P2.02-055 Pathologic Mediastinal Nodal and Metabolic Tumor Response to Predict Overall Survival in Stage IIIA-N2 NSCLC after Neoadjuvant Chemotherapy

Abstract

Neoadjuvant chemotherapy (NCT) is a therapeutic option that is used in patients with resectable stage IIIA-N2 NSCLC. We previously hypothesized that combined major histopathological mediastinal nodal response (≤10% residual tumor cells in nodal tissue) and metabolic FDG-PET response (ΔSUVmax ≥60%) on the primary tumor could be regarded as a powerful surrogate of overall survival (OS) in stage IIIA-N2 NSCLC given NCT and confirmed mediastinal nodal disease at diagnosis. This phase II prospective multicenter study aimed to validate the predictive power for OS of our restaging algorithm. Patients with resectable stage IIIA-N2 NSCLC having mediastinal nodal disease proven by endosonography and primary tumor SUVmax at least 2.5 were eligible. All patients were scheduled for 3 cycles of NCT followed by video-assisted mediastinoscopy (VAM). A standardized PET/CT was performed at baseline, after one and three cycles. The primary endpoint was the predictive power for longer OS of a major histopathological mediastinal nodal response at VAM combined with a pre-defined primary tumor ΔSUVmax ≥60% at PET (good prognosis group) compared to all other situations (poor prognosis group). Under an assumption of a 2-year OS of 80% compared to 30% for the good versus poor prognosis group, respectively, 48 patients were required to have 80% power with 2-sided alpha of 0.05. We enrolled 32 patients between 2009 and 2014. Two patients demonstrated stage IV at PET/CT after cycle one. All 3 cycles were given to 30 patients of whom 29 underwent VAM and 22 underwent surgical resection. Objective response rate (RECIST 1.1) was 44%. Complete pathological response occurred in 2 patients. Median OS was 26 months (all 2-year events occurred). In ITT, combined major histopathologic nodal and metabolic tumor response was associated with a trend towards longer OS (HR 0.29, 95%CI 0.14-1.09, P=0.07). Major histopathologic mediastinal nodal response was significantly associated with longer OS (HR 0.25, 95%CI 0.02-0.51, P=0.006), while metabolic ΔSUVmax ≥60% primary tumor response was only associated with a trend towards better OS (HR 0.41, 95%CI 0.17-1.27, P=0.14). Complete pathological response to NCT in stage IIIA-N2 NSCLC is infrequent and therefore not useful as a surrogate for OS. Combined major pathologic nodal and metabolic tumor response was associated with a trend towards longer OS. By contrast, a major histopathologic mediastinal nodal response with ≤10% residual tumor cells at VAM is well suited to be adopted as a surrogate of OS.