Transgender women using hormone treatment show an increased risk of breast cancer compared with the cisgender male population, a study has suggested.
Although the risk in transgender women increased during a relatively short duration of hormone treatment, it is still lower than the cisgender female population.
As such, researchers say the absolute risk of breast cancer in transgender people remains low – so current breast cancer screening is sufficient for transgender people undergoing hormone treatment.
The findings, published in the BMJ, also show that transgender men had a lower risk of breast cancer compared with the cisgender female population.
Previous studies have shown that hormone replacement therapy (HRT) increases the risk of breast cancer in postmenopausal women, which suggested a similarly increased risk in trans women receiving hormone treatment.
But information about the breast cancer risk in transgender people is limited, so a research team, led by Professor Martin den Heijer at the University Medical Centre in Amsterdam, investigated breast cancer in transgender people receiving hormone treatment, in the context of the general Dutch population.
The study included 2,260 trans women and 1,229 trans men receiving hormone treatment at a clinic in Amsterdam between 1972 and 2016. National medical records were used to identify breast cancer cases.
The average age at the start of hormone treatment was 31 years for trans women and 23 for trans men. The average treatment time was 13 years for trans women and eight years for trans men.
Of the 2,260 trans women, 15 cases of invasive breast cancer were diagnosed at an average age of 50 and after an average 18 years of hormone treatment. This was higher than the general male population and lower than the general female population.
In 1,229 trans men, four cases of invasive breast cancer were identified at an average age of 47 years and after an average 15 years of hormone treatment. This was lower than expected compared with the general female population.
Despite the large sample size, the authors said this is an observational study, and as such, can’t establish cause. The researchers did point out some limitations, including missing or incomplete data about: type of hormone use, family history, genetic mutations, tobacco and alcohol use, and BMI.
Based on this study, the authors conclude that “the absolute overall risk of breast cancer in transgender people remains low and therefore it seems sufficient for transgender people using hormone treatment to follow screening guidelines as for cisgender people.”
As the risk of breast cancer in trans women increased during a relatively short duration of hormone treatment, they suggest it would be worthwhile for future studies to investigate in more detail the cause of breast cancer in transgender people receiving hormone treatment.