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Published: 22 August 2023

Screening for cervical cancer – why the number of years between screening tests has changed

By Dr Sarah Fitzgibbon, GP and Primary Care Clinical Advisor with CervicalCheck

In March 2020, the CervicalCheck screening programme changed its screening method from identifying early cell changes (known as smear tests) to HPV cervical screening. HPV (the human papillomavirus) is the main cause of most cervical cancers and so our cervical screening programme is now focused on identifying this main risk factor.

The development of cervical screening in Ireland

The previous screening method of identifying early cell changes was a good but slightly less reliable way of checking a person’s risk of developing cervical cancer. Originally, a smear test involved taking cell samples from the cervix using a spatula, smearing it onto a slide, and sending it to a laboratory for review under a microscope to look for changes to cells that could lead to cervical cancer. This then changed to using a liquid-based specimen – taking cell samples from the cervix using a brush, placing the sample in a liquid and sending it to a laboratory to be examined under a microscope. This method was in line with best international standards at the time.

The 2017 HIQA Health Technology Assessment which recommended the change to HPV screening, provided evidence that “over a six-year interval, women with negative primary HPV screening at baseline are less likely to develop severe precancerous abnormalities than women with negative primary cytology at baseline.” In other words, HPV testing has a better negative predictive value – a higher likelihood to be truly negative when testing negative - than previous screening methods.

HPV detection is a more precise and efficient screening tool, and it works differently from the previous method.

Why testing for HPV allows us to increase the time between screens

For most people, HPV goes away on its own and doesn’t cause any harm, but for some people the infection persists, and this can lead to cell changes.

Abnormal cells, or CIN (cervical intraepithelial neoplasia) are classified on a scale of one to three. CIN1 cell changes often return to normal in the absence of persistent HPV infection. Only around half of CIN has the potential to progress to invasive cancer and in the past, there was very little to guide us to know which CIN would progress and which would return to normal.

HPV research has shown us that people with persistent HPV infection are far more likely to progress to CIN2 or higher, resulting in an increased risk of developing invasive cancer. CIN2 and CIN3 are more likely to require treatment to prevent cancer developing.

This advance in scientific knowledge has allowed us to give much greater reassurance to women when they have a negative HPV test. It also allows us to offer screening at longer intervals – five years instead of three years – for those who are HPV negative. Switching to HPV screening reduces the number of lifetime tests required while expanding the eligible age range, meaning a woman will have one less test in her lifetime and still be screened for an extra five years, up to age 65.

For women who are found to have HPV on screening, it provides an opportunity for closer monitoring while the infection is active. About 1 in 9 women who attend for a screening test will be told they are HPV positive. If it is the first positive test for HPV, the cell samples taken during screening are then reviewed under a microscope. If the cells look normal, these women will then be invited to return in 12 months to have the test repeated. If the repeat test is also positive, women will then be referred for specialist review at a colposcopy clinic to take a closer look at the cervix, even if the cells still look normal. If the repeat test is negative, women can return to be screened for HPV again in five years’ time.

Previous screening methods of identifying changes in cells also resulted in some women attending colposcopy who didn’t need to. HPV testing reduces the likelihood of this happening. So, increasing the number of years between screening tests is safer and better for those taking part, because it reduces the time people spend attending medical appointments, and reduces their chance of having unnecessary medical treatments.

Limitations of HPV screening: not all cervical cancers are caused by HPV

Knowing whether HPV is present or not is the most useful predictor of whether a person may be at increased risk of developing cervical cancer. The limitation here is that not all cervical cancers are related to HPV, in which case a person may never get HPV and could still get cervical cancer. These types of cervical cancers were also not reliably picked up with previous screening methods.

There is also a small chance per test that a HPV negative result is false. A small number of people can unfortunately develop a rapidly progressing cancer, that spreads quickly between one HPV positive test and the next one 12 months later.

While it’s clear cervical screening cannot prevent all cancers, HPV cervical screening is a good tool to help assess the risk of HPV-related cervical cancer developing. There is no such thing as zero risk when it comes to cancer, but screening tests can help to significantly reduce the risk at a population level, and somewhat reduce the risk at an individual level.

The benefits of regular screening

Screening is a choice for everybody and works best when people come for screening at the required intervals. It’s one of the things women can do to reduce the possibility of cervical cancer developing. The change to HPV testing means fewer screening tests and it’s reassuring for women to know their HPV status.

When women with no symptoms of cervical cancer are screened, they have an 80% chance that cancer, if found, will be detected early – at stage 1. By the time women develop symptoms and present to gynaecology clinics, their cancer is usually at stage 2 or higher[1]. In Ireland, around half of all cervical cancers are found in people who have never been screened, or who have been screened less often than the recommended intervals.

Key points to remember

  • The increase in screening intervals is a positive outcome of worldwide research and is welcome progress for women’s health.
  • HPV testing is a better test that, for most participants, results in being invited for screening less frequently - every five years instead of every three years.
  • A negative HPV result is very reassuring. Cell changes caused by HPV that could lead to cervical cancer are very unlikely to develop if there is no HPV infection present.
  • A positive HPV result is not necessarily anything to be worried about; it provides women with an opportunity to be monitored more closely to prevent or reduce the possibility of cervical cancer developing.

Read more: Primary HPV Screening – what you need to know

[1] CervicalCheck Programme Report September 2017-March 2020