3514 - Impact of Changes in the IASLC 9th Edition Lung Cancer Staging System in Patients Treated with Concurrent Chemoradiotherapy for Locally Advanced Non-small Cell Lung Cancer
Presenter(s)
M. S. Kim1, B. Halmos2, B. M. Stiles3,4, W. R. Bodner III5, H. Cheng6, A. D'Aiello6, and N. Ohri2; 1Albert Einstein College of Medicine, Bronx, NY, 2Montefiore Einstein Comprehensive Cancer Center, Bronx, NY, 3Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, NY, 4Montefiore Medical Center/ Albert Einstein College of Medicine, Bronx, NY, 5Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY, 6Montefiore Medical Center, Bronx, NY
Purpose/Objective(s): The IASLC/AJCC 9th Edition Lung Cancer Staging System aims to improve prognostic accuracy. Here, we examine the impact of shifts from the 8th to 9th Edition among patients treated with concurrent chemoradiotherapy (CRT) for stage III non-small cell lung cancer (NSCLC). We hypothesized the 9th Edition’s sub-classification of N2 disease (N2a vs. N2b) would provide improved survival stratification, but volumetric disease burden would remain a dominant independent prognostic factor.
Materials/Methods: We reviewed patients treated at our institution with CRT after PET/CT staging for 8th Edition stage III NSCLC between 2010 and 2024. Staging was updated using the 9th Edition criteria, distinguishing between N2a (single-station) and N2b (multiple-station) mediastinal nodal involvement. We calculated frequencies of stage migration and examined characteristics associated with shifts. Associations between stage group and clinical outcomes, including progression-free survival (PFS) and overall survival (OS), were evaluated using Kaplan-Meier methods. We utilized Cox proportional hazard models to assess the potential prognostic value of disease stage alongside other factors such as gross tumor volume (GTV) and histology.
Results: 221 patients met inclusion criteria for this analysis. The median GTV was 47 cc (interquartile range: 16 to 100 cc). With a median follow-up of 62 months, the median PFS and OS durations were 13 months and 35 months, respectively. Using the 9th Edition, 84 (65%) N2 patients had N2a disease, and 45 (35%) had N2b disease. Restaging to the 9th Edition resulted in stage migration in 54 patients (24.5%), including 44 (20%) downstaged and 10 (4.5%) upstaged relative to 8th Edition staging.
Among 114 patients with 8th Edition stage IIIA disease, 32 (28%) shifted to stage IIB, and 10 (9%) shifted to stage IIIB using the 9th Edition. Among 88 patients with 8th Edition stage IIIB disease, 12 (14%) shifted to IIIA. Stage migration correlated strongly with tumor burden; the median GTV for 8th Edition IIIA patients downstaged 9th Edition IIB was 6 cc, compared to 49 cc for 8th Edition IIIA patients who were upstaged to 9th Edition IIIB (Kruskal-Wallis, p <0.001). Although the 9th Edition provided improved visual separation of Kaplan-Meier survival curves, stage group was not significantly associated with PFS or OS in univariate or multivariable Cox models. In multivariable analyses including age, ECOG PS, stage group, and histology, GTV remained the most significant independent predictor of both PFS and OS (HR 1.03 per 10 cc increase, p < 0.001). Squamous cell histology also emerged as a significant predictor of poorer OS (HR 2.12, p = 0.001).Conclusion: Adoption of the 9th Edition staging system results in stage migration for approximately one-quarter of stage III NSCLC patients treated with CRT. Stage group remains a relatively weak prognostic factor in this patient population. Outcome prediction models should include other clinical factors, such as disease volume and histology.