A new DNA breast cancer vaccine is safe in humans and holds promise for the treatment of early-stage disease, according to the results of a phase 1 study.1

The vaccine is directed against MGBA, a gene that encodes mammaglobin-A (MAM-A), a breast cancer–associated antigen with high tissue specificity.

In the study, 14 patients with stable metastatic breast cancer who had been off chemotherapy for at least 30 days received the vaccine. No serious adverse events were observed, although four patients developed a mild flu-like syndrome. Only one grade 2 event, a shingles outbreak, occurred. There were no grade 3 or 4 adverse events.

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Flow cytometry and ELISPOT analysis demonstrated significant increases in the number of immune cells targeting MAM-A after administration of the vaccine.

Although the study was not designed to evaluate clinical benefit, vaccination was associated with significantly improved 6-month progression-free survival compared with controls (53% vs. 33%; P=0.011).

William Gillanders, MD, of the Washington University School of Medicine in St. Louis, MO, who led the research team, spoke recently with Cancer Therapy Advisor and answered questions regarding the study.

CTA: What is the most important takeaway from this research?

Dr. Gillanders: We’re really excited about these results because we learned that targeting MAM-A is a safe and very promising therapy for breast cancer. Vaccines directed against other antigens are being developed, but this is the first study to look at a vaccine directed against MAM-A. This is a highly attractive target, because MAM-A is overexpressed in breast cancer, but not in other tissues.

CTA: What proportion of breast cancer patients might benefit from treatment with this vaccine?

Dr. Gillanders: Early studies indicated that up to 80% of breast cancer tumors express MAM-A, but more recent work suggests that it’s more like 60 to 70%. Luminal breast cancer tumors are more likely to overexpress MAM-A than other subtypes.

CTA: What is the next step in this research?

Dr. Gillanders: There is a growing realization that vaccine therapy will be most effective in earlier stages of cancer, and these are the patients we’ll be recruiting in our next trial. This trial has a unique design because we will administer the vaccine before surgery, therefore we will be able to evaluate the immune response in tumor tissue samples taken during surgery. This study will enroll patients who have luminal breast cancer, who often undergo 4 months of treatment with endocrine therapy before surgery. The vaccine will be administered during this period, so the study won’t entail any delay in their treatment.