Abstract
Adjuvant endocrine therapy is an integral component of care for endocrine-dependent breast cancer. The aim of this type of therapy is to counteract the production and the action of estrogens. The ovary is the primary site of estrogen production in premenopausal women, whereas, in postmenopausal women, the main source of estrogens is adipose tissue. Therefore, ovarian function suppression is an effective adjuvant strategy in premenopausal estrogen-dependent breast cancer. Similarly, the inhibition of estrogen action at the receptor site by tamoxifen has proven to be effective. To date, international consensus statements recommend tamoxifen (20 mg/day) for five years as the standard adjuvant endocrine therapy for premenopausal women. It should be noted that tamoxifen is a potent inducer of ovarian function and consequent hyperestrogenism in premenopausal women. In the present study, we report two cases of ovarian cyst formation with very high estrogen levels and endometrial hyperplasia during the administration of tamoxifen alone as adjuvant treatment for estrogen receptor-positive breast cancer in premenopausal women. These cases suggest that in young premenopausal patients with estrogen-dependent breast cancer, ovarian suppression is an essential prerequisite for an adjuvant endocrine therapy with tamoxifen. In this context, luteinizing hormone-releasing hormone agonist treatment by suppressing effective ovarian function may lead to a hypoestrogenic status that may positively impact breast cancer prognosis and prevent the effects of tamoxifen at the gynecological level. It is important to reconsider the action of tamoxifen on ovarian function and include these specific effects of tamoxifen in the informed consent of premenopausal patients who are candidates for tamoxifen alone as adjuvant endocrine treatment.