Background: Cancer trials involving multiple treatment lines substantially increase our understanding of therapeutic strategies. However, even when the primary end-point of these studies is progression-free survival (PFS), their statistical analysis usually focuses on each line separately, or does not consider repeated events, thus missing potentially relevant information. Consequently, the evaluation of the effectiveness of treatment strategies is highly impaired.
Methods: We evaluated the potentially different effect of bevacizumab (B) administered for the first- or second-line treatment of metastatic colorectal cancer (mCRC) in the ITACa (Italian Trial in Advanced Colorectal Cancer) randomized trial. The ITACa trial consisted of two arms: first-line chemotherapy (CT)+B followed by second-line CT alone versus first-line CT alone followed by second-line CT+B or CT+B+cetuximab according to KRAS status. Cox models for repeated disease progression were performed, and potential selection bias was adjusted using the inverse probability of censoring weighting method. Hazard ratios (HR) [95% confidence interval (CI)] for PFS (primary endpoint) were reported.
Results: The overall effect of B across the two lines resulted in a HR = 0.80 (95% CI 0.68-0.95, p = 0.008). Evaluating the differential effect of B in first- and second-line, the addition of B to first-line chemotherapy (CT) produced a 10% risk reduction (HR = 0.90, 95% CI 0.72-1.12, p = 0.340) versus CT alone; B added to second-line CT produced a 36% risk reduction (HR = 0.64, 95% CI 0.49-0.84, p = 0.0011) versus CT alone.
Conclusion: Our results seem to suggest that B confers a PFS advantage when administered in combination with second-line chemotherapy, which could help to improve current international guidelines on optimal sequential treatment strategies.
Keywords: metastatic colorectal cancer; repeated events; selection bias; sequential trial.
© The Author(s), 2020.