| Classification | Group I versus II | Group II versus III | Group III versus IV | Group IV versus V |
| All patients | ||||
| Albain et al. [5] | 1.93 (1.39–2.64) | 1.21 (0.90–1.66) | 1.88 (1.53–2.31) | |
| Sagman et al. [6] | 1.47 (1.00–2.11) | 1.73 (1.23–2.51) | 1.67 (1.29–2.15) | |
| Paesmans et al. [4] | 2.24 (1.77–2.87) | 1.74 (1.39–2.18) | 1.33 (1.00–1.77) | |
| Sculier et al. [2] | 2.17 (1.57–2.96) | 1.13 (0.84–1.53) | 1.77 (1.45–2.15) | |
| Patients with extensive disease | ||||
| Albain et al. [5] | 1.88 (1.53–2.31) | |||
| Sagman et al. [6] | 1.70 (1.30–2.18) | |||
| Paesmans et al. [4] | 1.52 (1.20–1.92) | 1.33 (1.00–1.77) | ||
| Sculier et al. [2] | 1.77 (1.45–2.15) | |||
| Foster et al. [7] | 1.18 (0.79–1.69) | 1.04 (0.71–1.57) | 1.59 (1.15–2.17) |
Data are presented as hazard ratios (95% CI).