Uterine fibroids are noncancerous growths of the uterus that often appear during childbearing years. Also called leiomyomas (lie-o-my-O-muhs) or myomas, uterine fibroids aren't associated with an increased risk of uterine cancer and almost never develop into cancer. Fibroids range in size from seedlings, undetectable by the human eye, to bulky masses that can distort and enlarge the uterus.