DNA Mismatch Repair Defects and Microsatellite Instability Status in Periocular Sebaceous Carcinoma

PURPOSE: To characterize mismatch repair protein expression and the role of DNA repair abnormalities in sebaceous carcinomas of the ocular adnexa. DESIGN: Retrospective case-series study. METHODS: We reviewed 10 cases of sporadic sebaceous carcinoma and 1 case involving a patient with a family history consistent with Muir-Torre syndrome. Immunohistochemistry was used to analyze the presence of 4 mismatch repair proteins (MLH1, MSH2, MSH6, and PMS2) in these tumors. DNA was extracted from 7 of the larger tumors as well as from adjacent normal control tissue and microsatellite instability (MSI) analysis using 5 highly sensitive mononucleotides and 2 pentanucleotides was performed. RESULTS: All 10 sporadic periocular sebaceous carcinomas maintained strong staining of the 4 mismatch repair genes, while tumor from the patient with MuirTorre syndrome showed loss of staining for the mismatch repair genes MSH2 and MSH6. MSI testing of 7 tumors identified no changes in sporadic cases and yielded results supporting presence of repeat sequence instability in the Muir-Torre-associated case. CONCLUSIONS: Sporadic sebaceous carcinoma of the ocular adnexa is not commonly associated with a loss of mismatch repair genes or microsatellite instability.