Transgender women prescribed gender-affirming hormone therapy have a 47-fold higher risk for developing breast cancer during a median of 18 years vs. cisgender men, although this observed risk remained lower than that for cisgender women, according to findings published in The BMJ.
“Large prospective studies have shown that hormone replacement therapy increases the risk of breast cancer in cisgender postmenopausal women, in particular in those using both estrogens and progestogens, which could suggest an increased breast cancer risk in trans women receiving hormone treatment compared with cisgender men,” Christel J. M. de Blok, MD, a doctoral student at VU University Medical Centre in Amsterdam, and colleagues wrote in the study background. “Currently, information about the risk of breast cancer in transgender people is limited.”
De Blok and colleagues analyzed data from 2,260 transgender women and 1,229 transgender men who visited the gender clinic of VU University Medical Centre Amsterdam between 1972 and 2016 for psychological, endocrine or surgical treatment and received gender-affirming HT. Researchers assessed data on age at initiation of HT, type of treatment, gender-affirming surgery and medical history. Participant data were linked to a statistics database in the Netherlands to determine data on breast cancer diagnoses and histology. Primary outcome was incidence and characteristics of breast cancer in transgender people, calculated as standardized incidence ratios (SIRs).
In transgender women, median age at start of HT was 31 years with a median treatment duration of 13 years. In transgender men, median age at start of HT was 23 years with a median treatment duration of 8 years.
Among transgender women, researchers observed 18 cases of breast cancer in 17 people, diagnosed after a median of 18 years of HT (15 invasive and three noninvasive). Median age at cancer diagnosis was 50 years, with 67% of breast cancer tumors of ductal origin. Compared with Dutch cisgender men, researchers observed a 46-fold higher overall risk for breast cancer (SIR = 46.7; 95% CI, 27.2-75.4); however, the risk for breast cancer among transgender women remained lower vs. Dutch cisgender women (SIR = 0.3; 95% CI, 0.2-0.4).
Among transgender men, researchers observed four cases of invasive breast cancer diagnosed at a median age of 47 years and a median of 15 years of HT, a rate that was lower vs. cisgender women (SIR = 0.2; 95% CI, 0.1-0.5).
“The absolute risk for breast cancer in transgender people is still low in this study and, more importantly, is not increased compared with cisgender women,” the researchers wrote. “We believe therefore that awareness in both doctors and transgender people is of more importance than the start of screening at a younger age or intensifying available screening, even though the median age at diagnosis in the current study was lower than in cisgender women.”
The researchers noted that transgender men and women who have not had a mastectomy are advised to undergo the same intensified breast cancer surveillance as their close female relatives if the risk for breast cancer is increased because of a familial predisposition. – by Regina Schaffer
Disclosures: The authors report no relevant financial disclosures.