P14.32 Patterns of invasion in Glioblastoma have unique radiological features, varied response to radiotherapy and long term outcomes

Abstract

Abstract BACKGROUND To assess the correlation of the three patterns of invasion of Glioblastoma (GB) with the respective MRI features, response to radiotherapy and disease free survival MATERIAL AND METHODS Histopathology of 62 patients with Glioblastoma who had undergone maximal safe resection (MSR)/ stereotactic biopsy (STB) & referred for adjuvant therapy was reviewed to assess the pattern of invasion. Three patterns were observed- single cell infiltration (pattern 1), perineuronal satellitosis (pattern 2) and vessel cooption (or perivascular spread, pattern 3), majority also had diffuse infiltration pattern in the background. The pre and post operative MRI scans were utilized for RT planning of 3DCRT/ IMRT/ VMAT, the modality decided by the treating oncologist. RT volumes were as per ESTRO-ACROP guidelines. Duration of radiotherapy- the Stupp regimen or a short course of hypofractionated radiotherapy (HFRT) (35Gy/10Fr- planned gap- completion of total dose) was based on the extent of resection (EOR) and KPS at the time of RT. Correlation of the pattern of invasion, MRI characteristics of each on the response to radiotherapy as assessed by RANO criteria and survival was analysed with the help of SPSS V21. RESULTS MRI findings after stratification of 62 patients, median age 43 years(18–70), M:F::42:20) into type 1:17, type 2:21 and type 3:24- patterns of invasion, were cortical tumours (subtle enhancement) close to SVZ, solid (+/- cystic) lesion in the eloquent cortex or large mass effect crossing the barriers respectively. OS of entire cohort at 1 year was 75%, with significant differences among groups (82% vs. 85% vs. 50%). Among pattern 1, those patients with IDH mutant (20%) & mean dose to C/L SVZ of 30Gy or more had longer DFS at 1 year (89% Vs. 38% & 85% vs. 0%, p<0.05). In pattern 2, EOR (gross total or near total resection Vs. only STB) showed a better DFS at 1 year (90% vs. 40%, p=0.095). In patients with pattern 3, 40% had post op KPS of <80 and 20% of them underwent HFRT who showed higher CR/PR rates compared to the conventional RT. HFRT in low KPS with m-MGMT showed higher local control at 6 months (100% Vs. 66%, p= 0.02). CONCLUSION Glioblastoma has three patterns of invasion with unique MRI features and aggressiveness for each. Identification of this may guide choice of adjuvant therapy, patterns of failure and therapy resistance