KS03.6.A HIGH RATE OF MULTIFOCAL RELAPSE AND SUBSEQUENT POOR PROGRESSION-FREE SURVIVAL POST SALVAGE RADIATION THERAPY FOR WHO GRADE 2-3 MENINGIOMA MANAGED WITH INITIAL SURGERY ALONE

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Abstract BACKGROUND Optimal initial management for patients with localised high risk meningioma remains uncertain with long natural history disease promoting the option of delaying adjuvant radiation therapy until relapse. This study assessed patterns of relapse and survival in a cohort of patients with high-risk meningioma managed with initial surgical therapy alone. MATERIAL AND METHODS Consecutive patients with meningioma referred for radiation therapy (IMRT) between January 2008-December 2021 were entered into an ethics approved database managed by the Neuro-oncology MDT. Categorisation and subsequent management plans were based by grade on WHO2007-2016 classification. Immediate or delayed referral pathway for IMRT was individualised by neurosurgical team. At time of subsequent referral for IMRT at relapse patients had tumour site / volume determined by MRI and Dotatate PET. Tumour volume, site of relapse in relation to initial cavity and number of recurrent foci of disease were recorded. For patients subsequently receiving IMRT an integrated-boost, generally 60Gy/54Gy, was used. Primary endpoints were site of relapse in relation to initial surgical cavity, number of foci, and median time from initial surgery. Secondary endpoints were median progression-free(mRFS)/overall survival(mOS) calculated from start salvage IMRT compared to cohort of intercurrent patients managed at initial diagnosis. RESULTS One hundred and five patients with meningioma were referred, with median follow-up for survivors of 3.6yrs (q1-3:1.5-7.7yrs). Median age was 59.2yrs; 59% had convexity meningioma; WHO2016 grade was G3 in 21%; Atypical(G2) in 66% and G1/no biopsy in 9% of patients. Twenty-two patients have subsequently relapsed post IMRT; with sixteen deceased for 8yrPFS and 8yrOS of 63.5% and 73.5% respectively. Forty-nine(46%) of patients were referred for IMRT at relapse, of which 39% had repeat resection prior to IMRT referral; and 14% were WHO2016 G3 at most recent resection. Based on MRI/Dotatate 61% had more than one focus of tumour around initial surgical cavity. Subsequent to salvage IMRT, fifteen of the 49 patients have had further relapse and eleven are deceased. Patients managed at relapse had worse PFS with 55.1% 8yrPFS vs 78.0% 8yrPFS (p=0.03); however equivalent OS with 68.8% 8yrOS vs 79.4% 8yrOS (p=0.62). CONCLUSION Patients with G2/3 meningioma managed with surgery alone upfront more often had relapses that were multifocal that were not managed with further salvage surgery. The subsequent progression-free survival was poor with a high rate of subsequent relapse post salvage IMRT, especially when compared to patients managed with IMRT at time of initial diagnosis.

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