Estrogens and Progestogens in Triple Negative Breast Cancer: Do They Harm?

SIMPLE SUMMARY: Young women treated for breast cancer may experience early menopause, which can negatively impact quality of life. The usual treatment for early menopause is hormone replacement. For hormone-sensitive breast cancers, however, hormones are not given as they can adversely affect the prognosis. In the case of triple-negative breast cancers (TNBC), which do not express the estrogen receptor (ER) and progesterone receptor (PR), research has not been able to show whether hormone replacement is safe yet. Theoretically, however, there are many possible mechanisms by which female hormones can have an effect on TNBC. We therefore reviewed the clinical and preclinical data investigating possible (in)direct effects of estrogens and progestogens on the course of TNBC. The ultimate aim is to provide practical recommendation on how best to treat chemotherapy-induced early menopause in TNBC patients. ABSTRACT: Triple-negative breast cancers (TNBC) occur more frequently in younger women and do not express estrogen receptor (ER) nor progesterone receptor (PR), and are therefore often considered hormone-insensitive. Treatment of premenopausal TNBC patients almost always includes chemotherapy, which may lead to premature ovarian insufficiency (POI) and can severely impact quality of life. Hormone replacement therapy (HRT) is contraindicated for patients with a history of hormone-sensitive breast cancer, but the data on safety for TNBC patients is inconclusive, with a few randomized trials showing increased risk-ratios with wide confidence intervals for recurrence after HRT. Here, we review the literature on alternative pathways from the classical ER/PR. We find that for both estrogens and progestogens, potential alternatives exist for exerting their effects on TNBC, ranging from receptor conversion, to alternative receptors capable of binding estrogens, as well as paracrine pathways, such as RANK/RANKL, which can cause progestogens to indirectly stimulate growth and metastasis of TNBC. Finally, HRT may also influence other hormones, such as androgens, and their effects on TNBCs expressing androgen receptors (AR). Concluding, the assumption that TNBC is completely hormone-insensitive is incorrect. However, the direction of the effects of the alternative pathways is not always clear, and will need to be investigated further.