Quality-adjusted time without symptoms or toxicity (Q-TWiST) is an outcome measure for cancer clinical trials, which was developed in the mid-1980s by Richard Gelber and Aron Goldhirsch to evaluate adjuvant chemotherapy. It is an adaptation of the QALY, the quality-adjusted life year. It is calculated as follows:

where TOX is the months spent with any burden of subjective treatment side effects, REL is the months following disease relapse, TWiST is defined as time without symptoms of disease and toxicity of treatment, and u is a utility coefficient, taking values between 0 and 1, to represent the value, relative to TWiST, of TOX and REL, respectively, and the subscript “t” is toxicity and “r” is relapse. The developers proposed to use arbitrary values for u and to ...