A VACCINE that could deal a serious blow to seven in 10 lethal cancers has been developed by scientists.

In tests, it shrank breast tumours by 80 percent and researchers believe it could also tackle prostate, pancreatic, bowel and ovarian cancers.

Even tumours that resist treatment with the best medicines on the market, including the "wonder drug" Herceptin, may be susceptible to the vaccine.

The experiments so far have been on mice - but researchers hope to pilot the drug on people within two years. If all goes well, the vaccine could be on the market by 2020.

Rather than attacking cancer cells, like many drugs, the new treatment harnesses the power of the immune system to fight tumours.

The search for vaccines has been hampered by fears that healthy tissue would be destroyed along with tumours.

Researchers from the University of Georgia and the Mayo Clinic in the US focused on a protein called MUC1 that is made in bigger amounts in cancerous cells than in healthy ones.

Not only is there more of it, but a sugar that it is "decorated" with has a distinctive shape.

The vaccine trains the immune system to recognise the rogue sugar and turn its arsenal against the cancer.

"Cancer cells have a special way of thwarting the immune system by putting sugars on the surface of tumour cells so they can travel around the body without being detected," researcher Professor Sandra Gendler said.

"To enable the immune system to recognise the sugar it took a special vaccine that had three parts to it."

She said it was this that "turned out to be a winning combination".