Abstract LB151: Association of radiotherapy with the risk of subtype-specific lung cancer among breast cancer survivors in the United States
Authors: Jiang Chenxi , Freedman Rachel A. , Jemal Ahmedin , Sung Hyuna 
Published: April 2024

Abstract
Background Breast cancer survivors face an elevated risk of subsequent primary lung cancer (SPLC), especially those who received radiotherapy. Nevertheless, the association of radiotherapy for breast cancer and the risk of subtype-specific lung cancer is unknown.
Methods Females diagnosed with first primary breast cancer at ages 20-84 years from 1992-2020 were identified from 12 Surveillance, Epidemiology, and End Results registries. Follow-up began at 2 months from breast cancer diagnosis and ended at subsequent lung cancer diagnosis, last known vital status, death, or December 31, 2020. Standardized incidence ratios (SIRs) and excess absolute risks (EARs, per 10,000 women) were calculated for each histological subtype of lung cancer (adenocarcinoma, squamous cell carcinoma, small cell carcinoma, large cell carcinoma, and others) using expected rates of each subtype in the SEER population. Subgroup analyses were conducted by treatment for breast cancer (radiotherapy yes or no/unknown), overall and stratified by the relative position (ipsilateral and contralateral) of the breast and SPLC.
Results Of all 550,007 breast cancer survivors (&gt;50 years old, 74%; non-Hispanic Whites, 67%; localized, 51%), 8,014 SPLCs were diagnosed during a mean follow-up of 9.7 years. 52.6% of the participants received radiotherapy treatment. Compared with the general population, breast cancer survivors had a statistically significantly higher risk of lung cancer with subtype-specific SIR being greatest for adenocarcinoma (Observed N=4337; SIR=1.20, 95% Confidence Interval [CI]=1.16-1.24; EAR=1.35), followed by squamous cell carcinoma (Observed N=1368; SIR=1.11, 95% CI=1.05-1.17; EAR=0.26) and small cell carcinoma (Observed N=1026; SIR=1.08, 95% CI=1.02-1.15; EAR=0.14). When stratified by radiotherapy receipt, the increased risk associated with adenocarcinoma did not vary across strata. In contrast, the increased risk for squamous and transitional cell carcinoma and small cell carcinoma were confined to those who received radiotherapy (SIR=1.16, 95% CI=1.08-1.24 vs SIR=1.06, 95% CI=0.98-1.15 for squamous and transitional cell carcinoma; SIR=1.15, 95% CI=1.06-1.25 vs SIR= 1.00, 95% CI=0.91-1.09 for small cell carcinoma). Further analysis by laterality showed that associations of treatment receipt with increased risk of lung cancer were confined to ipsilateral SPLC for these two subtypes.
Conclusion Different subtypes of lung cancer may have distinct associations with prior radiation treatment in individuals who have survived breast cancer. The findings have implications for evaluating risks and implementing surveillance for subsequent primary lung cancer in the growing population of breast cancer survivors.
Citation Format: Chenxi Jiang, Rachel A. Freedman, Ahmedin Jemal, Hyuna Sung. Association of radiotherapy with the risk of subtype-specific lung cancer among breast cancer survivors in the United States [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB151.