CTNI-55. INITIAL TEMOZOLOMIDE MONOTHERAPY WITHOUT RADIOTHERAPY MIGHT BE OF LIMITED BENEFIT IN THE TREATMENT OF ASTROCYTOMA, IDH-MUTANT, CNS WHO GRADE 2 AND 3

QUESTION The role of temozolomide chemotherapy alone in isocitrate dehydrogenase (IDH)-mutant astrocytomas has not been conclusively determined. Recent studies have linked temozolomide therapy with induction of hypermutation and poor clinical course in some IDH-mutant gliomas. METHODS In this retrospective, single-center study, 183 patients with astrocytoma, IDH-mutant, CNS WHO grade 2 or 3 diagnosed between 2003 and 2019 were included. Patients initially monitored by means of a wait-and-scan strategy, or treated with radiotherapy alone, or receiving temozolomide alone, after histological sampling through biopsy or tumor resection, were studied. Progression-free and overall survival was analysed. A matched-pair analysis accounting for post-surgical tumor volume was conducted. RESULTS Initial T2 tumor volume and WHO grade were associated with survival in univariate analyses (p < 0.01). The proportion of WHO grade 2 gliomas was highest in the wait-and-scan cohort (p < 0.01). Tumor volumes were largest in the temozolomide cohort (p < 0.01). Radiotherapy was associated with longer progression-free survival than temozolomide (6.2 vs 3.4 years, p = 0.02) and wait-and-scan strategies (6.2 vs 4 years, p = 0.03). Patients treated with radiotherapy showed longer overall survival than patients treated with temozolomide (14.4 vs 10.7 years, p = 0.02). Survival was longer in patients initially monitored by means of a wait-and-scan strategy than in patients treated with temozolomide (not reached vs 10.7 years, p < 0.0001). The same association was seen in a subgroup analysis of WHO grade 2 astrocytomas (p = 0.02) and by trend in a matched pair analysis (p = 0.09). CONCLUSION The results suggest superiority for progression-free survival of radiotherapy alone over temozolomide alone or wait-and-scan strategies and for overall survival of radiotherapy alone and wait-and-scan therapies over temozolomide in IDH-mutant WHO grade 2 and 3. Recent study results indicating that temozolomide might compromise prognosis in some patients with IDH-mutant gliomas might be supported by our data.