Wednesday January 15 2014
Cervical screening can detect abnormal cells on the cervix
"Women aged 50 and older are being warned of the dangers of skipping smear tests," BBC News reports, as a UK study into the impact of cervical cancer screening found that our current screening practices seem to work.
In England women are invited to have cervical cancer screening every three years between the ages of 25 and 49 (when rates of the cancer are at its peak), and every five years between the age of 50 and turning 65.
This research investigated whether it was useful to continue to screen for cervical cancer after the age of 50, and whether 64 was an appropriate age to stop screening. The short answer to both questions was yes.
A total of 1,341 women aged 65 to 83 were diagnosed with invasive cervical cancer over a five-year period in England and Wales. The screening history of these women was compared with those of 2,646 women of the same age without cervical cancer.
Women who did not attend screening tests as recommended were six times more likely to develop cervical cancer at these ages compared with women who did.
The research also indicated screening is appropriate up until the age of 64, but may be of limited benefit beyond 69.
However, given increasing life expectancy, screening in older women might be justified in the future. There is evidence that rates of cervical cancer can experience a smaller peak in women aged between 80 and 84.
NHS cervical screening for women aged 50 to 64 is free to attend.
Where did the story come from?
The study was carried out by researchers from Barts and The London School of Medicine and Dentistry and was funded by Cancer Research UK.
It was published in the peer-reviewed medical journal PLOS Medicine. The study was published as an open access document, meaning anyone can view the publication in full free online.
The media generally reported the story accurately, including expert commentary to inform women that screening usually picks up abnormal cells at an early stage when they can be removed to prevent the onset of cancer.
However, the reporting was skewed towards discussing the greater risks associated with not taking up cervical screening for women over 55, rather than whether 65 was an appropriate age to stop offering screening.
The second question was actually the primary aim of the study, as offering screening to a population that actually had no or very little risk of a specific disease would waste both people's time and NHS resources.
What kind of research was this?
This was a case-control study of women in the UK who developed cervical cancer over the age of 65 to see how effective cervical screening is in this older age group. It aimed to see if it is reasonable to stop routine cervical cancer screening at the age of 65.
A case-control study compares the characteristics of all the cases of a disease in a population with the characteristics of matched individuals without the disease.
What did the research involve?
Researchers looked at the GP records of women who were diagnosed with cervical cancer after the age of 65 and women of the same age who were not.
The cases were women registered with an NHS GP and diagnosed with cervical cancer in England between April 1 2007 and March 31 2012, and in Wales from January 1 2007 to December 31 2009.
Two women of the same age and place of residence were randomly selected using a computer programme to act as controls. The researchers chose one woman from the same GP practice and one woman from a different GP practice in case the uptake of screening was dependent on the GP.
Local NHS staff obtained the screening history data from NHS cervical screening records and made the data anonymous before sending it to the researchers.
The researchers excluded women aged 60 years or over on January 1 1988, as they may not have been invited to the NHS cervical screening programme.
They used appropriate statistical methods to determine the risk of developing cervical cancer at 65 years or older with each type of screening method result between the ages of 50 and 64.
The researchers performed additional "sensitivity" analysis to try to account for unknown factors that might have had an impact on the results, such as smoking or the number of sexual partners. Both of these are known risk factors for cervical cancer.
What were the basic results?
A total of 1,341 women aged between 65 and 83 were diagnosed with invasive cervical cancer in England and Wales. Similar numbers of women (range 404 to 435 women) were diagnosed in each five-year age bracket from 65 to 79, but relatively few (just 97 women) were aged 80 to 83.
The screening history of these women was compared with that of 2,646 women of the same age without cervical cancer.
The main findings were:
- women with adequate negative screening at age 50 to 64 had one-sixth of the risk of cervical cancer aged 65 to 83 compared with women who were not screened
- rates would have been 2.4 times higher if there was no screening programme for this age group
- screening at least every 5.5 years between the ages of 50 and 64 was associated with a 75% lower risk of cervical cancer
- the effect of screening reduces with age between the ages of 65 and 79 – the risk in well-screened women was half that of unscreened women by the age of 80
How did the researchers interpret the results?
The researchers concluded that, "Screening up to the age of 65 greatly reduces the risk of cervical cancer in the following decade, but the protection weakens with time and is substantially less 15 years after the last screen.
"In the light of increasing life expectancy, it would seem inappropriate for countries that currently stop screening between the ages of 60 and 69 to consider reducing the age at which screening ceases. To the contrary, consideration should be given to cost effective ways of increasing the age of the last screening."
This well-designed study presents valuable data on the benefits of cervical cancer screening in older age groups.
The researchers point out that their study was limited in that they did not have information on important risk factors for cervical cancer, such as smoking.
They attempted to account for this and other unknown confounders through additional sensitivity analysis. However, this may not have been adequate to account for all of the other risk factors not measured, and so introduces a degree of uncertainty to the results.
The researchers also suggest that the changing nature of cervical screening may have influenced the results. One such change is the introduction of tests for high-risk types of human papilloma virus (HPV). These are believed to cause most cervical cancers, as well as other risk factors such as smoking and low immunity.
These tests were not available for the women in this study and the researchers report that no long-term (15 to 20-year) studies have looked at the risk of cervical cancer after a negative HPV test. This may have a bearing on screening requirements for older women in the future.
The future effects of the recently introduced HPV vaccine may also need to be taken into account in the years to come, although the current vaccine does not protect against all strains of HPV.
For now, though, the results of this study should encourage women between the ages of 50 and 64 to take up the opportunity for cervical cancer screening that the NHS provides.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.