10109-CS-9 ACNU-based chemotherapy for Oligodendroglioma: an institutional retrospective study

Abstract Introduction Regarding oligodendroglioma, the standard treatment regimen worldwide, PCV; a combination chemotherapy of procarbazine, CCNU and vincristine, is associated with frequent adverse events, and in Japan, only ACNU, an analog of CCNU, is approved. We evaluated the long-term outcomes of a treatment strategy for oligodendroglioma, involving ACNU-based chemotherapy following maximal safe resection, with deferred radiation therapy. Methods This retrospective study included 50 patients (grade 2: n = 27; grade 3: n = 23) diagnosed with IDH-mutant, 1p/19q-codeleted oligodendroglioma between 2002 and 2022. Progression-free survival (PFS), overall survival (OS), and time to decline of performance status (defined as deterioration-free survival: DFS) were analyzed using the Kaplan-Meier method. Results Postoperative chemotherapy was administered in 94% of cases (PAV: n = 24; ACNU: n = 22; TMZ: n = 1 excluded). Median follow-up was 142.9 months for PAV and 50.6 months for ACNU. Although the 10-year PFS was 54.2% for grade 2 and 30.0% for grade 3 tumors (p = 0.0870), the 10-year OS was 92.4% and 80.8%, respectively (p = 0.5098), with comparable DFS (p = 0.6922). Comparing regimens, the 10-year OS was 82.3% for PAV, while all patients in the ACNU group remained alive. Five-year PFSs were almost identical: 58.9% (PAV) vs. 56.8% (ACNU), p = 0.9996. Treatment completion rates were 75% for PAV and 91% for ACNU. Conclusions Despite the chemo-first strategy, long-term OS was comparable to or exceeded that of previous PCV/RT clinical trials or large cohort studies. ACNU monotherapy showed similar efficacy to PCV and tolerability to TMZ, suggesting it as the most favorable chemotherapeutic option currently available in Japan considering the risk-benefit profile.