Factors in fibroid growth.

Uterine leiomyomas, commonly called fibroids, are benign tumours of myometrial origin. The tumours enlarge in as many as 30% of women over 30 years of age, causing significant morbidity. Recent research has been directed towards understanding the factors involved in their enlargement. The ovarian steroid hormones oestrogen and progesterone contribute to the pathology of leiomyomas but in unexpected ways. During the follicular phase, oestrogen maintains the high expression of several genes that are normally expressed in the expanding myometrium of pregnancy; however, increased mitotic activity is not induced. During the luteal phase, increased mitotic activity is observed in leiomyomas, particularly in younger women. Progesterone increases the mitotic rate of the tumours in vitro and may induce the production of growth factors and/or their respective receptors during the luteal phase. In addition, a number of non-random chromosomal translocations have been observed in developing clonal tumours. This review will survey factors that may promote enlargement of uterine leiomyomas.