From Wikipedia, the free encyclopedia. A leiomyoma (plural leiomyomas or leiomyomata) (leio- + myo- + -oma, smooth-muscle tumor) is a benign smooth muscle neoplasm that very rarely becomes cancer (0.1%). They can occur in any organ, but the most common forms occur in the uterus, small bowel, and the esophagus. Leiomyoma enucleated from a uterus.