A case of so-called benign metastasizing leiomyoma responsive to progesterone

A 47-year-old female, who had undergone hysterectomy and unilateral oophorectomy in 1975, was admitted to our hospital in 1989 because chest X-ray films revealed an increase in size and number of pulmonary nodules for two years. On admission, a left inguinal tumor was found and histologically it consisted of smooth muscle cells with nuclear atypia arranged in interlacing fascicles. An open-lung biopsy was performed. Pulmonary tumors revealed similar histology to the inguinal tumor. They were diagnosed as metastatic low-grade leiomyosarcoma, so-called benign metastasizing leiomyoma (BML), on the basis of location and history, reinforced by mild histologic atypia. The tumor contained a high progesterone receptor level (400 fmol/mg). Therefore, medroxyprogesterone acetate, 600 mg daily, was administered orally. At two years the pulmonary lesions had regressed. BML is a rare condition, considered to be pulmonary metastasis from low-grade leiomyosarcoma of the uterus. Measuring estrogen and progesterone receptors in lung biopy material may help determine the most appropriate therapy.