Cervical-cancer screening tests are about to changeby Nicky Pellegrino
Cervical-cancer screening tests have been helping to save lives for more than 25 years. Now the focus of the tests is going to change.
So, if the current system wasn’t broken, why fix it?
“What we’re doing is implementing best practice,” says Jane O’Hallahan, clinical director of the National Screening Unit. “The world is moving to a different primary test, because it’s HPV that causes pre-cancer and eventually the cancer.”
HPV is actually a group of viruses, usually spread through sexual contact, and there’s a lot of it about. Just because a woman tests positive for HPV doesn’t mean she’ll develop cervical cancer. In about 95% of cases, the body’s immune system fights off the virus, and even when it does cause cellular changes, these often don’t progress to invasive cancer. But it’s impossible to predict who the unlucky ones will be, and although incidence and mortality have halved since screening was introduced in 1990, about 60 New Zealand women still die from the disease each year.
One of the benefits of the new HPV test is that it’s going to be possible to self-screen, which should make it much easier to target those women who are avoiding the pap test, particularly those in the Maori, Pasifika and Asian communities.
“From our focus groups, we’ve found there are lots of reasons for women not engaging,” says O’Hallahan. “One of them is fear of the examination, perhaps because they’ve had bad experiences in the past.”
The other news for anyone who dreads the three-yearly test is that since abnormalities take a long time to develop, and this new system of screening detects the precursor to cell change, the interval between tests will be extended to five years.
Not everyone is convinced this is a wise idea. Cancer expert Associate Professor Brian Cox of the University of Otago has expressed concerns that we’ll miss more invasive cancers as a result. He believes we should hold off until we see how things work out in Australia, which is about to introduce five-yearly HPV testing.
“We’ve got a great opportunity to stay with what we’ve got and see if Australia has it right,” says Cox. “That would be the most prudent approach from a public-health perspective.”
Under the new system, if a woman tests positive for high-risk subtypes of HPV – 16 and 18 – her sample will be retested for signs of abnormal cells and at the same time she’ll be referred for colposcopy, in which a specialist takes a closer look at the cervix and potentially performs a biopsy. Meanwhile, those shown to be carrying other forms of HPV will be monitored annually.
Cox fears colposcopy services will struggle to cope with increased demand – O’Hallahan maintains there may be a temporary blip, but we’ll manage – and he points to a study in Finland, comparing both methods of screening, which found that the HPV test causes more overdiagnosis.
Other studies have given primary HPV testing a more favourable report, in particular Australia’s ongoing Compass trial, which found it was significantly better at detecting high-grade precancerous cervical lesions in women who had been vaccinated for the HPV virus.
And that’s the other key thing – even women who have been immunised need to show up for their five-yearly HPV tests. The earlier version of the Gardasil vaccine, funded for girls from 2008, protected against only four types of the virus – the two main cancer-causing ones and two responsible for genital warts. A new version has now extended this to an additional five types, but still doesn’t offer 100% protection.
Nevertheless, screening for the generation of women most likely to have been immunised will begin later – at age 25 rather than the current 20. This is because there’s evidence that screening any younger causes more harm than good, leading to overdiagnosis and unnecessary colposcopy, but not actually reducing cervical cancer rates.
The HPV test is due to be rolled out in November next year, and O’Hallahan is confident it’s set to make a successful screening system even better.
“This is really good news,” she says. “It’s a better test and you can have more confidence in it.”
This article was first published in the November 4, 2017 issue of the New Zealand Listener.
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