GENDER MEDICINE, INFERTILITY AND ERECTILE FUNCTION: Edited by Ryan Flannigan and Ranjith RamasamyTestosterone therapy and risk of breast cancer development: a systematic reviewRay, Ala,b; Fernstrum, Austina,b; Mahran, Amra; Thirumavalavan, Nannana,bAuthor Information aCase Western Reserve University School of Medicine bUniversity Hospitals Cleveland Medical Center, Urology Institute, Cleveland, Ohio, USA Correspondence to Austin Fernstrum, 11100 Euclid Avenue, Urology Institute, Cleveland, OH 44106, USA. Tel: +1 216 632 7567; e-mail: Austin.Fernstrum@uhhospitals.org Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Website (www.co-urology.com). Current Opinion in Urology: May 2020 - Volume 30 - Issue 3 - p 340-348 doi: 10.1097/MOU.0000000000000763 Buy SDC Metrics Abstract Purpose of review We aim to conduct a systematic review of the literature, document all reported cases of breast cancer development in cis men and female-to-male (FtM) transgender men undergoing testosterone replacement therapy (TRT), and determine if testosterone poses a substantial risk of breast cancer development and recurrence. Recent findings A systematic search through December 2019 was performed. Out of 1890, 15 studies were eligible for inclusion in the final analyses. In total, 22 patients have developed breast cancer while on testosterone treatment. Four cases were cis men, whereas 18 cases were FtM. Age ranged from 18 to 61 years. Testosterone treatment duration ranged from 5 weeks up to 25 years. Summary There is a relatively higher incidence of BCa in FtM on CSH therapy compared with cis men on TRT. Because of the small sample size of reported cases, we cannot delineate the exact relationship between testosterone therapy and BCa development. Additionally, we have limited data to suggest that TRT should or should not be contraindicated in cis men and FtM with a prior history of breast cancer. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.