[A Case of Response to Pembrolizmab in Unresectable MSI-High Transverse Colon Cancer].

A 80s man was diagnosed circulated type 2 colon cancer at the transverse colon, and pathological findings was adenocarcinoma( por1). Genomic findings were microsatellite instability-high(MSI-H), all RAS wild type and BRAFV600E mutated. Contrast-enhanced CT showed an enlarged lymph nodes(#221, #222, #223, #214)along the middle colic and superior mesenteric artery. Clinical diagnosis was a locally advanced unresectable transverse colon cancer, cT4aN3M1a(LYM), cStage Ⅳa. Drug therapy with pembrolizumab was prescribed. Six months later, contrast-enhanced CT and PET demonstrated remarkable shrinkage of the primary tumor and lymph nodes except 2 peri-colic enlarged lymph nodes. Primary lesion turned almost undetectable, however the biopsy demonstrated residual tumor. Two months later, CT showed that the residual lymph nodes had also disappeared.