Superficial spreading melanoma resembling Spitz nevus on the plantar surface.

Plantar melanoma Superficial spreading melanoma Spitz nevus Dr. Taizo Kato, Department of Dermatology, Tohoku University School of Medicine, 1-1 Seiryomachi, Aobaku, Sendai 98077 (Japan) The acral regions of the limbs are the commonest site for melanoma in the Japanese [1, 2]. This high proportion of acral melanoma may be the result of the relatively low occurrence of melanoma in other parts of the body, because the absolute incidence of melanoma on these regions among the general population is found to be similar in different races [3,4]. Acral lentiginous melanoma is a common type of melanoma arising in the acral regions in each race [58], and superficial spreading melanoma (SSM) is also prominent in Caucasians. In a study of melanoma in a white Caucasian population 20 out of 51 patients with plantar melanoma had SSM [9]. In contrast, acral lentiginous melanoma shows far higher frequency in Japanese than others [1, 2, 8, 10]. However, the number of other subtypes of melanoma in the acral regions has gradually increased in the Japanese [11]. Recently, we encountered a rare case of SSM which resembled Spitz nevus on the plantar surface. A 58-year-old male patient visited us with a 1-year-history of a red-brown macule on his left foot. The macule gradually increased in size and became slightly elevated. On physical examination, there was a symmetrical, ovoid nodule 17 × 21 mm in size with a regular border on the lateral aspect of his right foot (fig. 1). These clinical features suggested an epithelial tumor such as Bowen’s disease and hidracan-thoma simplex rather than malignant melanoma. However, the possibility of malignant melanoma was also kept in the differential diagnosis, because of the dark brown pigmentation occupying about half of the surface of the nodule (fig. 1). Histological sections obtained from the excisional biopsy revealed sharply demarcated, intraepidermal tumor nests of various sizes within the irregularly acanthotic epidermis and invasion of tumor cells into the dermis at the central portion. The entire lesion was histologically asymmetric in distribution of tumor cells. In addition, there was an upward pagetoid spread of melanocytes mainly as nests within the entire epidermis that was more prominent in the central portion (fig. 2) than on the periphery. Irregularly shaped, large tumor cells had basophüic nuclei and contained fine melanin granules. Scattered mitotic figures were observed. Kamino