Contralateral breast cancer after radiotherapy and hormone therapy in two cohorts of US breast cancer survivors.

ABSTRACT:

Background

Radiotherapy increases contralateral breast cancer risk, while hormone therapy reduces it; their combined effects are unclear.

Methods

Data from two US retrospective cohort studies of 5-year breast cancer survivors (stage I-III, ages 20-84), Kaiser Permanente (KP, 1990-2012) and SEER (1990-2013), were analysed. Contralateral breast radiation doses were estimated for the KP cohort. Multivariable Poisson regression estimated relative risks (RRs) and excess relative risks per Gray (ERR/Gy), stratified by hormone therapy use.

Results

KP cohort (n = 9053) included 353 contralateral breast cancer cases (73% ER+); SEER cohort (n = 244,834) included 10,470 cases (72% ER+). Among women with ER+ first breast cancer, radiotherapy increased the risk of ER+ contralatera

SUBMITTER: Veiga LHS 

PROVIDER: S-EPMC12819377 | biostudies-literature | 2026 Jan

REPOSITORIES: biostudies-literature