American scientists say they have developed a vaccine which has prevented breast cancer from developing in mice.
The researchers - whose findings are published in the journal, Nature - are now planning to conduct trials of the drug in humans.
But they warn that it could be some years before the vaccine is widely available.
The immunologist who led the research says the vaccine targets a protein found in most breast tumours.
Vincent Tuohy said: "We believe that this vaccine will someday be used to prevent breast cancer in adult women in the same way that vaccines have prevented many childhood diseases.
Unique challenge
"If it works in humans the way it works in mice, this will be monumental. We could eliminate breast cancer."
In the study, genetically cancer-prone mice were vaccinated - half with a vaccine containing á-lactalbumin and half with a vaccine that did not contain the antigen.
None of the mice vaccinated with á-lactalbumin developed breast cancer, while all of the other mice did.
The US has approved two cancer-prevention vaccines, one against cervical cancer and one against liver cancer.
However, these vaccines target viruses - the human papillomavirus (HPV) and the Hepatitis B virus (HBV) - not cancer formation itself.
In terms of developing a preventive vaccine, cancer presents problems not posed by viruses - while viruses are recognised as foreign invaders by the immune system, cancer is not.
Cancer is an over-development of the body's own cells. Trying to vaccinate against this cell over-growth would effectively be vaccinating against the recipient's own body, destroying healthy tissue.
