Breast Cancer Vaccine Shows Promising Results in Early Trial

Preliminary evidence indicates that new treatment is both safe and effective.

A new breast cancer vaccine developed at Washington University School of Medicine in St. Louis was found to be safe in patients with metastatic breast cancer in an early clinical trial.

The results of the trial also suggest that the vaccine helps to slow progression of the disease. The vaccine primes a type of white blood cell to target and destroy mammaglobin-A, a protein found almost exclusively in breast tissue and expressed at unusually high levels in breast tumors.

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

The vaccine would not be effective in the smaller percentage of breast cancer patients whose tumors do not produce mammaglobin-A, according to the press release.

In the study, which was published in the December 1, 2014 issue of Clinical Cancer Research, 14 patients with metastatic breast cancer who expressed mammaglobin-A were vaccinated in order to assess the vaccine’s safety. The authors reported that while patients experienced several mild or moderate side effects, including rash, tenderness at the vaccination site, and mild flu-like symptoms, there were no occurrences of severe or life-threatening side effects.

While this trial was primarily meant to test the vaccine’s safety, preliminary evidence indicated that the treatment slowed the cancer’s progression. Of the 14 patients who were vaccinated, about half showed no cancer progression a year after receiving the vaccine; comparatively, of the 12 patients in the control group who were not vaccinated, only one-fifth showed no cancer progression after a year.

The research team found these results to be particularly significant given that many of the patients had a weakened immune system due to their advanced disease and exposure to chemotherapy.

"Despite the weakened immune systems in these patients, we did observe a biologic response to the vaccine while analyzing immune cells in their blood samples," said Dr. Gillanders, a breast cancer surgeon at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University. "That's very encouraging. We also saw preliminary evidence of improved outcome, with modestly longer progression-free survival."

Dr. Gillanders and his colleagues now hope to follow up on their findings in a larger clinical trial, in which they plan to administer the vaccine to newly diagnosed breast cancer patients who are more likely to have stronger immune systems.

"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," Dr. Gillanders said. "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."