Novel Immunotherapy Vaccine Decreases Recurrence in HER2 Positive Breast Cancer Patients

A new breast cancer vaccine candidate, (GP2), provides further evidence of the potential of immunotherapy in preventing disease recurrence. This is especially the case for high-risk patients when it is combined with a powerful immunotherapy drug. These findings are being presented by The University of Texas MD Anderson Cancer Center at the 2014 American Society of Clinical Oncology’s Breast Cancer Symposium in San Francisco.

One of only a few vaccines of its kind in development, GP2 has been shown to be safe and effective for breast cancer patients, reducing recurrence rates by 57%. Further, women with the highest overexpression of HER2 (known as HER2 +3) had no cancer recurrences when they were administered the vaccine after completing trastuzumab (Herceptin), a type of immunotherapy drug known as a monoclonal antibody. HER2 is an oncoprotein that promotes tumor growth and is expressed to some extent in 75-80% of breast cancers.

“This is an important and different avenue in immunotherapy research, in that we are investigating ways to prevent cancer recurrence by stimulating the immune system to treat cancer,” says principal investigator Elizabeth Mittendorf, M.D., Ph.D., associate professor of Surgical Oncology. “The ultimate goal is to develop a preventative tool that will minimize the risk of recurrence in women who have already had breast cancer and for whom standard therapies have failed.”

The findings are the result of a phase II randomized trial that paired the GP2 vaccine, designed to stimulate the CD8+ cells, commonly known as “killer” or “toxic” T cells, with an immune stimulant known as granulocyte/macrophage colony stimulating factor (GM-CSF). The trial included 190 patients with varying levels of HER2; 89 women received the GP2 vaccine with a GM-CSF adjuvant and a control group of 91 patients received GM-CSF alone. Eight patients experienced early recurrence or developed a second malignancy and did not complete the vaccine trial. The vaccine is injected subcutaneously and the initial series consisted of monthly inoculations for six months, followed by four cycles of booster shots administered every six months thereafter. The patients were monitored for nearly three years.

For all 190 patients, including those who did not complete the trial, the disease-free survival (DFS) rate was 88% among those who received the vaccine and 81% in the control group - representing a 37% reduction in recurrence. Excluding the patients who did not complete the vaccine series, the results are higher - 94% DFS rate versus 85% who did not get GP2 - a 57% risk reduction.

HER2-positive breast cancer: What is it? HER2-positive breast cancer is a breast cancer that tests positive for a protein called human epidermal growth factor receptor 2 (HER2), which promotes the growth of cancer cells. In about 1 of every 5 breast cancers, the cancer cells make an excess of HER2 due to a gene mutation. This gene mutation and the elevated levels of HER2 that it causes can occur in many types of cancer — not only breast cancer. This is a gene mutation that occurs only in the cancer cells and is not a type of mutation that you can inherit from a parent.