DNA mismatch repair defects and microsatellite instability status in periocular sebaceous carcinoma

To characterize mismatch repair protein expression and the role of DNA repair abnormalities in sebaceous carcinomas of the ocular adnexa.

Retrospective case-series study.

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.

All 10 sporadic periocular sebaceous carcinomas maintained strong staining of the 4 mismatch repair genes, while tumor from the patient with Muir-Torre 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.

Sporadic sebaceous carcinoma of the ocular adnexa is not commonly associated with a loss of mismatch repair genes or microsatellite instability.