Demonstrating an improvement in survival compared to standard therapy often is a difficult hurdle for clinical trials in patients with solid tumors. Therefore companies often turn to tumor response as a surrogate marker to assess clinical benefit, an intuitive link that has not been directly proven.

Now a meta-analysis of colorectal cancer trials, published in The Lancet, has shown that tumor response may in fact predict survival in that disease. However, the relative improvement in survival is very small compared to the absolute improvement in response, suggesting that individual trials may be too small to make tumor response a replacement for survival data.