Folliculotropic Metastatic Melanoma: A Case Report and Review of the Literature

Abstract: Folliculotropic metastasis of cutaneous melanoma is rare, with only 5 published case reports in the English language literature since it was first described in 2009. We report a 41-year-old man with a primary cutaneous melanoma of the right upper preauricular region with metastatic spread to the parotid gland and pulmonary lymph nodes. Excision of the primary lesion was performed and immunotherapy was initiated. Sixteen months later, the patient presented with 2 new lesions of the left forehead and left neck. Histopathological examination was consistent with folliculotropic dermal deposits of metastatic melanoma. Deeper sectioning into the blocks revealed only sparse perifollicular pigment deposition and rare dermal melanocytes—a potential diagnostic pitfall had this been seen in the initial sections. This case represents the sixth and youngest patient to date with folliculotropic metastatic melanoma. This entity often presents in patients with advanced disease, including increased Breslow thickness and/or multiple metastases to lymph nodes, internal organs, or both. The folliculotropic metastases tend to be small and are often multiple. The precise relationship between folliculotropic primary melanoma and folliculotropic metastasis is unclear. In one reported case and in our patient, the primary tumor was noted to have a "folliculocentric" pattern. Because of the latter finding, the differential diagnosis includes multiple primary folliculotropic melanomas. Thus, clinical correlation and knowledge concerning the evolution of disease in the patient are critical. This case highlights a rare and unusual pattern of metastatic melanoma and potential problems in differential diagnosis.

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