HPV testing is an effective screening tool for cervical cancer
HPV testing is a more accurate method of predicting cervical cancer than cervical cytology, a large multinational cohort study has shown. After six years' follow-up the rate of cervical cancer was significantly lower in women negative for HPV than in women with negative cytology results.
Pooled data on 24,295 women from seven screening programmes in six European countries, including the UK, were analysed. All had a cytological smear and an HPV test at baseline.
Over six years 381 developed histologically confirmed cervical cancer (CIN3+). Women positive for both tests had a high rate of progression (34%) whereas those negative at baseline for both tests had a very low rate of progression (0.28%).
The rate of progression in smear-positive/HPV-negative women was 2.7%. In smear-negative/HPV-positive women the incidence increased continuously over time reaching 10% at six years.
The researchers looked at how reliable a negative result was at baseline. The progression rates to CIN3+ from a negative smear or a negative HPV result were 0.97% and 0.27% respectively over six years.
Over three years of follow-up (the most commonly recommended interval between smears in most European countries) the progression rates to CIN3+ were 0.51% for those with negative cytology alone and 0.12% for those with negative HPV status alone.
Cervical screening programmes do not want to miss abnormalities (false negatives) nor alarm too many women with no abnormalities (false positives). This study found that around 1:400 HPV-negative women developed CIN3+ over six years' follow-up compared with around 1:100 cytology-negative women. There was little difference in cervical cancer rates between women with negative results on both tests and women negative for HPV.
Identifying women at risk of developing cervical cancer using cytology has for many years been remarkably successful. More recently demonstrating the causative role of certain oncogenic wart viruses has enabled testing for HPV to improve sensitivity even further. Indeed HPV screening is known to be more sensitive in identifying high-grade CIN than cytology.
But could HPV screening replace cytology? And is it powerful enough to reduce the frequency of screening? The authors suggest that these findings make a good case for using HPV testing as the prime screening tool in programmes to prevent cervical cancer and that a six-year interval would be safe.
Dillner J, Rebolj M, Birembaut P et al. Long term predictive values of cytology and human papillomavirus testing in cervical cancer screening: joint European cohort study. BMJ 2008; 337: a1754Reviewer
Dr Chris Barclay