Written by Mr Angus McIndoe for Doctify
This week (24-30 January) is cervical cancer prevention week, find out more about getting involved at Jo Trust.org.uk. Even though cervical cancer is the most common cancer in women under 35 screening rates are at a 20-year low. We asked Mr Angus McIndoe, consultant gynaecologist at Nuada Group to tell us more about cervical screening and the infection that is associated with it, human papillomavirus (HPV).
What is cervical screening?
Cervical screening refers to testing the general female population with a smear test to detect precancerous abnormalities in the skin of the cervix. If left untreated, these abnormalities can lead to a cancer of the cervix. Smear tests are performed from age 20 or 25 depending upon which country you live in, at intervals of between one and three years. Screening is usually offered up to the age of 65.
What is HPV?
HPV refers to human papillomavirus. There are over 100 different types of HPV. These viruses are remarkably specific as to which skin they will grow on, so the virus that causes veruccas on the foot will not infect the hand. Similarly, the hand wart virus is different from the virus that causes genital warts. HPV are divided between high-risk types and low risk types depending upon whether they are associated with cancers, as many HPV types do not cause cancer.
Is HPV a sexually transmitted disease?
My patients are often very concerned about HPV being a sexually transmitted disease. Because HPV infection of the cervix causes no symptoms it is very difficult to trace where the virus came from and how long it has been present. A woman need have only one sexual partner to get an HPV infection. It is very common in our society and across the world.
Does HPV cause cancer anywhere else?
Because the HPV types that cause cancer of the cervix are relatively fussy about where they will grow, they are found in limited places on the body. However, HPV is associated with cancer of the vagina, vulva and anus. In addition, cancer of the throat and other head and neck cancers appear to be associated with HPV.
Will HPV vaccinations make smears unnecessary in the future?
Current UK vaccines cover only HPV type 16 and 18. These two types are found in about two thirds of cervical cancers but about two thirds have other high risk HPV types. The reason this doesn’t add up is that many cervical cancers have more than one HPV infection, so roughly one third of cancers will have HPV 16 or 18 and another high risk HPV. It looks like vaccination prevents roughly half of the cases of cervical cancer although more research is underway on this topic. Smear tests are therefore still necessary as the risk is still present, although perhaps reduced by 50%.
I’ve heard about the HPV urine test. Would you recommend this?
HPV urine testing has been tried in some pilot studies to see how it performs as an initial screening test. It has the great advantage over traditional screening that it is non invasive. In those pilot studies it picked up about three quarters of women who had high risk HPV infections but missed one quarter. Further research is needed but it is likely that the woman who test positive would need to go on and have a standard smear. It should not be seen as an alternative to current screening but rather a way to screen women who would otherwise not attend.
Why doesn’t the NHS recommend annual smears like in other countries?
The NHS currently recommends smears every 3 years because, using mathematical modelling, this has been shown to be a cost effective strategy. In theory screening every 3 years picks up about 88% of cancers, whereas screening every year would detect 94%, so the advantage is small. However, we know that smears are not very sensitive so the difference might actually be larger than this calculation. The main issue is that for most women, precancerous abnormalities persist for a number of years before they become cervical cancer so there is a relatively long window to detect the changes before they become a cancer.
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