Screening and cancer: the evidence

Screening saves lives. Cervical cancer screening saves lives

In the 1950s, the death rates for cervical cancer began to fall by about 1% a year. But since 1988, when the NHS Cervical Screening Programme was set up, rates have decreased more rapidly by around 7% a year. 1

A Cancer Research UK study estimated that cervical screening has prevented an epidemic that would have killed about 5,000 UK women every year. 2

Breast cancer screening saves lives

Many studies have shown that breast cancers are much easier to treat if they are detected early. 3

Two large systematic reviews of all the evidence about breast screening from around the world have concluded that screening reduces deaths from breast cancer by between 15 and 22%. 4,5

And the Advisory Committee on Breast Cancer Screening in the UK have estimated that around 1,400 lives are saved every year by breast screening. 6

There was some controversy during the early part of 2009 about the printed material that accompanies breast screening invitations. The authors of one of the systematic reviews were concerned that the leaflet did not represent the balance between benefits and potential harms accurately. 7

The potential harms of breast screening include overdiagnosis (the diagnosis of cancers which are slow-growing or do not grow at all, and would not have developed to cause the person harm during their lifetime), pain at the mammogram, and psychological distress after being recalled to further investigation (which would be unnecessary if the person was then found not to have cancer).

The printed material accompanying the breast screening invitation is under review but breast screening still remains the best chance of spotting breast cancer early and of successful treatment.

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Bowel cancer screening will save lives

Most bowel cancers start off as harmless growths called adenomas. Only a small proportion of adenomas become cancers and this process takes a long time. Doctors can remove the vast majority of adenomas relatively easily. So if adenomas can be spotted before they become cancerous, many cases of bowel cancer could be prevented 8. Adenomas don’t usually produce symptoms so screening is an important way of spotting these cancer precursors.

The NHS is now rolling out a national screening programme for bowel cancer that is expected to be complete by the end of 2009. Experts estimate that by 2025, more than 2000 lives could be saved every year by the bowel screening programme 9.

This screening programme will initially use a technique called faecal occult blood test (FOBT) to test for early signs of bowel cancer. Many studies have already shown that FOBT can reduce deaths from bowel cancer by about 20% 10-12. A clinical trial funded by Cancer Research UK will determine if a second technique, flexible sigmoidoscopy would be effective in preventing bowel cancer 13.

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Screening for prostate cancer is not clear cut

Raised levels of prostate-specific antigen (PSA) in the blood can indicate prostate cancer. PSA levels can be measured by a GP using a PSA test. But PSA levels can rise because of many other reasons. So the PSA test is not foolproof. On its own, it cannot confirm a diagnosis of prostate cancer.

The use of PSA testing as a screening test is still controversial 14, 15. All men have slightly different ‘normal’ levels of PSA. So not all men with high PSA levels have prostate cancer, and not all men with prostate cancer have high PSA levels 16.

Furthermore, not all prostate cancers are life-threatening. Around 80% of men over 80 have cancer cells in their prostate but only 1 in 26 will die from prostate cancer 17. Presently, there is no way of distinguishing these slow-growing tumours from more aggressive ones. Because of a positive PSA test, men could therefore have unnecessary treatment for tumours that might have posed them no problems 14, 15.

Instead of an organised screening programme, in the UK a programme called the Prostate Cancer Risk Management Programme is used. This is a shared decision-making approach between doctors and their patients, where doctors provide men with full information about the pros and cons of PSA testing. You can find out more information about PSA testing on our CancerHelp UK website.

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References

  1. Sasieni, P., J. Cuzick, and E. Farmery, Accelerated decline in cervical cancer mortality in England and Wales. Lancet, 1995. 346: p. 1566-7.
  2. Peto, J., et al., The cervical cancer epidemic that screening has prevented in the UK. Lancet, 2004. 364: p. 249-56.
  3. Etzioni, R., et al., The case for early detection. Nat Rev Cancer, 2003. 3: p. 243-52.
  4. Gøtzsche PC, Nielsen M. Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2006; Issue 4.
  5. Humphrey LL et al. Breast cancer screening: a summary of the evidence for the U.S. preventive services task force. Annals of Internal Medicine 2002; 137(5): 347-367.
  6. Advisory Committee on Breast Cancer Screening. Screening for breast cancer in England: past and future. J Med Screen. 2006;13(2):59-61.
  7. Gotzsche PC et al. Breast screening - the facts - or maybe not. BMJ 2009; 338:b86
  8. Scholefield, J., ABC of colorectal cancer. BMJ, 2000. 321: p. 1004-1006.
  9. Parkin, D.M., Tappenden, P., Olsen, A.H., Patnick, J., Sasieni, P., Predicting the impact of the screening programme for colorectal cancer in the UK. Journal of Medical Screening, 2008. 15: p. 163-174.
  10. Towler, B., et al., Screening for colorectal cancer using the faecal occult blood test, hemoccult. Cochrane Database Syst Rev, 2000. CD001216.
  11. Hardcastle, J., et al., Randomised controlled trial of faecal-occult-blood screening for colorectal cancer. Lancet, 1996. 348: p. 1472-7.
  12. Mandel, J., et al., Colorectal cancer mortality: effectiveness of biennial screening for fecal occult blood. J Natl Cancer Inst, 1999. 91: p. 434-7.
  13. UK Flexible Sigmoidoscopy Screening Trial Investigators, Single flexible sigmoidoscopy screening to prevent colorectal cancer: baseline findings of a UK multicentre randomised trial. Lancet, 2002. 359: p. 1291-300.
  14. Schroeder FH, Hugosson J, Roobol MJ, et al. Screening and prostate-cancer mortality in a randomized European study. N Engl J Med 2009;360:1320-8
  15. Andriole GL, Grubb RL III, Buys SS, et al. Mortality results from a randomized prostate-cancer screening trial. N Engl J Med 2009; 360:1310-9
  16. Punglia, R., et al., Effect of verification bias on screening for prostate cancer by measurement of prostate-specific antigen. N Engl J Med, 2003. 349: p. 335-42.
  17.  CancerStats