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. The factors that initiate fibroid growth are 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 one knows how many new cases of uterine fibroids occur within any given length of time nor how many women have fibroids at any time. It has been estimated that up to 20 to 30 percent of women of reproductive age have fibroids, though not all have been diagnosed. More careful studies, however, indicate that the prevalence may be much higher.