Primary leiomyosarcoma of the thyroid gland.

A primary leiomyosarcoma of the thyroid gland in a 72 year old Japanese woman is described. This is the second case reported in the English literature. The patient presented with a 7 month history of a gradually expanding tumor in the right neck. The surgical specimen taken by thyroid lobectomy revealed a relatively well demarcated tumor, 2 x 2 x 3 cm in size, confined to the right lobe. Histologically, the tumor showed a classical leiomyosarcomatous appearance of interlacing fascicles of spindle-shaped cells with occasional blunt-ended nuclei and a high frequency of mitotic figures. Immunohistochemistry of the tumor cells clearly showed smooth muscle differentiation; the cells were positive for desmin, muscle-specific actin and vimentin and negative for cytokeratin, epithelial membrane antigen, carcinoembryonic antigen, thyroglobulin and calcitonin. The patient was free of disease for 3 years and 11 months without further treatment when evidence of multiple bone metastases appeared on bone scintigraphy. She died of pneumonia 4 years and 3 months after the lobectomy.