Abstract:

True sebaceous skin tumors, including sebaceous adenoma, sebaceoma, and sebaceous carcinoma are rare. Cystic sebaceous tumors are a variant of these classic categories and have been characterized as a marker of Muir Torre syndrome (MTS). However, several cystic sebaceous tumors which are not associated with MTS have also been described. We report a 58 year old male who presented with a red brown papule on the posterior upper leg clinically diagnosed as an epidermal cyst and managed with punch removal. Histologic features were consistent with an atypical cystic sebaceous neoplasm that showed loss of nuclear expression of MLH1 and PMS2. The patient had a recent normal colonoscopy and no history of internal malignancy and no family history of colon cancer or other malignancies. He was referred for genetic counseling and no germline mismatch repair mutation was identified. Cystic sebaceous tumors displaying loss of immunohistochemical (IHC) staining of mismatch repair genes are associated with MTS, however these gene inactivations may also be due to gene hypermethylation. In these cases the tumor may be isolated and not associated with the comorbidities of MTS as seen in our patient. This case highlights this uncommon neoplasm and its frequent association with Muir-Torre syndrome as well as stains that can help support the tumors origin from sporadic mutation. This case also helps to review the workup of MTS and show that the full clinical picture is important in this process.

Financial Disclosure:
No current or relevant financial relationships exist.

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Nathanael Hathaway, MD