P12.30.A EPIDEMIOLOGY AND TREATMENT PATTERNS IN MIDH OLIGODENDROGLIOMAS AND DIFFUSE ASTROCYTOMAS: A LONGITUDINAL NATIONWIDE COHORT PERSPECTIVE

Abstract BACKGROUND Treatment of IDH-mutant (mIDH) gliomas, including oligodendrogliomas and diffuse astrocytomas, typically involve surgery, radiotherapy, and/or chemotherapy (RT/CT). Immediate post-surgery RT/CT is not indicated for all patients and active observation (AO) could be the first option, withholding a treatment with potential negative influence on the patients’ functioning and daily life. This study aims to describe treatment patterns of patients with mIDH gliomas who are not in immediate need of RT/CT after initial surgery. MATERIAL AND METHODS This retrospective longitudinal study utilized Danish administrative registries. Patients with mIDH glioma diagnosed between 2010 and 2022 were identified and for those initially managed with AO, patterns and duration of treatment sequences from diagnosis until end of follow-up or death, including AO, re-surgeries, 1st and 2nd RT/CT treatment and the following monitoring periods were analyzed. RESULTS In total, 439 mIDH patients, 168 (38%) with an oligodendroglioma and 271 (62%) with a diffuse astrocytoma, were retrieved over the period, corresponding to a mean age adjusted incidence rate of 0.58 per 100.000 person years. Of the 413 patients without prior malignancies, 237 (57%) did not require immediate RT/CT after surgery. Among these, the mean age was 40.3 years (SD 16.3) and 47.3% were women. Median time from diagnosis to RT/CT or re-surgery (Time To Next Intervention, TTNI) was 36.1 months. During follow-up (median (IQR) 6.1 (3.8-8.9) years), half of the patients (115/237) progressed to receive RT and/or CT with a median time of 69 months. Among these patients, 74% received RT and 82% received CT as first-line oncological treatment. Thereafter, 43% (49/115) progressed to a 2nd line, with only 14% receiving RT and 90% CT. Forty-eight percent of patients received on average 1.3 re-surgeries before the 1st RT/CT, and then <15% and <20% of cases received re-surgeries during monitoring period after 1st and 2nd line, respectively. Overall survival after 1, 5 and 10 years was 100%, 86.7% and 72.9 %, respectively. CONCLUSION Patients with mIDH gliomas managed with AO exhibit a median TTNI of approximately 3 years and high survival rates. Thus, it is crucial to develop more efficient strategies to further delay RT/CT and better preserve functioning and quality of life for this young, working-age population.