A 69-year-old female presented a 0.5 cm flat, pigmented skin lesion on the right dorsal forearm present for many years. She did not have any other skin lesions or any evidence of neurofibromatosis .The past medical history and the family history were unremarkable.
Microscopic examination of the biopsied skin lesion showed a normal epidermis with a pigmented spindle cell proliferation in the dermis (Figure 1A).
The tumor cells were spindled and elongated with wavy pink-blue cytoplasm within myxocollagenous matrix (Figure 1B).
The nuclei were oval, spindle or comma shaped with the finely dispersed chromatin. The nucleoli were inconspicuous. No mitotic figures are identified. Scattered cells with coarse granular dark-brown pigments in the cytoplasm were present in the tumor (Figure 1B inset). Immunostaining showed that the tumor cells were diffusely positive for Vimentin, S-100 protein, and Melanin-A (Figures 1C and 1D).