Contralateral breast cancer after radiotherapy and hormone therapy in two cohorts of US breast cancer survivors.
Loading...
Embargo End Date
ICR Authors
Authors
Veiga, LHS
Gierach, GL
Smith, SA
Howell, RM
Mille, MM
Saha, M
Curtis, RE
Ramin, C
Bodelon, C
Feigelson, HS
Aiello Bowles, EJ
Buist, DSM
Weinmann, S
Vo, JB
Lee, C
Berrington de Gonzalez, A
Gierach, GL
Smith, SA
Howell, RM
Mille, MM
Saha, M
Curtis, RE
Ramin, C
Bodelon, C
Feigelson, HS
Aiello Bowles, EJ
Buist, DSM
Weinmann, S
Vo, JB
Lee, C
Berrington de Gonzalez, A
Document Type
Journal Article
Date
2026-01-31
Date Accepted
2025-10-07
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+ contralateral breast cancer in non-users of hormone therapy (KP RR = 2.2, 95%CI:1.20-4.14; SEER RR = 1.12, 1.04-1.21), but not in users (KP RR = 0.88, 0.61-1.26; SEER RR = 1.03, 0.94-1.12). In KP, higher radiation dose increased risk of ER+ contralateral breast cancer among non-users (ERR/Gy=1.39, 95%CI:0.33,3.66), but not among users (ERR/Gy= -0.13, -0.36,0.23). Radiotherapy also increased risk of ER- contralateral breast cancer (KP RR = 1.85, 95%CI: 0.95-3.59; SEER RR = 1.12, 1.01-1.23), especially in younger exposed women (SEER RR = 1.31, 1.02-1.69 for age <40 vs 40+ years). Additionally, the risk increased linearly with radiation dose to the contralateral breast (ERR/Gy=0.87, 0.04,2.72). CONCLUSIONS: Radiotherapy increased contralateral breast cancer risk, but hormone therapy appeared to mitigate this risk for ER+ cases. These findings have important implications for individuals exposed to chest radiation.
Citation
British Journal of Cancer, 2026, 134 (2), pp. 269 - 278
Source Title
British Journal of Cancer
Publisher
SPRINGERNATURE
ISSN
0007-0920
eISSN
1532-1827
Collections
Research Team
Clinical Cancer Epidemiol