Three-year cervical screening is effective when HPV test and conventional examination are used together
Women who receive normal cervical screening results can safely attend screening just once every three years if both the human papillomavirus (HPV) test and conventional cytology test are used, a large new study has confirmed.
Currently in the US, women tend to go for cervical screening annually. In the UK, younger women are invited every three years, and older women every five years.
Traditional cytology tests examine cervical cells under a microscope to look for signs of abnormalities, whereas the newer HPV test detects the DNA of certain cancer-causing strains of the virus, and previous studies have suggested it may detect more problems.
Scientists at the National Cancer Institute in the US followed 331,818 women, aged 30 and older, who enrolled in a co-testing programme at Kaiser Permanente in Northern California between 2003 and 2005.
Participants were followed for five years to see whether they developed cervical cancer.
The researchers found that just 3.2 per 100,000 women per year developed cancer after receiving both a normal cytology test and a negative HPV result. Of women who had a normal cytology test alone, 7.5 per 100,000 per year developed cancer.
As well as confirming the safety of three-year screening intervals for most women, the study also revealed that HPV testing alone may be more accurate than the cytology test alone when determining a woman's risk of cervical cancer. Women who tested negative for HPV were around half as likely to subsequently develop cervical cancer as those who had a conventional test.
Furthermore, the risk of developing cervical cancer following HPV testing alone was similar to that following co-testing.
This suggests that an HPV test on its own may be as effective as a combination of HPV testing and cytology testing, although the researchers emphasised that further studies are needed to verify this.
Lead author Dr Hormuzd Katki, principal investigator in the National Cancer Institute's Division of Cancer Epidemiology and Genetics, said: "Our results are a formal confirmation that the three-year follow-up is appropriate and safe for women who have a negative HPV test and normal Pap result.
"These results also suggest that an HPV-negative test result alone could be enough to give a high level of security for extending the testing interval to every three years, but we'll need additional evidence from routine clinical practice, and formal recommendations from guideline panels, before that can be routinely recommended."
The researchers also noted that the study highlighted the benefits of conventional cytology testing for determining whether a woman with a positive HPV result should have further screening.
According to Dr Katki, women who tested positive for HPV and had an abnormal cytology test were more likely to have or develop cervical cancer or pre-cancerous cells than those who tested positive for HPV but had a normal cytology result.
Professor Peter Sasieni, cervical screening expert at Cancer Research UK, said: "Women can be reassured that the quality of the NHS cervical screening programmes is extremely high and prevents hundreds of women from developing cancer each year.
"But this very large study confirms that HPV testing is even better than the traditional cytology test at identifying women at risk of developing cervical cancer. The results add weight to the argument that cervical screening programmes could prevent more cancer by switching to HPV testing," he added.