1118 Background: Breast cancer incidence and mortality by sexual orientation and gender identity remain poorly characterized. We aimed to systematically review comparative studies in LGBTQ+ populations versus cisgender heterosexual comparators. Methods: We conducted a PRISMA 2020–guided systematic review evaluated breast cancer incidence and mortality in LGBTQ+ populations versus cisgender heterosexual comparators. PubMed, Embase, and Scopus were searched from inception to January 2026. Population-based cohort, registry, and health system studies reporting comparative incidence or mortality were eligible. Two reviewers independently screened records. Of 189 records, 105 were excluded at title/abstract, 84 underwent full-text review, and 8 studies were included. Due to heterogeneity in SOGI ascertainment, comparators, and effect measures, results were synthesized qualitatively. Results: Among transgender populations, breast cancer incidence varied by reference group. In a nationwide cohort, trans women had higher incidence vs cis men (SIR 46.7) but lower vs cis women (SIR 0.3), while trans men showed the inverse pattern (vs cis women SIR 0.2; vs cis men SIR 58.9). In a U.S. health system cohort, incidence was similar for FTM vs cis women (0.4% vs 0.5%) but higher for MTF vs cis men (0.2% vs 0.004%). Among sexual minority women, incidence did not differ from heterosexual women in UK Biobank (HR 0.63–0.93) or Nurses’ Health Study (aIRR 1.19; 95% CI, 0.92–1.53). Mortality data were sparse; one national linkage found higher breast cancer–specific mortality in same-sex partnered women (HR 3.24; 95% CI, 1.01–10.37). Conclusions: Breast cancer incidence in transgender populations is comparator-dependent: trans women have higher incidence vs cis men but lower vs cis women, with the inverse pattern in trans men; incidence among sexual minority women is similar to heterosexual women. Comparative studies. Study (Year) Data Source / Country SGM Population Comparator Outcome Key Estimate (95% CI) Yang 2025 UF Health IDR, USA FTM Cisgender women Incidence RR ≈ 0.72 (0.4% vs 0.5%) de Blok 2019 Nationwide registry, Netherlands Trans women Cisgender women Incidence SIR 0.30 (0.20–0.40) de Blok 2019 Nationwide registry, Netherlands Trans men Cisgender women Incidence SIR 0.20 (0.10–0.50) Brown 2014 VHA cohort, USA Transgender veterans Expected population Incidence SIR ~1 vs cis women; >1 vs cis men Underwood 2023 UK Biobank WSWM WSEM Incidence HR 0.93 (0.79–1.10) Underwood 2023 UK Biobank WSEW WSEM Incidence HR 0.63 (0.37–1.07) Huang 2024 Nurses’ Health Study, USA Lesbian women Heterosexual women Incidence aIRR 1.19 (0.92–1.53) Cochran 2012 NHIS mortality linkage, USA Same-sex partnered women Different-sex partnered Mortality HR 3.24 (1.01–10.37) Chan 2025 NCDB, USA TGD breast cancer cases Cisgender cases Overall survival 5-yr OS: 84.6% vs 91.7% (P=0.04)
Pustake et al. (Wed,) studied this question.