Case of concurrent benign metastasizing leiomyoma in the lung and retroperitoneum, with a focus on its etiology.

We report a rare, simultaneous occurrence of benign metastasizing leiomyoma in the lung and retroperitoneum in a 49-year-old woman who had previously undergone myomectomy at 35 years of age and hysterectomy at 45 years of age for multiple recurrences of histologically benign uterine leiomyomas. At 49 years of age, computed tomography-guided biopsy indicated benign metastasizing leiomyomas in the lung. In addition, a retroperitoneal leiomyoma was found that was resected along with both the ovaries via laparotomy. No sign or symptom of recurrence was observed 5 years later. The coexistence of benign metastasizing leiomyoma in the lung and retroperitoneum following surgery for conventional leiomyomas has rarely been reported. Further, the nature and etiology of benign metastasizing leiomyoma are still not well understood. This case is therefore worth reporting, and exploring its etiology is important.