Evaluation of effectiveness: Q-TWiST. The International Breast Cancer Study Group

The effectiveness of cancer treatments is often expressed in terms of disease-free survival or overall survival relative risk reduction or odds ratios, and the quality of life effects are often assessed separately from survival. Such end points and summary measures may be inadequate, however, for comparing two treatments in terms of their palliative effects because there is a trade-off between treatment toxicity and increased disease-free interval. Furthermore, this trade-off may depend on individual patient preferences and prognostic situations. The goal of this paper is to describe a method for evaluating the effectiveness of cancer treatments in terms of palliation by simultaneously considering both quality and quantity of time following treatment so that therapeutic choice may be determined according to patient preferences on quality of life and prognostic situation. The method we present is an extension of the Quality-adjusted Time Without Symptoms and Toxicity (Q-TWiST) method for comparing treatment effectiveness in clinical trials of adjuvant therapies. We illustrate an application using data from the International Breast Cancer Study Group Trial V which compares two chemotherapy schedules with different toxicities.