Plantar lentiginous melanoma: a distinctive variant of human cutaneous malignant melanoma.

The neoplastic system of human cutaneous melanoma includes three generaly recognized variants: lentigo maligna, superficial spreading melanoma, and nodular melanoma. Lentiginous melanomas other than lentigo maligna constitute a fourth group, of which plantar lentiginous melanoma qualifies as an anatomic subgroup. Histologically and clinically, plantar lentiginous melanoma (PLM) is characterized by a period of radial growth and often by one or more foci of regression. In 27 of 33 plantar melanomas, a characteristic lentiginous, radial component of melanocytic proliferation was noted. In the remaining six cases, histological material failed to document a radial component. Eighteen of the 27 patients with PLM were blacks, and 18 patients died of distant metastasis. Tumors invasive to level II did not metastasize, but at levels IV and V and in tumors with a high mitotic rate, the prognosis was poor. The presence of lymph node metastases at the time of initial therapy correlated with a poor prognosis group.