An experimental vaccine has shown promising results against an aggressive form of breast cancer, according to the results of a recent clinical trial.

The new neoantigen DNA vaccine developed for preventing the recurrence of tumors in triple-negative breast cancer was found to be "well-tolerated" and effective in stimulating the immune system, according to a small trial conducted at Washington University School of Medicine in St. Louis.

Triple-negative breast cancer is called so because cancer cells test negative for hormones estrogen or progesterone receptors (ER or PR) and the protein called HER2. It is an aggressive form of cancer that grows faster and accounts for about 10-15% of all breast cancers. They are more common in women younger than age 40, who are Black, or who have a BRCA1 mutation.

Currently, there are no targeted therapies for triple-negative breast cancer, and hence treatment involves traditional approaches that include surgery, chemotherapy, and radiation therapy. The researchers believe the new vaccine has the potential to become a targeted treatment strategy to prevent tumor recurrence in triple-negative breast cancer.

In the phase I trial, researchers evaluated the safety of the experimental vaccine in 18 patients with triple-negative breast cancer that had not spread to other organs and found that half of the patients remained cancer-free three years after the treatment.

Since this was an early-stage trial, the focus was on evaluating the vaccine's safety, and no control group was included to assess efficacy. However, the researchers used historical data from triple-negative breast cancer patients treated with standard care to understand the efficacy. The results were published in Genome Medicine.

"These results were better than we expected. Obviously, it's not a perfect comparison, and we acknowledge the limitations of this type of analysis, but we are continuing to pursue this vaccine strategy and have ongoing randomized controlled trials that do make a direct comparison between the standard of care plus a vaccine, versus standard of care alone. We are encouraged by what we're seeing with these patients so far," said senior author Dr. William E. Gillanders in a news release.

"We are excited about the promise of these neoantigen vaccines. We are hopeful that we will be able to bring more and more of this type of vaccine technology to our patients and help improve treatment outcomes in patients with aggressive cancers," Dr. Gillanders added.

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