Transgender and breast cancer risk
High breast density and oestrogen increase breast cancer risk
Everyone is susceptible to breast cancer. Two important factors that increase risk are lifetime exposure to high levels of sex hormones, particularly oestrogen, and having a high breast density, as seen on a mammogram (3).
Dense breasts have relatively higher amounts of glandular tissue (milk ducts and milk lobules) and supportive tissue and lower amounts of fatty tissue (4). Most breast cancers develop in ducts and lobules. Cis males have less breast tissue, which is mainly composed of fatty and fibrous tissue with only small amounts of glandular tissue (5).
Hormone replacement therapy (HRT) used to manage the symptoms of menopause, which includes synthetic oestrogens with (combined) or without progesterone, has been associated with an increased risk of breast cancer in cis women, especially during long-term (over 5 years) use of combined HRT (6).
Breast cancer in trans women
Few studies have examined the risk of breast cancer in trans women (1, 7, 8, 9). The most robust evidence to date is from a Dutch study in 2019, which found that breast cancer was more common in trans women (average age was 31) who undergo hormone treatment than cis men, but less common than in cis women (1).
Trans women often receive hormone therapy, which includes oestrogen and often anti-androgens, and may also include progesterone, to help breast tissue development. Studies show that cis women (aged between 50-79 years) who receive HRT are at a higher risk of getting breast cancer, however, this risk depends on the type of HRT and the duration of use (6). Those taking the contraceptive pill, which also contains synthetic oestrogen and progesterone, have a slightly increased risk (10). This suggests that trans women who take hormone therapy may also have an increased risk of developing breast cancer.
Another Dutch study (11) examined what proportion of breast lesions in trans women were benign (non-cancerous) or cancerous. They found around 90% were benign, similar to the percentage found in cis women.
Breast cancer in trans men
Even fewer studies have investigated breast cancer risk in trans men. The most comprehensive is the previously mentioned 2019 Dutch study (1), which found that trans men who undergo hormone treatment had a lower risk compared to cis women (whose average age was 23), but a higher than cis men. Other studies have also identified a lower risk of breast cancer for trans men compared to cis women (12, 13).
Many trans men have a double mastectomy (breast tissue removal) as part of gender reassignment, which may reduce breast cancer risk. However, not all breast tissue is routinely removed, and not all trans men undergo mastectomies, meaning they may remain at higher risk (2).
The impact of high levels of testosterone on breast tissue is unclear. Testosterone therapy in trans men alters the composition of breast tissue by reducing the amount of glandular tissue and increasing the amount of fibrous connective tissue (2). Some studies suggest that in cis women elevated testosterone increases breast cancer risk (14). This is because aromatase (an enzyme found in the breast and other tissues) converts testosterone to oestrogen, raising overall oestrogen levels, which increases breast cancer risk.
However, a study of European trans men found taking testosterone reduces oestrogen levels (15). The same study found those who have their ovaries removed as part of their gender reassignment also had reduced levels of oestrogen. Exposure to lower levels of oestrogen helps reduce breast cancer risk (4).
Another study found that taking testosterone for at least 12 months may reduce the risk of certain types of benign breast lesions (abnormal areas of breast tissue) (16).
Screening and breast self-checking
Although trans men and trans women are at a lower risk of breast cancer compared to cis women, everyone is susceptible to breast cancer, especially if you have not had a double mastectomy.
We recommend regular self-checking for everyone, regardless of gender. Please see our short video for guidance on how to check your breasts.
The NHS offers screening mammography to trans women and trans men who have not undergone a double mastectomy. Only individuals who are registered as a female with their GP are automatically invited for breast screening. For more information please see NHS population screening: information for trans and non-binary people – GOV.UK (www.gov.uk).
Glossary
Trans men: individuals assigned female sex at birth, who identify as men.
Trans women: individuals assigned male sex at birth, who identify as women.
Cis men: individuals assigned male sex at birth who identify as men.
Cis women: individuals assigned female sex at birth who identify as women.
Non-binary: individuals who do not identify with either male or female gender.
For more resources on transgender and non-binary people and cancer please visit