High progesterone levels during the luteal phase related to the use of an aromatase inhibitor in breast cancer patients.

OBJECTIVE: To evaluate the hormonal profile in three breast cancer patients who underwent controlled ovarian stimulation in the presence of the aromatase inhibitor letrozole. PATIENTS AND METHODS: In IVF University referral center, a case series of three breast cancer patients who underwent controlled ovarian stimulation (COS) with recombinant FSH and letrozole were investigated. Ovulation was induced with hCG (case No. 1) or with GnRH agonist (case No. 2-3). The primary outcome of our study was the detection of progesterone levels in the luteal phase. RESULTS: Very high progesterone values (mean 186.6 ± 43.6 ng/mL) during the luteal phase were recorded in all three cases. CONCLUSIONS: High progesterone levels can be related to the use of letrozole independently of the most commonly used trigger regimen. Although progesterone has long been considered a protective factor against breast cancer, several studies have demonstrated that progesterone could expand a transformation-sensitive stem cell population in the mammary glands. The estrogen negative feedback effect on the hypothalamus-pituitary axis and the disruption of steroid biosynthesis and could represent an intriguing reason behind this phenomenon. Our results highlight the need to evaluate further the increase in progesterone levels in the luteal phase in women with breast cancer undergoing COS with letrozole.