Clinical Trials

Clinical Trials: A Practical Guide ■❚❙❘Figure 1. Kaplan–Meier survival functions by treatment group for the pancreatic cancer trial data.1.00Treatment A (new)Treatment B (standard)0.75Proportion surviving0.500.2500 6 12 18 24 30 36 42 48Time (months)Number of patients at risk.Time (months) 0 6 12 18 24 30 36 42 48Treatment A 18 17 15 14 14 13 12 6 2Treatment B 18 16 11 8 7 6 6 4 2In other words,^ 1 – dS(t j) =1× 1 – d 2× ... × 1 – d n n j( ) ( ) ( ) n 1 2 jwhere t 1≤ t j≤ t k.Table 3 displays the derivation of the KM estimate of survival function for patientsreceiving treatment A from the pancreatic cancer trial. The table estimates thatthe proportion of surviving patients is 87.5% at 12 months, 80.8% at 36 months,and 54.5% by the end of the study.Kaplan–Meier survival curvesThe KM estimates of the survival curves by the two treatment groups for thepancreatic cancer trial data are displayed in Figure 1. The survival curve is shown241