(ChemotherapyAdvisor) – Patients with breast cancer who were disease-free following standard of care therapy and subsequently received the AE37 vaccine had a higher rate of disease-free survival (DFS) at follow-up vs controls, early analyses of a phase 2 study presented during the 2012 Breast Cancer Symposium have found.

Although clinical benefit is observed “particularly in patients with low HER2-expressing tumors,” the benefit “appears to persist” in those with triple negative breast cancer (TNBC), noted Elizabeth A. Mittendorf, MD, of The University of Texas MD Anderson Cancer Center, Houston, TX, and colleagues.

The ongoing trial is enrolling patients with node positive or high-risk node negative breast cancer with any degree of HER2 expression (IHC 1+, 2+ or 3+ or FISH > 1.2) and randomly assigning them to either AE37, a hybrid peptide vaccine created by adding the Ii-Key moiety (LRMK) to the HER2 helper epitope, AE36 (HER2 aa776-790) plus GM-CSF or GM-CSF alone. Each patient receives “6 monthly intradermal inoculations followed by booster inoculations administered every 6 months,” Dr. Mittendorf reported.

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A total of 254 patients have been enrolled, 105 in the vaccine group and 149 in the control group. At a median follow-up of 22.3 months, DFS in the vaccine group was 90.3% vs 81.1% in the control group (P=0.46), a 49% risk reduction, she reported.

Among those with low HER2 (IHC 1+ or 2+) expression, the DFS rate was 89.8% in the vaccine group (n=53) compared with 68.2% in the control arm (n=77; P=0.12), a 68% risk reduction. Patients with TNBC (ER/PR negative, HER2 1+ or 2+) had a DFS rate of 83.3% in the vaccine group (n=13) vs 47.6% in the control group (n=23; P=0.23), also a 68% risk reduction. In the TNBC control group, patients had a larger percentage of tumors >2cm (70% vs 31%; P=0.02); otherwise, the TNBC and low HER2 expression vaccine and control groups were well matched, including those with high grade tumors, rate of node positivity, and ER/PR status.

Per protocol, the patients will be followed for 5 years. “However, these data suggest that a subsequent phase 3 trial should evaluate the vaccine in patients with low HER2-expressing disease to include TNBC,” she concluded.