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Last Updated: Friday, 14 October 2005, 23:18 GMT 00:18 UK
Advance could boost smear tests
By Zoe Smeaton

Smear cells
There is scope for human error in the current test
The highly promising results achieved by a prototype cervical cancer vaccine have raised hopes of an end to routine smear testing.

The results of a study of more than 12,000 women revealed that Merck's vaccine Gardasil had proved 100% effective against two strains of the sexually transmitted human papilloma virus (HPV) which are together responsible for around 70% of cervical cancer cases.

But experts are now warning women not to become complacent about cervical smear tests, which they say will remain vital for some time.

And recent developments suggest that the screening method itself could soon become far more reliable and efficient than the current service.

Women must be aware that the battle is not over
Dr Nick Coleman

Dr Nick Coleman, of the Medical Research Council's Cancer Cell Unit in Cambridge, said: "Although the media reported on the vaccine as a potential lifesaver, which it is, women must be aware that the battle is not over.

"Quite the opposite in fact, and screening must continue, although that screening may become very different in the future.

"If the vaccine is effective we will probably see more normal samples from women coming in so we will need a very reliable test to identify abnormalities, and one that can be performed by computers."

Human error

Currently, the cervical screening process, which Cancer Research UK reported last year is saving around 4, 500 women's lives each year, relies upon experts identifying changes in cervical cells which could indicate a risk of cancer developing later.

The vaccine is very impressive but even in an ideal scenario with 100% vaccine coverage of schoolgirls by 2010 we wouldn't see the effects until 2030-2040
Professor Margaret Stanley

Dr Coleman said: "To screen a sample an expert needs to look at thousands of cells very quickly.

"They are looking for quite subtle changes, yet dozens of cells are whizzing past their eye every second."

This leaves the process open to considerable human error.

But research by Dr Coleman and other scientists into the cell division cycle and proteins known as Minichromosome Maintenance Proteins (MCMs) has led to optimism that a more efficient screening test may soon be made available.

MCMs are needed for the DNA in a cell to replicate, and their presence in cells has been shown to indicate that the cells are in a state known as the cell cycle, meaning they will soon divide to form two new ones.

As any cancerous tumour contains many rapidly dividing cells, there will also be an abnormally high number of cells containing MCM proteins here, and these can be detected using specific proteins that will bind to them, and will also bind to a second protein that is labelled in some way - for instance with a fluorescent tag - to allow easy visualisation.

Dr Coleman explained that the test for MCM presence is more straightforward as it might, for instance, just require looking for the presence of the marker's colour.

Sensitive test

He said: "A computer could even perform this test, and it is so sensitive that we would be sufficiently confident in a negative result to say that the patient can be reassured and does not need any further testing now.

"The computerised screening technique is already licensed to a company, Tripath Imaging, in America and this is enabling large scale studies, which are continuing to go well."

Earlier this month, TriPath Imaging announced that preliminary results from two retrospective research studies in which cervical cell specimens were tested with the company's own marker used to detect indicators of cell cycle progression, had been very positive.

And Professor Margaret Stanley, of Cambridge University, an expert in HPV and cervical cancer, agrees that screening using this technique will be extremely valuable in the future, especially given the limitations of the vaccine.

She said: "The vaccine is very impressive but it is not licensed yet and even in an ideal scenario with 100% vaccine coverage of schoolgirls by 2010 we wouldn't see the effects until 2030-2040.

"And even then, again in an ideal world, only 70% of cervix cancers will be prevented.

"Screening therefore has to continue for the foreseeable future, although the frequency of cervical sampling and the detection methods will be different to the current practice.

"The MCM's are an excellent mass screening method because they detect dividing cells, and one can then apply other molecular methods (to test the samples further if necessary)."

Dr Coleman added: "It is important to realise the limitations of the vaccination.

"It only offers protection against two strains of the HPV virus and it is possible that if the vaccine does eradicate these then other strains may evolve sufficiently to take their place.

"Perhaps we would need to keep continuously adding to the vaccine, so we are certainly going to have to continue to screen now and in the future."




SEE ALSO
Cervical cancer jab 'in a year'
07 Oct 05 |  Health

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