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.
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.
What are the benefits of cancer 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.
Currently there is no population screening programme yet for the prevention of ovarian cancer. Research using ultrasound scan and CA125 blood test shows some promising results but is still not ready and convincing to establish population screening programme.
Selective Screening using these tests is available for women at higher risk (10% or more life-time risk) of developing cancer by having strong family history or genetic mutation (BRCA1 or BRCA2).
Risk of ovarian cancer can be reduced by using oral contraceptive pills.
Women with genetic mutation can reduce their risk down to the level of population by having both tubes and ovaries removed.
There is no population screening programme to prevent endometrial cancer. Research using ultrasound scan to check for thick endometrial lining shows some promise but results are not yet sufficiently convincing to establish a population screening programme for endometrial cancer. Benefit of such screening in improvement of survival is not entirely clear.
Women with strong family history of lynch syndrome genetic mutation or associated cancers are at very high-risk of developing endometrial cancer. They are usually offered hysterectomy after completion of family. Meanwhile they may benefit from screening with ultrasound scan, Pipelle endometrial sampling or hysteroscopy at regular interval. They may also benefit from progesterone releasing intra-uterine devices such as Mirena ® IUS (Coil).
Risk of endometrial cancer can also be reduced by healthy life style, weight management and by using combined oral contraceptive pills.
NHS cervical screening programme established in 1988 has been highly successful in reducing the incidence of the cervical cancer.
Who is eligible?
All eligible women aged between 25 and 64 in England are automatically invited for the cervical cancer screening test. Women aged 25 to 49 receive invitations every 3 years. Women aged 50 to 64 receive invitations every 5 years.
How does cervical screening work?
Test is designed to detect precancerous cells with a aim to treat pre-cancer so they do not progress to cancer. Approximately 1 in 20 women have abnormal cell on smear. In addition to the abnormal cells, test for human papillomavirus (HPV) is carried out in those with low-grade cell abnormality. HPV test helps to decide if woman needs to be referred to colposcopy clinic.
Many women with abnormal tests are referred to colposcopy clinic for further tests. Remaining low-risk women with abnormal test are advised to have earlier than normal repeat of their screening test.
After treatment with loop biopsy women are advised to have a test-of-cure screening test in six months at GP. This test is examined again for abnormal cells and presence of HPV virus. If found negative women are discharged back to routine three or five yearly screening test.
Is my risk of cancer higher if I do not take part in screening?
Not taking part in cervical screening programme is the biggest risk for developing cervical cancer. However it is also important to note that cervical screening is not 100% accurate and do not prevent all cervical cancers.
There is currently no population screening programme for vulval cancer.
However during cervical cancer screening test (smear test), the nurse or doctor may routinely examine vulval skin.
Women with higher risk such as chronic skin conditions (for e.g. Lichen Sclerosus) or precancerous conditions (VIN) may benefit from regular vulval skin examinations.
Cancer Research UK, http://www.cancerresearchuk.org/health-professional/cervical-cancer-statistics
NHS CSP, Public Health England, https://www.gov.uk/guidance/cervical-screening-programme-overview