CHICAGO – , 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.