Oncocytic metaplasia occurring in melanoma

Oncocytosis is a cellular feature characterized by the presence of a finely granular eosinophilic cytoplasm due to the accumulation of mitochondria. While this histologic trait can be found in normal tissues, it is also seen pathologically as a degenerative phenomenon. We recently reviewed a spectrum of oncocytic melanocytic nevi that did not have clinical significance. We now describe similar changes in melanoma.

We retrospectively reviewed 12 melanomas noted to have prominent granular eosinophilic cytoplasm and completed ultrastructural studies. We obtained patient histories and clinical follow-up information from the patients' physicians.

All cases were primary melanomas and showed prominent oncocytosis in the majority of the lesional melanoma cells. Oncocytosis was observed in both melanoma in situ and invasive melanoma with a wide range of Breslow thicknesses (range, 0.45-5.05 mm). It occurred in the presence and absence of ulceration, regression, vascular invasion, and brisk tumor infiltrating lymphocytes. Ultrastructural studies revealed melanocytes with numerous distorted mitochondria.

Melanoma is capable of presenting in a variety of histologic guises, including oncocytic change. While our observations are preliminary, this pathologic curiosity likely represents a degenerative phenomenon of little prognostic importance.