Malignant Melanoma with Probable Smooth Muscle Differentiation
A 63-year-old woman presented with an ulcerated reddish nodule on the left toe (fig. ). No pigmentation was observed in the lesion. The patient had no other pigmented lesion, which was suspected as malignant melanoma. Leiomyosarcoma was highly suspected based on an incisional biopsy performed at another hospital; thus, the patient was referred to our institution. Subsequently, the left toe was amputated. Histopathologically, the neoplasm occupied the entire dermis (fig. ) and was composed of pleomorphic spindle cells with eosinophilic cytoplasm, blunt-ended nuclei, and perinuclear vacuoles (fig. ). Mitosis was frequently observed (47 mitosis/10 high-power fields). Alfa smooth muscle actin (α-SMA; fig. ) and desmin (fig. ) were diffusely positive. S-100 was focally positive (fig. ). At that time, these findings suggested a diagnosis of cutaneous leiomyosarcoma. Seven months after the amputation, the patient presented with left groin lymph node swelling. Analysis of the excised lymph node showed replacement of lymph node tissue with a cytologically uniform eosinophilic spindle cell neoplasm (fig. ). Immunohistochemically, the spindle cells were diffusely positive for S-100 (fig. ) and α-SMA (fig. ). Staining for microphthalmia transcription factor (MiTF; fig. ) and HMB45 (fig. ) was focally positive. Melan-A-positive cells were scarcely observed (fig. ). Since whole tissues were embedded in paraffin block, electron microscopic analysis could not be performed. Finally, we made the diagnosis of spindle cell melanoma with probable smooth muscle differentiation. Two years after lymph node dissection followed by 5 courses of chemotherapy (dacarbazine, nimustine hydrochloride, vincristine sulfate, and interferon beta), no local recurrence or distant metastasis was observed.