How is cancer diagnosed? Tests, scans and biopsy

There is no single test for cancer

The US National Cancer Institute (NCI) explains that when you have a symptom or a screening result that suggests cancer, your doctor will try to find out whether it is caused by cancer or by something else. There is no single test that can diagnose cancer. Instead, doctors usually build up a picture step by step (NCI: How Cancer Is Diagnosed):

1. Your history and an examination. Your doctor asks about your symptoms, your personal and family medical history, and examines you.
2. Lab tests on blood, urine or other body fluids.
3. Imaging tests (scans) that make pictures of the inside of the body.
4. A biopsy, which NCI describes as often the only way to tell for sure whether cancer is present.

Not everyone has every test, and the order can differ. NCI also points out that symptoms which can be caused by cancer are most often caused by something else, such as an illness, an injury or a benign tumour (NCI: Symptoms of Cancer). If you are still at the stage of deciding whether to see a doctor, our page on cancer warning signs may help.

Lab tests: what blood and urine tests can show

NCI explains that high or low levels of certain substances in the body can be a sign of cancer, so lab tests that measure them can help doctors make a diagnosis. But NCI is clear that abnormal lab results are not a sure sign of cancer, that normal results vary from person to person and even day to day, and that it is possible to have normal results with cancer or abnormal results while healthy. That is why lab tests alone cannot say for sure whether you have cancer. Common examples NCI lists include:

• Complete blood count (CBC) - measures red cells, white cells and platelets. NCI notes it can help diagnose some cancers, especially leukaemias.
• Blood chemistry tests - show how well organs such as the kidneys and liver are working.
• Urinalysis and urine cytology - can help diagnose kidney and bladder cancers.
• Sputum cytology - looks for abnormal cells in mucus coughed up from the lungs.
• Immunophenotyping and cytogenetic analysis - specialised tests on blood, bone marrow or tissue, used especially for blood cancers.

Can a blood test diagnose cancer?

This is one of the most common questions. Some blood tests help, but on their own they usually cannot confirm or rule out cancer. Two types of test are often in the news:

• Tumour markers are substances made by cancer cells, or by other cells in response to cancer. NCI explains that most are made by normal cells too, that a raised level does not mean someone has cancer, and that not everyone with a particular cancer has a raised marker. So they are usually combined with biopsies or imaging. Tumour markers are also used to help plan treatment and check how well it is working (NCI: Tumor Markers).
• Liquid biopsy and multi-cancer detection tests look for cancer cells or pieces of tumour DNA in the blood. NCI notes that studies of tumour markers for screening people without symptoms have generally found they do not work well, and that for newer multi-cancer detection tests much remains to be learned about their benefits and harms.

If you see a test advertised as able to find "any cancer" from a single blood sample, talk to your doctor before paying for it.

Imaging tests (scans)

Imaging tests create pictures of areas inside the body that help a doctor see whether a tumour is present. NCI describes the main types:

• X-rays use low doses of radiation to make pictures.
• CT scans use an x-ray machine linked to a computer to make detailed 3-D pictures. A contrast dye is sometimes given to make areas easier to see.
• MRI uses a powerful magnet and radio waves. The machine is noisy, and a contrast agent is sometimes injected.
• Ultrasound uses sound waves that people cannot hear to make pictures.
• Nuclear scans, including bone scans and PET scans, use a small amount of radioactive material (a tracer) that collects in certain tissues and shows up on a scanner.

Biopsy: the test that usually confirms cancer

NCI explains that in most cases doctors need a biopsy to be certain whether cancer is present. In a biopsy, a doctor removes a sample of abnormal tissue, and a pathologist examines it under a microscope and runs other tests. The findings are written up in a pathology report. A sample can be taken in different ways:

• With a needle - for example in some breast, prostate and liver biopsies, and in bone marrow tests.
• With endoscopy - a thin, lighted tube is passed into the body through a natural opening, such as in a colonoscopy or bronchoscopy.
• With surgery - either removing the whole abnormal area (excisional biopsy) or just part of it (incisional biopsy).

Some biopsies need a sedative or local, regional or general anaesthesia. Your doctor will explain what to expect and any risks for your type of biopsy.

Waiting for and reading results

NCI notes that results are often posted in a patient portal before your doctor can discuss them, and that it is normal to feel anxious and want answers straight away. Your doctor is the best person to explain what all your results mean together. It can help to write your questions down - see our questions to ask your doctor - and to take someone with you to the results appointment.

If cancer is found

If tests show cancer, NCI explains that more tests may be done to find out whether it has spread and how far. This is called staging, and the pathologist may also give the tumour a grade. Further tests on the tumour, sometimes called biomarker testing, can help doctors choose treatment. Our guides to cancer stages explained and types of cancer treatment explain these next steps, and finding trusted support lists places to turn for help.

Diagnosis and screening are different

Diagnostic tests are used when there is a symptom or an abnormal result. Screening tests are for people without symptoms, and NCI notes that an abnormal screening result usually needs diagnostic tests to follow. See cancer screening explained.

Sources

• National Cancer Institute: How Cancer Is Diagnosed
• National Cancer Institute: Tumor Markers
• National Cancer Institute: Symptoms of Cancer
• National Cancer Institute: Cancer Screening Overview (PDQ)

Published and last reviewed: 16 October 2026.