According to a report presented at the annual meeting for the American Association for Cancer Research in San Diego this week, a vaccine has been discovered which may reduce deaths in women with an aggressive type of breast cancer by boosting their immune systems.

The vaccine targets a protein called HER2/neu that is associated with aggressive tumors and works best in women who have lower but still elevated levels of the protein. This group of women accounts for about half of all breast cancer patients.

The vaccine also proved to help reduce deaths in women with higher levels of the protein, who account for about 25 percent of women with breast cancer.

The study involved 165 women, who had been treated for breast cancer but were disease free at the time of the study. A little more than half of the women received the vaccine.

Immunity was boosted in all the women who received the vaccine but those with low or intermediate levels of HER2/neu had a stronger immune response than those with high levels.

Among the low or intermediate level group, only about 10 percent of those vaccinated suffered a recurrence compared with 20 percent who didn’t get the vaccine. None of these vaccinated women died versus 38 percent who were not vaccinated.

Among the group with high levels of the protein, cancer recurred in the same number of women regardless if they had the vaccine or not. But among those with a recurrence of the disease, those with the vaccine were 50 percent less likely to die.

The researchers say more studies are needed and caution that it remains unclear whether women with lower levels of HER2/neu naturally have a better prognosis than women with higher levels or if the vaccine made the difference.