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Cancer Awareness GuideGeneral information & support

Cancer screening explained

Screening means checking for early signs of a disease in people who do not have symptoms. For some cancers, screening programmes can help find changes early, when they are often easier to treat.

For information only - this is not medical advice. Decisions about screening should be made with your doctor or your national screening programme.

Why screening matters

The US National Cancer Institute (NCI) explains that screening tests can help find cancer at an early stage, before symptoms appear, and that cancer found early may be easier to treat. By the time symptoms appear, a cancer may have grown and spread (NCI Cancer Screening Overview). That is the idea behind national screening programmes for certain cancers. The World Health Organization (WHO) adds that screening programmes are effective for some, but not all, cancer types.

Kinds of screening test

According to NCI, screening can involve:

  • A physical exam and health history - checking for lumps or anything unusual, and asking about health habits and past illnesses.
  • Laboratory tests on samples such as blood, urine or tissue.
  • Imaging - procedures that make pictures of areas inside the body, such as a mammogram.
  • Genetic tests that look for gene changes linked to a higher risk of certain cancers. See is cancer hereditary? for how inherited risk is assessed.

Screening is not a diagnosis

NCI notes that screening tests usually do not diagnose cancer. If a result is abnormal, more tests - called diagnostic tests, which may include a biopsy - are needed to find out whether cancer is present. The NHS in England explains it the same way: a "screen positive" result means you will be offered further tests, and a normal result means you are at low risk at the moment, not that you will never develop the condition (NHS: Screening).

Screening has limits and risks too

NCI lists several possible downsides that are worth understanding before any test:

  • False positives: a result can look abnormal when there is no cancer, which can cause worry and lead to more tests.
  • False negatives: a result can look normal even when cancer is present, so new symptoms should still be checked.
  • Overdiagnosis: some cancers found by screening would never have caused symptoms or become life-threatening, but may still be treated.
  • Procedure risks: some tests, such as colonoscopy, can occasionally cause problems like bleeding.

Because of this, NCI recommends informed and shared decision-making: your health care provider should talk you through the benefits and harms of a test and include you in the decision.

How to know what is right for you

  • Screening recommendations depend on your age, sex, family history and other factors. NCI notes that people at higher risk, such as those with a strong family history or certain inherited gene changes, may need screening earlier or more often.
  • Which programmes are offered, and at what ages, varies by country. Check your own national health service for the current programmes.
  • Your doctor or national health service is the right source for what you should do and when.

Guides to specific screening tests

Each test has its own purpose, preparation and limits. Our plain-language guides explain the most common ones, using NCI, USPSTF and NHS information:

Do not start or skip any screening based on a website. Speak with your doctor or follow your country's official screening programme. If you have symptoms, do not wait for a screening invitation - see a doctor. Our list of signs worth discussing with a doctor may help, along with questions to ask your doctor.

Sources

Last reviewed: 21 October 2026.

Common questions

At what age should I be screened?

It depends on the cancer, your personal risk factors and your country's programme. Ask your doctor or check your national health service's official guidance.

Does a normal screening result mean I do not have cancer?

Not with certainty. NCI notes that false-negative results are possible, and the NHS explains that a normal result means low risk at the moment. If you develop symptoms, see a doctor.

If my screening test is abnormal, do I have cancer?

Not necessarily. Screening tests usually do not diagnose cancer. An abnormal result leads to further diagnostic tests, and false-positive results are possible.

Which cancers have screening tests?

It varies by country. For example, the USPSTF recommends screening for breast, cervical and colorectal cancer in certain age groups, and lung cancer screening for some people with a heavy smoking history. It says PSA screening for prostate cancer is an individual decision for men aged 55 to 69.