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Immune checkpoint inhibitors yielded unprecedented outcomes in patients with mismatch repair deficient/ microsatellite instability-high (dMMR/MSI-H) metastatic colorectal cancer (mCRC), but clinical decision-making in this rapidly evolving treatment landscape is challenging. Since performance status (PS) represents a well-established prognostic factor in clinical practice, we investigated whether worse PS, overall or related to either patients' frailty or high tumour burden, could affect the outcomes in this whole patients' population and according to immune checkpoint inhibitor treatment type.We conducted a global study at Tertiary Cancer Centres and collected data of patients with dMMR/MSI-H mCRC treated with anti- programmed-death (ligand)-1 (PD(L)-1) monotherapy or anti-PD-1/anti- cytotoxic T-lymphocyte antigen 4 combination.The cohort included 502 patients. At a median follow-up of 31.2 months, worse PFS and OS were reported in patients with patient-related PS ≥ 1 (adjusted-HRs: 1.73, 95%CI: 1.06-2.83, p = 0.004 and 2.06, 95%CI: 1.13-3.74, p = 0.001, respectively) and cancer-related PS ≥ 1 (adjusted-HRs: 1.61, 95%CI: 1.19-2.17, p = 0.004 and 1.87, 95%CI: 1.32-2.66, p = 0.001, respectively). Anti-PD-1/anti- cytotoxic T-lymphocyte antigen 4 combination did not provide significantly better survival compared to anti-PD(L)-1 monotherapy in PS 0 subgroup (PFS HR = 0.62, 95%CI: 0.37-1.02, p = 0.059; OS HR = 0.59, 95%CI: 0.32-1.11, p = 0.100) and in patient-related PS ≥ 1 (PFS HR 0.93, 95%CI: 0.31-2.83, p = 0.899; OS HR 1.22, 95%CI: 0.34-4.37, p = 0.760), but the difference was significant and clinically meaningful in the subgroup with cancer-related PS ≥ 1 (PFS HR = 0.32, 95%CI: 0.19-0.53, p lt; 0.001; OS HR = 0.26, 95%CI: 0.14-0.48, p lt; 0.001).In patients with dMMR/MSI-H mCRC, an extensive evaluation of clinical variables including PS may be implemented in the therapy decision-making.

Background We pooled data from 2 cohorts of immune checkpoint inhibitors-treated microsatellite instability-high/mismatch repair-deficient (MSI/dMMR) metastatic colorectal cancer patients to evaluate the prognostic value of RAS/BRAFV600E mutations and Lynch syndrome (LS). Patients and Methods Patients were defined as LS-linked if germline mutation was detected and as sporadic if loss of MLH1/PMS2 expression with BRAFV600E mutation and/or MLH1 promoter hypermethylation, or biallelic somatic MMR genes mutations were found. Progression-free survival (PFS) and overall survival (OS) were adjusted on prognostic modifiers selected on unadjusted analysis (P < .2) if limited number of events. Results Of 466 included patients, 305 (65.4%) and 161 (34.5%) received, respectively, anti-PD1 alone and anti-PD1+anti-CTLA4 in the total population, 111 (24.0%) were treated in first-line; 129 (28.8%) were BRAFV600E-mutated and 153 (32.8%) RAS-mutated. Median follow-up was 20.9 months. In adjusted analysis of the whole population (PFS/OS events = 186/133), no associations with PFS and OS were observed for BRAFV600E-mutated (PFS HR= 1.20, P = .372; OS HR = 1.06, P = .811) and RAS-mutated patients (PFS HR = 0.93, P = .712, OS HR = 0.75, P = .202). In adjusted analysis in the Lynch/sporadic status-assigned population (n = 242; PFS/OS events = 80/54), LS-liked patients had an improved PFS compared to sporadic cases (HR = 0.49, P = .036). The adjusted HR for OS was 0.56 with no significance (P = .143). No adjustment on BRAFV600E mutation was done due to collinearity. Conclusion In this cohort, RAS/BRAFV600E mutations were not associated with survival while LS conferred an improved PFS.

795 Background: Immune checkpoint inhibitors (ICI) are the new standard of care for some MSI/dMMR advanced tumors in first-line setting or after progression under conventional chemotherapy. Frequency of MSI/dMMR increasing with age, the tolerability and efficacy of ICIs in elderly patients, appears as a crucial clinical issue. We aimed to evaluate the tolerability and efficacy of ICIs in ≥ 75 years patients with metastatic MSI/dMMR gastro-intestinal (GI) cancer. Methods: All pts with MSI/dMMR metastatic GI cancer treated by anti-PD1 ± anti-CTLA4 without concomitant chemotherapy at Saint-Antoine hospital and included in our prospective, monocenter cohort, were analyzed. Pts were divided into the elderly (≥75 years) and non-elderly (

171 Background: ICI have demonstrated efficacy in patients (pts) with MSI/dMMR mCRC . Lynch (LS) vs sporadic (Sp) status, BRAFV600E and RAS mutations (mt) are known factors of clinical and molecular heterogeneity in this population. We aimed to evaluate the prognostic value of these parameters in ICI-treated MSI mCRC pts. Methods: Pts are drawn from international cohorts (France, Italy, Spain, and USA). Pts were considered to have cancer linked to LS only in case of determined germline mutation and Sp in case of loss of MLH1/PMS2 protein expression associated with BRAF V600E mutation and/or hypermethylation of MLH1 promoter, or in case of biallelic somatic mutations of MMR genes. Survival analyses: progression-free survival (PFS) per iRECIST criteria and overall survival (OS) were adjusted on prognostic modifiers, selected on unadjusted analysis (p < 0.2) in case of limited number of events. Results: On the 466 pts included, 112 (24%) received ICI in first line, 305 (65%) received anti-PD1 alone, 161 (35%) anti-PD1 plus anti-CTLA4, 129 (29%) had BRAFV600Emt and 153 (34%) RASmt. Median follow-up was 24.0 months. In adjusted analysis of the whole population (n=466; 186 PFS events and 143 OS events), no association with PFS and OS was observed for BRAFV600E mt (PFS HR 1.20 [0.80 to 1.79], p=0.372; OS HR 1.06 [0.66 to 1.70], p= 0.811) and RASmt (PFS HR 0.93 [0.64 to 1.36], p= 0.712; OS HR 0.75 [0.48 to 1.17] p= 0.202). Adjusting factors were age, ECOG status, number of prior chemotherapies, treatment type (bi vs monotherapy), sidness (right vs left + rectum), primary tumor surgery. Concerning the population with determined Lynch status (n= 242; 83 PFS events and 54 OS events), PFS results are displayed. The analysis of impact of LS was not adjusted on BRAFV600E mutational status due to collinearity. In adjusted analysis, LS improved PFS compared with Sp (HR = 0.49, 95%CI (0.25 to 0.96), p = 0.036). Adjusted HR for OS was 0.56 without reaching significance 95%CI (0.25 to 1.22), p = 0.143. Conclusions: In this analysis of ICI-treated MSI/dMMR mCRC pts, RAS/BRAFV600E mutations are not associated with survival while Lynch syndrome pts demonstrated improved PFS. [Table: see text]

Immune checkpoint inhibition (CPI) for metastatic colorectal cancer (mCRC) with deficient mismatch repair (dMMR) demonstrates high clinical activity that appears durable, but the impact of CPI on pathological tumor response is unknown. In this retrospective analysis, our objective was to assess pathological response and clinical outcomes in dMMR mCRC patients treated with CPI prior to surgical resection of primary and/or metastatic tumor. Among 121 advanced dMMR mCRC patients treated with CPI at 2 institutions between November 2016 and December 2018, 14 underwent surgery. Pathologic complete response was noted in the resected specimens of 13 patients despite the presence of residual tumor on preoperative imaging in 12 of those patients. With median follow-up of 9 months, no patients have had disease relapse or progression. For this small retrospective study, the data suggest that residual radiographic tumor may not require systematic resection following response to anti-PD1–based therapy. However, larger prospective studies are warranted.

In their article, Fucà et al highlight that early tumor shrinkage and depth of response predict the prognosis of patients with metastatic colorectal cancer (mCRC) microsatellite instability (MSI-H)/deficient mismatch repair (dMMR) treated by immune checkpoint inhibitors (ICI). We are surprised that no cases of pseudoprogression (PSPD) were reported in their study. PSPDs were described under ICI in patients treated for MSI/dMMR mCRC. In a cohort of 123 patients treated with anti-PD1±antiCTL-4 for MSI/dMMR mCRC, we reported 12 patients with PSPD, representing 10% of the cohort. Of 12 patients with PSPD, 8 secondary achieved an objective response and were alive and free of progression at the data lock. Conversely, in Fucà’s article, no PSDP was observed and the patients with primary radiological progression (21.7%) had a poor overall survival. These differences between the two series could be probably explained by the following points. First, Fucà et al use RECIST 1.1 criteria for radiological evaluation. Second, the first imaging was done after 8–9 weeks of treatment in Fucà’s article, which may be late to detect PSPD. In conclusion, if the first evaluation is made during the first 3 months of treatment, using iRECIST criteria seems mandatory to avoid stopping treatment prematurely, especially in patients receiving anti-PD1 alone.

Immunotherapies are part of the therapeutic strategy in many cancers and are indicated for metastatic colorectal adenocarcinoma with loss of expression of MisMatch Repair system proteins or with microsatelite instability (dMMR/MSI) in the United States. The rate of pathological response to immunotherapy remains poorly documented, but several cases of complete or major pathological response have recently been described. We decided to report the case of a complete pathological response to immunotherapy of a dMMR/MSI colorectal adenocarcinoma in a 74-year-old patient, initially inoperable due to duodenal invasion. Three months after the introduction of immunotherapy, the patient developed drug-induced colitis that contraindicated further treatment. Histological examination of the subtotal colectomy specimen revealed no residual tumour cells. The patterns of tumour regression were mainly represented by colloid regression, infarctoid-type necrosis and a resorptive inflammatory reaction. Although the operative indications for patients with metastatic dMMR/MSI colorectal cancer treated by immunotherapy are still very limited, the number of such specimens is expected to increase rapidly. The management of these specimens, as well as the possibility of a complete histological response, must be known by pathologists who play a key role in the pathophysiological knowledge of these lesions.

Simple Summary Microsatellite instability (MSI) is a molecular indicator of defective DNA mismatch repair (dMMR). MSI/dMMR status is observed in approximately 5% of metastatic colorectal cancers (mCRC) but 10–18% of localized colorectal cancers. MSI/dMMR status is a major predictive biomarker for the efficacy of immune checkpoint inhibitors (ICIs). This review presents the current and future challenges of ICIs for patients with MSI/dMMR colorectal cancer. Abstract Microsatellite instability (MSI) is a tumor phenotype related to a deficient DNA mismatch repair system (dMMR). This phenotype, observed in 5% of metastatic mCRC but 10–18% of localized CRC, is associated with high tumor mutational burden with highly immunogenic neoantigens. It has emerged as a major predictive biomarker for the efficacy of ICIs. In this review, we will present a comprehensive overview of the literature concerning the efficacy of ICIs in MSI/dMMR mCRC, with a focus on new developments in first-line metastatic setting. Then, we will present current and future challenges of immuno-oncology for patients with MSI/dMMR metastatic CRC.

Background The efficacy of immune checkpoint inhibitors (ICIs) in microsatellite instability-high/DNA mismatch repair (MSI/dMMR) metastatic colorectal cancer (mCRC) is well established. ICIs are responsible for pseudoprogression (PSPD) that complicates clinical decisions. We evaluated the PSPD frequency in patients with MSI/dMMR mCRC treated with ICIs. Patients and methods Consecutive patients with MSI/dMMR mCRC treated with ICIs from February 2015 to December 2019 at Saint-Antoine Hospital were included. Imaging was retrospectively and centrally reviewed according to Response Evaluation Criteria in Solid Tumours, version 1.1 (RECIST 1.1) and immune RECIST (iRECIST). PSPD was defined as an unconfirmed disease progression by iRECIST. Results One hundred twenty-three patients with MSI/dMMR mCRC were included. Thirty-six patients (29%) had radiological PD according to RECIST 1.1 during the median follow-up of 22.3 months (95% confidence interval [CI], 1.5–62.2), including 22 in the first 3 months (the primary radiological PD). Twenty-nine patients continued ICIs beyond PD. Twelve patients experienced PSPD, representing 10% of the population and 52% of the primary radiological PD. The median time to PSPD was 5.7 weeks (95% CI, 4.1–11.4). No PSPD was observed after 3 months. The PSPD incidence was 14.8% in patients treated with anti-PD1 alone (n = 9/61) and 4.8% in case of anti-PD1 plus anti-CTLA-4 (n = 3/62). Eight patients with PSPD experienced an objective response. The 2-year progression-free survival and overall survival rates for patients with PSPD were 70.0% (95% CI, 32.9–89.2) and 75.0% (95% CI, 29.8–93.4), respectively. Conclusion Patients with MSI/dMMR mCRC treated with ICIs experienced PSPDs. PSPD occurred within the first 3 months and represented most of the primary radiological PDs. The use of iRECIST criteria should be questioned after 3 months.

Metastatic colorectal cancers (mCRC) harboring microsatellite instability (MSI) are sensitive to immune checkpoint inhibitors (ICIs), but the mechanisms of resistance to ICIs remain unclear. Dissociated responses in patients with ICI-treated cancer suggest that certain organs may serve as sanctuary sites due to the tumor microenvironment. This case series describes five patients with ICI-treated MSI mCRC with disease progression limited to the adrenal glands. At ICI initiation, three patients were free of metastasis in the adrenal glands. Four patients experienced objective response per RECIST (Response Evaluation Criteria in Solid Tumors) while treated with ICI. ICI treatment was discontinued due to progressive disease limited to the adrenal glands (n=3) or toxicity (n=2). The time between ICI initiation and progression in the adrenal glands ranged from 11 to 39 months. Adrenalectomy (n=3) and stereotactic body radiation therapy (n=2) were performed. At the last follow-up, all patients were alive and progression free. Molecular analyses were performed in one patient. A significant impairment of the antigen presentation pathway was observed in the ICI-resistant lesion of the adrenal gland, which could be explained by the presence of glucocorticoids in the adrenal gland microenvironment. We also detected an overexpression of TSC22D3, a glucocorticoid-target gene that functions as a mediator of anti-inflammation and immunosuppression. This case series suggests that the adrenal glands may be the sanctuary sites for ICI-treated MSI mCRC through the glucocorticoid-induced impairment of the antigen presentation machinery.

Background Cancer patients are thought to have an increased risk of developing severe Coronavirus Disease 2019 (COVID-19) infection and of dying from the disease. In this work, predictive factors for COVID-19 severity and mortality in cancer patients were investigated. Patients and Methods In this large nationwide retro-prospective cohort study, we collected data on patients with solid tumours and COVID-19 diagnosed between March 1 and June 11, 2020. The primary endpoint was all-cause mortality and COVID-19 severity, defined as admission to an intensive care unit (ICU) and/or mechanical ventilation and/or death, was one of the secondary endpoints. Results From April 4 to June 11, 2020, 1289 patients were analysed. The most frequent cancers were digestive and thoracic. Altogether, 424 (33%) patients had a severe form of COVID-19 and 370 (29%) patients died. In multivariate analysis, independent factors associated with death were male sex (odds ratio 1.73, 95%CI: 1.18-2.52), ECOG PS ≥ 2 (OR 3.23, 95%CI: 2.27-4.61), updated Charlson comorbidity index (OR 1.08, 95%CI: 1.01-1.16) and admission to ICU (OR 3.62, 95%CI 2.14-6.11). The same factors, age along with corticosteroids before COVID-19 diagnosis, and thoracic primary tumour site were independently associated with COVID-19 severity. None of the anticancer treatments administered within the previous 3 months had any effect on mortality or COVID-19 severity, except cytotoxic chemotherapy in the subgroup of patients with detectable SARS-CoV-2 by RT-PCR, which was associated with a slight increase of the risk of death (OR 1.53; 95%CI: 1.00-2.34; p = 0.05). A total of 431 (39%) patients had their systemic anticancer treatment interrupted or stopped following diagnosis of COVID-19. Conclusions Mortality and COVID-19 severity in cancer patients are high and are associated with general characteristics of patients. We found no deleterious effects of recent anticancer treatments, except for cytotoxic chemotherapy in the RT-PCR-confirmed subgroup of patients. In almost 40% of patients, the systemic anticancer therapy was interrupted or stopped after COVID-19 diagnosis., Highlights • A total of 1289 patients with solid tumours and COVID-19 were analysed. • Mortality and COVID-19 severity were mainly driven by patient general characteristics. • Overall, we found no deleterious effects of recent anticancer treatments on mortality. . • Systemic anticancer treatment was interrupted or stopped in 39% of patients.

Background: The novel COVID-19 outbreak spread rapidly around the world Cancer patients (pts) consist of a highly vulnerable group due to underlying malignancy and/or treatment-induced immunosuppression A high mortality rate from COVID-19 in cancer pts was previously reported France is the fourth most affected country, with more than 150,000 infected individuals and over 28,000 deaths GCO-002 CACOVID-19 study is a large French nationwide cohort of COVID-19 pts with solid tumors with the aim to identify risk factors of COVID-19 severity and evaluate impact on cancer treatment Methods: Bispective multicenter cohort set up by the French Cooperative Groups in solid cancers: ANOCEF-IGCNO (CNS tumors), ARCAGY-GINECO (gynecological and breast cancers), FFCD (digestive cancers), GERCOR (digestive and other solid cancers), GORTEC/intergroupe ORL (head and neck cancers (HNAmgen, Pierre Fabre;Sandoz;Honoraria (self), Advisory/Consultancy, Research grant/Funding (self), Travel/Accommodation/Expenses: Bayer;Novartis;Honoraria (self): Celgene;HalioDx;Lilly;Honoraria (self), Travel/Accommodation/Expenses: BMS;Roche;Honoraria (self), Research grant/Funding (self): Incyte;Honoraria (self), Advisory/Consultancy, Travel/Accommodation/Expenses: Ipsen;Merck;Servier;Research grant/Funding (self): Integragen;Travel/Accommodation/Expenses: AAA;Pfizer A Turpin: Honoraria (self): Servier;Advisory/Consultancy: Mylan;Merck Serono;Amgen;Travel/Accommodation/Expenses: Merck;Sanofi;Pfizer;AstraZeneca I L Ray-Coquard: Honoraria (self), Advisory/Consultancy: Abbvie;Agenus;Advaxis;Honoraria (self), Honoraria (institution), Advisory/Consultancy, Research grant/Funding (self), Research grant/Funding (institution): BMS;MSD;Honoraria (self), Advisory/Consultancy: PharmaMar;Genmab;Pfizer;Deciphera;Mersena;Amgen;Tesaro;Clovis;Honoraria (self), Advisory/Consultancy, Research grant/Funding (institution): Merck Serono;Novartis;Honoraria (self), Advisory/Consultancy, Research grant/Funding (institution), Travel/Accommodation/Expenses: AstraZeneca;Honoraria (self), Honoraria (institution), Advisory/Consultancy, Research grant/Funding (self), Research grant/Funding (institution), Travel/Accommodation/Expenses: Roche;Honoraria (self), Honoraria (institution), Advisory/Consultancy, Travel/Accommodation/Expenses: GSK;Non-remunerated activity/ies: GINECO;ENGOT;GCIG;European community;ESMO;ASCO;ESGO;IGSC;Inca;Swiss and German Health Authorities;Italian Health Authority;Belgium Health Authority J Thariat: Honoraria (self): BMS;Honoraria (institution), Travel/Accommodation/Expenses, Full/Part-time employment: Centre Francois Baclesse;Leadership role: President of the French Head and Neck Intergroup, GORTEC secretary;Non-remunerated activity/ies: Director of Easy-CRF society;Research grant/Funding (institution): Nanobiotix G Ahle: Travel/Accommodation/Expenses: Abbvie;Biogen;Novartis;Roche;Sanofi;Non-remunerated activity/ies: ANOCEF;NENO;AlSacEP R Mathieu: Honoraria (self), Research grant/Funding (self): Astellas;Honoraria (self): AstraZeneca;Ferring;Ipsen;Janssen;MSD;Pfizer;Sanofi;Takeda D Debieuvre: Honoraria (self), Advisory/Consultancy, Research grant/Funding (institution), Travel/Accommodation/Expenses: Pfizer;Roche;Novartis;BMS;MSD;Honoraria (self), Research grant/Funding (institution), Travel/Accommodation/Expenses: AstraZeneca;Honoraria (self), Research grant/Funding (institution): Chugai;Honoraria (self), Advisory/Consultancy, Research grant/Funding (institution), Travel/Accommodation/Expenses: Boerhinger-Ingelheim;Research grant/Funding (institution): Chiesi;Sandoz;Takeda;GSK;Research grant/Funding (self): Lilly A Canellas: Honoraria (self), Advisory/Consultancy: BMS;Honoraria (self), Travel/Accommodation/Expenses: AstraZeneca;Travel/Accommodation/Expenses: Oxyvie;LVL Medical;Boerhinger Ingelheim A-C Hardy-Bessard: Advisory/Consultancy: Clovis;Novartis;Roche;MSD;AstraZeneca;GSK L Mansi: Honoraria (institution), Advisory/Consultancy: Sandoz;Advisory/Consultancy: Roche;Eisai;Pfizer;Novartis;Speaker Bureau/Expert testimony: Exact Sciences;Travel/Accommodation/Expenses: Lilly P Gorphe: Honoraria (self): Intuitive Surgical;Non-remunerated activity/ies: Chair, scientific board, French Head and Neck Intergroup;Research grant/Funding (institution): MSD A IDBAIH Ahmed: Research grant/Funding (institution): Transgene;Sanofi;Air Liquide;Travel/Accommodation/Expenses: Carthera;Leo Pharma G Zalcman: Honoraria (self), Honoraria (institution), Research grant/Funding (institution), Travel/Accommodation/Expenses: BMS;Honoraria (self), Honoraria (institution), Travel/Accommodation/Expenses: AstraZeneca;Honoraria (institution), Research grant/Funding (institution), Travel/Accommodation/Expenses: Roche;Honoraria (institution): Takeda;Travel/Accommodation/Expenses: Pfizer;AbbVie;MSD O Bouche: Honoraria (self), Advisory/Consultancy, Travel/Accommodation/Expenses: Roche;Honoraria (self), Advisory/Consultancy: Merck KgaA;Bayer;AstraZeneca;Grunenthal;MSD;Honoraria (self), Speaker Bureau/Expert testimony: Amgen;Pierre Fabre;Honoraria (self), Speaker Bureau/Expert testimony, Travel/Accommodation/Expenses: Servier All other authors have declared no conflicts of interest

Over the past years, colorectal cancer (CRC) was subtyped according to its molecular and genetic characteristics, allowing the development of therapeutic strategies, based on predictive biomarkers. Biomarkers such as microsatellite instability (MSI), RAS and BRAF mutations, HER2 amplification or NTRK fusions represent major tools for personalized therapeutic strategies. Moreover, the routine implementation of molecular predictive tests provides new perspectives and challenges for the therapeutic management of CRC patients, such as liquid biopsies and the reintroduction of anti-EGFR monoclonal antibodies. In this review, we summarize the current landscape of targeted therapies for metastatic CRC patients, with a focus on new developments for EGFR blockade and emerging biomarkers (MSI, HER2, NTRK).

International audience; Immune checkpoints inhibitors (ICIs) have been a breakthrough, with unique response and survival patterns compared with chemotherapy for patients with advanced Mismatch Repair-deficient/Microsatellite instable (dMMR/MSI) colorectal cancer, but have shown disappointing results in Mismatch Repair-proficient/Microsatellite stable (pMMR/MSS) colorectal cancer. As up to 50% of patients harboring dMMR/MSI advanced cancers will ultimately progress after PD-1 blockade, biomarkers are needed to predict response/resistance to immunotherapy and to select patients for immunomodulating combination therapies. Patients with pMMR/MSS colorectal cancer present with distinct immune profiles compared to dMMR/MSI tumors, giving evidence of different immune escape mechanisms, which could be overcome through individualized immunotherapeutic strategies. In this review we discuss the latest developments in the field of immunotherapy for dMMR/MSI and pMMR/MSS colorectal cancers, and unresolved questions and considerations concerning the use of ICI therapies in this population. Future immunomodulation strategies based on biomarker selection (tumor mutational burden, Immunoscore®, mutational profile) are discussed.

3580 Background: Immune checkpoint inhibitors (ICI) have demonstrated efficacy in patients (pts) with MSI/dMMR mCRC. We aimed to evaluate clinical, pathological and molecular factors associated with progression-free survival (PFS) and overall survival (OS) in ICI-treated pretreated mCRC patients (pts). Methods: Pts are drawn from a prospective cohort of all patients treated with ICI for MSI/dMMR mCRC at Saint-Antoine Hospital, Paris, France. All MSI/dMMR mCRC pts with disease progression after ≥ 1 prior systemic treatment (fluoropyrimidine and oxaliplatin or irinotecan ± targeted therapy) were included. MSI/dMMR status was centrally reviewed. Lynch syndrome or sporadic status was determined according to MMR gene germline mutational testing, MLH1 methylation status and BRAFV600E mutation. PFS and objective response rate (ORR) were assessed using iRECIST criteria. The impact of Lynch syndrome on PFS was analyzed apart from the multivariate analysis due to the interaction with the BRAFV600E mutation status. Results: Of 130 included pts, 66 received anti-PD1 alone, 1 anti-PDL1 alone and 63 anti-PD1 plus anti-CTLA4. 71% have had at least 2 prior lines of treatment. 33 patients (25%) have BRAFV600Emutation (mt) and 49 (38%) RASmt. The ORR for the whole population was 62.8 % IC95% [53.8; 71.1]. Median follow-up was 21.0 months, median PFS and OS were not reached. Results of PFS unadjusted and adjusted analysis are displayed in the table. BRAFV600E and RAS mutation were not associated with PFS and OS in multivariate analyses. After adjustment for the treatment type, Hazard Ratio (HR) for PFS between patients with proven Lynch syndrome (N=44) and patients with proven sporadic tumors (n= 44) was 0.57 (95%IC 0.26 -1.26). Conclusions: In this cohort, main known clinical, pathological and molecular factors do not influence the efficacy of ICI in pre-treated MSI/dMMR mCRC.[Table: see text]

e15537 Background: Inhibitors of tropomyosin receptor kinase (TRK) have shown promising activity against neurotrophic TRK ( NTRK) fusion-driven cancers, regardless of tumor histotype or cell of origin. NTRK gene fusions are observed in less than 1% of colorectal cancers (CRCs). CRCs harboring wild-type BRAF and KRAS and MisMatch Repair deficiency (dMMR)/MicroSatellite Instability (MSI) due to MLH1 hypermethylation have been associated with NTRK fusions in small cohorts of non-metastatic tumors. We aimed at evaluating the incidence of NTRK fusions among dMMR/MSI metastatic CRCs (mCRC) for which there is a need for innovative therapies, as well as the associated clinical characteristics of these patients (pts) carrying NTRK fusion-positive tumors. Methods: Tumor samples of dMMR/MSI mCRC pts, paired primary and metastasis or primary alone, were obtained from a French multicenter retrospective cohort and from a single-center cohort of patients treated by immune checkpoint inhibitors (ICI) (Saint-Antoine Hospital, Paris). Clinico-pathological data including KRAS and BRAFV600E status, MMR proteins and MLH1 methylation status were available for all pts. All samples were screened for TRK expression by immunohistochemistry (IHC) using a pan-TRK antibody (clone EPR17341, Abcam; positivity: 1% of labeled tumor cells)) and for NTRK1 and NTRK3 gene rearrangements, by fluorescent in situ hybridation (FISH). A threshold of 15% nuclei positive for a break apart signal was considered positive for gene rearrangement. Results: A total of 158 pts with dMMR/MSI mCRCs (paired samples: n=39; primary only: n=119) were screened. Tumor samples of 10 patients (6.3%) harbored NTRK fusion genes by FISH ( NTRK1=8; NTRK3=2). Only four of these 10 patients had TRK immunoreactivity. One patient showed a discordance between metastasis harboring NTRK1 fusion (+) and primary tumor being negative. Eight tumors were sporadic with MLH1 hypermethylation. The remaining 2 cases were related to a MMR gene germline mutation (Lynch syndrome) with concurrent loss of MSH2 and MSH6 expression and isolated loss of MSH6 respectively. One Lynch-related tumor was KRAS mutated, one sporadic MLH1-negative tumor was BRAF V600E mutated. Four patients out of 91 treated by ICI had tumors with NTRK fusions. Three have shown radiological response according to iRECIST criteria (two complete responses, one partial response with 25 to 54 months of follow up) and one had primary resistance to ICI. Conclusions: Frequency of NTRK1/3 fusions is 6.3% in our dMMR/MSI mCRCs population. These fusions are not restricted to sporadic cases. The diagnostic accuracy of pan-TRK IHC is low. Optimal testing algorithms for theragnostics remain to be defined in this setting.

Microsatellite instability (MSI) is a tumor phenotype linked to somatic or germline (Lynch syndrome) inactivating alterations of DNA mismatch repair genes. A broad spectrum of neoplasms exhibits MSI phenotype, mainly colorectal cancer, endometrial cancer, and gastric cancer. MSI tumors are characterized by dense immune infiltration and high load of tumor neo-antigens. Growing evidence is accumulating on the efficacy of immune checkpoint inhibition for patients treated for MSI solid tumors. We present a comprehensive overview of MSI phenotype, its biological landscape and current diagnostic methods. Then we focus on MSI as a predictive biomarker of response to immune checkpoint inhibition in the context of colorectal cancer and non-colorectal tumors.

Microsatellite instability (MSI) is a predictive biomarker for the efficacy of immune checkpoint inhibitors, regardless of the tumor type. While clinical characteristics of MSI cancer patients have been largely described in tumor localizations frequently associated with this genetic phenotype (i.e. colorectal cancer, endometrial cancer), it remains poorly characterized in other neoplasms. Pan-tumor high-throughput genome sequence analyses have contributed to the broadening of knowledge about the landscape of MSI. This review aims at synthetizing the literature concerning the frequency of MSI status in solid cancers, according to the cancer stage and the hereditary or sporadic origin of the mismatch repair deficiency. We then check for other cancers frequently associated with MSI and describe the clinical and pathological characteristics that should suggest a MSI phenotype.