A TEST for the sexually transmitted virus that causes cervical cancer should replace the smear test as the basis of mass screening programmes, say researchers who have just done a trial involving 11,000 women.
Many countries around the world offer women a smear test every few years, in which cells scraped off the cervix are examined for signs of cancer. Such screening has reduced deaths from cervical cancer, cutting deaths by 40 per cent in the UK, for example. But a team led by Peter Sasieni of Cancer Research UK thinks a new screening method based on a test for the human papilloma virus (HPV) would save even more lives. The samples would still be taken in the same way.
Virtually all cervical tumours start when HPV triggers mutations by interfering with cell division. Vaccines against HPV are being developed but none is yet available.
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While the strain of HPV responsible for cervical cancer infects many women, only a tiny proportion of those infected ever develop tumours. The idea of using an HPV test as the primary means of screening is simply to identify all those at risk. Only women who test positive for the virus would go on to have a smear test, Sasieni proposes. If this was positive, they would undergo further tests. If the smear test was negative, they would have another in a year. Women who test negative for HPV would not have another HPV test for five years.
The advantage of the HPV test is that it gives a yes or no answer, whereas smear tests rely on the judgement of technicians looking at cervical cells (pictured above) under a microscope. Even though Sasieni鈥檚 proposed screening regime would still ultimately rely on the smear test, he says that by focusing on those at most risk and ensuring they have more frequent tests, it should improve the detection rate.
But the latest trial did not test this approach to screening directly. Instead, all the women were given both the HPV and the smear test. Around 9 per cent carried HPV, but very few had signs of pre-cancerous cells. Of the 90 women eventually confirmed to have precancerous cells by further tests, 97 per cent would have been picked up by the HPV test compared with just 76 per cent with the smear test, says the team.
In countries with private health care services, women are likely to be offered both tests. The US approved HPV testing for this purpose earlier this year. For cash-strapped state services, doing both would be too expensive. Until trials have been carried out using the exact screening method envisaged by Sasieni, health services are likely to stick with the smear test. 鈥淲e鈥檝e got a very successful screening programme. We鈥檙e not going to abandon that for something relatively new without more evidence,鈥� says a spokesperson for the UK鈥檚 National Health Service.
鈥淢ajor medical shifts require very, very strong evidence,鈥� agrees Mark Schiffman of the National Cancer Institute in Washington DC. The countries most likely to adopt HPV screening quickly, he says, are those that currently have a poor smear test screening programme, or none at all.