By Lisa Winter    December 1, 2014 

There are roughly 300,000 new cases of breast cancer each year in the United States, and one in eight American women are predicted to deal with the disease at some point during their lives. Breast cancer is responsible for an estimated 40,000 deaths per year in the US, though that number has had a downward trend over the last few years because of early detection and aggressive treatment. The development of a new vaccine could drive down that mortality rate even further.

A small, phase 1 study using 14 individuals with stable yet metastatic breast cancer has shown that a vaccine is safe. Additionally, there was evidence it was able to prompt the immune system to attack tumor cells and slow down the spread of disease. William Gillanders of the Washington University School of Medicine in St. Louis is senior author on the paper, which was published in the journal Clinical Cancer Research.

The vaccine works by telling immune cells to target a protein called mammaglobin-A, which has been explored as a biomarker for breast cancer for nearly 20 years. The function of this protein is not very clear, but it belongs to a superfamily of proteins that are useful in cell signaling and immune response. Upon receiving the vaccine, the immune system is then supposed to kill cells expressing the protein.

Researchers have determined that 40-80% of breast tumors express it in much higher quantities than is seen in healthy tissue. All 14 patients in the clinical trial expressed high levels of the protein. However, that does leave 20-60% of breast cancer patients who do not express abnormal amounts of the protein. Without the mammaglobin-A target, the vaccine cannot work on these patients.

“Being able to target mammaglobin is exciting because it is expressed broadly in up to 80 percent of breast cancers, but not at meaningful levels in other tissues,” Gillanders said in apress release. “In theory, this means we could treat a large number of breast cancer patients with potentially fewer side effects.”

As this study was primarily focused on the safety of the vaccine, it was encouraging that there were only eight instances of mild to moderate side effects, including flu-like symptoms, tenderness at the injection site, and a rash. 

In addition to the safety of the vaccine, the researchers actually saw early evidence that the vaccine was effective. One year after receiving the vaccine, 7 of the 14 participants did not experience progression of disease. This was statistically significant, as the disease of only one-fifth of the control group had not progressed. Future studies dedicated to the efficacy of the vaccine are needed to explore these results further. The researchers speculate that using this vaccine on patients whose disease is not as advanced could yield even better results.

“If we give the vaccine to patients at the beginning of treatment, the immune systems should not be compromised like in patients with metastatic disease,” Gillanders concluded. “We also will be able to do more informative immune monitoring than we did in this preliminary trial. Now that we have good evidence that the vaccine is safe, we think testing it in newly diagnosed patients will give us a better idea of the effectiveness of the therapy.”