Undergoing hormone treatment can increase the risk of breast cancer in transgender women, according to a new study from the Netherlands.

Prof. Martin den Heijer and his colleagues at the University Medical Centre in Amsterdam examined the susceptibility of transgender people to developing breast cancer compared to the general population.

They looked at data from 2,260 transgender women and 1,229 transgender men that are receiving hormone treatment at an Amsterdam specialist clinic from 1972 to 2016.

The average age of trans women undergoing treatment was 31 years, while for trans men it was 23 years. Meanwhile, the average time for their hormone treatment was 13 years for trans women and 8 years for trans men.

The researchers then compared the information with those from medical records regarding breast cancer cases in the country.

Breast Cancer Risk Among Transgender Women

Den Heijer and his team discovered 15 invasive breast cancer cases among the trans women involved in the study. These patients had an average of 50 years and had been undergoing hormone treatment for an average of 18 years.

The incidence of breast cancer is considered to be higher compared to the general population of cisgender men, or those who identify with the gender they were assigned at birth. However, it is lower compared to the population of cisgender women.

Meanwhile, the researchers found only four invasive breast cancer cases among the trans men. These patients had an average of 47 years and had been receiving treatment for an average of 15 years.

Breast cancer incidence in trans men was lower compared to the general population of cisgender women.

Limitations Of The Study

While the researchers tried to use a relatively large sample size for the study, the results are merely observational and cannot establish a cause. There are also certain limitations to its findings such as incomplete or missing data regarding the type of hormones used in the treatment.

The team also failed to factor in the participants' body mass index, alcohol and tobacco use, and family history, as well as the instances of genetic mutations involved in such treatments.

"The absolute overall risk of breast cancer in transgender people remains low," the researchers conclude.

"Therefore it seems sufficient for transgender people using hormone treatment to follow screening guidelines as for cisgender people."

Den Heijer and his colleagues believe future studies would serve well to look into the cause of breast cancer among trans people undergoing hormone treatment. This is important given the sudden increase in cancer risks among trans women while they received gender affirming treatment.

Other Health Risks Associated With Hormone Treatments

In 2018, a Kaiser Permanente-led research discovered an increased risk for cardiovascular problems among trans women undergoing hormone treatment. Among the health issues found in the study include blood clots, heart attacks, and strokes.

The researchers said trans women were twice as likely to develop a blood clot condition known as venous thromboembolism compared to cisgender men or women.

Trans women were also 80 to 90 percent more susceptible to strokes and heart attacks compared to cisgender women.

However, the study found no such increase in health risks among trans men receiving hormone therapy.

The findings of the University Medical Centre are featured in the journal The BMJ.

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