In leiomyoma of the uterus, both aromatase and 17β-hydroxysteroid dehydrogenase (17β-HSD)
type I are overexpressed compared with myometrium. This suggests that leiomyoma cells
convert circulating androstenedione into estrone (via aromatase), then into the active
form of estrogen, estradiol (via 17β-HSD type I). In vitro experiments and several
clinical findings support the notion that in situ estrogen plays a role in leiomyoma
growth under hypoestrogenemic conditions, such as natural menopause and therapy with
gonadotropin-releasing hormone (GnRH) agonists. GnRH agonists abolish estrogen production
both in situ in leiomyoma and in the ovary, leading to quick and profound regression
of the leiomyoma. Aromatase inhibitors also inhibit estrogen synthesis in both leiomyoma
and the ovary and may be used therapeutically. Certain doses of competitive aromatase
inhibitors would completely inhibit estrogen production in leiomyoma, whereas ovarian
production of estrogen would continue at reduced levels. This may lead to advantageous
therapeutic conditions in which leiomyoma regresses without adverse symptoms related
to estrogen depletion because levels of ovarian estrogen would be insufficient to
support leiomyoma growth but sufficient to prevent symptoms associated with deficiency.
This article discusses the potential uses of aromatase inhibitors.
KEYWORDS
Leiomyoma of the uterus - aromatase - estrogen - aromatase inhibitor
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Makio ShozuM.D.
Department of Obstetrics and Gynecology, Kanazawa University School of Medicine
13-1 Takara-machi, Kanazawa 920-0934, Japan