HPV screening is better than cytology-based screening for prevention of cervical cancer
Human papilloma virus (HPV) infection is one of the most common sexually transmitted diseases. Although more than half of sexually active men and women may contract genital HPV at some time in their lifetime, most infections are harmless and short lived. However, women who have a persistent HPV infection of the cervix (the lowest part of the uterus or womb) have an increased risk of precancerous changes called cervical intraepithelial neoplasia (CIN) that can develop into cervical cancer.
Screening to prevent cervical cancer is currently offered to women every three to five years depending on their age. Since 2008 the NHS Cervical Screening Programme has been based on cells being brushed from the cervix into a liquid preservative (rather than a ‘Pap’ smear on a slide) and examined in the laboratory under a microscope (cervical cytology). Any cell abnormalities of CIN are graded from borderline and low grade to high grade. A large proportion are found to be borderline or low grade. It has been shown that if these cells test negative for HPV they are benign and the women can be returned to routine recall for screening. Women with abnormal cells positive for HPV are offered examination of the cervix for further testing and, if necessary, treatment. If that examination is satisfactory, they are also returned to routine recall for screening.
An alternative testing strategy that has been explored is to screen the cells taken into liquid preservative for HPV and then to carry out cytology-based screening if the virus is found. This approach has been shown to lead to the detection of a larger number of treatable pre-cancerous lesions. However, since most higher grade CIN lesions do not become invasive or lead to death, further evidence is needed regarding the long term outcome of these different laboratory approaches to screening.
An international HPV screening working group reported online in The Lancet on 3 November 2013 the results of a follow-up study of the 176,464 women who had taken part in four randomised trials of the two screening methods in Sweden, the Netherlands, England and Italy. One hundred and seven women with invasive cervical carcinomas were identified by examination of screening, pathology and cancer registries and by review of pathology specimens and reports.
At three and a half years after screening, the number of women who had developed cancer following a negative HPV-based test was one third the number who had developed cancer after a negative cytology-based test; at six and a half years the number with cancer after negative HPV testing was one quarter the number after negative cytology. The working group concluded that HPV-based screening provided 60-70% greater protection against the development of invasive cancer of the cervix than cytology-based screening. The total incidence of invasive cancer five and a half years after a negative HPV test was lower than that three to five years after a negative cytology test, so the retesting interval could be extended safely to five years for all ages. Six NHS screening laboratories are starting pilot studies of HPV primary screening this year.