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The microsatellite instability (MSI) phenotype is related to a deficiency of the DNA mismatch repair (dMMR) system and is observed in 5% of metastatic colorectal cancers (mCRCs). MSI/dMMR phenotype testing should be routine for all CRCs regardless of stage. Two complementary techniques with a high concordance (90–97%) allow us to determine the MSI/dMMR status of a tumor: immunohistochemistry and polymerase chain reaction. Since 2020 and the results of the phase III KEYNOTE 177 trial, pembrolizumab [anti-programmed cell death protein 1 (PD1)] is the new standard of care in first-line MSI/dMMR mCRC. To date, no combination of chemtotherapy ± targeted therapy with immune checkpoint inhibitors (ICIs) has been validated in the management of MSI/dMMR mCRC, and it is not known whether this combination would be beneficial. It is also unclear whether dual therapy with two ICIs is more effective than monotherapy. Several phase III trials are ongoing to answer these questions. Despite a high response rate and long-term benefit of a first line by anti-PD1, 30–50% of patients with MSI/dMMR mCRC experience an early or secondary progression. There are currently no validated predictive biomarkers of anti-PD1 ± anti-cytotoxic T lymphocyte antigen-4 resistance in patients with MSI/dMMR mCRC. In case of early progression on ICIs, the first two questions to consider are the possibility of pseudoprogression and the correct diagnosis of MSI/dMMR status. To date, there are no data on the use of adjuvant ICIs for MSI/dMMR resected colon cancers. By contrast, data are accumulating regarding the efficacy of neoadjuvant ICIs, with at least two-thirds of patients in the different trials in pathological complete response, making it possible to envisage ‘Watch and wait’ strategies in future.

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).

BackgroundImmune checkpoint inhibitors (ICIs) are highly effective in patients with microsatellite instability/mismatch repair-deficient (MSI/dMMR) metastatic colorectal cancer (mCRC). Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 criteria may underestimate response to ICIs due to the pseudoprogression phenomenon. The GERCOR NIPICOL phase II study aimed to evaluate the frequency of pseudoprogressions in patients with MSI/dMMR mCRC treated with nivolumab and ipilimumab.MethodsPatients with MSI/dMMR mCRC previously treated with fluoropyrimidines, oxaliplatin, and irinotecan with/without targeted therapies received nivolumab 3 mg/kg plus ipilimumab 1 mg/kg every 3 weeks for four cycles then nivolumab 3 mg/kg every 2 weeks until progression or a maximum of 20 cycles. Computed tomography scan tumor assessments were done every 6 weeks for 24 weeks and then every 12 weeks. The primary endpoint was disease control rate at 12 weeks according to RECIST 1.1 and iRECIST by central review.ResultsOf 57 patients included between December 2017 and November 2018, 48.0% received ≥3 prior lines of chemotherapy, 18.0% had BRAF V600E mutation, and 56.0% had Lynch syndrome-related cancer. Seven patients (12.0%) discontinued treatment due to adverse events; one died due to a treatment-related adverse event. The disease control rate (DCR) at 12 weeks was 86.0% with RECIST 1.1% and 87.7% with iRECIST. Two pseudoprogressions (3.5%) were observed, at week 6 and at week 36, representing 18% of patients with disease progression per RECIST 1.1 criteria. With a median follow-up of 18.4 months, median progression-free survival (PFS) and overall survival (OS) were not reached. The 12-month PFS rate was 72.9% with RECIST 1.1% and 76.5% with iRECIST. The 12-month OS rate was 84%. Overall response rate was 59.7% with both criteria. RAS/BRAF status, sidedness, Lynch syndrome, and other baseline parameters were not associated with PFS.ConclusionPseudoprogression is rare in patients with MSI/dMMR mCRC treated with nivolumab and ipilimumab. This combined ICI therapy confirms impressive DCR and survival outcomes in these patients.Trial registration number NCT03350126.

Opinion statement The BRAF activating mutation, harbored by approximately 10% of colorectal cancers (CRC), confers dramatic prognosis to advanced diseases. In early-stage setting, the identification of the BRAF mutation does not impact the therapeutic decision. Yet, the BRAF mutation could be considered as a stratification factor in adjuvant trials, because of its prognostic impact after relapse. Moreover, both BRAF mutation and mismatch repair (MMR) statuses should be determined in all CRC to help identify sporadic tumors versus Lynch syndrome-related tumors. Indeed, in patients with MMR-deficient (dMMR) tumors and MLH1 loss of expression, the BRAF V600E mutation indicates a sporadic origin. In advanced BRAF -mutated CRC, the standard of care remains fluoropyrimidine-based cytotoxic regimen in combination with bevacizumab. Although a recent meta-analysis showed that there was insufficient data to justify the exclusion of anti-EGFR monoclonal antibodies, antiangiogenic agents should be preferred in the first-line setting. Despite the lack of a randomized phase 3 study dedicated to BRAF -mutated CRC, chemotherapy intensification combining a quadruple association of 5-fluorouracil, oxaliplatin, irinotecan (FOLFOXIRI), and bevacizumab seems like a valid option. Although first results with BRAF inhibitors as single agents in BRAF -mutated CRC were disappointing, their association with therapies targeting the MAPK pathway seems to overcome the primary resistance to BRAF inhibition. In the field of sporadic CRC, the BRAF mutation is strongly associated with MMR deficiency. Considering breakthrough results of immune checkpoint inhibitors in dMMR repair tumors, determination of the MMR status appears to be mandatory. Given the dramatic prognosis conferred by the BRAF mutation, patients with BRAF -mutated advanced CRC need to be systematically identified and proposed for clinical trial enrolment in order to benefit from innovative therapies.

In the era of immune checkpoint inhibitors, understanding the metastatic microenvironment of proficient mismatch repair/microsatellite stable (pMMR/MSS) colorectal cancer (CRC) is of paramount importance to both prognostication and the development of more effective novel therapies. In this study, primary and paired metastasis tissue samples were collected from patients with resectable metastatic CRC treated with adjuvant FOLFOX or peri‐operative chemotherapy in the MIROX phase III prospective study. In total, 74 cancer tissues were stained for CD3, CD8, Forkhead box protein 3 (FOXP3), programmed cell death protein‐1 (PD‐1, invasive front, stromal, intra‐epithelial compartments), and programmed death‐ligand 1 (PD‐L1, tumor, immune cells). The immune profiling of primary CRC had a limited value to predict the immune context of paired metastases for all markers but CD3+. The expression of CD8 and PD‐L1 was higher in metastases after neoadjuvant FOLFOX. In metastases, both CD3 T cells at the invasive front and PD‐L1 expressions on immune cells were predictive of better disease‐free survival. These results show that the effect of FOLFOX on modifying the immune microenvironment in resected CRC metastases and measurement of PD‐L1 expression and tumor‐infiltrating CD8 T cells in pMMR/MSS metastatic tissue samples could improve treatment strategies of metastatic CRC patients. Here, we characterized the immune microenvironment of proficient mismatch repair/microsatellite stable oligometastatic patients with colorectal cancer (CRC) treated with the neoadjuvant FOLFOX. Primary tumor immune profiling had limited predictive value in estimating the metastatic immune context. CD3 T cells and PD‐L1 immune cells at the invasive front were predictive of disease‐free survival. In addition, the expression of CD8 and PD‐L1 was higher after FOLFOX treatment. Thus, CD8high/PD‐L1high signature could be related to chemotherapy response and could improve treatment strategies of metastatic patients with CRC.

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.

BackgroundSarcopenia and growth differentiation factor 15 (GDF-15) are linked to poor cancer survival. In this exploratory analysis, we evaluated their interaction with nivolumab-ipilimumab efficacy in chemoresistant metastatic colorectal cancer (mCRC) harboring microsatellite instability and/or mismatch-repair deficiency (MSI/dMMR), based on the final survival analysis of the NIPICOL phase II trial.Patients and methods57 patients with MSI/dMMR chemoresistant mCRC received nivolumab-ipilimumab for 3 months (3M), then, nivolumab alone for 9M. Skeletal muscle mass index (SMI) was evaluated by CT scan at baseline and 12M to assess sarcopenia. GDF-15 levels were assessed at baseline and 3M. Main endpoints were overall survival (OS) and immune Response Evaluation Criteria In Solid Tumors progression-free survival (iPFS).ResultsAfter excluding three patients not confirmed as MSI/dMMR by central review, the overall median follow-up was 60.4 months. The 3-year and 5 year iPFS rates were 72.0% and 65.3%, with OS rates of 77.5% and 73.3%, respectively. Among 49 patients with evaluable GDF-15, high-baseline GDF-15 was associated with poorer survival: 3-year iPFS rate of 56.3% for GDF-15≥2500 versus 81.7% for GDF-15<2500 (PFS HR=2.45, 95% CI 0.91 to 6.55), 3-year OS rates of 61.4% versus 84.5% (OS HR=2.08, 95% CI 0.70 to 6.22). Of the 48 evaluable patients for SMI, 31 (65.0%) displayed sarcopenia at baseline. 11 out of 20 (55%) patients with baseline sarcopenia and assessed for SMI at 12M, reversed sarcopenia by 12M. They had higher baseline GDF-15 levels and greater GDF-15 decrease by 3M (delta mean change: −69.8% vs −40.3%) compared with patients who remained sarcopenic.Conclusion1-year nivolumab-ipilimumab demonstrates consistent efficacy after 5-year follow-up in an MSI/dMMR chemoresistant mCRC population. GDF-15 confirms to be a promising biomarker for sarcopenia and survival.Trial registration number NCT03350126.

BackgroundSubgroup analyses of randomized trials suggest the superiority of immune checkpoint inhibitor-based therapy over chemotherapy in patients with mismatch-repair deficient (dMMR) and/or microsatellite instability-high (MSI-high) advanced gastric or gastroesophageal junction adenocarcinoma. However, these subgroups are small and studies examining prognostic features within dMMR/MSI-high patients are lacking.MethodsWe conducted an international cohort study at tertiary cancer centers and collected baseline clinicopathologic features of patients with dMMR/MSI-high metastatic or unresectable gastric cancer treated with anti-programmed cell death protein-1 (PD-1)-based therapies. The adjusted HRs of variables significantly associated with overall survival (OS) were used to develop a prognostic score.ResultsOne hundred and thirty patients were included. At a median follow-up of 25.1 months, the median progression-free survival (PFS) was 30.3 months (95% CI: 20.4 to NA) and 2-year PFS rate was 56% (95% CI: 48% to 66%). Median OS was of 62.5 months (95% CI: 28.4 to NA) and 2-year OS rate was 63% (95% CI: 55% to 73%). Among the 103 Response Evaluation Criteria in Solid Tumors-evaluable patients, objective response rate was 66% and disease control rate 87% across lines of therapy. In the multivariable models, Eastern Cooperative Oncology Group Performance Status of 1 or 2, non-resected primary tumor, presence of bone metastases and malignant ascites were independently associated with poorer PFS and OS. These four clinical variables were used to build a three-category (ie, good, intermediate, and poor risk) prognostic score. Compared with patients with good risk, patients with intermediate risk score had numerically inferior PFS and OS (2-year PFS rate: 54.3% versus 74.5%, HR 1.90, 95% CI: 0.99 to 3.66; 2-year OS rate: 66.8% versus 81.2%, HR 1.86, 95% CI: 0.87 to 3.98), whereas patients with poor risk score had significantly inferior PFS and OS (2-year PFS rate: 10.6%, HR 9.65, 95% CI: 4.67 to 19.92; 2-year OS rate: 13.3%, HR 11.93, 95% CI: 5.42 to 26.23).ConclusionsOverall outcomes with anti-PD-1-based therapies are favorable in MSI-high gastroesophageal adenocarcinomas. However, within this overall favorable subgroup a more accurate prognostication using baseline clinical characteristics might identify patients at higher risk of rapid disease progression who may deserve intensified immunotherapy combination strategies.

BackgroundTumors with mismatch repair deficiency (MMRd) classically display concomitant loss of MLH1/PMS2 or MSH2/MSH6 on immunohistochemistry (IHC) with microsatellite instability-high (MSI-High) status on molecular testing. Nevertheless, a different phenotype can occur in up to 15% of MMRd tumors (unusual phenotype). Data on the efficacy of immunotherapy in this population remain scarce.MethodsWe conducted a retrospective study within the IMMUNODIG MSI cohort including patients with advanced gastrointestinal MMRd tumors treated with immune checkpoint blockade in the real-world setting. We selected patients with both IHC and MSI assays data available. Unusual MMRd tumors were classified into four distinct groups: (1) isolated loss of PMS2 or MSH6 with MSI-H (isolated/MSI-H), (2) complex loss of MMR proteins with MSI-H (complex/MSI-H), (3) loss of one or more MMR proteins without MSI-H (MMRd-IHC/microsatellite stability (MSS) or MSI-low (MSI-L)), and (4) four MMR proteins retained with MSI-H (retained IHC/MSI-H).ResultsOut of 759 patients in the IMMUNODIG-MSI cohort, 571 patients met inclusion criteria. Of these, 90 (15.8%) had an unusual phenotype (47 isolated/MSI-H, 19 complex/MSI-H, 16 MMRd-IHC/MSS or MSI-L and 8 retained IHC/MSI-H). Compared with classical phenotypes, patients with a tumor harboring an unusual phenotype had a younger age at treatment (p=0.005), increased RAS mutation (p=0.005), reduced BRAF p.V600E mutation rates (p<0.001), a higher proportion of Lynch syndrome (p<0.001) and a higher prevalence of non-colorectal cancers (p=0.021). After a median follow-up of 28.1 months (mo), there was a significant difference in progression-free survival, with median values of not reached, 66.4 mo, 37.2 mo, 18.3 mo and 5.5 mo for complex/MSI-H, isolated/MSI-H, classical, retained IHC/MSI-H and MMRd-IHC/MSS or MSI-L subgroups, respectively (p<0.001). Notably, objective response rates were 59.1%, 58.7%, and 63.2% for complex/MSI-H, isolated/MSI-H and classical contrasting with 50% and 25% for retained IHC/MSI-H and MMRd-IHC/MSS or MSI-L, with no complete response observed in the latter two.ConclusionOur findings underscore the need for dual testing and advocate for the presence of both MMRd-IHC and MSI-H for optimal immunotherapy response. Of note, complex MMR aberrations and isolated PMS2/MSH6 losses with MSI-H may represent promising candidates for enhanced immunotherapy efficacy.

Background Current knowledge on prognostic biomarkers (especially BRAFV600E/RAS mutations) in metastatic colorectal cancer (mCRC) is mainly based on mCRC patients with proficient mismatch repair (pMMR) tumors. It is uncertain whether these biomarkers have the same prognostic value in mCRC patients with deficient mismatch repair (dMMR) tumors. Methods This observational cohort study combined a population‐based Dutch cohort (2014–2019) and a large French multicenter cohort (2007–2017). All mCRC patients with a histologically proven dMMR tumor were included. Results In our real‐world data cohort of 707 dMMR mCRC patients, 438 patients were treated with first‐line palliative systemic chemotherapy. Mean age of first‐line treated patients was 61.9 years, 49% were male, and 40% had Lynch syndrome. BRAFV600E mutation was present in 47% of tumors and 30% harbored a RAS mutation. Multivariable regression analysis on OS showed significant hazard rates (HR) for known prognostic factors as age and performance status, however showed no significance for Lynch syndrome (HR: 1.07, 95% CI: 0.66–1.72), BRAFV600E mutational status (HR: 1.02, 95% CI: 0.67–1.54), and RAS mutational status (HR: 1.01, 95% CI: 0.64–1.59), with similar results for PFS. Conclusion BRAFV600E and RAS mutational status are not associated with prognosis in dMMR mCRC patients, in contrast to pMMR mCRC patients. Lynch syndrome is also not an independent prognostic factor for survival. These findings underline that prognostic factors of patients with dMMR mCRC are different of those with pMMR, which could be taken into consideration when prognosis is used for clinical decision‐making in dMMR mCRC patients and underline the complex heterogeneity of mCRC. An original research article to provide insight in the prognostic value of Lynch syndrome, BRAFV600E and RAS mutation status on survival outcomes with pooled individual patient data from the large Dutch and French deficient mismatch repair (dMMR) / microsatellite instability‐high (MSI‐H) metastatic colorectal cancer (mCRC) cohort. Lynch syndrome, BRAFV600E and RAS mutational status are not independently associated with overall survival in dMMR/MSI‐H mCRC patients treated with palliative first‐line chemotherapy, in contrast to proficient MMR mCRC patients. This could be taken into consideration when prognosis is used for clinical decision‐making in dMMR mCRC patients and underline the complex heterogeneity of mCRC.