Omitting the 5-fluorouracil bolus in metastatic colorectal cancer: impact on survival and toxicity in a retrospective multicentre cohort.

INTRODUCTION: The clinical value of the 5-fluorouracil (5-FU) bolus in modern multidrug regimens for metastatic colorectal cancer (mCRC) is uncertain, with concerns about added haematologic toxicity. This study assessed the impact of omitting the 5-FU bolus on survival and toxicity in patients receiving mFOLFOX6-based chemotherapy. MATERIAL AND METHODS: In this retrospective multicentre cohort, 267 mCRC patients treated between June 2020 and June 2024 at Menoufia University Hospitals and the National Cancer Institute, Cairo University, received either bolus-free nbFOLFOX (n = 141) or standard mFOLFOX6 (n = 126), with or without bevacizumab or anti-epidermal growth factor receptor therapy. Progression-free survival (PFS) and overall survival were analysed using Kaplan-Meier and Cox models. RESULTS: Bolus omission produced a statistically significant but clinically small PFS improvement (mean 10.029 vs. 9.319 months; hazard ratio [HR] 1.532, 95% CI: 1.194-1.967; p = 0.001). Overall survival was similar between groups (mean 21.7 vs. 20.7 months; median 20.667 vs. 20.633 months; HR 1.242, 95% CI: 0.966-1.597; p = 0.089). Multivariate analysis identified bolus inclusion as an independent predictor of inferior PFS (HR 1.433, p = 0.006). High-grade neutropenia was significantly reduced with nbFOLFOX (14.9% vs. 25.4%, p = 0.019). CONCLUSIONS: Omitting the 5-FU bolus does not compromise survival and reduces haematologic toxicity, supporting individualised treatment decisions, particularly in settings of drug shortages or high toxicity risk.