Optimal timing of chemoradiation after resection or biopsy of glioblastomas: a nationwide population-based study

BACKGROUND: This study investigated the optimal timing of concurrent chemoradiotherapy (CCRT) following surgery for patients with newly diagnosed glioblastoma (GBM). The focus was on understanding whether the interval between surgery and CCRT impacts survival outcomes. METHODS: Data from the Korean National Health Insurance Research Database ( https://opendata.hira.or.kr/ ) were collected to retrospectively review 3,586 patients diagnosed with GBM in South Korea between 2008 and 2021. Patients were divided into early CCRT (≤ 21 days between surgery and CCRT) and late CCRT (> 21 days between surgery and CCRT) groups and further categorised based on the type of surgery (biopsy alone or surgical resection). The study estimated overall survival (OS) and conducted univariable and multivariable Cox regression analyses. RESULTS: The median overall survival (OS) for the entire cohort was 19.98 months (95% Confidence Interval CI: 19.12-20.86 months). In univariable analysis, the late CCRT group demonstrated a longer median OS compared to the early CCRT group (20.47 vs. 17.94 months, P = 0.0002, log-rank test). However, this difference was not significant in multivariable analysis (Hazard Ratio HR = 0.98, 95% CI: 0.782-1.091, P = 0.6663). Subgroup analysis revealed that late CCRT was associated with prolonged OS in patients who underwent surgical resection (adjusted HR = 0.85, 95% CI: 0.752-0.955, P = 0.0065), whereas in the biopsy-alone group, late CCRT was associated with shorter OS (adjusted HR = 1.80, 95% CI: 1.378-2.346, P < 0.0001). CONCLUSIONS: Patients who initiated CCRT more than 21 days post-resection demonstrated improved overall survival (OS) compared to those who began CCRT earlier. In contrast, among patients who underwent biopsy alone, initiating CCRT within 21 days was associated with better outcomes. These findings suggest that the optimal timing for CCRT initiation in GBM may depend on the extent of residual tumour.