Benign metastasizing leiomyoma of the lung: potential role of low-grade malignancy

We report here 2 cases of multiple metastatic lung tumors after hysterectomy for leiomyoma. One patient was diagnosed as having a benign metastasizing leiomyoma (BML), while the other patient simultaneously developed a left pelvic tumor and multiple lung tumors, both of which were finally diagnosed as low-grade endometrial stromal sarcomas (ESSs). The metastatic potential of BML is not completely understood, but previously reported cases of BML may include low-grade ESS, which may play a significant role in the metastasis of benign uterine tumors.