Uterine fibroids may 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.

The growth patterns of uterine fibroids vary …some fibroids continue to grow slowly; other fibroids remain of the same size or shrink on their own with time.

Pharmacists say fibroids range in size from seedlings, undetectable by the human eye, to bulky masses that distort and enlarge the uterus. Fibroids may be single or multiple. Fibroids in extreme cases expand the uterus so much that it reaches the rib cage.

Uterine fibroids are caused by genetic alterations. Many fibroids contain alterations in genes different from those in normal uterine muscle cells. Hormones… estrogen and progesterone, two hormones stimulate development of the uterine lining during each menstrual cycle in preparation for pregnancy; appear to promote the growth of fibroids.

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