Cancer screening

What is cancer screening?#

Cancer screening looks for early signs of disease, or for indications that a person is more likely to develop cancer because of their age, sex or other risk factors. In most cases, finding cancer early increases the chances of successful treatment. Sometimes screening can even help prevent cancer from developing in the first place.

It is important to remember that a screening test cannot diagnose cancer on its own. If a screening test is abnormal, further investigations are needed to confirm what the result means.

Types of screening#

There are three broad approaches to screening.

• Population-based screening offers a test to an entire target group. For example, all people in a given age range may be invited to screen for bowel cancer.
• Targeted risk screening focuses on selected groups who are at higher risk. For example, genetic screening may be offered to people with a strong family history of breast cancer.
• Opportunistic screening happens when a person is having other medical care. For example, a doctor may order a test while the patient is in the clinic for another reason.

When population-based screening is introduced#

Organising screening for a whole population is a major undertaking, so it is usually only set up when a number of conditions are met:

• The cancer is common and causes significant illness (morbidity) and death (mortality).
• The test can detect the cancer at an early stage, or pick up signs that the cancer may develop later.
• Effective treatment is available, and that treatment works better, or is safer, more affordable or more acceptable, when started early.
• The screening test is acceptable to the people being asked to take it. People tend to avoid tests that are unpleasant or painful, especially when they have no symptoms.
• Screening, including follow-up testing and treatment, can be made available to most of the target population.
• The benefit of screening outweighs the risk for that population.
• The target population can be identified and invited, for example through a central register and mailed invitations.
• The program is cost-effective.

These strict requirements mean that well-established population-based programs currently exist for only a few cancers, most commonly breast, cervical and bowel cancer. Researchers continue to develop and trial screening tests for other cancers, so the range of programs may expand in the future.

How established screening programs work#

Population-based programs aim to detect pre-cancerous changes or early-stage cancers before symptoms appear, when there is the best chance of successful treatment and survival. People within the target age range are invited to take part.

Breast cancer screening#

Breast screening aims to reduce deaths from breast cancer through early detection. Many programs offer regular mammograms to women, and to some trans and gender-diverse people, within a defined age range, often around every two years. People outside that range, or with particular risk factors, may still be eligible and can ask a healthcare provider about their options.

Bowel cancer screening#

Bowel screening aims to reduce deaths from bowel cancer through early detection. Many programs offer a simple test kit at regular intervals to people within a target age range. These kits can usually be completed at home and returned for testing.

Cervical cancer screening#

Cervical screening aims to prevent cancer by detecting pre-cancerous changes, and to reduce deaths through early detection. Many programs recommend that women and other people with a cervix, who have ever been sexually active, have a cervical screening test at regular intervals within a defined age range. The test can usually be arranged through a local doctor or healthcare provider.

The benefits of screening#

Cancer screening has substantially reduced illness and death from cancer in many countries. Where organised cervical screening has been in place for some time, deaths from cervical cancer have fallen markedly.

Challenges and limits of screening#

Even valuable screening programs face challenges when trying to reach large numbers of people:

• Some people find screening tests invasive, uncomfortable or embarrassing and may not want to take part. Programs continually look for ways to make testing more acceptable, such as offering self-testing options for cervical screening.
• Some people fear medical tests or procedures and avoid screening altogether. It can help to discuss any worries with a healthcare provider, and to bring a family member or friend along for support.

Screening tests are not perfect and carry a small chance of harm:

• False negative – the test suggests a person does not have cancer when in fact they do.
• False positive – the test suggests a person may have cancer when they do not, which can cause unnecessary worry and lead to further tests such as a biopsy.
• Side effects – some screening tests carry a small risk of complications.
• Over-diagnosis – detecting a disease that would never have caused symptoms or shortened the person’s life.

Because of these risks, it is best to screen only when you are eligible and due, or when a doctor advises it.

Screening is for people without symptoms#

Screening is designed for people who feel well and have no symptoms. If you have any concerns or worrying symptoms, see your doctor without delay rather than waiting for a routine screening test.

Reducing your risk of cancer#

You can lower your risk of cancer by:

• having regular screening tests when you are due
• not smoking, and avoiding second-hand tobacco smoke
• limiting your exposure to the sun and UV radiation
• being physically active
• maintaining a healthy body weight
• avoiding or limiting alcohol
• eating a healthy diet

Key points#

• In most cases, early detection of cancer increases the chances of successful treatment, and screening can sometimes help prevent cancer altogether.
• A screening test cannot diagnose cancer by itself; an abnormal result needs further investigation.
• Screening may be offered to a whole population, to selected high-risk groups, or opportunistically during other care.
• Population-based programs are most established for breast, cervical and bowel cancer.
• Screening is for people without symptoms; if you have symptoms, see your doctor without delay.

Where to get help and trusted information#

For evidence-based global health guidance, see Source: World Health Organization (WHO).