Validation and comparison of several published prognostic systems for patients with small cell lung cancer.

The aim of the present study was to validate and compare published prognostic classifications for predicting the survival of patients with small cell lung cancer. We pooled data from phase III randomised clinical trials, and used Cox models for validation purposes and concordance probability estimates for assessing predictive ability. We included 693 patients. All the classifications impacted significantly on survival, with hazard ratios (HRs) in the range 1.57-1.68 (all p<0.0001). Median survival times were 16-19 months for the best predicted groups, while they were 6-7 months for the most poorly predicted groups. Most of the paired comparisons were statistically significant. We obtained similar results when restricting the analysis to patients with extensive disease. Multivariate Cox models for fitting survival data were also performed. The HRs for a single covariate were 8.23 (95% CI 5.88-11.69), and 9.46 (6.67-13.50), and for extensive disease were 5.60 (3.13-9.93), 12.49 (5.57-28.01) and 8.83 (4.66-16.64). Concordance probability estimates ranged 0.55-0.65 (overlapping confidence intervals). Published classifications were validated and suitable for use at a population level. As expected, prediction at an individual level remains problematic. A specific model designed for extensive-disease patients did not appear to perform better.