A vaccine that targets the sugar coating on tumours shows early promise as a powerful new weapon against deadly cancers.

The vaccine trains the immune system to recognise altered sugary proteins found on the surface of many cancer cells.

In mouse tests it dramatically shrank tumours mimicking 90% of human breast and pancreatic cancer cases, including those resistant to standard therapies.

"The vaccine elicits a very strong immune response," said leading researcher Professor Geert-Jan Boons, from the University of Georgia.

"It activates all three components of the immune system to reduce tumour size by an average of 80%."

When cells become cancerous, carbohydrate sugars on their surface proteins undergo distinct changes. The new vaccine targets short sugar molecules on a protein called MUC1 which is abundant on cancer cells.

"This is the first time that a vaccine has been developed that trains the immune system to distinguish and kill cancer cells based on their different sugar structures on proteins such as MUC1," said co-author Professor Sandra Gendler, from the Mayo Clinic in Arizona.

"We are especially excited about the fact that MUC1 was recently recognised by the (US) National Cancer Institute as one of the three most important tumour proteins for vaccine development."

MUC1 is found on more than 70% of lethal cancers. Many types of cancer, including breast, pancreatic, ovarian and multiple myeloma, produce MUC1 with shortened sugar molecules in 90% of cases, according to the scientists.