Virilization of a 46,XX Fetus Following Aromatase Inhibitor Treatment of Breast Cancer.

Virilization of the 46,XX infant may be attributed to maternal or fetoplacental origin. Maternal sources may be endogenous, as with an androgen-producing tumor, or drug-related. Iatrogenic virilization by maternal drug exposure is rarely reported, with individual case reports and case series demonstrating the effects of progesterone and other medications affecting the pituitary-ovarian axis.1-3 The class of medications known as aromatase inhibitors are recognized as effective in treating hormone receptor-positive breast cancer by preventing the conversion of androgens into estrogens by aromatase. In fetal development, placental aromatase plays a critical role in preventing virilization of the XX fetus by maternal and fetal androgens during development. In the setting of placental aromatase deficiency, the XX fetus may be virilized. It is conceivable, therefore, that maternal exposure to aromatase inhibitors early in gestation may lead to in utero virilization, though there have been no known reports of this phenomenon to date. We present a case of virilization of a 46,XX infant attributed to pharmacologic aromatase inhibition. The infant's parents provided informed consent for the reporting of this case.