NCMP-22. TREATMENT-RELATED ADVERSE EFFECTS IN PATIENTS WITH MALIGNANT GLIOMA: ESTABLISHMENT OF KEY FEATURES FOR PSEUDOPROGRESSION AND TREATMENT-INDUCED NECROSIS.

Abstract

OBJECTIVE: Pseudoprogression (PP) and treatment-induced necrosis (TN) are insufficiently characterized, clinically challenging conditions. Since both entities radiographically mimic recurrent disease, patients frequently require surgical interventions to guide management. We aimed to characterize the clinical and radiographic features of PP and TN that may facilitate non-invasive differentiation from recurrent disease. METHODS: Patients with malignant glioma and a diagnosis of either PP (appearance <6 months post-radiotherapy [RT] completion) or TN (appearance >6 months post-RT) were retrospectively identified and compared using clinical-radiographic and histopathological data. Each imaging event/lesion diagnosed as PP or TN was evaluated as a region of interest (ROI) by T1+C weighted MRI and correlated to the respective RT dose distribution. RESULTS: Cumulatively, PP (n=27) and TN (n=37) groups comprised 137 individual radiographic ROIs (n=62 biopsy-proven, n=75 radiographic diagnosis). Most patients received concurrent and sequential chemotherapy. Gender and KPS did not differ significantly between groups. Patients with PP had mostly glioblastomas (81 vs 40%; p<0.002), fewer IDH1 mutations (p<0.006), a greater incidence of recurrence (p=0.03) and a shorter median overall survival (3.25 years vs. not reached (62% survival estimate at 24.5 years); p<0.0001). PP lesions occurred earlier (median onset post-RT: 1 vs. 11 months; p<0.00001), mostly during anti-neoplastic treatment (85 vs 32%; p<0.0005), and necessitated more steroid-based interventions (p<0.04). TN lesions often initially appeared periventricularly (n=22/37; 60%), were more numerous (median: 2 vs. 1 ROIs; p=0.01), and contained fewer malignant elements upon biopsy (p=0.008). While distance from the tumor resection cavity (RC) varied considerably for TN lesions (median: 21.5mm; range: 078mm), PP predominantly developed at the RC as a non-nodular, ring-like enhancing structure (p<0.0001). CONCLUSIONS: PP and TN appear to occur in clinically distinct patient populations and differ significantly in spatio-temporal radiographic pattern and histopathology. Increased familiarity with their unique features will improve patient management and may avoid unnecessary surgical procedures.