What is the clinical benefit of preoperative chemoradiotherapy with 5FU/leucovorin for T3-4 rectal cancer in a pooled analysis of EORTC 22921 and FFCD 9203 trials: surrogacy in question?

BACKGROUND: Two phase III trials of neoadjuvant treatment in T3-4 rectal cancer established that adding chemotherapy (CRT) to radiotherapy (RT) improves pathological complete response (pCR) and local control (LC). We combined trials to assess the clinical benefit of CRT on overall (OS) and progression free survival (PFS) and to explore the surrogacy of pCR and LC. PATIENTS AND METHODS: Individual patient data from European Organisation for Research and Treatment of Cancer (EORTC) 22921 (1011 patients) and FFCD 9203 (756 patients) were pooled. Meta-analysis methodology was used to compare neoadjuvant CRT to RT for OS, PFS LC and distant progression (DP). Weighted linear regression was used to estimate trial-level association (surrogacy R(2)) between treatment effects on candidate surrogate (pCR, LC, DP) and OS.
RESULTS: The median follow-up was 5.6 years. Compared to RT (881 pts), CRT (886 pts) did not prolong OS, DP or PFS. The 5-y OS-rate was 66.3% with CRT versus 65.9% in RT (hazard ratios (HR) = 1.04 {0.88-1.21}). CRT significantly improved LC (HR = 0.54, 95%confidence interval (CI): 0.41-0.72). PFS was validated as surrogate for OS with R(2) = 0.88. Neoadjuvant treatment effects on LC (R(2) = 0.17) or DP (R(2) = 0.31) did not predict effects on OS.
CONCLUSION: Preoperative CRT does not prolong OS or PFS. pCR or LC do not qualify as surrogate for PFS or OS while PFS is surrogate. Phase III trials should use OS or PFS as primary endpoint.