Re-Evaluating Disease-Free Survival as an Endpoint vs Overall Survival in Stage III Adjuvant Colon Cancer Trials
Abstract Background Disease-free survival with a 3-year median follow-up (3-year DFS) was validated as a surrogate for overall survival with a 5-year median follow-up (5-year OS) in adjuvant chemotherapy colon cancer (CC) trials. Recent data show further improvements in OS and survival after recurrence, in patients who received adjuvant FOLFOX. Hence, re-evaluation of the association between DFS and OS and determination of the optimal follow-up duration of OS to aid its utility in future adjuvant trials are needed. Methods Individual patient data from nine randomized studies conducted between 1998 and 2009 were included; three trials tested biologics. Trial-level surrogacy examining the correlation of treatment effect estimates of 3-year DFS with 5 to 6.5-year OS was evaluated using both linear regression (R2WLS) and Copula bivariate (R2Copula) models and reported with 95% confidence intervals (CIs). For R2, a value closer to 1 indicates a stronger correlation. Results Data from a total of 18,396 patients were analyzed (median age = 59 years; 54.0% male), with 54.1% having low-risk tumors (pT1-3 & pN1), 31.6% KRAS mutated, 12.3% BRAF mutated, and 12.4% microsatellite instability high/deficient mismatch repair tumors. Trial level correlation between 3-year DFS and 5-year OS remained strong (R2 =0.82, 95% CI = 0.67 to 0.98; R2 =0.92, 95% CI = 0.83 to 1.00) and increased as the median follow-up of OS extended. Analyses limited to trials that tested biologics showed consistent results. Conclusion Three-year DFS remains a validated surrogate endpoint for 5-year OS in adjuvant CC trials. The correlation was likely strengthened with 6 years of follow-up for OS.