Conditional Survival Estimates for Malignant Glioma Patients by RPA Class: Secondary Analysis of RTOG 9006

Abstract

The RTOG recursive partitioning analysis (RPA) for malignant glioma patients is a key prognostic factor correlated with survival for patients with a malignant glioma, which was established using data from RTOG 9006. While such data is useful when counseling patients on survival outcomes at the time of diagnosis, the utility of such data diminishes over time. Conditional survival (CS) is a way to provide 'real-time' estimates of how survival changes over time. The primary objective of this secondary analysis is to report conditional survival estimates for patients with malignant gliomas enrolled on RTOG 9006 stratified by RPA class. RTOG 9006 was a phase III trial of patients diagnosed with malignant gliomas randomized to BCNU and hyper-fractionated radiation therapy (RT) vs. BCNU and conventionally fractionated RT that showed no significant differences in toxicities or oncologic outcomes. We performed a post-hoc analysis of RTOG 9006 using data obtained from the NCI NCTN Data Archive to evaluate conditional survival estimates for different RPA subgroups. Eligible patients included those with a known RPA class who were enrolled on RTOG 9006 (n = 632). Conditional survival estimates from the time of diagnosis and following 1-, 3-, and 5-y of survival were calculated using the Kaplan-Meier method. Cox proportional hazards modeling was performed to evaluate the prognostic significance of treatment arm, histology, extent of surgical resection, and RPA class following 1-, 3-, and 5-y of survival. For RPA Group I (n = 68), OS at 1-y from diagnosis was 95.58%. At 1- (n = 65), 3- (49) and 5-y (42) of survivorship, the chances of surviving an additional 1-y were 84.62, 91.84, 98.62% respectively (See Table 1). RPA class continued to be significantly correlated with survival following 1- and 3-y of survival irrespective of treatment arm. Treatment arm was not significantly correlated with conditional survival at any time point following treatment completion, and there was no interaction between treatment arm and RPA subgroups. Histology was significant at all time points. Conditional risk of death for patients treated for malignant gliomas in RPA Group I remains low at levels similar to those at initial diagnosis. Conditional risk continuously improves for RPA Groups IV-V as patients live longer. In most groups, the lowest survival odds were found in patients who have already survived 1 year.