December 2015 Case of the Month

38 year-old man presented to his primary care provider with left facial mass near the temporal region.  An excision/curettage was performed with the following histologic features.  What is your diagnosis?

2x
2x

A portion of epidermis overlies a hypercellular tumor with somewhat nodular architecture. The tumor occupies the majority of dermis and involves all margins.

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10x
10x

Tumor is arranged in solid sheets with monomorphic nuclei.

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Ki-67
Ki-67

Modestly elevated index.

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2x
2x

A portion of epidermis overlies a hypercellular tumor with somewhat nodular architecture. The tumor occupies the majority of dermis and involves all margins.

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December 2015 Case of the Month

   Answer: Sebaceous Carcinoma

The predominant histologic impression is that of an adnexal tumor, and the focal vacuolated cells are representative of sebaceous differentiation.  By IHC the tumor was positive for keratins (low and high molecular weight), p63, CK5, D2-40, and weak expression of androgen receptor.  The tumor was negative for Sox-10, synaptophysin, chromogranin, TTF-1, GFAP, and myosin.  A modest Ki-67 proliferative index was present.  Overall, the morphologic and immunophenotypic features are consistent with a sebaceous carcinoma.  Importantly, the primary care physician was notified of the positive margins and additional excision was recommended.  Sebaceous carcinoma is a relatively rare neoplasm, traditionally classified into ocular and extraocular types.  This tumor is capable of metastatic spread, and if seen in the setting of multiple sebaceous tumors or visceral carcinoma would raise the possibility of Muir-Torre syndrome (a hereditary defect in the mismatch repair genes).