Malignant Proliferating Trichilemmal Tumor: A Subtle Presentation in an African American Woman and Review of Immunohistochemical Markers for This Rare Condition.

A malignant proliferating trichilemmal tumor (MPTT) is thought to represent the malignant counterpart of a benign proliferating trichilemmal cyst, a keratin-filled lesion that derives from the outer hair root sheath. The clinical appearance of MPTTs does not always correlate with their histopathologic behavior, emphasizing the need for biopsy and histopathological analysis. Here, we present a 46-year-old African American woman who was evaluated for an ostensibly benign cyst on her scalp that was diagnosed as an MPTT following histopathological examination. She was treated with simple surgical resection that was flush with the cyst margins, followed by Mohs surgery to ensure complete resection. As immunohistochemistry (IHC) has often been used to characterize MPTTs, we also review the various IHC markers reported in the literature.