Pulmonary benign metastasizing leiomyoma associated with intravenous leiomyomatosis of the uterus: clinical behavior and genomic changes supporting a transportation theory.

Benign metastasizing leiomyoma is a rare lesion characterized by benign-appearing smooth muscle tumor most frequently involving the lung and usually associated with a benign leiomyoma or intravenous leiomyomatosis of the uterus. The pathogenetic mechanism of the tumor has not been clarified, but the possibilities including hormone-sensitive in situ proliferations of smooth muscle bundles, mechanical displacement or intravascular spread of preexisting benign uterine tumor tissue, and metastasized very low-grade uterine leiomyosarcoma have been proposed. We described a case of pulmonary benign metastasizing leiomyoma associated with a uterine intravenous leiomyomatosis in a 46-year-old woman with a result of comparative genomic hybridization study. The 2 lesions showed significantly overlapping, if not identical, complex genomic changes in the comparative genomic hybridization, suggesting that the 2 lesions are closely related to each other. Unresected pulmonary nodules were left untreated for 13 months after the hysterectomy and wedge biopsy of 3 pulmonary nodules to show no further growth, suggesting clinical behavior of nonmalignant tumor in our case. Benign metastasizing leiomyomas may comprise a heterogeneous group of tumors in terms of their malignant potential and pathogenetic mechanism.