A cancer vaccine has shown promising results in a small study with women with advanced breast or ovarian cancer, at times improving overall survival time and stopping the disease in some breast cancer patients, according to research published Tuesday.

Scientists at the National Cancer Institute enrolled 26 patients with breast or ovarian cancer that had spread to other organs and assigned them to monthly vaccinations with the PANVAC vaccine. These patients were already heavily pretreated, with 21 of them receiving at least three prior chemotherapy regimens.

The PANVAC vaccine contains transgenes for MUC-1, CEA and three T cell costimulatory molecules. It coaxes the body to attack tumor cells.

Among the 12 patients with breast cancer, median time to progression was 2.5 months and median overall survival was 13.7 months. Four patients had stable disease.

For the 14 patients with ovarian cancer, median time to progression was two months and median overall survival was 15 months.

Side effects were generally mild, mostly reactions at the injection site.

"With this vaccine, we can clearly generate immune responses that lead to clinical responses in some patients," said lead researcher James Gulley, M.D., Ph.D., director and deputy chief of the clinical trials group at the Laboratory of Tumor Immunology and Biology at the National Cancer Institute.

According to Gulley, interest in cancer vaccines is increasing and more study is needed to determine which vaccines will benefit which patients. "The sustained benefit seen in some patients in this study underscores the potential for therapeutic vaccines to impact clinical outcomes without toxicity," he said. "However, more studies in the appropriate patient populations are required to adequately assess efficacy."