Risks of second primary cancers among 584,965 female and male breast cancer survivors in England: a 25-year retrospective cohort studyResearch in context

Summary: Background: Second primary cancers (SPCs) after breast cancer (BC) present an increasing public health burden, with little existing research on socio-demographic, tumour, and treatment effects. We addressed this in the largest BC survivor cohort to date, using a novel linkage of National Disease Registration Service datasets. Methods: The cohort included 581,403 female and 3562 male BC survivors diagnosed between 1995 and 2019. We estimated standardized incidence ratios (SIRs) for combined and site-specific SPCs using incidences for England, overall and by age at BC and socioeconomic status. We estimated incidences and Kaplan–Meier cumulative risks stratified by age at BC, and assessed risk variation by socio-demographic, tumour, and treatment characteristics using Cox regression. Findings: Both genders were at elevated contralateral breast (SIR: 2.02 (95% CI: 1.99–2.06) females; 55.4 (35.5–82.4) males) and non-breast (1.10 (1.09–1.11) females, 1.10 (1.00–1.20) males) SPC risks. Non-breast SPC risks were higher for females younger at BC diagnosis (SIR: 1.34 (1.31–1.38)