Case of leiomyosarcoma arising from subserosal leiomyoma.

Uterine leiomyosarcoma (LMS) is a rare tumor. It has not been established if these tumors arise de novo or from pre-existing leiomyomas (LM). We report a case herein of LMS arising from a subserosal LM. A 47-year-old nulliparous woman was diagnosed with a uterine tumor measuring 30 cm in diameter by pelvic magnetic resonance imaging. Serum CA-125 level was 369 U/mL, and the lactate dehydrogenase level was elevated (565 IU/L, respectively). Positron emission tomography-computed tomography revealed abnormal uptake (SUVmax = 25.29) of the abdominal tumor. Upon laparotomy, a large tumor with solid and cystic components was shown to arise from a subserosal LM, with invasion into the greater omentum and small intestine. Abdominal hysterectomy, bilateral salpingo-oophorectomy, omentectomy and small intestine resection were performed. Macroscopic findings showed that the LMS was adherent to a subserosal LM, without continuity between the tumor and the uterus. Our case supports the hypothesis that LMS can arise from a pre-existing LM.