Assessing the long term impact of HPV screening on cervical cancer detection

The Swedish study - a long-term follow-up of a national randomised controlled trial, entitled Swedescreen - found that the protection of HPV-based screening after five years was about the same as for cytology (or cell)-based screening after three years. "This indicates that five-year screening intervals could be used with HPV-based screening, instead of the current three-year intervals," says Miriam Elfström from the institute's Department of Medical Epidemiology and Biostatistics, and the first author of the study.

HPV is a virus capable of infecting humans, typically through sexual contact. Most HPV infections cause no physical symptoms, though in a few cases, HPV can lead to certain cancers, such as cervical cancer. In fact, HPV infection appears to be a necessary factor - in over 90 per cent of cases in fact - in the development of cervical cancer.

Nonetheless, cervical screening programmes have often relied solely on cytology to identify women at risk from developing cervical cancer. While HPV testing has a higher sensitivity for cervical intraepithelial neoplasia (CIN) - the potentially pre-malignant transformation of certain cells on the surface of the cervix - it has, until now, been unclear whether HPV-based screening leads to over-diagnosis of lesions that will not progress to cancer.

So after 13 years, the Karolinska Institutet wanted to assess the impact of HPV testing. Swedescreen, which began in 1997, enrolled more than 12 000 women aged between 32 and 38 from across all of Sweden. The women were randomised to either double testing with both HPV testing and cytology, or only received a cytology test.

The researchers also investigated the duration of the protective effect of the two screening methods, by comparing the incidence of pre-cancerous lesions in women who had negative test results in the screening over time.

The study was supported by the EU-funded PREHDICT project, which received nearly EUR 3 million in funding and was completed in April 2013. It has also received support from COHEAHR, another EU-funded project that got underway in November 2013 and is due for completion in 2018. COHEAHR aims to enable policy makers to make informed decisions on HPV prevention strategies.

The Karolinska Institutet study of the Swedescreen trial was published in the British Medical Journal (BMJ).