Colorectal carcinomas with isolated loss of PMS2 staining by immunohistochemistry

Abstract

Context.-Isolated loss of PMS2 staining is an uncommon immunophenotype in colorectal carcinomas, accounting for approximately 4% of tumors with microsatellite instability. Limited information regarding these tumors is available in the literature. Objective.-To compare the clinicopathologic features of colorectal carcinomas with isolated PMS2 loss by immunohistochemistry to those with other forms of mismatch repair deficiency. Design.-Ninety-three colorectal carcinomas with isolated PMS2 loss by immunohistochemistry and 193 with other forms of mismatch repair deficiency were identified. Forty (43%) of the isolated PMS2 loss cases and 35 control cases (18%) had a known germline mutation or a clinical diagnosis of Lynch syndrome. Results.-Overall, isolated PMS2-loss tumors occurred in significantly younger patients (P