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The immune system is the body's defense against infection and other health threats. Vaccines work by stimulating the immune system to build defenses against a specific threat. The vaccines we know best build defenses against bacterial or viral infections. The idea of using a vaccine to try to prevent or treat breast cancer makes sense. Still, results from earlier studies on experimental vaccines targeting breast cancer haven�t shown consistent benefits. A new study has found that an experimental vaccine targeting HER2-positive breast cancer cells lowered the risk of the cancer coming back (recurrence) in women diagnosed with HER2-positive, early-stage breast cancer. About one out of every four breast cancers is HER2-positive. HER2-positive breast cancers tend to be more aggressive than HER2-negative breast cancers. The experimental AE37 vaccine has two active parts: a piece of the HER2 protein (the AE37 peptide); this protein tells the immune system to target HER2-positive cancer cells the GM-CSF (granulocyte-monocyte colony stimulating factor) protein; GM-CSF bolsters specialized immune system cells (T cells) to specifically recognize and destroy HER2-postive breast cancer cells An earlier study found that women given the AE37 vaccine developed an immune response to the HER2 protein. That study also showed the vaccine to be safe and well-tolerated. 201 women diagnosed with early-stage, HER2-positive breast cancer participated in this latest study on AE37. They were believed to be cancer-free after surgery and other treatments. Half the women got the AE37 vaccine every 6 months, starting after other treatments were finished; the other half didn�t get the vaccine. Half the women were followed for at least 22 months; the others for shorter periods of time. The researchers analyzed how many women had the cancer come back and determined that the risk of recurrence 2 years after treatment was 43% lower in the women who got the vaccine compared women who didn�t get the vaccine: 10.3% of women who got the vaccine would have a recurrence 18.0% of women who didn�t get the vaccine would have a recurrence While these results look very promising, this is an early study and it will probably be some time before a breast cancer vaccine is generally available. Still, there is hope that one day doctors will use vaccines to effectively and safely help prevent and treat cancer, including breast cancer.