Eccrine porocarcinoma with melanocyte colonization.

We describe a 74-year-old Japanese man with a pigmented eccrine porocarcinoma (malignant eccrine poroma). The patient had a brown-black nodule measuring 9 x 7 mm on his leg. Microscopically, the tumour, which had invaded the reticular dermis, was composed of poroid cells with large and small intracytoplasmic lumina. The tumour cells showed cytological pleomorphism and frequent, often abnormal, mitotic figures. Many dendritic melanocytes containing melanin were intermingled with the tumour cells. The poroid cells were diffusely positive for cytokeratin, while the dendritic cells containing melanin were positive for S-100 protein and HMB-45. Ten months of follow-up revealed no recurrence or metastasis of the tumour.