Guidance

Topic 2: background to cervical screening

Updated 10 October 2024

Applies to England

1. Topic 2 learning objectives

The trainee should know about:

• epidemiology
• natural history of cervical cancer
• HPV and hrHPV primary screening
• the principles of screening
• future developments for cervical screening

The trainee should understand:

• risk factors for cervical cancer
• factors that reduce the risk of cervical cancer
• the effectiveness and limitations of cervical screening

The trainee will be able to:

• explain the rationale of primary HPV screening to people attending their screening test
• prepare them for potential results they may receive

1.1 Guidance for the trainer

Signpost the trainee to reading and resources on all topics in this section including:

• data from the National Cancer Intelligence Network (NCIN)
• Cancer Research UK cancer statistics for professionals
• Research by F X Bosch and others on the causal relation between human papillomavirus and cervical cancer
• annual statistics for the cervical screening programme
• IARC Handbooks of Cancer Prevention, Volume 10. Cervix Cancer Screening
• Research by J Peto and others on how cervical screening prevents cervical cancer in the UK
• Research by H C Kitchener and others reporting on ARTISTIC: a randomised trial of human papillomavirus (HPV) testing in primary cervical screening

1.2 Teaching resource

Refer to PowerPoint presentation 2 for subject areas in Topic 2.

2. Epidemiology, natural history of cervical cancer including human papillomavirus

2.1 Epidemiology

Provide an overview of epidemiology including the information that:

• cancer of the cervix uteri is the second most common cancer among people worldwide; approximately 80% of cases occur in developing countries and in many regions cervical cancer is the most common cancer in women
• in Europe, around 24,400 women were estimated to have died from cervical cancer in 2012 (the UK mortality rate is the ninth lowest in Europe)
• worldwide, more than 265,000 people are estimated to have died from cervical cancer in 2012, with mortality rates varying across the world
• in females in the UK, cervical cancer is the 19th most common cause of cancer death, with around 850 deaths in 2016
• in females in the UK, cervical cancer is the 14th most common cancer, with around 3,200 new cases in 2016
• cervical cancer accounts for 2% of all new cancer cases in females in the UK (2016)
• deaths from cervical cancer have fallen in the UK, in England by over 70% since the early 1970s, with the lowest number (721) recorded in 2013
• 83% of people survive cervical cancer for at least 1 year
• 67% of people survived for 5 years or more for patients diagnosed with cervical cancer during 2010 to 2011 in England and Wales
• it is estimated that cervical screening saves approximately 5000 lives per year in England
• in the UK between 2010 and 2012, 78% of cervical cancer cases were diagnosed in 25 to 64 year olds, and an average of 11% of cases were diagnosed in people aged 75 years and over

2.2 Natural history of cervical cancer

The human papillomavirus (HPV) is a necessary but insufficient cause of cervical cancer. People acquire HPV through sexual contact and this can enter the cervical epithelium at the site of the transformation zone (TZ). In most people infection with HPV is transient and the immune system clears it within a year or 2.

In some individuals the immune system is unable to clear the virus and persistent infection can lead to the development of abnormal cell changes in the cervix called cervical intraepithelial neoplasia (CIN).

Human papillomavirus and primary HPV screening

In 2016, the UK National Screening Committee (UK NSC) recommended that the NHS Cervical Screening Programme (NHSCSP) should adopt the test for HPV as the primary (first) test carried out.

Laboratories now screen all cervical samples for high risk HPV (hrHPV) subtypes as the first test. Cytology is the triage test, only used when hrHPV is found.

There are over 100 types of HPV. Most do not cause significant disease in humans. However, a number of high risk strains (notably types 16 and 18) are agents causing cervical cancer. Unlike subtypes 6 and 11 (which cause genital warts) these high risk types do not produce visible symptoms.

Almost all cervical cancers (99.7%) contain hrHPV DNA. Looking at cases of cervical intraepithelial neoplasia (CIN), the higher the grade of CIN, the more frequently hrHPV is found. This suggests that people who do not have hrHPV are extremely unlikely to develop cervical cancer in the short to medium term. Primary testing for hrHPV means those at higher risk have further tests more quickly, and those at low risk of cervical cancer can be reassured.

Method of hrHPV infection

hrHPV is easily transmitted during sexual contact between people including same sex partners. There are 2 important factors to bear in mind, that:

• hrHPV is asymptomatic, so it may have been present and undetected for many years; infection may have nothing to do with a person’s current relationship
• a partner may have acquired the virus many years earlier and passed it on unknowingly

A positive test result for hrHPV types does not imply infidelity or promiscuity by either partner.

Risk factors for cervical cancer

Factors that increase risk include:

• not attending for screening
• persistent infection with hrHPV
• having many sexual partners (or a sexual partner with many sexual partners)
• smoking
• immunosuppressive disorders, including human immunodeficiency virus (HIV) infection
• using the contraceptive pill
• having children at a young age
• sexual debut at a young age
• not being vaccinated against HPV

Factors that reduce risk include:

• regular attendance for screening
• regular condom use
• late first pregnancy
• total hysterectomy (for reasons other than cervical cancer)
• being vaccinated against HPV
• stopping or not smoking

3. Criteria for a population-based screening programme

The World Health Organization (WHO) published a paper by Wilson and Jungner in 1968, outlining 10 criteria upon which to base the decision whether to screen for a condition. The criteria state that:

• the condition sought should be an important health problem
• there should be an accepted treatment for patients with recognised disease
• facilities for diagnosis and treatment should be available
• there should be a recognisable latent or early symptomatic stage
• there should be a suitable test or examination
• the test should be acceptable to the population
• the natural history of the condition, including development from latent to declared disease should be adequately understood
• there should be an agreed policy on whom to treat as patients
• the cost of case finding (including diagnosis and treatment of patients diagnosed) should be economically balanced in relation to possible expenditure on medical care as a whole
• case finding should be a continuing process and not a ‘once and for all’ project

4. Effectiveness and limitations of cervical screening

Cervical screening is a beneficial programme which saves lives by preventing the development of cervical cancer. It does however have some limitations and drawbacks. These include

• detecting HPV infection and minor abnormalities in cervical cells which would have cleared up on their own without people ever knowing about them
• causing people worry when a minor abnormality or HPV infection is found
• not picking up every abnormality of the cervix (cervical screening is not a diagnostic test)
• not being able to prevent every case of cervical cancer (regular cervical screening can prevent around 70% of cervical cancers developing)
• some people finding the test a painful, uncomfortable or embarrassing experience

No screening test is 100% effective. In cervical screening this is because:

• an HPV infection or abnormal cells can sometimes be missed (a ‘false negative’ result)
• abnormal cells can develop and turn into cancer in between screening tests
• there is a small chance that a result says abnormal cells are found when the cervix is normal (a ‘false positive’ result)

If screening does not find abnormal cells this does not guarantee that the person does not have them, or that they will never develop in the future.

5. Future developments in cervical screening

The UK NSC advises ministers and the NHS in the 4 UK countries about all aspects of population screening and supports implementation of screening programmes. The UK NSC recommends the following developments when the cervical screening programme has implemented HPV primary screening:

• the introduction of self-sampling (primary HPV testing by the use of HPV self-sampling kits is a strategy that may encourage people who have not previously attended to be screened)
• the introduction of extended screening intervals; hrHPV testing is more sensitive for high grade CIN than cytology and gives a high negative predictive value, potentially allowing people to be screened less frequently in the future