Differential censoring in overall survival in phase 3 oncology clinical trials

Abstract

In phase 3 oncology clinical trials, identifying and understanding potential sources of differential censoring (DC), which describes censoring imbalance between treatment arms, in overall survival (OS) endpoints is vital to reduce bias and misinterpretation of OS benefit. Among 322 trials, 34 (11%) trials exhibited DC overrepresented in the control arm (DCC). Compared to trials without DC or those with DC overrepresented in the experimental arm (DCE), trials with DCC showed higher rates of OS benefit (56% vs 32%; odds ratio [OR] 2.26, 95% CI 1.04-4.90; P=.04) and were associated with patient withdrawal (median 8.0% vs 3.8%; P=.0002), lack of double blinding (15% vs 48%, OR 0.19, 95% CI 0.06-0.56; P=.003), and better global quality of life in the experimental arm (32% vs 13%, OR 3.01, 95% CI 1.26-7.19; P=.01). OS DCC is a prominent challenge that requires rigorous trial design and comprehensive patient and mortality follow-up to reduce bias in interpreting OS benefit.