Understanding response terms on your scan report

These are the four standard words doctors use to describe how a cancer has changed on scans during treatment. Complete response means no measurable cancer can be seen. Partial response means the cancer has shrunk by at least a defined amount but is still visible. Stable disease means the cancer has not shrunk enough to count as a response and has not grown enough to count as progression. Progression, sometimes written as progressive disease, means the cancer has grown by a defined amount or new areas have appeared. The amounts that separate these categories are set by agreed international rules, most often RECIST for solid cancers, so that doctors and hospitals describe response in the same way.

The terms sound simple, but their meaning for any one person depends heavily on context. The biggest misunderstanding is around stable disease, which many people hear as "nothing is happening" or "treatment has failed". In advanced cancers, where the aim is often to control the disease for as long as possible, stable disease can be a very good result, and treatment frequently continues. Partial response is also often misread as a half success, when it usually means treatment is clearly working. Complete response is encouraging, but because scans cannot detect very small amounts of cancer, it does not by itself mean the cancer has gone for good.

Different cancers and treatments may use adapted rules. Lymphoma assessment often uses PET-CT activity scores, blood cancers use blood and bone marrow measures, and immune treatments have their own versions of the rules to allow for early swelling. Scan reports may also use related phrases such as "no evidence of disease", "mixed response" or "reduction in size". Your oncologist will explain which terms apply to you and what they mean for your treatment. This page explains the vocabulary; it cannot interpret any individual report.

The aim of treatment changes the meaning

The same result can mean different things depending on whether treatment aims to shrink, control or prevent return.

Terms describe scans, not how you feel

Symptoms and quality of life are considered separately.

Ask what the result means for the plan

The most useful question is what happens next.

It cannot tell you what your own scan result means or what will happen next. That depends on your cancer, treatment aim and full medical picture, and your oncologist will explain it.

It also cannot give figures about what each result means for the future. Outcomes vary widely, and any such discussion belongs with your oncologist.

What stable disease really means

Stable disease is a measurement category, not a judgement. It covers a range from slight shrinkage to slight growth. In many advanced cancers, holding the cancer steady while you live well is exactly what treatment aims to do, and it can continue for a long time. Your oncologist may continue the same treatment, change to a gentler one, or pause, depending on your situation.

Why the rules use defined amounts

Scans have a natural margin of measuring variation. Using defined amounts of change prevents small, meaningless differences from being called response or progression. This is why a report may describe tumours as slightly smaller yet still classify the result as stable.

Reading reports before appointments

Many people see reports on apps or portals before meeting their oncologist. If you do, remember that reports are written for doctors, and terms may not mean what they seem. Try to wait for the discussion if you can.

Terms in blood cancers

Leukaemia and myeloma use their own response categories based on blood and bone marrow tests. Ask your haematology team to explain these.

How target areas are chosen

At the baseline scan, radiologists choose a limited number of measurable tumours, called target areas, and record their sizes. Other areas of disease are noted but not measured in the same way. At each later scan, the same target areas are measured again and added up, and the total is compared with the baseline or the smallest total so far. New areas of cancer count as progression regardless of the target measurements.

Why glands have special rules

Normal glands can be a certain size, so the rules treat glands differently from other tumours. A gland that shrinks back into the normal size range may count as responding, even though it is still visible on the scan.

Response in bone

Cancer in bone is hard to measure on CT, and bone can look more active as it heals. Bone scans, MRI or PET-CT may be used alongside, and oncologists read bone changes carefully.

Questions about the terms

Useful questions include: which category is my result, how was it measured, what was the aim of treatment, and what happens next.

How long a response lasts

Doctors may also talk about how long a response lasts. This depends on the cancer and treatment, and your oncologist can discuss it.

What to do next

Ask your oncologist which response terms apply to you, what your result means for the plan, and when the next assessment will be; bring someone to results appointments; and report new symptoms promptly.