Progesterone from ovulatory menstrual cycles is an important cause of breast cancer

On May 30, 2023 the leading scientific journal dealing with basic and clinical breast cancer research “Breast Cancer Research (BCR)” published the Perspective Review paper  “Progesterone from ovulatory menstrual cycles is an important cause of breast cancer” by Herjan J.T. Coelingh Bennink, Iman J. Schultz, Marcus Schmidt, V. Craig Jordan, Paula Briggs, Jan F.M. Egberts, Kristina Gemzell-Danielsson, Ludwig Kiesel, Kirsten Kluivers, Jan Krijgh, Tommaso Simoncini, Frank Z. Stanczyk and Robert D. Langer.

The most important message of this narrative review paper is that progesterone from normal menstrual cycles causes most BCs, whereas estrogens and androgens may stimulate existing hormone receptor positive BC, but do not cause BC. Four authors of this paper are related to Pantarhei (HCB, IJS, JFME and JK) and the other nine authors are experts in the field of Reproductive Endocrinology and Oncology, supporting this rather thought-provoking paper, that will hopefully lead to a reappraisal and a turnaround of the medical view and opinion on the cause of breast cancer and change the negative perception of estrogens.

Abstract: Many factors, including reproductive hormones, have been linked to a woman’s risk of developing breast cancer (BC). We reviewed the literature regarding the relationship between ovulatory menstrual cycles (MCs) and BC risk. Physiological variations in the frequency of MCs and interference with MCs through genetic variations, pathological conditions and or pharmaceutical interventions revealed a strong link between BC risk and the lifetime number of MCs. A substantial reduction in BC risk is observed in situations without MCs. In genetic or transgender situations with normal female breasts and estrogens, but no progesterone (P4), the incidence of BC is very low, suggesting an essential role of P4. During the MC, P4 has a strong proliferative effect on normal breast epithelium, whereas estradiol (E2) has only a minimal effect. The origin of BC has been strongly linked to proliferation associated DNA replication errors, and the repeated stimulation of the breast epithelium by P4 with each MC is likely to impact the epithelial mutational burden. Long-lived cells, such as stem cells, present in the breast epithelium, can carry mutations forward for an extended period of time, and studies show that breast tumours tend to take decades to develop before detection. We therefore postulate that P4 is an important factor in a woman’s lifetime risk of developing BC, and that breast tumours arising during hormonal contraception or after menopause, with or without menopausal hormone therapy, are the consequence of the outgrowth of pre-existing neoplastic lesions, eventually stimulated by estrogens and some progestins.