Pulmonary metastases from benign-appearing smooth muscle tumors of the uterus.

A 42-year-old woman was found to have multiple pulmonary nodules 7 years after hysterectomy for leiomyoma. Thoracotomy revealed multiple well differentiated smooth muscle masses containing epithelial inclusions. This patient is similar to others previously reported as examples of "multiple pulmonary fibroleiomyomatous hamartoma" on the basis of slow-growth, benign-appearing histology, and the presence of epithelial elements. Evidence is presented which suggests that these cases represent metastasis from well differentiated leiomyosarcomas. There is a frequent association with uterine smooth-muscle tumor, cases with equally benign-appearing histology have shown lymph node metastasis, the nonmesenchymal elements have been shown to represent engulphed bits of adjacent pulmonary tissue, and the histologic di-ferentiation of benign from malignant mesenchymal tumors is known to be unreliable in some cases. Unlike more anaplastic leiomyosarcomas, this condition may be associated with few symptoms and prolonged survival despite widespread disease.