What causes uterine fibroids?
The cause of uterine fibroids is not known. Fibroids begin when abnormal cells grow in the muscular wall of the uterus (myometrium). Fibroids contain muscular and fibrous tissue similar to the normal tissue of the uterus, but fibroid tissue serves no useful purpose. Recently, gene mutations have been discovered in fibroid cells that alter the cell's growth. It is very likely that the cause of fibroids relates to genes, but the entire mechanism has not yet been worked out. There may
also be environmental causes that stimulate fibroid growth. It is important to realize that there is no evidence that fibroids turn into cancer. Fibroids are benign from the beginning and remain benign.
Uterine fibroids develop from the smooth muscular tissue of the uterus (myometrium). A single cell reproduces repeatedly, eventually creating a pale, firm, rubbery mass distinct from neighboring tissue. Fibroids range in size from seedlings, undetectable by the human eye, to bulky masses that can distort and enlarge the uterus. They can be single or multiple, in extreme cases expanding the uterus so much that it reaches the rib cage.
The female hormones estrogen and progesterone are necessary for fibroids to grow. Fibroids do not occur before puberty when estrogen and progesterone production begins, and fibroids shrink after menopause when hormone production declines. It appears that fibroids start from a single cell mutation, but growth of the fibroid requires the complex interaction of estrogen, progesterone, and cell growth factors. Studies are now under way to try to determine how fibroids arise and what influences their growth.
Fibroids usually do not develop until between ages twenty-five and thirty-five. You might expect that women with fibroids are making too much estrogen or progesterone. However, if we measure hormone levels in the blood, these women have absolutely normal amounts. It appears that the muscle cells in the uterus undergo a change that causes these cells to use up, or metabolize, more of the estrogen and progesterone in the blood than usual. As a result, the cells are stimulated to overgrow, causing a round swelling of the uterine muscular wall. Importantly, this change in metabolism does not appear to affect any other area of the body. Women with fibroids are not more prone to fibrocystic changes in the breast, a totally unrelated condition and they are not more prone to develop any other benign or cancerous conditions. |
