Complete response
A complete response means that all signs of cancer being assessed have disappeared according to the method used.
It does not necessarily mean that every cancer cell has gone or that the cancer can never return. Scans have a limit to what they can detect. In some cancers, additional tests or a period of follow-up are needed before the result can be interpreted more fully.
Partial response
A partial response means that the measurable cancer has reduced enough to meet the relevant response criteria, but has not disappeared completely.
Under RECIST 1.1, a commonly used system for solid tumours, this usually requires at least a 30% reduction in the sum of selected target-lesion diameters compared with the starting measurement. That number belongs to a formal measurement system. It does not mean that every tumour in the body has shrunk by exactly 30%.
Stable disease
Stable disease means that the measured change is not enough to qualify as either a partial response or progressive disease.
It is not automatically a poor result. When treatment is intended to control an advanced cancer, preventing growth may represent meaningful benefit. The time for which disease remains stable, symptoms and treatment side effects all affect how the result is judged.
Progressive disease
Progressive disease means that the assessment meets criteria for cancer growth or new disease.
In RECIST 1.1, progression based on target lesions requires both a relative increase and a minimum absolute increase from the smallest previous sum. New lesions or clear worsening of non-target disease can also matter.
Not every tiny change on a scan is progression. Measurement variation, inflammation and treatment effects can complicate interpretation. Some immunotherapy assessments use modified criteria because apparent early worsening may occasionally need confirmation.
What is RECIST?
RECIST stands for Response Evaluation Criteria in Solid Tumours. It provides standard rules for selecting measurable lesions and comparing their size over time. It is particularly important in clinical trials, where consistent definitions allow treatments to be compared.
Clinical decisions do not always follow RECIST as a simple automatic rule. Some cancers are better assessed with different criteria, functional imaging, tumour markers, pathology or cancer-specific response systems. Bone disease and blood cancers are examples where ordinary diameter measurements may not tell the whole story.
Why does the overall clinical picture matter?
A scan category is considered alongside:
- symptoms and examination;
- blood tests and tumour markers where relevant;
- side effects and organ function;
- the aim of treatment;
- how long the benefit has lasted;
- whether changes are confined to one area or seen more widely.
This wider process is explained in How do doctors know if cancer treatment is working?.
Occasionally, most disease remains controlled while one area grows. The team may consider whether a local treatment or a change in systemic treatment is appropriate. That depends on the cancer and cannot be decided from the response label alone.
Why is scan timing important?
Treatment needs time to produce an interpretable effect. Scanning very early can show little change or create uncertainty. Repeating scans too often also exposes patients to additional radiation for CT and PET-CT, can identify incidental findings, and may not change management.
The article on why cancer scans are not done more often discusses this balance.
Questions to ask
- Which response criteria were used?
- Which lesions were measured or considered?
- Is the result definite, or does it need confirmation?
- What does this result mean for the aim of my treatment?
- How do my symptoms and blood tests fit with the scan?
- Will treatment continue, change or be reviewed again later?
Response terms provide a shared clinical language. Their value comes from using them in context, not treating one word on a report as the whole treatment decision.
