An experimental vaccine for breast cancer has completely eliminated tumours during trials on mice, researchers say.

The vaccine targets breast cancer caused by an excess of a protein called HER2 — and even destroyed tumours resistant to current drugs.

So-called HER2-positive cancers account for up to 30 per cent of all cases of breast cancer and tend to be highly aggressive.

The US team said it might also be used to prevent initial development of the tumours in cancer-free women.

But British experts warned the vaccine was at a very early stage, and it was not known if it would work in humans.

The study, by Wayne State University in Detroit, Michigan, is published in the journal Cancer Research.

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

The protein, known as 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 promotes normal cell growth.

But HER2-positive breast cells can contain many more receptors than is typical, promoting a particularly aggressive type of tumour.

There are drugs to treat this form of the disease, including Herceptin, but they do not work for a significant proportion of patients.

The new vaccine contains genes that produce the HER2 receptor, and a compound which stimulates the immune system.

The researchers used electrical pulses to deliver the injected vaccine into leg muscles in mice.

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