| Summary: | Abstract Background Patients with microsatellite instability-high (MSI-H) colorectal cancer (CRC) generally have a better prognosis than patients with microsatellite stable (MSS) CRC. However, some MSI-H CRC patients do not gain overall survival benefits from immune checkpoint-blockade treatment. In other words, heterogeneity within the subgroup of MSI-H tumors remains poorly understood. Thus, an in-depth molecular characterization of MSI-H tumors is urgently required. Methods Here, we use nonnegative matrix factorization (NMF)-based consensus clustering to define CRC MSI-H subtypes in The Cancer Genome Atlas and a French multicenter cohort GSE39582. CIBERSORT was used to calculate the proportions of 22 lymphocytes in tumor tissue in MSI-H subtypes. Results MSI-H CRC samples basically clustered into two subgroups (MSI-H1 and MSI-H2). MSI-H1 was characterized by a lower BRAF mutational status, higher frequency of chromosomal instability, global hypomethylation, and worse survival than MSI-H2. Further examination of the immune landscape showed that macrophages of the M2 phenotype were enriched in MSI-H1, which may be associated with poor prognosis in this subgroup. Conclusions Our results illustrate the genetic heterogeneity in MSI-H CRCs and macrophages may serve as good targets for anticancer therapy in MSI-H1. Graphical abstract
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