Abstract

Panfolliculoma is a benign tumor with differentiation towards the upper and lower segments of the hair follicle. Only two published cases have documented its malignant counterpart, panfollicular carcinoma. A 58-year-old male presented to Dermatology for evaluation of a 6-mm, firm nodule on the scalp, of unknown duration. A punch biopsy specimen showed a proliferation composed of various follicular-type structures with connection to the epidermis, and multilobulated and infiltrative architecture. In the upper dermis the tumor showed peripheral palisading of basaloid cells resembling hair follicular germ, with focal retraction effect at the periphery of the lobules and myxoid stroma. Other features included: matrical differentiation shown by ghost cells, focal sebaceous differentiation, several keratin-filled cysts reminiscent of follicular infundibula, and focal squamous differentiation shown by horn pearl formation. Notably, some of the lobules exhibited central necrosis and prominent mitotic figures. The deeper portion of the tumor showed prominent clear-cell changes consistent with trichilemmal differentiation, infiltration into a desmoplastic stroma, and perineural invasion of a 0.08-mm-diameter nerve. The upper portion of the tumor was diffusely positive for bcl-2, and peripherally positive for BerEP4. Variable (nuclear, cytoplasmic, and membrane) expression of beta-catenin was noted throughout the tumor. Herein, we report the third case of panfollicular carcinoma. Perineural invasion has not been described previously, and can be a clue to the malignant nature of such tumors.