Abstract B054: Intersection of rurality and county-level income on second primary lung cancer risk for breast, prostate, and colorectal cancer survivors

Abstract

Abstract Background: Breast, prostate, and colorectal cancer survivors have an increased risk of developing second primary cancers (SPCs), among which lung cancer is the most frequently diagnosed. While it has been established that rural residence and residence in low-income areas are independently associated with worse cancer outcomes, limited research has examined their joint effect on lung SPC risk. To advance understanding of how geographic and socioeconomic disparities impact cancer survivorship, we examined the interaction of rurality and county-level income on the risk of developing lung SPC for these three cancers. Methods: We conducted a retrospective cohort study using data from the 2000-2022 Surveillance, Epidemiology, and End Results (SEER 17) Program. Exposures were rurality (categorized into four levels using USDA Rural-Urban Continuum Codes) and county median household income (categorized into tertiles). The primary outcome was diagnosis of a second primary cancer of the lung/bronchus ≥12 months after diagnosis of the first cancer. Adjusted cause-specific Cox proportional hazards models were performed. The combined effects of rurality and income were tested through their interaction; additive interaction was quantified using relative excess risk due to interaction (RERI). Results: Among 2,426,187 survivors aged 20-84 years, 1.8% developed lung SPC. Prevalence was highest among survivors of prostate cancer (n=991,938; 2.2%), followed by colorectal cancer (CRC) (n=477,068; 1.8%), and lowest among breast cancer (n=957,181; 1.4%) survivors. Across all cancer types, lung SPC occurred more frequently among survivors living in rural (1.9%–3.1%) and lowest-income (1.6%–2.7%) areas. In adjusted models, survivors living in fully rural counties showed a 14%-19% elevated risk of developing lung SPC among prostate (HR=1.19, 95% CI=1.12-1.28) and breast (HR=1.14, 95% CI=1.05-1.24) cancer survivors. Living in low-income areas was associated with greater risk of developing lung SPC by 13%-33% for survivors of prostate (HR=1.33, 95% CI=1.27-1.39), colorectal (HR=1.22, 95% CI=1.13-1.30), and breast (HR=1.13, 95% CI=1.07-1.19) cancer. Relative to survivors in fully urban/high-income counties, survivors residing in fully rural, low-income counties experienced an excess risk of developing lung SPC, with an increase of 60% (HR=1.60, 95% CI=1.50-1.70) for prostate, 34% (HR=1.34, 95% CI=1.24-1.46) for breast, and 32% (HR=1.32, 95% CI=1.20-1.45) for CRC survivors. However, a statistically significant positive additive interaction was observed only among CRC survivors (RERI=0.66; 95%CI=0.10-1.22; p=0.021). Conclusions: Rural residence and residence in low-income areas jointly increased the risk of lung SPC for CRC survivors only, suggesting that socioeconomic deprivation may be an important driver of disparities beyond the effect of geographic location alone. Further research and targeted interventions are needed to better understand and address the specific barriers faced by CRC survivors residing in rural and socioeconomically disadvantaged communities. Citation Format: Firas F. Osmani, Saarib M. Zafar, Jorge Cortes, Ramzi G. Salloum, Meng-Han Tsai. Intersection of rurality and county-level income on second primary lung cancer risk for breast, prostate, and colorectal cancer survivors [abstract]. In: Proceedings of the 19th AACR Conference on the Science of Cancer Health Disparities; 2026 Oct 18-21; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2026;35(10 Suppl):Abstract nr B054.