Preventative cancer screening: Prospects and implications

By Caitlin Davies

In the UK, there are currently three cancer screening programmes; these are designed to check for any pre-cancerous abnormalities or early signs of developing cancer. Each programme screens for a particular type of cancer – and is targeted at age groups that are most prone to developing the disease: mammogram screenings for women aged 50-71 to prevent the development of breast cancer, cervical smear tests for women and individuals with a cervix aged 25-64 to prevent the development of cervical cancer and bowel scopes for all individuals aged 55-74 to prevent the development of bowel cancer (Cancer Research UK, 2015). Healthy, asymptomatic individuals from the general population are regularly invited to attend these screening appointments. If an individual has a family history of cancer or has a known genetic mutation that makes them more susceptible to developing cancer, it is likely that their GP will invite them for screenings more regularly than the screening programme schedule. (Cancer Research UK, 2015).

Whilst screening may allow for early detection of cancer, its association with health risks leaves the health service with serious responsibilities to provide individuals with the necessary resources to make an informed decision (Public Health England, 2020). Some cancers do not have an associated national screening programme, because it has been concluded that the benefits do not outweigh the risks, an example being prostate cancer. The reason being that, whilst the PSA test (a test that monitors the prostate-specific antigen levels in the blood to indicate whether there is a chance a male has prostate cancer) has been shown to reduce a man’s chance of dying from prostate cancer, the test also produces large quantities of false negatives and false positives (NHS England, 2017). This is particularly harmful, as a false negative may result in an individual not receiving the treatment that he needs, referred to as underdiagnosis, whilst a false positive may result in an individual receiving harmful treatment even though they don’t actually have prostate cancer, referred to as overdiagnosis (NHS England, 2017). 

Additionally, the PSA test cannot differentiate between slow growing prostate cancers (that may never affect life expectancy) and aggressive prostate cancers, so the test can also result in overtreatment that causes more harm than good. As a result, there is instead an informed-choice programme which enables males over the age of 50 to enquire about obtaining a PSA test on the NHS, while fully educating them on the risks and  benefits (NHS England, 2017). Furthermore, the individual will also be offered additional tests such as an MRI scan and a biopsy before being given a confirmed prostate cancer diagnosis. Lastly, in order to avoid overtreatment, the individual may be given the chance to participate in active surveillance which is where the individual does not receive treatment if the cancer is particularly slow growing, due to the treatment being deemed to be more harmful than leaving the cancer alone.

These phenomena are not just specific to prostate cancer, they apply to all cancers, even those types which are preventatively screened for such as cervical cancer. For some cancers however, the benefits of screening are seen to outweigh the risks, especially in certain age ranges, but the risks must always be considered. Currently, smear tests which test for the presence of high risk strains of HPV in cells collected from the cervix, to determine if the individual is at risk of developing cervical cancer, are offered every 3 years for women and individuals with a cervix aged 25-49 and every 5 years for those aged 50-64 (Cancer Research UK, 2020). After the age of 65, an individual will only be invited again if one of their last three tests was classified as abnormal (Cancer Research UK, 2020). Pre-2003, the age bracket for screening invitations was 20-64, but after a number of new studies showed that screening was not as effective in preventing cervical cancer in women and individuals with a cervix aged under 25, it was raised to 25-64, a decision that was maintained even after a review in May 2009, on the premise of additional novel studies that solidified the previous conclusion (Albrow et al., 2012). 

However more recently, there has been a large public outcry to re-lower the age bracket back to 20-64 after a number of tragic cases of women below 25 dying from cervical cancer surfaced on social media (Mirror.co.uk, 2012). In spite of this, the current age bracket has remained and the risks of screening younger women and individuals with a cervix reinforced. This is because numerous studies show that invasive cervical cancer in those aged under 25 is rare (Jo’s Cervical Cancer Trust, 2014) but the chance of detecting abnormal cytological changes which will resolve themselves and therefore do not require treatment is high (Sasieni, Adams and Cuzick, 2003). For women below the age of 25 screened twice, there is a 1 in 3 risk of receiving an abnormal test result on at least one occasion (UK National Screening Committee, no date). This may therefore lead to further investigation and overtreatment which is dangerous as there is risk that those individuals may give birth prematurely in the future as a result (UK National Screening Committee, no date). 

Additionally, it is now known that screening women and individuals with a cervix aged 22-24 does not affect the incidence rates of cervical cancer in those individuals once they reach ages 25-29, thereby posing no real health benefit (Sasieni, Castanon and Cuzick, 2009). Moreover in 2008, there was the introduction of the HPV vaccination programme aimed at protecting teenage girls from the most high risks strains of HPV in order to reduce the risk of developing cervical cancer (GOV.UK, 2011). Whilst this does not prevent development entirely, it  further reduces the need for screening before the age of 25. Some argue however, that the vaccination programme has had a negative effect on appointment uptake in those eligible for routine smear tests, as they already feel adequately protected, suggesting that efforts would be better focused on encouraging those already eligible to attend their appointments (Albrow et al., 2012).

As always, it is important that individuals receive all the information they need in order to make informed decisions about their own health. Individuals will always be encouraged to seek advice from their GP if they notice any abnormal symptoms developing, in order to receive appropriate medical attention when required, as this is when a preventative screening appointment is no longer appropriate. Additionally, individuals are encouraged to ensure their GP is aware of any family history of cancer as this may affect how often you are screened. The pursuit for early onset detection of cancer, whilst requiring strong national structures for delivery of screening, also relies on wide-scale public health measures to increase the reach of these national programmes.

Reference List:

Albrow, R. et al. (2012) ‘Cervical screening in England: The past, present, and future’, Cancer Cytopathology, 120(2), pp. 87–96. doi: 10.1002/cncy.20203.

Cancer Research UK (2015) Understanding cancer screening, Cancer Research UK. Available at: https://www.cancerresearchuk.org/about-cancer/screening/understanding-cancer-screening (Accessed: 6 September 2020).

Cancer Research UK (2020) About cervical screening | Cervical cancer | Cancer Research UK. Available at: https://www.cancerresearchuk.org/about-cancer/cervical-cancer/getting-diagnosed/screening/about (Accessed: 6 September 2020).

GOV.UK (2011) HPV vaccine to change in September 2012, GOV.UK. Available at: https://www.gov.uk/government/news/hpv-vaccine-to-change-in-september-2012 (Accessed: 6 September 2020).

Jo’s Cervical Cancer Trust (2014) Cervical screening aged 24 or under, Jo’s Cervical Cancer Trust. Available at: https://www.jostrust.org.uk/information/cervical-screening/cervical-screening-under25 (Accessed: 6 September 2020).

Mirror.co.uk (2012) ‘Watching her waste away broke my heart’: Mum’s grief after daughter died because she was too young for a smear test, mirror. Available at: http://www.mirror.co.uk/news/real-life-stories/too-young-for-a-smear-test-23-year-old-died-846540 (Accessed: 6 September 2020).

NHS England (2017) Prostate cancer – PSA testing, nhs.uk. Available at: https://www.nhs.uk/conditions/prostate-cancer/psa-testing/ (Accessed: 6 September 2020).

Public Health England (2020) ‘Cervical screening, helping you decide’, p. 16.

Sasieni, P., Adams, J. and Cuzick, J. (2003) ‘Benefit of cervical screening at different ages: evidence from the UK audit of screening histories’, British Journal of Cancer, 89(1), pp. 88–93. doi: 10.1038/sj.bjc.6600974.

Sasieni, P., Castanon, A. and Cuzick, J. (2009) ‘Effectiveness of cervical screening with age: population based case-control study of prospectively recorded data’, The BMJ, 339. doi: 10.1136/bmj.b2968.

UK National Screening Committee (no date) Cervical cancer consultation Q&A. Available at: https://legacyscreening.phe.org.uk/cervicalcancer-qa (Accessed: 6 September 2020).

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