P17.05.A DISTRIBUTION AND PROGNOSTIC SIGNIFICANCE OF MYELOTOXICITY IN NEWLY DIAGNOSED GLIOBLASTOMA IN A REAL-LIFE COHORT: TIME TO TREAT MORE AGGRESSIVELY?

Abstract BACKGROUND Glioblastoma is among the most lethal primary brain tumors in adults. While chemotherapy remains a cornerstone of treatment, it frequently induces varying degrees of myelotoxicity. The CeTeG regimen is associated with a higher incidence of myelotoxicity than the Stupp protocol, yet both regimens adhere to standardized dosing, despite known inter-individual variability in hematologic tolerance. The purpose of this study is to evaluate the prognostic impact of myelotoxicity and Pneumocystis jirovecii prophylaxis on overall survival in glioblastoma patients. METHODS This retrospective single-center study analyzed newly diagnosed glioblastoma patients who underwent surgery, radiotherapy, and chemotherapy between December 2016 and December 2020. Serial blood counts were assessed throughout radiochemotherapy, with myelotoxicity classified as pathological at ≥ grade 2 per CTCAE criteria. The severity of hematologic toxicity was correlated with clinical parameters and survival outcomes. RESULTS Among 161 patients, 133 (83%) experienced myelotoxicity, while 28 (17%) did not. Female patients exhibited greater susceptibility to myelotoxicity (p=0.007), independent of treatment regimen. In multivariable analysis controlling for MGMT status, age, extent of resection, and Karnofsky performance score, leukopenia ≥CTC°2 correlated with improved survival in both the overall and CeTeG cohorts (overall: median OS [mOS] 25 vs. 15 months, p=0.03; median PFS [mPFS] 13 vs. 7 months, p=0.02; CeTeG cohort: mOS 37 vs. 17 months, p=0.02; mPFS 18 vs. 9 months, p=0.04). Neutropenia ≥CTC°2 similarly conferred a survival advantage in the overall cohort (mOS 25 vs. 15 months, p=0.03; mPFS 15 vs. 7 months, p=0.03). Patients receiving Pneumocystis jirovecii prophylaxis demonstrated significantly longer survival in both the overall and Stupp cohorts (overall: 21 vs. 13 months, p=0.007; Stupp: 19 vs. 13 months, p=0.005). This benefit was also observed in patients with grade 3-4 lymphopenia (overall: 21 vs. 13 months, p=0.03; Stupp: 15 vs. 11 months, p=0.04). CONCLUSIONS Myelotoxicity during initial glioblastoma treatment may correlate with improved survival. Additionally, Pneumocystis jirovecii prophylaxis is a critical component of the Stupp regimen, conferring a significant survival benefit. These findings suggest that blood parameters could serve as biomarkers to personalize chemotherapy dosing, potentially allowing for higher individualized dosing beyond current standardized protocols.