Hopes of a vaccine for cancer received a boost this week following trials of a new therapy that successfully blocked tumor growth in animals. The experimental vaccine protected animals from cancer for up to five months, and stopped tumors growing bigger in those that already had the disease.

In a trial, researchers transplanted breast tumors into mice before giving them two injections of the vaccine, two weeks apart. The first injection primed the immune system and the second acted as a booster. The trial showed the vaccine triggered a release of antibodies that suppressed tumor growth for up to 150 days. The mice showed no side effects.

In a second trial, genetically engineered mice bred to develop breast cancer within 28 days were given a modified version of the DNA vaccine that also blocked a gene linked to cancer.  "Normally all these mice develop cancer within a month, but in the trial 80 per cent remained cancer-free and lived for up to one and a half years," said Holmgren, whose study was published in the Proceedings of the National Academy of Sciences on Monday.

The researchers believe the vaccine was successful because it works differently from previous DNA vaccines. Instead of targeting cancerous cells that are constantly mutating, the vaccine acts on healthy cells that the tumor recruits to build up its blood supply.  The researchers have teamed up with a Swedish company to manufacture antibodies that could be used in a human cancer vaccine. If the vaccine is effective in human trials, it could potentially help give protection against a range of cancer varieties.  A cancer vaccine could be used to prevent cancers returning in patients who have already been operated on, or received chemotherapy or radiotherapy.