Tumoral Melanosis Arising on a Mycosis Fungoides Plaque

Tumoral melanosis is a rare histopathological phenomenon characterized by confuent dermal nodular aggregates of heavily melanized polygonal cells consistent with melanophages. The initial occurrence of tumoral melanosis always raises the suspicion of a regressed melanocytic proliferation, especially a melanoma. Regression can be recognized by the presence of dermal fibrosis, vascular proliferation, and usually a band-like infiltrate of lymphocytes and melanophages in variable numbers. However, these changes are non-specific, and similar findings can be seen in regression of pigmented epithelial lesions, such as basal cell carcinoma, Bowen’s disease, solar lentigo, and rarely, in mycosis fungoides (1,2). We present a case of tumoral melanosis which arose on a plaque of mycosis fungoides and discuss the possible underlying pathological mechanisms.