, irinotecan demonstrated an acceptable AE profile. Efficacy data appeared comparable with current standard of care (including by KRAS mutation status). Biomarker analyses were hypothesis-generating, warranting further exploration., Gov Identifier: ClinicalTrials.gov; NCT03374254., Competing Interests: Disclosure R. Kim reports honoraria from Taiho; advisory/consultancy roles with Bayer Servier, Ipsen, and Roche; and speakers bureau for Eisai, Pfizer, and Incyte. M. Tehfe reports advisory/consultancy roles with Merck & Co., Inc., Rahway, NJ, USA, BMS, Taiho, and Pfizer; and speakers bureau for BMS and Taiho. P. Kavan reports advisory/consultancy role with Merck; expert testimony for Merck & Co., Inc., Rahway, NJ, USA; and an institutional educational grant to their institution. J. S. Kortmansky reports research funding to their institution from Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, and Genentech. E. X. Chen reports advisory/consultancy roles from AstraZeneca, Eisai, and GSK and research funding to their institution from AstraZeneca, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, BMS, Novartis, Roche, Zymeworks, and 1Globe. C. H. Lieu reports advisory/consultancy roles with Natera; and research funding to their institution from Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA. M. Fakih reports advisory/consultancy roles with AstraZeneca, Bayer, Bristol Myers Squibb, GlaxoSmithKline, Incyte, Mirati, Nouscom, PsiOxus, Roche/Genentech, and Taiho. K. Spencer reports advisory/consultancy roles with QED Therapeutics, Helsinn, Lynx Group, and Caris. Q. Zhao reports stock ownership at Merck & Co., Inc., Rahway, NJ, USA. R. Predoiu, C. Li, P. Leconte, and D. Adelberg report employment with Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA. P. Leconte and D. Adelberg report stock ownership at Merck & Co., Inc., Rahway, NJ, USA. E. G. Chiorean reports advisory/consultancy roles with Astellas, Bayer, Cardiff, Foundation, G1 Therapeutics, Ipsen, Noxxon, Novartis, Merck & Co., Inc., Rahway, NJ, USA, Pfizer, and Stemline; research funding to their institution from Aadi, Biosplice, BioMed Valley, Boehringer Ingelheim, Clovis, Corcept, Erasca, Fibrogen, Lona, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Novartis, Rafael, and Stemline; and travel/accommodations from G1 Therapeutics. J. Chaves and L. Wong report no conflicts of interest., (Copyright © 2024 Elsevier Inc. All rights reserved.)

For colorectal cancer (CRC), surgical resection remains essential for achieving good prognoses. Unfortunately, numerous patients with locally advanced CRC and metastatic CRC failed to meet surgical indications or achieve pathological complete response after surgery. Perioperative therapy has been proven to effectively lower tumor staging and reduce recurrence and metastasis. Immune checkpoint inhibitors (ICIs) have shown unprecedented prolongation of survival time and satisfactory safety in patients with high microsatellite instability/deficient mismatch repair (MSI-H/dMMR), while the therapeutic effect obtained by patients with mismatch repair-proficient or microsatellite stable (pMMR/MSS) was considered minimal. However, recent studies found that certain CRC patients with dMMR/MSI-H presented intrinsic or acquired immune resistance, and pMMR/MSS CRC patients can also achieve better efficacy. Therefore, more predictors are required for screening patients with potential clinical benefits. Since the discovery of synergistic effects between immunotherapy, chemotherapy, and radiotherapy, different immunotherapy-based therapies have been applied to the perioperative therapy of CRC in an increasing number of research. This review comprehensively summarized the past and current progress of different combinations of immunotherapy in perioperative clinical trials for CRC, focusing on the efficacy and safety, and points out the direction for future development., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Chen, Zhou, Han, Wei and Qiu.)

Introduction: The US Food and Drug Administration (FDA) approved pembrolizumab for patients with unresectable or metastatic solid tumors with tumor mutational burden (TMB) of ≥ 10 mutations/megabase. However, the clinical implications of this universal cutoff of TMB ≥ 10 for patients with microsatellite stable (MSS) metastatic colorectal cancer (CRC) remain debatable., Areas Covered: In this review, we discuss the tissue agnostic approval of pembrolizumab, its efficacy, and clinical relevance in the management of patients with MSS CRC patients with high TMB (defined as TMB ≥ 10). We also elaborate on molecular subgroups of MSS CRC that influence the immune checkpoint inhibitor (ICI) response for patients with MSS CRC, including pathogenic POLE and POLD1 mutations associated with ultramutated tumors., Expert Opinion: Patients with microsatellite stable CRC with TMB ≥ 10 without POLE and POLD1 mutations may not significantly benefit from immune checkpoint inhibitors therapy. Predetermined cutoff TMB ≥ 10 mutation per MB does not seem to define a universal cutoff for the benefit of disease-agnostic ICI therapy, particularly for patients with MSS CRC. Patients with POLE/POLD1 mutations with MSS CRC represent a unique biological subgroup of MSS CRC with favorable responses to ICI therapy.