M 58, left cheek.

Figs.1-4: H&E, Fig 5: S-100, Fig 6. HMB45

CLICK ON THE FIGS FOR ENLARGED VIEW

Diagnosis:
Dermal melanoma
Comment:

Well circumscribed dermal nodule composed of epitheliod and spindled melanocytes with large nucleoli and numerous mitotic figures.
Intracytoplasmic melanin pigment is not noted.
The neoplastic cells are strongly positive for S-100 and focally positive for HMB 45.
Overlying epidermis is raised and separated from the tumor by a clear Grenz zone.
No junctional melanoma component, epidermal pagetoid spread or ulceration.
No precursor nevoid lesion or evidence of regression.
Non-brisk dermal lymphocytic response but no lymphohistiocytic invasion.
Picture is that of a metastatic melanoma.
If no clinical or radiologic evidence of a primary melanoma is found in the patient, the lesion may be a rare subtype of melanoma called primary dermal melanoma.