| Classification | Group I | Group II | Group III | Group IV | Group V | Overall | p-value |
| All patients | |||||||
| Albain et al. [5] | 17.0 (14.4–20.8) | 10.6 (7.5–12.5) | 10.5 (9.4–11.5) | 7.3 (6.4–11.5) | 1.58 (1.45–1.72) | <0.0001 | |
| Sagman et al. [6] | 15.7 (13.4–19.1) | 13.3 (10.6–16.7) | 9.5 (8.8–10.0) | 6.4 (4.7–7.1) | 1.60 (1.47–1.75) | <0.0001 | |
| Paesmans et al. [4] | 19.4 (13.9–23.9) | 11.1 (10.6–11.8) | 7.1 (6.6–8.7) | 6.4 (4.0–7.3) | 1.68 (1.53–1.84) | <0.0001 | |
| Sculier et al. [2] | 15.9 (13.5–19.9) | 10.4 (7.6–13.0) | 10.5 (9.6–11.2) | 6.8 (6.1–7.8) | 1.57 (1.45–1.71) | <0.0001 | |
| Patients with extensive disease | |||||||
| Albain et al. [5] | 10.5 (9.4–11.5) | 7.3 (6.4–8.3) | 1.87 (1.51–2.31) | <0.001 | |||
| Sagman et al. [6] | 15.9 (11.0–21.3) | 9.6 (9.0–10.3) | 6.4 (4.7–7.1) | 1.70 (1.35–2.13) | <0.001 | ||
| Paesmans et al. [4] | 10.9 (10.0–11.6) | 7.1 (6.6–8.7) | 6.3 (4.0–7.3) | 1.44 (1.27–1.64) | <0.001 | ||
| Sculier et al. [2] | 10.5 (9.6–11.2) | 6.8 (6.1–7.8) | 1.72 (1.41–2.10) | <0.001 | |||
| Foster et al. [7] | 9.7 (8.8–10.7) | 9.5 (7.0–11.1) | 9.4 (8.6–10.4) | 6.4 (3.3–7.8) | 1.23# (1.12–1.35) | <0.001 |
Data are presented as hazard ratios (95% CI), unless otherwise stated. For the calculation of the overall hazard ratio, only patients with all classifications available were considered (n = 588 for all patients; n = 383 for patients with extensive disease). The calculation of the hazard ratio was made using the classification as a continuous covariate. #: groups IV and V pooled.