CHICAGO (FRONTLINE MEDICAL NEWS) Both transgender men and transgender women had an increased risk of breast cancer compared with a male, but not a female, reference population, said Christel de Blok, MD, sharing results of a Dutch national study.

The study included 3,078 transgender people (2,064 transgender women) who began hormone therapy (HT) at age 18 years or older. The mean age at which transgender women began HT was 33 years; for transgender men, the mean age was 25 years. In all, transgender women in the study had a total of 30,699 person-years of exposure to HT; for transgender men, the figure was 13,155 person-years.

Overall, there were 16 observed cases of breast cancer in transgender women and four in transgender men. After gender-affirming surgery, the transgender women were followed for a median of 146 months, and experienced a median of 193 months of HT. Transgender men who had mastectomies were followed for a median 93 months, and those who had a hysterectomy-oophorectomy were followed for a median 144 months. Transgender men received a median 176 months of HT.

“Breast cancer can still occur after mastectomy in [transgender] men,” Dr. de Blok said at the annual meeting of the Endocrine Society. “What is interesting is that three out of the four cases of breast cancer in [transgender] men happened after mastectomy.”

In the Netherlands, one in eight women and one in 1,000 men will develop cancer at some point during their lives. In patients who have had a subtotal mastectomy and who are BRCA-1/2 carriers, there is still an approximate 5% residual risk of breast cancer, said Dr. de Blok.

A literature review conducted by Dr. de Blok and her colleagues revealed 19 cases of breast cancer in transgender women and 13 in transgender men. However, a more general study of incidence and characteristics of breast cancer in transgender people receiving hormone treatment had not been done, said Dr. de Blok, of the VU University Medical Center, Amsterdam.

The investigators examined data for adult transgender people seen at their center from 1991 to 2017 and started on hormone treatment. This clinic, said Dr. de Blok, sees about 95% of the transgender individuals in the Netherlands.

The study was able to capitalize on comprehensive information from national databases and registries. Investigators drew from a national histopathology and cytopathology registry as well as from a national vital statistics database. A comprehensive cancer database was used to establish both reference incidence values for males and females and the number of expected cases within the study group.

In both transgender men and women, exactly 50% of cases were ductal carcinoma, compared to 85% in the group of reference women.

An additional 31% of the breast cancers in transgender women were lobular, 6% were ductal carcinoma in situ (DCIS), and the remainder were of other types. Of the cancers in transgender women, 82% were estrogen receptor positive, 64% were progesterone receptor positive, and 9% were Her2/neu positive.

For transgender men, there were no lobular carcinomas; 25% were DCIS, and 25% were of other types. Half of the cancers were estrogen receptor positive, and half were progesterone receptor positive; 25% were Her2/neu positive, and there was one case of androgen receptor positive breast cancer.

Dr. de Blok explained that their analysis compared the observed cases in both transgender men and women to the expected number of cases for the same number of males and females, yielding two standardized incidence ratios (SIRs) for each transgender group.

For transgender women, the SIR for breast cancer compared with males was 50.9 (95% confidence interval, 30.1-80.9). The SIR compared to females was 0.3 (95% CI, 0.2-0.4). This reflected the expected case number of 0.3 for males and the 58 expected cases for a matched group of females.

For transgender men, the SIR for breast cancer compared with males was 59.8 (95% CI, 19-144.3), while the SIR compared to females was 0.2 (95% CI, 0.1-0.5). The expected cases for a similar group of males would be 0.1, and for females, 18.

In many cases, whether a transgender person receives standardized screening mammogram reminders will depend on which sex is assigned to that individual in insurance and other administrative databases, Mr. de Blok noted. When electronic health records and other databases have a binary system, at-risk individuals may fall through the cracks.

Dr. de Blok reported no conflicts of interest.

SOURCE: de Blok C, et al. ENDO 2018, abstract OR 25-6 .


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