An experimental vaccine to spur the immune system to fight breast cancer seemed to reduce the risk of death in a significant number of women, according to a clinical trial monitored by the U.S. military.

The U.S. military said late Sunday that the vaccine, which is designed to treat a type of breast cancer that develops the HER2 protein, reduced mortality by 50 percent and lowered mortality by 100 percent in women with a different type of breast cancer or low levels of HER2.

The vaccine was licensed to the biotech company Aphtera Inc. and its named NeuVax, said Dr. Linda Benavides, the author of the research study. Although the introduction of the drug to the market is not certain, the drug is being prepared for a last phase of clinical trials.

Researchers said that one fourth of the patients with breast cancer have gene mutation that develops HER2 protein and this type tends to be deadlier than other forms of the disease. So far the majority of the patients had been treated with Herceptin, an antibody-based drug manufactured by Genentech Inc.

The next period of trials for NeuVax plans to involve from 700 to 1,000 patients, concentrating on women who aren't eligible for Herceptin, Benavides said.

In 2007, Genentech's treatment for breast cancer Herceptin triggered $1.29 billion in U.S. sales and it is the third biggest product in the company after Avastin and Rituxan, Bloomberg noted.

Shares of Genentech were 1.29 percent down o 0.98 cents to $75.81 on Monday morning.