BMET-09CUMULATIVE INTRACRANIAL TUMOR VOLUME (CITV) ENHANCES THE PROGNOSTIC VALUE OF THE LUNG-SPECIFIC-GRADED PROGNOSTIC ASSESSMENT (GPA) MODEL

Abstract

BACKGROUND: Management of patients afflicted with brain metastasis requires tailoring of therapeutic strategies based on survival expectations. As such, the development of prognostic indices is of critical importance in this patient population. OBJECTIVE: The purpose of this study was to determine whether the cumulative intracranial tumor volume (CITV) of brain metastasis augment the prognostic value of the lung-specific-Graded Prognostic Assessment (GPA) index. METHODS: Patient data was derived from 365 lung cancer patients with brain metastasis (BM) that were consecutively treated at the University of California, San Diego/San-Diego-Gamma-Knife-Center (UCSD/SDGKC). CITV was analyzed to determine the volume cutoff that maximized sensitivity and specificity for one-year survival on the ROC curve. Multivariate Cox proportional hazard modeling was performed, and overall survival was estimated by the Kaplan-Meier method risk stratifying by lung-specific-GPA with or without this optimal CITV. The prognostic value of these models (lung-specific GPA +/- CITV) was quantitatively compared using net reclassification improvement (NRI > 0) and integrated discrimination improvement (IDI). RESULTS: For the UCSD/SDGKC cohort, the CITV cutoff that had the greatest survival discrimination at one year was 4cm3. The addition of CITV to the lung-specific GPA indices significantly improved the prognostic value of lung-specific GPA (with NRI > 0 of 0.430 (CI = 0.228-0.629) and IDI of 0.029 (CI = 0.004-0.073)). These findings were validated in an independent cohort of 1,638 lung cancer BM patients that were SRS treated at the Katsuta Hospital Mito GammaHouse (KHMGH), Japan. CONCLUSION: In independent cohorts, the addition of CITV to lung-specific-GPA index significantly improved the prognostic value of this index.