Risk of Primary Lung Cancer in Women with Personal History of Breast Cancer and Subsequent Treatment Modality in an Integrated Health System.
BACKGROUND Breast cancer is the most common malignancy among U.S. women, and survivors face increased risk for subsequent malignancies, including lung cancer. Prior studies have reported associations between breast cancer treatments and lung cancer, but contemporary data remain limited. This study evaluates lung cancer risk following breast cancer, stratified by treatment modality, within an integrated health system. METHODS A retrospective cohort study of women diagnosed with breast cancer from 2010-2021 was conducted within Kaiser Permanente Northern California. Exclusion criteria included prior or early post-diagnosis lung cancer, early death, or lack of health plan membership. The primary outcome was subsequent primary lung cancer. Cumulative incidence was estimated using competing-risk methods, with death as a competing event. Associations with breast cancer treatments were evaluated using Fine-Gray regression. RESULTS Among 42,290 women followed for a median of 4.6 years, 324 (0.8%) developed lung cancer. The five-year cumulative incidence was 0.66%, with the highest incidence among current smokers (2.9%) and women aged 65-74 years and ≥75 years (1.1% and 1.2%, respectively). After adjusting for demographic, clinical, and tumor-related factors, breast cancer treatment exposures were not associated with lung cancer. Hispanic women demonstrated a significantly lower hazard of lung cancer compared with White women (HR 0.54, 95% CI 0.33-0.88). CONCLUSIONS Lung cancer risk among breast cancer survivors has increased over time, however risk was driven by patient-level factors, rather than breast cancer treatment exposures.