Concept Architecture
Concept
Theoretically, Time Without Symptoms of Progression (TWiST) is a survival-based outcome measure that quantifies the duration during which a patient remains alive without disease progression or treatment-related toxicity. It is a component of the Quality-Adjusted Time Without Symptoms or Toxicity (Q-TWiST) framework and is based on partitioning overall survival into clinically distinct health states. The concept exists to measure the period of survival that is generally regarded as the most desirable from the patient's perspective, namely survival free from both disease progression and significant treatment toxicity.
Mathematically, TWiST is represented as the duration of overall survival after excluding periods of treatment toxicity before progression and survival following disease progression. Within the Q-TWiST framework, TWiST may be weighted by a utility value, although the unadjusted TWiST itself is measured simply as time. The mathematical framework partitions survival into mutually exclusive health states whose durations sum to overall survival.
In practice, TWiST is estimated using time-to-event data from clinical trials or observational studies. Kaplan?Meier survival curves or parametric survival models are commonly used to estimate the expected duration spent in each health state. In health economics and oncology, TWiST provides an interpretable measure of treatment benefit and serves as an input to quality-adjusted survival analyses such as Q-TWiST.
Purpose
Used to quantify symptom-free and progression-free survival, compare treatment benefits in oncology, partition survival into clinically meaningful health states, and support quality-adjusted survival and economic evaluations.
Mathematical Formulae
Primary Formula
OS = TWiST + TOX + REL
or equivalently
TWiST = OS ? TOX ? REL
where:
- OS = overall survival
- TWiST = time without symptoms of progression or toxicity
- TOX = time with treatment-related toxicity before progression
- REL = time after disease progression (relapse)
Supporting Formulae
Quality-adjusted survival (Q-TWiST):
Q-TWiST = u?TWiST?(TWiST) + u?TOX?(TOX) + u?REL?(REL)
where:
- u?TWiST?, u?TOX? and u?REL? are utility weights assigned to each health state.
Related Mathematical Methods
- Kaplan?Meier survival analysis
- Partitioned survival analysis
- Area-under-the-survival-curve estimation
- Quality-adjusted survival (Q-TWiST)
- Utility weighting
- Parametric survival modelling
Example
A clinical trial reports a mean overall survival of 30 months. Patients experience an average of 4 months with treatment-related toxicity before progression and 8 months following disease progression.
The time without symptoms of progression is:
TWiST = 30 ? 4 ? 8 = 18 months
If the utility assigned to the TWiST state is 1.00, the patient experiences 18 quality-adjusted months during the symptom-free, progression-free period before considering the utility-adjusted contribution of the remaining health states.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| SUM | =SUM(B2:D2) | Calculate total overall survival from partitioned health states |
| Subtraction | =B2-C2-D2 | Calculate TWiST from overall survival, toxicity and post-progression time |
| SUMPRODUCT | =SUMPRODUCT(B2:D2,E2:G2) | Calculate Q-TWiST using utility weights |
| AVERAGE | =AVERAGE(B2:B100) | Estimate mean TWiST across study participants |
VBA (Optional)
Automate calculation of TWiST and Q-TWiST for patient-level survival datasets and generate comparative treatment summaries.
Sources
- Gelber RD, Goldhirsch A, Cole BF. Quality-of-life-adjusted evaluation of therapies for advanced breast cancer: the Quality-Adjusted Time Without Symptoms or Toxicity (Q-TWiST) method. Journal of Clinical Oncology.
- Glasziou PP, Simes RJ, Gelber RD. Quality-adjusted survival analysis. Statistics in Medicine.
- Revicki DA, Feeny D, Hunt TL, Cole BF. Analyzing oncology clinical trial data using quality-adjusted survival methods.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes. Oxford University Press.
- Briggs A, Claxton K, Sculpher M. Decision Modelling for Health Economic Evaluation. Oxford University Press.
Related Concepts (2)
Library
Tools & Resources
1
Tufts CEA Registry — Center for the Evaluation of Value and Risk in Health (CEVR), Tufts Medical Center, Ongoing database ed., 2024 (Tufts Medical Center)
A comprehensive database of more than 14,500 standardised cost-effectiveness (cost-per-QALY) ratios and over 21,900 utility weights, extracted from thousands of peer-reviewed cost-utility analyses — an essential reference for benchmarking ICERs and sourcing utility values.
Registry / DatabaseView source →
Frequently Asked Questions (6)
What is time without symptoms of progression?
A phase within the Q-TWiST framework covering the period free of significant treatment toxicity or disease progression symptoms, typically weighted highest.
Source: Gelber et al. 1989
What does time without symptoms of progression represent in a treatment course?
Within a course of cancer treatment this phase is the stretch during which a patient has come through the toxic period of active treatment but has not yet experienced a return or worsening of disease. It is the time of relatively good health that a treatment aims to lengthen, free of both the side effects of therapy and the symptoms of progression. Because it is the period patients most value, it carries the greatest weight in quality-adjusted survival. Gelber and colleagues (1989) place it at the centre of the framework.
Source: Gelber et al. 1989
Why is time without symptoms weighted highest in Q-TWiST?
Time without symptoms of progression is weighted highest in Q-TWiST because it is the period of best quality of life, free of both treatment toxicity and the symptoms of disease progression, so patients value it most highly. The toxicity and relapse phases involve burdens that reduce their value, so they receive lower weights. Assigning the symptom-free period the highest weight, often one, reflects that this is the good-quality survival a treatment aims to provide, against which its costs in toxicity and relapse are set.
Source: Gelber et al. 1989
How does time without symptoms fit into quality-adjusted survival?
Time without symptoms of progression fits into quality-adjusted survival as the most valued of the phases whose weighted durations are summed to give the Q-TWiST measure. Its duration, weighted highly, contributes most to the quality-adjusted total, while the toxicity and relapse phases contribute less because of their lower weights. A treatment that lengthens the symptom-free period therefore raises quality-adjusted survival substantially, whereas one that extends life mainly in toxicity or relapse adds less, which is the distinction the measure captures.
Source: Gelber et al. 1989
How is time without symptoms of progression measured?
Time without symptoms of progression is measured as the period of a patient's survival during which they are free of significant treatment toxicity and of symptoms from disease progression, determined from clinical definitions of when toxicity and progression occur. It is bounded by the end of the toxicity phase and the onset of relapse or progression. The length of this period is then weighted, usually most highly, in the Q-TWiST calculation, so its measurement depends on the clinical criteria used to mark the phase boundaries.
Source: Gelber et al. 1989
Why does time without symptoms of progression matter in evaluating treatments?
Time without symptoms of progression matters in evaluating cancer treatments because it captures the good-quality survival a treatment provides, distinct from time spent in toxicity or after relapse. A treatment's value depends not only on how long it extends life but on how much of that time is free of symptoms and toxicity. By isolating and weighting this period, evaluation can distinguish treatments that lengthen good-quality survival from those that merely extend life in poorer states, which is central to judging their worth to patients.
Source: Gelber et al. 1989
Trust Record
Verified by Dr Darrin Baines
British health economist
Professional identity: darrinbaines.org
Verification date: 17 Sep 2025
Content version: 1.0.0
Canonical Identity
- Term code
- HE-EE-QALY-010
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