Screening for cervical cancer is a complex area and the Scally report (Dr Gabriel Scally's scoping inquiry was published in September) highlights these difficulties and how the CervicalCheck system has let women and their families down.
I am a GP, and I have wondered how this could have happened. There is a sense that doctors and nurses trusted a system and perhaps didn’t always communicate the complexities involved as well as we should have. As we move forward, we need to know the facts so we can make decisions about screening. I wanted to try and understand what has happened so I could inform my patients properly.
I used available Irish data and consulted with other GPs and health economists in Hiqa, but I take responsibility for the summary I present here.
– Cervical cancer is the eighth commonest cancer in Ireland. On average, each year, there are 277 cases of cervical cancer resulting in 88 deaths in women. Almost half of women are under 45 when they are diagnosed. Cervical cancer is generally caused by HPV (human papillomavirus). The first stage is the development of pre-cancerous cells, referred to as cervical intraepithelial neoplasia, or CIN. Progression from pre-cancerous cells to cancer takes on average 10 to 20 years.
– Cervical cancer screening was introduced to detect pre-cancerous changes that could be treated to prevent them developing into cervical cancer. The screening test is not designed for diagnosing cervical cancer, which presents with symptoms such as irregular vaginal bleeding, spotting or discharge, bleeding after sex and/or pelvic pain. It is also possible to develop cervical cancer between screening tests, so women who have symptoms such as vaginal bleeding or pelvic pain should always see their GP.
– The Irish cervical screening programme (CervicalCheck) was introduced in 2008 and aims to detect pre-cancerous changes in the cells. Women attend their GP or practice nurse (usually) for what is commonly called their smear test. This involves collecting cells from the cervix or neck of the womb, which are then sent to a laboratory for analysis. If pre-cancerous changes are found and thought to be very suspicious (high-grade abnormalities), the woman is referred to a specialist for colposcopy.
If there are minor changes in the cells (low-grade abnormalities), the sample is checked to see if the HPV virus is present. If HPV is detected, the woman is referred for colposcopy. During colposcopy, the specialist takes a more detailed look at the cervix and may take a biopsy and/or apply treatment to the abnormal area.
The biopsy is assessed in a laboratory where it is interpreted as either normal, pre-cancer (CIN) or cervical cancer (though this is not always apparent). Further treatment and monitoring of the abnormalities is determined by the specialist in the colposcopy or gynaecology clinic.
– It is important to remember that no screening test is 100 per cent accurate – some results can be false positives (ie, the screening test says the result is positive, but there is no clinically significant disease on further testing), and some are false negatives (ie, test result is negative, although disease is actually there – this leads to delayed diagnosis, which for cervical cancer screening means a delay in diagnosing pre-cancerous changes, which could then progress to cervical cancer).
Key questions about cervical screening
What is the chance of a false negative test result?
On average, for every 1,000 tests carried out, 959 tests will be negative, but 4 of these will be a false negative.
What is the chance of a false positive result?
On average, for every 1,000 tests carried out, 41 of these will be positive, requiring a repeat test or referral for colposcopy. Of the 41 tests, 12 will be confirmed as CIN requiring treatment (true positives). The remaining 29 will be confirmed as false positives.
If I have a normal smear test result, what is my chance of developing cervical cancer in the next three to five years?
Assuming 250,000 women attend for screening each year in CervicalCheck, in women with a negative screening test, 39 will go on to develop invasive cervical cancer within 3.5 years and 90 will go on to develop invasive cervical cancer within 5.5 years. This includes true negatives and false negatives.
What was the controversy with CervicalCheck and the Scally report?
The controversy surrounding the CervicalCheck programme relates to the identification of false negative results by the screening programme. An audit was undertaken to check the quality of the programme. This audit involved reviewing previous cervical screening tests in women who had subsequently developed cervical cancer. The focus was on false negative results, ie, women who had a normal screening test but went on to develop cervical cancer.
The Scally report reviewed this process and highlighted the difficulty in conducting these audits due to a concept called ‘recall bias’, ie, those reviewing the slides as part of the audit may be aware the woman went on to develop cervical cancer.
The report was critical of the process, particularly that the women involved were not informed of this audit and that the HSE policy on Open Disclosure was not generally followed. The report also highlighted the significant delays experienced by women and many examples of poor communication with the women affected and their families.
We do not yet know if Ireland has a different rate of false negative results for cervical cancer screening compared with other countries.
Going forward
There is a proposed new cervical cancer screening strategy that is due to be introduced shortly in CervicalCheck. In the new system, all samples will first be tested for HPV and further tests will be carried out on those who test HPV-positive.
The main advantage of the new test is that it has fewer false negatives. This means that assuming 250,000 women attend for screening each year in CervicalCheck, in women with a negative screening test, 12 will go on to develop invasive cervical cancer within 3.5 years and 22 will go on to develop invasive cervical cancer within 5.5 years, and this includes true negatives and false negatives.
This new test is in use in the UK already and this is a summary of the information that is given to women:
– one in 20 women will have an abnormal smear test result.
– one in 2,000 have cervical cancer.
– So only 1 per cent of women with an abnormal smear will have cancer.
Preventing cervical cancer
All of us want to prevent cervical cancer so women and their families do not have to undergo highly challenging treatments and experience personal tragedy. Cervical screening will never prevent all cases of cervical cancer.
We do know the HPV vaccine prevents cervical cancer. It is offered free of charge to girls in the first year of secondary school, with evidence to support expanding the vaccination programme to include boys. HPV vaccination prevents seven out of 10 cervical cancers and works best when given at the age of 12 to 13 years. It also protects against a range of other cancers that occur in men and women.
All international evidence indicates the vaccine is extremely safe and it represents our best chance to ensure as few women as possible experience cervical cancer in the future.
Prof Susan Smith is professor of Primary Care Medicine at the Royal College of Surgeons in Ireland (RCSI). She also works as a GP in Inchicore, Dublin 8
