How do we know?

Cancer screening can be an effective way of detecting cancer early or preventing it from developing in the first place1.

Cervical screening can prevent cancer developing by detecting changes in the cervix. Scientists estimate that in the UK cervical screening is saving up to 5000 lives each year2, and that cervical screening can prevent at least:

• 75% of cervical cancers in women in their 50s and 60s,
• 60% of cervical cancers in women in their 40s,
• 45% of cervical cancers in women in their 30s3

Breast screening can detect breast cancer early. Many scientists believe that breast screening saves lives4. But there is some controversy about how many lives are saved by breast screening each year5. The figure could lie anywhere between 3004 and 14006 lives.

Bowel screening with the current test, the faecal occult blood test (FOBT), reduces the chances of dying from bowel cancer by around 16% in men and women aged 45 to 747. The programme is predicted to save around 2000 lives in the UK each year8.

The English government have committed to introducing a new screening test, called Flexible Sigmoidoscopy or Flexi-Scope, into the national bowel screening programme in the coming years. A 16-year trial, which Cancer Research UK helped to fund, suggested that Flexi-Scope can reduce cases of bowel cancer by a 23% and deaths by 31%9. Once this has been fully rolled out, it could save thousands of lives each year.

It is not clear whether or not screening for prostate cancer with the PSA test saves lives10,11. The PSA test leads to a lot of false alarms, where men have a positive result in the test, but do not actually have prostate cancer. Also prostate cancer is very common, and many of cases grow slowly but do not cause a man any problems during his lifetime. PSA testing picks up many slow-growing prostate cancers, leading to unnecessary treatments with serious side effects.10,11.

This is why there is no national prostate cancer screening programme in the UK.

All screening tests have the potential to do harm as well as good. So tests are offered only to those for whom the benefits are most likely to outweigh the risks. This will depend on things like how common the cancer is and how well the test works in a certain group.

For breast screening the benefits are thought to outweigh the harms for women aged 50 to 73+. In younger women with a significant family history of breast cancer, there may also be an overall benefit to screening. But for other women under 50, the benefits seem to be outweighed by the harms, including anxiety, exposure to small amounts of radiation, and picking up and treating cancers that wouldn’t have caused any harm over a woman’s lifetime12.

Cervical screening detects changes in the cervix. The benefits are thought to outweigh the harms for women from their mid 20s to their mid 60s. In younger women these changes are very common and usually return to normal within around a year13. Screening these women could mean treating a lot of women with changes that would disappear on their own14. The treatment for these changes can increase the chances of having a baby born before 37 weeks15.

Bowel screening currently uses the faecal occult blood test (FOBT). FOBT can result in false alarms. More than 1 in 10 people with a positive result will turn out, after further tests, not to have cancer16. These further tests usually include a colonoscopy, where a tiny camera on a flexible tube is used to examine the bowel. Since this test carries a risk of tearing the bowel wall17, it is not usually appropriate to screen people at low risk of developing bowel cancer, such as those under 50.

FOBT works by detecting blood in the stools. But since growths and cancers in the bowel do not bleed all the time, FOBT will miss quite a large proportion of bowel cancers16.