Pregnancy, progesterone and progestins in relation to breast cancer risk

• Published in: Journal of steroid biochemistry and molecular biology Vol. 97; no. 5; pp. 441 - 450
• Main Authors: Campagnoli, Carlo, Abbà, Chiara, Ambroggio, Simona, Peris, Clementina
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01.12.2005; Elsevier Science
• Subjects: Biological and medical sciences; Breast cancer; Breast Neoplasms - chemically induced; Estrogen Replacement Therapy - adverse effects; Female; Gynecology. Andrology. Obstetrics; Hormone Replacement Therapy - adverse effects; Humans; Mammary gland diseases; Medical sciences; Pregnancy; Progesterone; Progesterone - adverse effects; Progesterone - therapeutic use; Progestins; Progestins - adverse effects; Progestins - therapeutic use; Risk Factors; Tumors; Pregnancy; Breast cancer; Progesterone; Progestins; Human; Review; Epidemiology; Ovarian hormone; Mammary gland diseases; Tumor; Hormone replacement therapy; Mammary gland; Sex steroid hormone
• ISSN: 0960-0760; 1879-1220
• DOI: 10.1016/j.jsbmb.2005.08.015

In the last two decades the prevailing opinion, supported by the “estrogen augmented by progesterone” hypothesis, has been that progesterone contributes to the development of breast cancer (BC). Support for this opinion was provided by the finding that some synthetic progestins, when added to estrogen in hormone replacement therapy (HRT) for menopausal complaints, increase the BC risk more than estrogen alone. However, recent findings suggest that both the production of progesterone during pregnancy and the progesterone endogenously produced or exogenously administered outside pregnancy, does not increase BC risk, and could even be protective. The increased BC risk found with the addition of synthetic progestins to estrogen in HRT seems in all likehood due to the fact that these progestins (medroxyprogesterone acetate and 19-nortestosterone-derivatives) are endowed with some non-progesterone-like effects which can potentiate the proliferative action of estrogens. The use of progestational agents in pregnancy, for example to prevent preterm birth, does not cause concern in relation to BC risk.