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Cancer Study Headline, Translated: Response Rate
How to read cancer study headlines about response rate, tumor shrinkage, durability, side effects, and trial phase.
Original commentary from the Cancer Explained editorial team.
Please note: this page is educational only — it is not medical advice, and it does not speculate about anyone’s health beyond reliable public reporting. For questions about your own health, talk with your healthcare team.
The number in the headline
When a cancer story says a drug "worked in 60% of patients," the 60% is almost always the response rate.
Response rate means the share of people in a study whose tumors shrank by a set amount, measured on scans. It is not the share who were cured. It is not the share who lived longer. It is a measurement of tumor size at particular moments in time.
That distinction is the whole point of this page.
How a response is actually counted
Researchers use a standard rulebook so that different trials can be compared. For solid tumors this is usually RECIST, short for Response Evaluation Criteria in Solid Tumors.
Tumors are measured on scans before treatment, then measured again on a schedule. The categories are:
- Complete response: all measurable tumor has disappeared.
- Partial response: the total size has shrunk by at least 30%.
- Stable disease: neither shrunk enough for a partial response nor grown enough to count as worse.
- Progressive disease: grown by at least 20%, or a new tumor has appeared.
The objective response rate adds complete and partial responses together. So a 60% response rate usually means 60% of people had tumors shrink by at least 30% at some point.
Notice what is left out. Someone with stable disease for two years counts as a non-responder. Someone whose tumor shrank 31% for six weeks counts as a responder.
Why response rate is not survival
A tumor getting smaller is good evidence that a drug is doing something. It is weaker evidence that a person will live longer or feel better.
Tumors can shrink and then regrow quickly. A drug can shrink tumors while causing side effects severe enough to cancel out the benefit. And a cancer's response in one place says nothing about deposits too small to measure.
This is not a theoretical worry. Regulators sometimes approve drugs on response rate alone while recording that survival benefit has not been shown, and later trials do not always confirm it.
What to look for underneath the number
Was the response confirmed? A single scan can mislead. Good trials require a second scan, usually at least four weeks later, showing the shrinkage held.
Who judged it? An independent radiology review is more reliable than assessment by the treating doctor, who knows what the patient received.
How long did responses last? Look for duration of response, and for progression-free survival — time before the cancer grew again. A 60% response rate lasting a median of two months is a different drug from one lasting two years.
What was the denominator? Some trials calculate the rate among everyone enrolled; others only among those who actually received the treatment. The second number is always more flattering.
What phase was it? NCI describes phase 1 trials as small, around 15 to 30 people, testing safety and dose. Phase 2 includes 50 to 100 people and looks at whether the treatment seems to work. Phase 3 compares against current standard treatment in 100 to several thousand people, with random assignment. Only phase 3 is designed to show one treatment beats another. Our page on trial endpoints explains how these measures are chosen.
Was there a comparison group? Without randomization, a response rate floats free. NCI notes that randomization exists to prevent bias — including the unconscious kind, where healthier patients end up in the treatment group.
Where response rate genuinely helps
None of this makes it a bad measure. It answers a real question quickly: does this drug do anything to this cancer at all?
That is exactly what early-phase research needs. A drug that shrinks no tumors in phase 2 does not proceed. Response rate also reads out fast, in weeks or months, where survival takes years. In a rare cancer, or where no treatment exists, it may be the only practical measure available.
The error is treating a useful early signal as a final answer.
Reading a headline in practice
Three quick tests:
- Ask what the percentage is measuring. Shrinkage, survival, or something else.
- Ask what it is compared with. If nothing, note that.
- Ask how long it lasted. If the headline does not say, the article usually does not either.
Questions worth raising with a care team
- How many people were in the study, and how many were like me in cancer type and stage?
- Were responses confirmed on a second scan, and how long did they last on average?
- What serious side effects occurred, and in what proportion of people?
- Was there a comparison group, and if so what did it receive?
- Is this treatment available now, or only within a trial? Our guide on comparing a trial to standard treatment covers that decision.
What this does not mean
- It does not replace the full source, the trial publication, the drug label, a guideline, or a discussion with a care team.
- It does not tell any one person which treatment, screening, or supportive-care decision is right.
- A headline does not apply to every cancer type, stage, age, biomarker profile, or level of personal risk.
- Response rate is not a cure rate, and a high one does not establish that people live longer.
- This page explains how to read results. It is not medical advice.
Sources
- National Cancer Institute, How Do Clinical Trials Work?: https://www.cancer.gov/research/participate/clinical-trials/how-trials-work
How this page was made
An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.
The National Cancer Information Foundation publishes Cancer Explained. It is not a diagnostic service, does not recommend treatments, and is not for emergencies.
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Put the story in context
Prevention, possible warning signs, screening, and diagnosis
This story relates to response rate. The information below is general: it does not reveal anything else about a public person’s health, and not every point applies to every cancer. Personal advice depends on age, symptoms, family history, exposures, and medical history.
Prevention and risk reduction
Not every cancer can be prevented. Avoiding tobacco, protecting skin from ultraviolet radiation, limiting alcohol, staying active, and receiving recommended HPV or hepatitis B vaccination can lower the risk of certain cancers. A risk factor is not a prediction or a cause in one individual.
Symptoms and possible early signs
Possible signs vary and are often caused by conditions other than cancer. Changes worth discussing include a new lump, unexplained bleeding or weight loss, a persistent cough, lasting bowel or bladder changes, a changing skin spot, or symptoms that persist or worsen. Some early cancers cause no symptoms.
Screening and early detection
Screening looks for certain cancers before symptoms begin. Recommended tests exist only for some cancers and depend on age and risk. Screening can have benefits and harms; it is not the same as evaluating a new symptom, and there is no single routine scan or blood test that reliably screens for every cancer.
How cancer is diagnosed
Diagnosis may involve a history and exam, imaging, laboratory tests, and often a biopsy. Pathology can identify the cancer type and may test biomarkers that guide treatment. Symptoms, screening results, tumor markers, or online stories alone cannot confirm cancer.
A public story may encourage questions, but it should not be used to estimate your risk or choose testing. Contact a healthcare professional about a persistent or concerning change. Seek urgent care for severe or rapidly worsening symptoms.