AN EXPERIMENTAL breast cancer vaccine has the potential to wipe out resistant and recurring tumours in many women, say researchers.

The treatment would be tailored to women with HER2-positive cancers, which account for up to 30% of all cases and tend to be highly aggressive.

In mice, HER2-positive tumours were completely eliminated by the vaccine with no evidence of toxicity.

Even cancers resistant to drugs that specifically target this type of tumour, such as Herceptin, were eradicated.

The treatment seems so safe that scientists have suggested giving it to cancer-free women as a preventative measure.

Women who test HER2 positive are genetically programmed to have breast tumours that are unusually sensitive to a natural growth-stimulating protein.

Human epidermal growth factor helps breast cancer cells to multiply. It does this by binding on to HER2, a "receptor" molecule on the surface of the cells, which activates a signalling pathway triggering growth.

HER2-positive tumours have larger numbers of these receptors than normal, and are highly affected by the growth factor.

Herceptin, which is available to HER2 positive patients on the NHS, blocks the receptors so the growth factor cannot attach to them. However, many patients develop resistance to anti-HER2 drugs.

Vaccines against HER2 offer an alternative approach.

Today scientists reported early results from a vaccine consisting of genes encoding the HER2 protein together with an immune system stimulant.

When the vaccine was injected into the leg muscles of mice the gene produced huge numbers of HER2 receptors. This alerted the animals' immune systems, causing them to target HER2 with antibodies and "killer" T-cells - destructive white blood cells that act as the body's stormtroopers.

Study leader Professor Wei-Zen Wei, from the Karmanos Cancer Institute in Detroit, US, said: "While HER2 receptors are not usually seen by the immune system when they are expressed at low level on the surface of normal cells, a sudden flood of receptors alerts the body to an invasion that needs to be eliminated.

"During that process, the immune system learns to attack cancer cells that display large numbers of these receptors.

"The immune response against HER2 positive receptors we saw in this study is powerful, and works even in tumours that are resistant to current therapies. The vaccine could potentially eliminate the need to even use these therapies."

Part of the vaccine consisted of an agent that temporarily removed a "brake" from the immune system, allowing it to respond much more strongly.

When HER positive breast tumours were implanted in the vaccinated mice, they were wiped out by the animals' primed immune systems.

Dr Sarah Rawlings, from the charity Breakthrough Breast Cancer, said: "This is very early research that has only been carried out in mice so we don't actually know if it could be used in women.

"Much more research is needed to find out if it works, to either treat HER2-positive breast cancer or prevent the disease, and if there are any side effects."

The findings are published in the journal Cancer Research.