Fifty-seven RCTs with 11,160 participants were included.
Adding another drug to a single-agent regimen improved tumour response (OR 0.42, 95% CI: 0.37, 0.47), 1-year survival (OR 0.80, 95% CI: 0.70, 0.91) and median survival (OR 0.83, 95% CI: 0.79, 0.89), but was also associated with significantly increased grade 3 and 4 toxicity of all types.
Adding another drug to a double-agent regimen improved tumour response (OR 0.66, 95% CI: 0.58, 0.75), but had no statistically significant effect on 1-year survival (OR 1.01, 95% CI: 0.85, 1.21) or median survival (OR 1.00, 95% CI: 0.94, 1.06). Three-drug regimens were associated with statistically significantly greater grade 3 and 4 haematological toxicity in comparison with two-drug regimens, and also with statistically significantly higher incidences of infection and mucositis.
Heterogeneity statistics for each comparison were reported in the review.