Table 9 Commonly encountered DNA-mismatch repair immunohistochemical staining patternsa

From: Practical issues related to uterine pathology: staging, frozen section, artifacts, and Lynch syndrome

 Diffuse MLH1 and PMS2 loss

MLH1 promoter methylation»MLH1 germline mutation>MLH1 somatic mutation

 Diffuse MSH2 and MSH6 loss

MSH2 germline mutation> MSH6 germline mutation, EPCAM deletion, MSH2 somatic mutation

 Diffuse MSH6 loss

MSH6 germline mutation> MSH6 somatic mutation

 Diffuse PMS2 loss

  PMS2 germline mutation

  1. aOn rare occasions, the tumor shows loss of expression of three or four proteins together; this may be due to combinations of germline and somatic mutations or germline mutations with MLH1 promoter methylation. Another rare occurrence is loss of protein expression in a geographically discrete portion of the tumor. These cases are thought to have either somatic mutations or MLH1 promoter methylation confined to tumoral subclones.
Back to article page