MSH6 and neoplasm: After the failure of two prior chemotherapy regimens, whole-exome sequencing revealed that tumor tissue had high tumor mutation burden (689 Muts), high microsatellite instability, and some somatic mutations, including PTEN (copy number loss and p.N323fs), MSH6 (p.F1088fs), TP53 p.R273C, ASXL1 p.G645fs, ATR p.S1843P, and CDKN2A p.A118P.