Cleveland Clinic has released early findings from the first phase of a clinical trial for a preventive breast cancer vaccine, showing promising immune responses in participants.

The vaccine is designed to prevent triple-negative breast cancer, considered the most aggressive and deadly form of the disease. According to researchers, approximately 74% of participants developed an immune response following vaccination.

“About three quarters of these patients developed an immune response,” said Thomas Budd, the lead researcher for the trial. “We have identified a dose, and we know it produces an immune response. Whether that response translates into reducing recurrence or preventing breast cancer is something we don’t yet know from this phase.”

Dr. Budd said 35 participants were enrolled in the first phase of the study. All either had triple-negative breast cancer or were considered at high risk for developing it.

Researchers also found the vaccine was well tolerated. Reported side effects were mild and primarily limited to skin inflammation at the injection site.

The trial will now move into phase two, which will focus on determining whether the vaccine reduces the risk of cancer recurrence and, potentially, whether it can prevent breast cancer in high-risk patients.

Phase two of the trial is expected to begin late next year and is projected to last between two and three years.