Lymph node melanosis in a patient with metastatic melanoma of unknown primary

Tumoral or nodular melanosis in the skin is considered a variation of completely regressed melanoma, presenting clinically as a suspicious pigmented papule or nodule. Microscopically, the lesion consists of a nodular accumulation of heavily pigmented melanophages in the dermis, staining positive for immunohistochemical markers of histiocytic lineage (CD68) and negative for those of melanocytic lineage (S100, HMB-45, Melan-A). This process is rarely described in lymph nodes. We present a report of a patient with melanosis involving multiple lymph nodes of an axillary dissection, done for metastatic melanoma with an unknown primary, and discuss possible prognostic and treatment factors.