Compared to men the risk of breast cancer was far higher for trans women - PA

Trans women who undergo sex change procedures must be warned that their risk of developing breast cancer increases by 46 times, in comparison to men.

A new study of more than 2,000 women who had transitioned from men showed that around 1 in 200 developed breast cancer compared to fewer than one in 8,000 of men.

Although the risk was around one third less than naturally born women, experts from the Netherlands said it was important that doctors and patients were aware of the increased threat, which is likely to be caused by injections of female hormones.

Lead author Dr Martin den Heijer of Amsterdam University Medical Centre, said: “We do believe that it is important that possible risks and side-effects of the hormone treatment are openly discussed with the people who receive this treatment.

“This enables trans women to make educated decisions about the treatment. In our practice, we advise trans women to participate in the population- based screening program for breast cancer.”

Around 55,000 women are diagnosed with breast cancer in Britain each year and there are approximately 11,000 deaths. But gender reassignment is on the rise with some NHS trusts such as Imperial in London carrying out 250 operations a year, compared to just 54 across the whole health service in 2000.

Previous studies have shown that hormone replacement therapy (HRT) increases the risk of breast cancer in postmenopausal women, which could suggest a similarly increased risk in trans women receiving hormone treatment, the authors said.

Of the 22,60 trans women involved in the study 15 cases of invasive breast cancer were diagnosed at an average age of 50 years and after an average 18 years of hormone therapy.

However the researchers said it was still unclear whether some of the breast cancer cases were also caused by genes or lifestyle factors, as the team only had genetic information for one trans-gender woman in the study, who turned out to carry a mutation in the BRCA gene which causes breast cancer.

Writing in the BMJ the authors concluded that “it would be worthwhile for future studies to investigate in more detail the cause of breast cancer in transgender people receiving hormone treatment.”

The study also showed that transgender men had a lower risk compared with 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.