[So-called benign metastasizing leiomyoma of the lung presenting with bone metastases].

The patient, a 42-year-old woman, was admitted to our hospital because of abnormal shadows on chest X-ray films obtained during a routine medical check-up. Her medical history included a uterine myomectomy at the age of 21, and thereafter, periodic lumbago and back pain for which she had not sought any medical treatment. Chest computed tomography detected a number of pulmonary nodules in both whole lung fields, and magnetic resonance imaging revealed many spherical metastatic lesions in the thoracic and lumbar vertebrae. Although we initially suspected lung cancer, no primary lesion was found. A thoracoscopic lung biopsy revealed leiomyomatous tumors that were histologically similar to the uterine myoma removed 21 years previously. The final diagnosis was so-called benign metastasizing leiomyoma (BML). Because the removed tumor contained a high concentration of progesterone receptors (240 fmol/mg), a gonadotropin-releasing hormone analogue was administered, and proved effective in relieving the patient's periodic lumbago and back pain. The findings in this case suggested that the so-called BML was in fact a metastasis of a low-grade uterine leiomyosarcoma.