Partial response: what it means during chemotherapy

Partial response means that, on scans compared with those taken before treatment, the cancer has shrunk by at least a defined amount but can still be seen. The amount of shrinkage needed is set by agreed international rules, most commonly RECIST for solid cancers, which add together the sizes of selected tumours and compare the totals. To count as partial response, there must also be no new areas of cancer and no clear growth elsewhere. For lymphoma and some other cancers, similar categories are based on PET-CT activity rather than size alone. In plain terms, partial response is a sign that treatment is having a real, measurable effect.

Many people hear "partial" and assume it means treatment is only half working, or is disappointing. That is rarely the right reading. For many cancers, especially when chemotherapy is used to control advanced disease, partial response is a good result and one of the most common outcomes of effective treatment. When chemotherapy is given before surgery, partial response usually means tumours have shrunk enough to make the operation easier or more likely to succeed. In some situations, such as lymphoma or cancers where the aim is to remove all visible disease, the team may be aiming for complete response and may discuss further steps.

What happens next depends on your cancer and the plan. Often treatment continues as planned, with another assessment later. Sometimes partial response leads to surgery, radiotherapy or a change to maintenance treatment. Occasionally, if side effects are heavy and the cancer is responding, the team may adjust amounts or timing. Your oncologist will explain what your partial response means for you and why they recommend the next step. This page explains the term; it cannot interpret your own scan.

Shrinkage is measured, not guessed

Radiologists measure selected tumours in a consistent way at each scan.

Response can deepen over time

Some cancers keep shrinking with further cycles.

It often means carrying on

Many people continue the same treatment after a partial response.

It cannot tell you what your partial response means for your future, or how much your cancer has shrunk. Only your oncologist can explain your results and what they mean.

It also cannot give figures about outcomes linked to partial response. These vary widely between cancers and people.

Why a partial response can feel disappointing

After difficult cycles, many people hope to hear that the cancer has gone. Hearing "partial" can feel like a letdown, even when it is good news. It is normal to have mixed feelings. Asking your oncologist to explain what the result means in the context of your treatment aims often helps put it in perspective.

When the team aims for more

In some cancers, such as certain lymphomas or cancers treated with the aim of removing all disease, the team may hope for complete response. If a partial response is seen at an interim point, they may continue, add treatment or plan further steps. Ask what the target is.

Tumour markers and partial response

Blood markers may fall alongside a partial response, but they do not always move in step with scans. Your oncologist reads them together.

Sharing news with family

Family members may also misunderstand the word partial. Explaining that it usually means treatment is working can help.

How the measurement works in practice

At the baseline scan, radiologists select measurable tumours and add up their sizes. At the assessment scan, the same tumours are measured and added up again. If the total has fallen by at least the amount defined in the rules, and nothing has grown significantly or appeared new, the result is called partial response. If the fall is smaller, the result is usually called stable disease, even though tumours have shrunk a little.

Partial response before surgery

When chemotherapy is given before an operation, as in some breast, rectal, oesophageal, stomach and bladder cancers, partial response can make surgery less extensive or more likely to remove all visible cancer. After surgery, the tissue is examined to see how much cancer remains, which gives more detailed information than scans.

Partial response in lymphoma

In lymphoma, response is often assessed with PET-CT activity as well as size. A partial metabolic response means activity has fallen but not disappeared. What happens next depends on the type of lymphoma, the point in treatment and the treatment plan.

Partial response and symptoms

Shrinking tumours often, but not always, ease symptoms such as pain, breathlessness or trouble swallowing. Some symptoms come from side effects instead, so feeling unwell does not mean the response is not real.

Maintenance treatment after a response

For some cancers, after a response to chemotherapy, a gentler maintenance treatment is given to help keep the cancer controlled for longer. Your oncologist will discuss whether this applies to you.

Keeping perspective between scans

The time between scans can bring worry about whether the response will hold. Staying in touch with your team, reporting symptoms and focusing on day-to-day life can help.

Written summaries

Ask for a short written summary of your result and plan, which helps when explaining to family or other doctors.

Clinical trials and partial response

In clinical trials, partial response is often confirmed with a second scan some weeks later. Outside trials, oncologists use judgement about when to repeat scans.

Response in blood cancers

In myeloma and some leukaemias, partial response is defined by falls in specific blood or urine proteins or in abnormal cells, not by scans.

What to do next

Ask your oncologist what your partial response means for the plan, what the aim of treatment is, whether treatment will continue or change, and when the next assessment will be; and keep reporting new symptoms.