Abstract
Pilomatricoma is a benign follicular adnexal neoplasm with matrical differentiation. It typically occurs as a firm papule/nodule on the head/neck of a child. Recurrence following simple excision is uncommon. Microscopically it is characterized by aggregations of basophilic matrical cells admixed with eosinophilic ghost cells in a variably altered (inflamed/calcified) stroma. Pilomatrical carcinomas are exceptionally rare, their pathogenesis is unclear and criteria for their diagnosis are controversial. We report the case of a 40-year-old male with a postauricular lesion, clinically thought to be a cyst. This was excised and the histopathological features were those of a pilomatricoma. Two years later the lesion recurred. Following excision and microscopy the tumor was seen to be circumscribed and composed largely of basaloid cells displaying prominent mitotic activity and areas of coagulative necrosis. These findings fell within the spectrum of proliferative pilomatricoma. Complete removal was recommended but the patient declined this step. Five years later the lesion recurred. After initial incomplete excision and subsequent comprehensive re-excision, the tumor was seen to have evolved to a frankly malignant matrical carcinoma. It exhibited central cystic and peripheral invasive components in a desmoplastic stroma, marked cytological atypia, a brisk mitotic rate and zones of geographic necrosis. We add this case to rare existing reports of progression of pilomatricoma to pilomatrical carcinoma. In this instance, a gradual change from benign to intermediate to malignant neoplasia was observed in a 7-year period. Whether this pathogenesis of pilomatrical carcinoma is the norm or exceptional remains to be determined.
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