Risk of Breast Cancer Among Transgender People
In a Dutch study published by de Blok et al in The BMJ, researchers found an increased risk of breast cancer in transgender women compared with cisgender men, and a lower risk of breast cancer in transgender men than in cisgender women.
Methods
This retrospective, nationwide cohort study included 2,260 adult transgender women (male sex assigned at birth, female gender identity) and 1,229 adult transgender men (female sex assigned at birth, male gender identity) receiving treatment at a specialized gender clinic in Amsterdam. Participants had received gender-affirming hormones—transgender women were mostly treated with a combination of antiandrogens and estrogens, and transgender men were treated with one of three forms of testosterone.
The primary outcome measure was collection of data of the incidence and characteristics of breast cancer among the transgender study population vs the cisgender (defined as a person whose gender identity corresponds with the sex assigned to them at birth) population. Researchers collected data on age at the start of hormone treatment, type of treatment, gender-affirming surgery, and medical history.
Findings
Among the 2,260 transgender women in the study, 15 cases of invasive breast cancer were identified. The median duration of hormone treatment in this cohort was 18 years. The incidence of breast cancer was 46-fold higher among transgender women than in cisgender men (standardized incidence ratio = 46.7, 95% confidence interval [CI] = 27.2–75.4), but was a lower risk than that in cisgender women (standardized incidence ratio = 0.3, 95% CI = 0.2–0.4). Most tumors occurring in the population of transgender women were of ductal origin and were estrogen receptor– and progesterone receptor–positive; 8.3% were HER2-positive.
Among the 1,229 transgender men in the study, four cases of invasive breast cancer were identified. The median duration of hormone treatment in this cohort was 15 years. The incidence of breast cancer was lower in transgender men compared to cisgender women (standardized incidence ratio = 0.2, 95% CI = 0.1–0.5). Three of the four cases of breast cancer were of ductal origin; two cases were estrogen receptor– and progesterone receptor–positive, one was HER2-positive, and one was androgen receptor–positive.
The researchers concluded, “This study showed an increased risk of breast cancer in transgender women compared with cisgender men, and a lower risk in transgender men compared with cisgender women. In transgender women, the risk of breast cancer increased during a relatively short duration of hormone treatment and the characteristics of the breast cancer resembled a more female pattern. These results suggest that breast cancer screening guidelines for cisgender people are sufficient for transgender people using hormone treatment.”
Disclosure: For full disclosures of the study authors, visit bmj.com.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
