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Background
Transgender, nonbinary, and gender diverse individuals encompass a broad spectrum of people whose gender identity differs from sex assigned at birth. These individuals may pursue gender-affirming hormonal and/or surgical care at some point in their lives, which may in turn impact their breast cancer risk. There is a paucity of data on transgender/gender diverse breast cancer incidence because transgender patients are not represented in large population databases that audit mammography screening results. Based on available data, breast cancer risk in transgender people does not appear to exceed known differences in risk seen in cisgender men and women. However, gender-affirming hormone therapy and/or surgeries have implications for breast cancer risk and potentially screening methods especially for high-risk individuals. Gender-affirming treatment transgender men (assigned female at birth [AFAB]) who take testosterone develop histologic changes in the breast tissue akin to menopausal women. Transgender men may also pursue top surgery (breast removal) which, unlike risk reducing mastectomy, is a cosmetic procedure akin to reduction mammoplasty, which retains breast tissue and the nipple areolar complex. Transgender women (assigned male at birth [AMAB]) who take estrogen develop dense breast tissue consisting of ducts, lobules, and fibrous connective tissue. The largest cohort of transgender individuals followed for breast cancer incidence in Europe, show in situ and invasive cancers in the transgender population at a younger age, and after a relatively short duration of hormone treatment. In that series transgender women had a higher breast cancer incidence than cisgender men and less than that of cisgender women. Transgender men had higher rate of breast cancer than cisgender men and lower rate than cisgender women. Case reports show breast cancer in transgender patients at younger average age than cisgender patients. Deleterious mutations in genes such as <em>BRCA1/2, PALB2</em> and <em>TP53</em> significantly increase an individual’s risk for developing breast cancer. Mutations in other genes, such as <em>CHEK2, ATM</em> and <em>BARD1</em>, have more moderate breast cancer risk compared to <em>BRCA1/2, PALB2</em> and <em>TP53</em>, though increased screening and additional modalities, such as MRI, are still recommended.

Educational Goals / Teaching Points
This exhibit will review breast cancer risk in relation to gender-affirming hormone therapy, including variables that put patients at high risk for breast cancer, and propose an approach to breast cancer screening for average and high-risk transgender patients.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Screening for high-risk transgender individuals should be based on history of gender-affirming medical and/or surgical treatment and consider all risk factors including inherited risk.

Conclusion
Inclusive breast screening recommendations are important in order to identify cancer early, when it remains curative.