Kaplan-Meier plot of TTF stratified by M420 deletion status. The median follow-up was 61 months. Patients carrying M420del had a significantly greater risk of treatment failure (P = .0005; FDR = 0.004). The 95% confidence limits are depicted by the shaded areas. Numbers of patients at risk of an event at successive 20-month time points are given below the x-axis.