What are uterine fibroids? Uterine fibroids are lumps that grow on your uterus. You can have fibroids on the inside, on the outside, or in the wall of your uterus. Your doctor may call them fibroid tumors, leiomyomas, or myomas. But fibroids are not cancer. You do not need to do anything about them unless they are causing problems. Fibroids are very common in women in their 30s and 40s. By the time they are 50, about 80 women out of 100 have fibroids. But fibroids usually do not cause …