What is cancer screening?
Cancer screening is testing healthy people for signs of a precancer or an early stage of cancer. There are two types of screening programmes. Population screening
tests everyone within a specific age groups. Selective screening
is where people at higher risk of developing cancer (e.g. strong family history of cancer) are screened.Why there aren’t screening programme for all cancers?
For screening programme to be successful there are at least four criteria to be met.
What are the benefits of cancer screening?
- Cancer: should have detectable pre-cancer or early cancer phase that is long enough to employ realistic screening intervals.
- Screening test: should be Effective (Low false negative rate and reasonable low false positive rate), Easily implementable, Safe, Well-tolerated and Cost-effective.
- Diagnostic test: should be available with good efficacy (low false positive and low false negative rate).
- Treatment: There should be an effective and easily deliverable treatment of pre-cancer or early stage of cancer detected by screening.
Cancer screening can significantly reduces the lifetime risk of developing cancer. For e.g. Cervical cancer screening has more than halved the risk of cervical cancer in England since the introduction of screening programme. In fact the highest risk currently of developing cervical cancer is related to not taking part in screening. Are there any dangers or disadvantages of cancer screening?
Screening test can have false positive results (abnormal test results despite not having precancer or cancer) that may lead to unnecessary invasive procedures. Abnormal screening test is usually followed by further investigations and procedures that carry their own risk of side-effects. Taking part in cancer screening can provide reassurance to most women but some may find the process and results stressful leading to anxiety. Any benefit of cancer screening therefore has to be weighed with the risks of the screening and subsequent procedures.
Screening test results can also be false negative, where an existing cancer is missed. This fortunately is not common. Screening tests are not perfect and false negative rate can never be 0%. However most screening programme adjust interval of screening test on the safer side in a way that there is still good possibility to detect precancer on the subsequent round of screening even if missed due to false negative test in the previous round.
Population screening programmes are aimed to be cost-effective. These generally means that the screening test and interval of screening is implemented using the best possible ratio of highest prevention rate with lowest possible cost and side-effects. In other words more prevention is although possible by increasing frequency of screening test but is usually comes at possibly higher cost and side-effects.