Cervical cancer vaccine shows promising results but smear tests still vital

Oct 16 2005

Hopes of an end to routine smear testing have been raised by promising results achieved by a prototype cervical cancer vaccine.

In a study of more than 12,000 women it has been revealed that Merck's vaccine Gardasil has proved 100% effective against two strains of the sexually transmitted human papilloma virus (HPV) which together are 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.

The current cervical screening process, which according to Cancer Research UK 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.

Recent developments suggest that the current screening method could soon become far more reliable and efficient and the scope for human error reduced.

In order to screen a sample an expert needs to look at thousands of cells very quickly.

They are looking for quite subtle changes, while dozens of cells are passing their eye every second, which leaves the process open to considerable human error.

Dr Nick Coleman, of the Medical Research Council's Cancer Cell Unit in Cambridge, warns that although the media reported the vaccine as a potential lifesaver, which it is, women must be aware that the battle is not over, and current screening must continue.

Coleman says that if the vaccine is effective they expect to see more normal samples from women and they will need a very reliable test to identify abnormalities that can be performed by computers.

But new research by Dr Coleman and other scientists into the cell division cycle and proteins known as Minichromosome Maintenance Proteins (MCMs) promises 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 explains that the test for MCM presence is more straightforward as it might just require looking for the presence of the marker's colour, which a computer could do.

As the test is so sensitive they would be sufficiently confident in a negative result to say that the patient can be reassured and does not need any further testing at present.

This new computerised screening technique is already licensed to a company, Tripath Imaging, in America and which has enabled large scale studies to be carried out.

Earlier this month, the company 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.

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.

Professor Stanley says that the vaccine is very impressive but it is as yet unlicensed and even in an ideal scenario with 100% vaccine coverage of schoolgirls by 2010 we wouldn't see the effects until 2030-2040.

Stanley believes that even in an ideal world, only 70% of cervix cancers will be prevented, and screening has to continue for the foreseeable future.

Dr Coleman also says that 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.