Analysis of survival by tumor response.

The common practice of comparing the survival of responders and nonresponders when reporting the results of cancer chemotherapy treatment is investigated. The usual method of comparing responders and nonresponders is biased in favor of responders, and these results are frequently misinterpreted as providing evidence that response prolongs survival, or that the treatment under study is effective. Two valid methods for comparing responders and nonresponders are discussed and recommendations are made concerning the analysis of survival by response. A comparison of survival by response category may be useful descriptively, but such a comparison should not be used for inference concerning treatment effectiveness.