The cervical screening programme in Wales introduced a change on New Year’s Day 2022. I don’t think it was thought to be controversial, but it has proven so.
As we reported at the time, Wales introduced HPV testing in place of cytology in September 2018. For years researchers had been calling for a change from 3-yearly cytology to 5-yearly HPV testing. Several studies have shown that the risk of pre-cancerous lesions (pre-cancer) within 6 years of a negative HPV test is similar to the risk of pre-cancer within 3 years of a negative cytology test. This is partly because HPV testing is better than cytology at detecting pre-cancers and partly because HPV is detectable longer before the development of cervical cancer than are abnormal cells. The proposal was a win-win – it would prevent more cervical cancers, and it would save the NHS money. But, in 2018, Wales only switched to HPV testing; they did not lengthen the screening interval. Now, just over three years later they have changed the screening interval too. Louise Dunk, the head of Cervical Screening Wales, said: “It is a really positive development that this more effective test will mean that women and people with a cervix, who test negative for HPV, now only need to attend their testing every five years, rather than three.”
Unfortunately, not everyone agreed! On Thursday afternoon (6 January 2022) the BBC website reported that 526,000 people had signed a petition calling for a rethink. As of Friday morning (08:00 on 7 January), the petition had attracted over 850,000 signatures.
The problem is that whereas testing for HPV once every 5 years will prevent more cancers than testing with cytology once every 3 years (i.e. using a new test at a longer interval), switching from 3-yearly HPV testing to 5-yearly HPV testing (i.e. using the same test at a longer interval) will result in slightly more screened women developing cervical cancer. Had both changes been made at once, there would probably have been little public outcry. But since Wales switched to HPV testing three years ago, people see this new change and worry that it has been done to save money because, compared to the screening offered over the last three years, it will result in more women suffering from cervical cancer.
The question we need to ask is whether it is ever justified to do less screening if that will mean more people get (or die of) cancer?
To understand why many screening and public health experts (including this author, the UK National Screening Committee, the American Cancer Society, and the US Preventive Services Task Force) support a 5-year screening interval after a negative HPV test we need to consider: the difference between public health and clinical medicine; the fact that all interventions have harms as well as benefits; and the reality that the NHS’s budget is finite so if we spend more on screening, we will spend less on other health services.
Public health versus clinical medicine
In clinical medicine a patient presents to their doctor with a health problem. The interaction is initiated by the patient seeking help. And, very often, it is clear that the patient is sick and needs treatment. In medical screening things are very different. In the UK, it is not the participant who seeks-out the doctor, but the health service that identifies and invites the individual to be screened. People being screened are not aware that they may have a health problem. They are invited to come for screening because we may be able to detect disease before it starts causing problems. Ideally screening will find disease early enough so that it can be more easily treated and so more serious illness can be prevented.
It might never seem appropriate to refuse an effective treatment to someone who is sick. But there is a question as to how far one should go to prevent deaths in the general population. We design safer roads and safer cars and require people to wear seatbelts. But we do not impose a 20mph speed limit on all roads or encourage people to wear crash helmets when travelling in cars.
Doing cervical screening (or breast screening or bowel screening) every month would probably prevent more cancer deaths than screening once every two, three or five years. But does it really make sense to have monthly screening?
The harms of cervical screening
What are the harms of cervical screening? They are, for the most part, minor. But they do affect a lot of people (over 3 million people are tested within the cervical screening programme in England each year). Most women find cervical screening uncomfortable, and some find it painful. Many people get a little bit anxious whilst awaiting their screening test result and most who have a positive test are anxious until they get to see a doctor and have further tests. A small proportion of screened women will be treated for “pre-cancer”. For some that treatment may be very painful. It can lead to severe bleeding, and it may increase the chances of a premature birth should the patient subsequently become pregnant. These treatment side-effects are a small price to pay to prevent cancer, but not everyone who is treated for “pre-cancer” would develop cancer if they weren’t treated. The more frequently we screen, the more treatments will be carried out.
The cost of screening
It is quite complicated to calculate the complete cost of screening. The HPV test alone is about £20. If you wanted to go privately for cervical screening it would cost you about £200 a time. So, the cost to the NHS of doing a million extra screening tests is probably about £50million.
The NHS could do a lot with that extra £50million. It could for instance be used to try to ensure that more of the 12 million women aged 25-49 in the UK are screened at least once every 10 years. If that proportion could be increased from 80% to 90%, far more cancers could be prevented than by providing 3-yearly rather than 5-yearly screening after a negative HPV test.
What are the benefits of screening with different tests at different intervals?
In 2017, we published a paper modelling the effect of different hypothetical screening programmes. We estimated that the old cervical screening programme (offering cytology every 3 years from 25 to 49 and every 5 years from aged 50-64) prevented some 5787 cervical cancers each year in the UK. We also estimated that using that same test but screening half as often (every 6 or 10 years depending on age) would save about 5427 cervical cancers. The more frequent screening prevents about 360 additional cancers. By changing to HPV testing, we estimated that screening every 3 or 5 years (depending on age) would prevent about 6408 cancers, whereas HPV testing with 6- and 10-year intervals would prevent about 6237 cancers each year. Thus, compared with cytology every 3 (and then 5) years, HPV testing every 6 (and then 10 years) would prevent an additional 450 cancers each year, whereas compared with HPV testing every 3 (and then 5) years it would allow an additional 171 cancers.
The UK’s National Screening Committee has recommended HPV testing every 5 years from age 25 to 64. We did not model that explicitly, but others have. They anticipated that 3-yearly rather than 5-yearly HPV testing from age 25 to 49 would result in 151 fewer cancers and 19 fewer deaths each year in the UK. Three-yearly screening requires just over 1 million additional screens each year across the UK. Thus, it takes about 55,000 additional screens to prevent one additional cervical cancer death. Even if those women died on average 45 years prematurely, each additional screen would, on average, result in an additional 7 hours of life.
For comparison, if instead of doing an extra million tests a year in relatively well screened women, we did an extra 120,000 tests a year in under-screened individuals to ensure that 90% of the eligible population are screened at least once every 10 years between 25 and 49, we could prevent an additional 705 cervical cancers each year.
Weighing up the benefits and harms
The UK National Screening Committee recommended a screening interval of 5 years after a negative HPV test based on “an annual reduction in health-related costs and an uncertain impact on quality adjusted life years”. According to my calculations, they presumably felt that an additional one million screens and possibly an additional 100,000 positive screening tests, 40,000 referrals to a gynaecologist and 10,000 additional women treated for “pre-cancer” was not justified to prevent 150 cervical cancers and 20 deaths from cervical cancer. While this may seem like discriminating against females by not prioritising their health, the committee considered the best scientific evidence, and the decision was an attempt to balance the substantial benefit additional cervical screening offers to a tiny proportion of women against the rather more common but less severe side-effects of screening.
I can understand why over 850,000 have signed a petition to keep cervical screening every 3 years, but I also completely understand why the UK National Screening Committee made its recommendation. From a public health perspective, I would still recommend reinviting women 5 years (and not 3 years) after a negative HPV test and concentrating resources on encouraging and enabling those eligible who have not been screened at all over the last 6 years to get screened.
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