A KRAS mutation is associated with an immunosuppressive tumor microenvironment in mismatch-repair proficient colorectal cancer.

609Background: KRAS-mutant (KRASmut) colorectal cancers (CRCs) are associated with worse prognosis and resistance to therapy. We have previously shown that KRASmut CRCs have different transcriptomic signature of stromal and immune-related genes compared to KRAS-wild type (KRASwt) tumors. Here, we validated the immune-related changes in the tumor microenvironment associated with the KRAS mutation in CRC to guide the design of novel immunotherapy strategies. Methods: The expression of different immune markers (T cells, B cells, macrophages, natural killer cells, and immune check ligands) were assessed using multiplex immunofluorescence (M-IF) technique in both tumor core (TC) and invasive margin (IM). Sequential slides were cut from paraffin blocks of CRC resected at our institute. Each slide was stained with 4 immune markers using M-IF technique. The stained slides were scanned, and quantification of immune cells was done using ImageJ software. Student’s t test was used for statistical analyses. DNA was ex...