They may grow within the wall of the uterus or they may project into the interior cavity or toward the outer surface of the uterus. In rare cases, they may grow on stalks or peduncles projecting from the surface of the uterus. Fibroids are often referred to as tumors, but they are not cancerous. The cause of fibroid growth is not known. The vast majority of fibroids occur in women of reproductive age, and according to some estimates, they are diagnosed in black women two to three times more frequently than in white women.
Fibroids are the most frequently diagnosed tumor of the female pelvis.
It is important to know that these are benign tumors. They are not associated with cancer, they virtually never develop into cancer, and they do not increase a woman's risk for uterine cancer. No risk factors have been found for uterine fibroids other than being a female of reproductive age. However, some factors have been described that seem to be protective. It is not yet known whether having children actually protects a woman from developing fibroids or whether fibroids contributed to the infertility of women who had no children.