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Approximately half of microsatellite instability-high (MSI-H)/mismatch repair-deficient (dMMR) tumors do not respond to PD-1 blockade, indicating the importance of the identification of predictive biomarkers associated with less responsiveness to PD-1 blockade. Among 45 MSI-H/dMMR gastrointestinal (GI) tumors, a low tumor mutational burden (TMB) and PTEN mutations were mutually exclusive and were associated with poor clinical outcomes to PD-1 blockade. PTEN mutations in the phosphatase domain were associated with lower responsiveness to PD-1 blockade together with decreased CD8 + T cells and increased tumor-associated macrophages, while those in the C2 domain were not. Importantly, among 20 patients showing disease progression within 6 months after PD-1 blockade, 4 had a low TMB (20%), and 8 had PTEN phosphatase domain mutations (40%). Other gene alterations, such as STK11, FBXW7, JAK1, B2M, and HLA mutations, were also observed in non-responders.Research.

BackgroundDespite unprecedented benefit from immune checkpoint inhibitors (ICIs) in patients with mismatch repair deficient (dMMR)/microsatellite instability high (MSI-H) advanced gastrointestinal cancers, a relevant proportion of patients shows primary resistance or short-term disease control. Since malignant effusions represent an immune-suppressed niche, we investigated whether peritoneal involvement with or without ascites is a poor prognostic factor in patients with dMMR/MSI-H metastatic colorectal cancer (mCRC) and gastric cancer (mGC) receiving ICIs.MethodsWe conducted a global multicohort study at Tertiary Cancer Centers and collected clinic-pathological data from a cohort of patients with dMMR/MSI-H mCRC treated with anti-PD-(L)1 ±anti-CTLA-4 agents at 12 institutions (developing set). A cohort of patients with dMMR/MSI-high mGC treated with anti-PD-1 agents±chemotherapy at five institutions was used as validating dataset.ResultsThe mCRC cohort included 502 patients. After a median follow-up of 31.2 months, patients without peritoneal metastases and those with peritoneal metastases and no ascites had similar outcomes (adjusted HR (aHR) 1.15, 95% CI 0.85 to 1.56 for progression-free survival (PFS); aHR 0.96, 95% CI 0.65 to 1.42 for overall survival (OS)), whereas inferior outcomes were observed in patients with peritoneal metastases and ascites (aHR 2.90, 95% CI 1.70 to 4.94; aHR 3.33, 95% CI 1.88 to 5.91) compared with patients without peritoneal involvement. The mGC cohort included 59 patients. After a median follow-up of 17.4 months, inferior PFS and OS were reported in patients with peritoneal metastases and ascites (aHR 3.83, 95% CI 1.68 to 8.72; aHR 3.44, 95% CI 1.39 to 8.53, respectively), but not in patients with only peritoneal metastases (aHR 1.87, 95% CI 0.64 to 5.46; aHR 2.15, 95% CI 0.64 to 7.27) when compared with patients without peritoneal involvement.ConclusionsPatients with dMMR/MSI-H gastrointestinal cancers with peritoneal metastases and ascites should be considered as a peculiar subgroup with highly unfavorable outcomes to current ICI-based therapies. Novel strategies to target the immune-suppressive niche in malignant effusions should be investigated, as well as next-generation ICIs or intraperitoneal approaches.

Background. KRAS is one of the most frequently mutated oncogenes in colorectal cancer (CRC). Recently, a novel therapy targeting KRAS G12C mutation has demonstrated promising activities for corresponding advanced solid tumors, including metastatic CRC (mCRC). However, the prognostic impact of the KRAS G12C mutation remains unclear in patients with mCRC. Materials and Methods. We retrospectively reviewed medical records of patients with mCRC who received first-line chemotherapy between January 2005 and December 2017 at four large oncology facilities in Japan. Survival outcomes were compared between patients with KRAS G12C and those with non-G12C mutations. Results. Among 2,457 patients with mCRC, 1,632 met selection criteria, and of these, 696 had KRAS exon 2 mutations, including 45 with KRAS G12C mutation tumors. Patient characteristics were not significantly different between the KRAS G12C and non-G12C groups. At a median follow-up of 64.8 months, patients with the KRAS G12C mutation showed significantly shorter first-line progression-free survival (PFS; median, 9.4 vs. 10.8 months; p = .015) and overall survival (OS; median, 21.1 vs. 27.3 months; p = .015) than those with non-G12C mutations. Multivariate analysis also showed that KRAS G12C mutation was significantly associated with shorter PFS (hazard ratio [HR], 1.43; 95% confidence interval [CI], 1.04-1.96, p = .030) and OS (HR, 1.42; 95% CI, 1.01-2.00; p = .044). Conclusion.We demonstrate that, compared with non-G12C mutations, KRAS G12C mutation is significantly correlated with shorter first-line PFS and OS. These findings indicate the relevance of a stratified treatment targeting KRAS G12C mutation in mCRC.