Breast malignancy in female-to-male transsexuals: systematic review, case report, and recommendations for screening.

Background: Female-to-male (FtM) transsexuals may use testosterone therapy for masculinization, which potentially influences the risk of breast cancer development. Guided by our case report, we aimed to investigate the evidence regarding the risk of testosterone therapy on breast malignancy in female-to-male transsexuals and evaluate breast cancer screening in this subgroup.

Methods: We conducted a systematic literature search according to the PRISMA checklist in June 2020 in PubMed/MEDLINE and Ovid/EMBASE. Reference lists of included articles were screened to find additional articles that met the inclusion criteria. All cohort studies and case reports evaluating breast cancer in FtM transsexuals after testosterone therapy were included.

Results: We found 23 cases of FtM transsexuals who developed breast cancer after testosterone therapy, including our own case. Moreover, we evaluated ten retrospective cohort studies investigating breast malignancy in the transsexual population. The cohort studies showed no elevated risk in FtM transsexuals compared to natal women. Including our own case, nine cases were described in which breast malignancy was incidentally found during routine histological examination after mastectomy. High-level evidence for a correlation between testosterone therapy and breast malignancy is missing.

Conclusion: Few cases are described of FtM transsexuals with breast malignancy. However, cases such as these make physicians aware of the possibility of breast cancer in FtM transsexuals. Radiological screening of FtM transsexuals for breast cancer prior to mastectomy and histological screening of the mammalian tissue after mastectomy should be considered; physicians should decide together with every individual FtM transsexual if screening is necessary.