There’s a new study out from the Netherlands examining the prevalence of breast cancer in transgender people. Gooren et al found that trans women and trans men who have had hormone therapy may be at the same level of risk for breast cancer as cis men.

Why might the risk of breast cancer be different for trans people than for cis people? Some cancers are estrogen or progesterone sensitive. That means they grow in response to those hormones. Giving estrogen to a person with estrogen-sensitive cancer would accelerate the growth of the cancer and potentially threaten their lives. Some cancers also appear more often in one sex than in the other. Breast cancer is more common in cis women than in cis men, but it still happens in cis men. How the incidence of breast cancer would be different for trans women and trans men has been a question in the trans health literature for some time.

For trans women, the development of breasts and increase in breast tissue might increase their risk for breast cancer. Trans women also receive estrogen and/or progesterone, which may affect an estrogen or progesterone sensitive cancer. This study’s authors found 8 cases of breast cancer in trans women in the medical literature, ranging from 1968 to 2013. Three of those cases appeared not to be related to hormones. The other five occurred within 5-10 years of starting hormone therapy. These cases also follow the (cis women) pattern of ductal carcinomas being the most common cancer.

For trans men, the presence of breast tissue is a risk, even after top surgery. Remember that top surgery does not remove all breast tissue! And estrogen levels continue to be at a “female” level, especially with testosterone’s ability to aromatize to estrogen. Or at least, estrogen levels continue to be at that level until an oophorectomy. Additionally, trans men may be reluctant to be screened for breast cancer because it’s deemed a “female” process and may aggravate dysphoria. 4 cases of breast cancer among trans men were found in the literature, from 2003 to 2012. The cancers were detected within 2-10 years of starting hormone therapy, and three of the four were ductal carcinomas.

The present study looked through the records of the VU University Medical Center in Amsterdam, which has records dating back to 1975. They looked at records from 1975 to 2006. The average age for starting hormones was 29, and they had an average follow-up time of 21-23 years. They were able to follow up with 3102 trans people: 2307 trans women and 795 trans men – the “classic” 3:1 ratio.

Of this sample, only 3 cases of breast cancer were reported. Two were trans women, one a trans man. One of the women had an unknown cancer which could not be proven to be from the breast. The other had an estrogen sensitive, progesterone insensitive ductal carcinoma (again, the most common form of breast cancer). The man in this sample had a benign but rare tumor, a tubular adenocarcinoma, after top surgery. The tumor was estrogen and progesterone sensitive.

Three out of 3102 is not many! That’s 0.097%. And even if you break it down by gender, 0.87% of the trans women in this study had breast cancer and 0.13% of the trans men in this study had breast cancer. Here’s another way of looking at the data: The authors calculated the incidence based on these data, per 100,000 person-years. I’ve included their 95% confidence interval in parentheses when it was disclosed. They are as follows…

Trans women: 4.1 (0.8-13)

Cis women: 154.7-170

Trans men: 5.9 (0.5-27.4)

Cis men: 1.1-1.2

In other words, if you saw 100,000 trans women in 1 year, maybe 4 of them would have breast cancer.

These data indicate that both trans men and trans women fall into the range expected for cis men for breast cancer. Given that prevalence, the authors argue that trans people of all genders should be treated under the “male” breast cancer guidelines. Risk factors for male breast cancer include: presence of the BRCA1 and BRCA2 genes, obesity, low levels of testosterone (androgen deprivation) and high levels of estrogen (estrogen exposure). Feminizing hormones automatically create two of those conditions (androgen deprivation and estrogen exposure), but so far that doesn’t seem to be increasing the rate of breast cancer in trans women. The authors also point out that testosterone may be preventative for breast cancer in trans men, also based on these data and the known risk factors for breast cancer.

Limitations of this study include the usual cautions about generalizability. This study was limited to one clinic in the Netherlands – its results may not be applicable to other countries. Especially of note is that Europe tends to use cyproterone acetate for an anti-androgen. Cyproterone acetate is not available in the United States, where spironolactone is the standard anti-androgen. The authors were also not clear about surgical status, and the presence or absence of gonads may also affect breast cancer rates. The authors also point out that their follow-up time was relatively short – an average between 21 and 23 years. But on the whole I don’t find much to criticize in their observations based on what they published.

I find these results reassuring. While some medical providers have already started thinking that their trans patients are at relatively low risk for breast cancer, there’s been little data supporting it. Data is important. Without it, we could not have the safest, evidence-based, most effective treatments we have today.

So what can you do with these data? You can keep in mind the non-gendered risk factors for breast cancer, which include:

Age (being over age 55)

Mutation in the BRCA1, BRCA2, and other genes

Personal or family history of breast cancer. The more closely (genetically) related the family members are, the higher the risk

Previous exposure to radiation in the chest area

Exposure to DES while in the womb

Drinking alcohol

Smoking tobacco

Obesity

Lack of exercise

As you can see, some of these risk factors are changeable. Some are not. Change the ones you can to minimize your risk. And consult your physician to figure out which screenings would be best for you. Options include breast self-exams, clinical breast exams, and mammograms.

This research article was published in the Journal of Sexual Medicine. The abstract is publicly available.

Remember: Stay healthy, stay safe, and have fun!

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