Incidence of breast cancer in a cohort of 5,135 transgender veterans.

Transgender (TG) persons often receive, or self-treat, with cross-sex hormone (CSH) treatments as part of their treatment plans, with little known about their incidence of breast cancer. This information gap can lead to disparities in the provision of transgender health care. The purpose of the study was to examine the incidence of breast cancer in the largest North American sample of TG patients studied to date to determine their exposure to CSH, incidence of breast cancer, and to compare results with European studies in transsexual populations. We used Veterans Health Administration (VHA) data from 5,135 TG veterans in the United States from 1996 to 2013 to determine the incidence of breast cancer in this population. Chart reviews were completed on all patients who developed breast cancer. Age-standardized incidences of breast cancer from the general population were used for comparison. Person-years of exposure to known CSH treatment were calculated. Ten breast cancer cases were confirmed. Seven were in female-to-male patients, two in male-to-female patients, and one in a natal male with transvestic fetishism. Average age at diagnosis was 63.8 (SD = 8.2). 52 % received >1 dose of CSH treatment from VHA clinicians. All three males presented with late-stage disease were proved fatal. The overall incidence rate was 20.0/100,000 patient-years of VHA treatment (95 % CI 9.6-36.8), irrespective of VA CSH treatment. This rate did not differ from the expected rate in an age-standardized national sample, but exceeded that reported for smaller European studies of transsexual patients that were longer in duration. Although definitive conclusions cannot be made regarding breast cancer incidence in TG veterans who did or did not receive VA CSH due to the sample size and duration of observation, it appears that TG veterans do not display an increase in breast cancer incidence. This is consistent with European studies of longer duration that conclude that CSH treatment in gender dysphoric patients of either birth sex does not result in a greater incidence than the general population.