Risk Factors for Tamoxifen-Induced Ovarian Hyperstimulation in Breast Cancer Patients

Adjuvant endocrine therapy is an integral component of care for hormone-dependent breast cancer. Tamoxifen is a potent inducer of ovarian function and consequent hyperestrogenism in premenopausal women. However, the incidence rate and risk factors associated this phenomenon remain unclear. Data of patients younger than 60 years who received adjuvant tamoxifen therapy for hormone-dependent breast cancer (stages 0-III) and who underwent regular follow-up of laboratory results for follicle-stimulating hormone and estradiol levels were retrospectively analyzed. Univariate and multivariate analyses were performed to identify clinicopathologic factors related to ovarian hyperstimulation. Among 205 patients, 19 (9.3%) showed high values of serum estradiol during tamoxifen therapy. The mean (± SD) serum concentrations of estradiol and follicle-stimulating hormone were 1047.97 ± 638.8 pg/mL and 11.5 ± 7.3 mIU/mL, respectively. A mean of 400.83 days elapsed from the start of the single administration of tamoxifen to the initial detection of a high concentration of estradiol. Univariate and multivariate analyses showed that younger age (< 40 years) and only endocrine therapy without chemotherapy were significantly related to a higher prevalence of ovarian hyperstimulation (P = .015, relative risk = 7.49 for age < 40 years; P = .017, relative risk = 32.9 for no chemotherapy). Pathologic stages and tumor characteristics were not related to the manifestation of ovarian hyperstimulation. Young age (< 40 years) and endocrine treatment without chemotherapy were risk factors for the incidence of ovarian hyperstimulation during tamoxifen treatment. Close monitoring of endocrine parameters during treatment with tamoxifen especially in this patient group is essential. With the increasing use of extended long-term treatment with tamoxifen, monitoring endocrine parameters is increasingly important. Hyperestrogenism during tamoxifen treatment may adversely affect tamoxifen effect. We found that about 10% of patients showed hyperestrogenism during tamoxifen treatment. Younger age and endocrine therapy without cytotoxic chemotherapy were related to this phenomenon.