Follicular Malignant Melanoma: A Rare Morphologic Variant of Melanoma. Report of a Case and Review of the Literature.

Follicular malignant melanoma (FMM) is an exceedingly rare variant of melanoma. Only 8 cases have been reported in the literature thus far. Often bland on physical examination, FMM shows a striking histologic pattern, with atypical melanocytes sometimes consuming the entire follicle and extending into the dermis. Criteria have been suggested to help distinguish FMM from lentigo maligna melanoma; however, no clear criteria distinguish this cancer clinically. FMM cannot be distinguished from follicular metastases of melanoma based on histology, requiring close clinical correlation and detailed history taking on the part of the practitioner. In this publication, we present a case of FMM and a review of the literature. A 59-year-old man was incidentally found to have a small flesh-colored papule on the arm during a skin cancer screening. Biopsy revealed atypical melanocytes extending from the follicular infundibulum into the reticular dermis. Immunohistochemical staining confirmed the melanocytic origin of the neoplasm. The patient underwent wide local excision with 2-cm margins. Sentinel lymph node biopsy was negative for melanoma. We present this case to highlight an unusual type of melanoma and illustrate how it may be distinguished from other neoplasms.