Test Details: Immunohistochemical testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody. Loss of nuclear staining suggests microsatellite instability. Lack of PMS2 staining is generally due to mutations in MLH1 and raises suspicion for germline mutations. Germ line mutations in PMS2 are associated with increased risk of colorectal cancer, hereditary nonpolyposis colon cancer, Lynch syndrome, Turcot syndrome and endometrial cancer. Loss of nuclear expression of PMS2 only indicates high probability of Lynch syndrome (sequencing and/or large deletion/duplication testing of germline PMS2 may be indicated).