The combination of fluorouracil, leucovorin, irinotecan, and oxaliplatin (FOLFIRINOX) is the standard of care for advanced pancreatic cancer, but causes hematological and gastrointestinal toxicities, leading to treatment delay and dose reduction; optimal modification based on toxicities is needed. Therefore, we evaluated the effect of initial relative dose intensity (RDI) on FOLFIRINOX efficacy by conducting a Japanese nationwide survey. We evaluated overall survival (OS) and progression-free survival (PFS) of patients administered two or more cycles of FOLFIRINOX, and determined RDIs for each drug within the first two cycles. RDI's effect on efficacy was evaluated using a multivariate analysis with a Cox regression hazard model. Of 399 patients enrolled, 359 and 346 were evaluated for OS and PFS, respectively. Median RDI was 71.8%, 64.7%, 23.4%, and 76.9% for oxaliplatin, irinotecan, and bolus and continuous infusions of 5-FU, respectively. A high RDI for 5-FU bolus resulted in poor prognosis in terms of PFS (hazard ratio: 1.34; p = 0.022) and negatively correlated with objective response (coefficient: -0.70; p = 0.021), and a high RDI for CPT-11 positively correlated with objective response (coefficient: 1.02; p = 0.031). In conclusion, low and high RDIs for irinotecan and 5-FU bolus, respectively, resulted in poor FOLFIRINOX efficacy.
Keywords: dose response relationship; fluorouracil; irinotecan; leucovorin; oxaliplatin.