Nonlinear relationship between rheumatoid arthritis disease duration and lung cancer risk in a Chinese cohort: a threshold effect study.

Patients with rheumatoid arthritis (RA) face an increased risk of lung cancer, yet the pattern of association between disease duration and lung cancer risk remains unclear. This study aimed to investigate the time-dependent relationship between RA disease duration and lung cancer risk, identifying potential nonlinear associations and clinical risk thresholds. This single-center retrospective cohort study included 4736 RA patients meeting the 2010 ACR/EULAR criteria who attended the First Teaching Hospital of Tianjin University of Traditional Chinese Medicine between January 2014 and December 2024. Restricted cubic spline analysis was used to identify the inflection point, based on which patients were stratified into disease duration < 10 years and ≥ 10 years groups. One-to-one propensity score matching (PSM) was performed to balance baseline age, sex, hypertension, diabetes, and hyperlipidemia, resulting in 3942 matched patients for final analysis. The primary outcome was lung cancer confirmed by histopathology or imaging. Multivariable logistic regression was used to analyze associated factors, and restricted cubic splines evaluated the nonlinear relationships between RA disease duration, age, and lung cancer risk. In the matched cohort, 72 patients (1.83%) developed lung cancer. The incidence was 2.59% (51 cases) in the ≥ 10 years group, significantly higher than 1.07% (21 cases) in the < 10 years group (p = 0.001). Multivariable analysis showed that RA disease duration of ≥ 10 years was significantly associated with lung cancer risk (adjusted OR 2.36, 95% CI 1.27-4.37, p = 0.007). Restricted cubic spline analysis revealed a significant nonlinear relationship between RA disease duration and lung cancer risk, with risk beginning to increase notably when disease duration reached approximately 10 years. Age also showed a nonlinear association with lung cancer risk, with an accelerated risk increase after 63 years. RA disease duration ≥ 10 years is significantly associated with increased lung cancer risk, exhibiting a clear nonlinear growth pattern. Given the retrospective design and the absence of smoking data, these findings should be regarded as hypothesis-generating rather than practice-changing, and prospective validation is required before more intensive lung cancer surveillance can be recommended for RA patients with prolonged disease duration.