Uterine leiomyomas (fibroids) are benign smooth muscle tumors originating from the uterus, and affect up to 77% of all reproductive-age women in the United States. No effective treatments other than myomectomy or hysterectomy exist, and approximately 200,000 hysterectomies are performed for leiomyoma annually in the United States. The prevalence of uterine leiomyoma is much higher in African-American women compared with Caucasian-American women or other races. Compared with Caucasian-American women, African-American women develop leiomyomas at an earlier age, and have more numerous and symptomatic tumors.
One study found strikingly higher aromatase mRNA levels in leiomyoma compared with adjacent myometrium in African-American (83 fold), Caucasian-American (38 fold), and Japanese women (33 fold). Among the four major promoters that regulate aromatase expression in leiomyoma, the proximal promoter II accounted for higher aromatase mRNA levels in tissues from African-American women. Estrogen receptor subtype α mRNA levels were significantly, and 1.8- to 2.6-fold, higher in leiomyoma compared with adjacent myometrium in all groups, whereas leiomyoma estrogen receptor subtype β mRNA levels were significantly elevated only in Japanese women.
Leiomyoma tissues from African-American women contained the highest level of aromatase expression, which may result in elevated tissue concentrations of estrogen, and account for the higher prevalence and earlier incidence.