Preventing cervical cancer: how a screening switch and HPV vaccination should cut cancer rates

While cervical cancer rates have fallen in the UK since the mid-90s, stats from the last decade show a slight increase in the incidence of the disease. And this has coincided with a shift in the age at which women are diagnosed.

“The peak age for developing cervical cancer is now 25-29, which is a big change from before,” says Professor Peter Sasieni, a cancer prevention expert at King’s College London.

Back in the 70s, cervical cancer incidence peaked in women aged 50-64. And according to Sasieni, several factors could explain how this has changed. One is the success of the cervical screening programme in preventing cervical cancer in older women. Another is an increase in an underlying cause of cervical cancer, infection with the human papillomavirus (HPV).

“Sexual behaviour has changed a lot over the years. A lot of women aged 25-29 will not have had the HPV vaccine, so increasing rates of infection would increase the number of cervical cancer cases,” says Sasieni.

But 10 years after the HPV vaccination programme started, and with a change in the way samples are tested after cervical screening being introduced this year, how will cervical cancer rates change in the future?

The screening switch

“We’re expecting to see a fall in cervical cancer rates over the next 10 years or so as a result of the roll out of HPV primary screening,” says Sasieni.

Highly-anticipated changes to the UK’s cervical screening programme, called HPV primary testing, will switch the order in which samples are tested.

Right now, samples taken during screening are sent to be analysed under a microscope, to look for abnormal cell changes that could lead to cancer.

With the changes to the programme, samples will first be tested for the presence of the human papillomavirus (HPV), which is responsible for almost all cases of cervical cancer. If the test is positive, the sample will then be analysed by specialists under the microscope to look for cell changes.

This approach to screening has been shown to be much more effective at preventing cancer.

“We think the switch could result in about 500 fewer cancers a year in England, which means it would prevent around a fifth of cervical cancers that we have at the moment,” says Sasieni.

But although the programme has already been rolled out in Wales and will be introduced in England at the end of 2019 and Scotland in 2020, the effects of HPV primary screening on cervical cancer rates won’t be seen for a few years.

“There’s a few reasons why we’ll see a delay in the effects of the HPV primary test,” says Sasieni. “The first is that most people won’t have HPV primary screening in 2019. Screening runs in 3-year cycles, so it will take a few years before everyone has had the new test.”

Testing for HPV first is a better way of identifying people who are at higher risk of developing cervical cancer. But the impact this has on cervical cancer rates won’t be immediate.

“With HPV primary testing we’ll be able to detect and remove more pre-cancers, so you’ll find much fewer screening-detected cancers 3 years later,” says Sasieni.

“That’s what we saw in trials of the test, there’s virtually no difference between the two screening methods for the first 2 to 3 years, and then there’s a substantial difference beyond that.”

Seeing the effects of HPV vaccination

Changing the screening programme won’t be the only thing that contributes to falling cervical cancer rates. We’ll also start to see the effects of the HPV vaccination programme in the years to come.

The HPV vaccine offered by the NHS protects against 4 types of HPV infection. Two are linked to cancer: HPV 16 and 18, which together cause around 7 in 10 cervical cancer cases. The vaccine also protects against HPV 6 and 11, which cause most genital warts. A different vaccine was offered for the first 3 years, which only protected against HPV 16 and 18.

An HPV vaccine has been available to girls aged 11-13 in the UK since 2008 as well as some older girls as part of a catch-up programme. And it has led to a dramatic reduction in HPV infection in this age group. Figures released last year by Public Health England suggest there’s been an almost 90% reduction HPV 16 and 18 infections in young women following vaccination.

According to Sasieni, all evidence suggests that this will have a dramatic effect on cervical cancer rates in vaccinated women. And this will start to become apparent as the first group of women who were vaccinated reach screening age.

“Most cervical cancers in women aged 25-29 are picked up through screening. But in women who were vaccinated against HPV, we should see far fewer cancers developing. And that will mean that rates will fall dramatically as this vaccinated group of women reach screening age,” he says.

Sasieni’s team has predicted that cervical cancer rates in women aged between 25 and 29 will decrease by 55% thanks to the HPV vaccine. But that’s only if current vaccination rates are maintained and if women attend regular screening.

But while the HPV vaccine is expected to have a big impact on cervical cancer rates in young women, it won’t help women who were too old to be vaccinated when the programme was introduced.

“Unfortunately, there’s very little point in vaccinating women who are already in their mid-20s or older, because the vaccine only works by preventing the HPV infection and most women are already infected by this point. It’s too late,” says Sasieni.

According to Sasieni, screening is important for these women.

Screening saves lives

“We think we’re preventing at least 7 in 10 cervical cancers in older women through screening,” says Sasieni.

But while cervical screening is hugely effective, screening attendance is falling. And this points to a potentially worrying trend on the horizon.

“I think partly because of the success of vaccinations and the screening programme there’s a danger that women may stop going to screening because they think it’s not important. If that were to happen we would eventually see a substantial increase in cervical cancer in older women,” says Sasieni.

Other reasons why people may choose not to go for cervical screening are that some women don’t know screening is for people without symptoms. And there are also other practical or cultural reasons why they might find it difficult to make or attend an appointment.

This is particularly worrying, he says, because when cervical cancer is diagnosed in older women it tends to be picked up at a later stage, when it’s more difficult to treat.

“Screening is extremely effective at preventing cervical cancer”, says Sasieni, “but only if women keep going.”

Katie