Spindle cell malignant melanoma metastatic to the breast from a pigmented lesion on the back. A case report

Tumors metastatic to the breast are quite unusual (1.2% of all tumors). Malignant melanoma is an exception and is one of the principal metastasizing tumors, described mainly as a primary tumor. There are 5 different cytologic patterns; the spindled pattern is very uncommon, more difficult to diagnose and can be confused with a wide range of sarcomatous lesions. Nevertheless, there are some cytologic features that allow differentiation from similar tumors.

A 30-year-old woman presented with a firm, deep, nontender mass in the upper outer quadrant of the right breast. Fine needle aspiration cytology was performed, and the aspiration smears showed spindle-shaped neoplastic cells arranged singly or in clusters with marked nuclear atypia. Melanin pigment was sometimes seen in the cytoplasm of some cells. Pathologic study of the breast tumor corroborated the diagnosis, and later study revealed lymph node metastases and relapse in the breast area and on a scar on the back. Two years earlier, biopsy of a pigmented lesion on the back was diagnosed as a cellular blue nevus.

The cytologic features of spindle cell melanoma are distinctive. The presence of atypical fusiform cells with elongated cytoplasm; enlarged nuclei, some of them binucleated or multinucleated; prominent nucleoli; intranuclear cytoplasmic inclusions; and melanin pigment can help to diagnose these unusual metastases to the breast. This case was the first of malignant metastatic melanoma with the spindled pattern in which the diagnosis was made by fine needle aspiration cytology.