Researchers at Brooke Army Medical Center reported yesterday at the 2008 annual meeting of the American Association for Cancer Research that clinical trials are indicating their HER2 peptide E75 vaccine is a success in reducing the risk of recurrence and cutting the mortality rate by half when cancer does recur.

The vaccine is most effective in low-expressing HER2-positive breast tumors in reducing the number of recurrences.  There were no deaths at all associated with the cancer recurrence in the study group of women with this type of cancer who were vaccinated.

Linda C. Benavides, MD, general surgery resident at Brooke Army Medical Center in San Antonio, Texas, says the vaccine may offer the hope of adjuvant therapy options for HER2 low-expressors, the most common form of breast cancer.  Adjuvant therapy enhances the effect of the original treatment for cancer, which can include any one or combination of surgery, chemotherapy, or radiation.  One common form of adjuvant therapy is with the drug trastuzumab, which is not indicated for low-expressing forms of breast cancer.

About 25% to 30% of all patients with early stage breast cancer have an over-expressed HER2.  More than half of all cases of breast cancer are of the HER2 low-expressing type and not candidates for trastuzumab adjuvant treatment.

The most recent trial for the E75 vaccine involved 163 patients with breast cancer, 92 of whom were vaccinated.  Of patients vaccinated, 34% (or 29 individuals) were determined to be HER2 over-expressors and the remaining 66% (56 individuals) were low expressors.

The unvaccinated control group of 71 patients included 33% (22 individuals) over-expressors and 67% (44 individuals) low-expressors.  All HER2 over-expressing study participants shared the same prognostic outlook and treatment options.  The only statistical difference was the high rate of hormone receptor-negative tumors in the over-expressors in both the control and vaccinated groups.

After vaccination, study participants experienced similar immunologic responses in general but the low-expressors were observed to have a greater number of CD8+ T cells that were E75 specific than the over-expressors had.

During follow-up studies approximately 30 months after vaccination the control group and the vaccinated HER2 over-expressors had similar rates of recurrence, 18.2% and 13.8%, respectively, although the mortality rate in the vaccinated group was reduced by more than half.

Study participants who were vaccinated low-expressors had only a 10.7% rate of recurrence and there were no deaths (0%) among the low-expressors.  Mortality in the control group was 38%.

A phase III trial is expected.

Source: American Association for Cancer Research