Progesterone and not estrogens or androgens causes breast cancer

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Acknowledgements

The authors thank Amanda Prowse and Jan Egberts (T4C Communications, Hilversum, The Netherlands) for their valuable editorial support. Data sharing is not applicable to this article as no new data were created or analyzed in this study.

Potential conflict of interest

H. J. T. Coelingh Bennink is President of Pantarhei Oncology (subsidiary of Pantarhei Bioscience), the company developing the fetal estrogen estetrol for the treatment of advanced breast and prostate cancer, but this is outside the scope of the present letter. F. Z. Stanczyk has no conflict of interest.

Source of funding

None.