Extraocular sebaceous carcinoma in situ: report of three cases and review of the literature.

Extraocular sebaceous carcinoma is a rare neoplasm. Purely in situ extraocular sebaceous carcinoma is extremely rare and somewhat controversial. Review of the literature reveals only three reported cases, two of which involved the head and neck and one the arm. The ones on the head and neck arose in association with an actinic keratosis. We report three cases of extraocular sebaceous carcinoma in situ and describe the first report of immunoperoxidase screening for mismatch repair proteins in such tumors.