Tumor cells often grow and spread because the body doesn't recognize them as foreign. The vaccines aim to re-educate the immune system to recognize cancer cells as alien invaders that need to be attacked and annihilated.
Both studies were presented here at the annual meeting for the American Association for Cancer Research (AACR).
Vaccine Targets HER2/neu
The breast cancer vaccine targets a protein called HER2/neu that is associated with aggressive tumors. In high amounts, the protein speeds up tumor growth and the risk of death.
About 25% of women with breast cancer fall into this category. In the new study, the vaccine reduced their risk of death by 50%.
Importantly, the vaccine worked even better in women who had lower but still elevated levels of HER2/neu, says researcher Linda C. Benavides, MD, of Brooke Army Medical Center in San Diego.
None of the women in this category -- which accounts for about half of breast cancer patients -- died.
If the vaccine pans out in future study, "we'll have an option for the largest subset of breast cancer patients, who really haven't been considered before," Benavides tells WebMD.
She notes that women with high expression of Her2/neu can benefit from targeted therapies, such as Herceptin. But the only options for women with lower expression are conventional chemo, surgery, or radiation, she says.
Breast Cancer Vaccine Cuts Deaths
The study involved 165 women, about one-third of whom had high levels of HER2/neu. The rest had lower or intermediate levels.
All the women had been treated for breast cancer but were disease-free at the time of the study.