CHICAGO – After five major surgeries for a particularly aggressive form of breast cancer, Patricia Thomas called the little pinprick she received in a government study the simplest procedure she’s undergone.

That pinprick above her knee was an experimental vaccine derived from tiny bits of tumor protein that researchers hope will keep the 70-year-old Arlington, Va., woman’s cancer from returning.

Though only preliminary, early results in Thomas and 13 other vaccinated survivors of advanced breast cancer suggest the researchers might be on the right path.

They have detected signs that the vaccine triggered an immune-system response in all 14 that might potentially fight recurring cancer cells, said co-researcher Dr. George Peoples Jr. of Walter Reed Army Medical Center.

Peoples presented study results Wednesday at an American College of Surgeons meeting in Chicago. He stressed that the experimental vaccine is not a cancer cure, but said it might someday help prevent the disease in high-risk women.

Dr. Clifford Hudis, a breast cancer specialist at Memorial Sloan-Kettering Cancer Center, called the results promising and said they bolster previous evidence from similar breast cancer vaccine research.

While it’s unclear if the results will translate into disease prevention, “it’s a critical first step,” Hudis said.

Vaccine studies are a burgeoning area of cancer research. Unlike traditional vaccines, which generally aim to prevent disease, some experimental cancer vaccines are designed to treat or cure existing disease.

The women studied at Walter Reed all had received conventional treatment for cancer that had spread to the lymph nodes. They had no symptoms when they were vaccinated but likely had lingering cancer cells and face a high risk of relapse.

Peoples said if his study continues to show positive results, within a few years the vaccine might be tried in healthy women at high risk for breast cancer.

“This is a field that deserves a lot of work” and the early findings “suggest they’re on the right track,” said Dr. Harmon Eyre, the American Cancer Society’s chief medical officer.

Eyre said that vaccines have already shown promise in preventing cancers related to infections. The hepatitis B vaccine given to U.S. newborns also prevents hepatitis-related liver cancer, and an experimental vaccine against a virus linked to cervical cancer also has had good results.

The vaccine used in the Walter Reed study was safe and caused no serious side effects. Cancer has recurred in two women, but they had the weakest immune response to the vaccine, Peoples said.

Cancer also has returned in four of 20 women with advanced breast cancer who were not vaccinated. The disease recurred much more quickly in the unvaccinated group, after an average of about five months, compared with about 10 months in the vaccinated women.

In the study, led by Walter Reed’s Dr. Craig Shriver, vaccinated women got shots monthly for six months. The women have been followed an average of about 11/2 years.

Thomas, diagnosed three years ago, said she initially was told she had a less than 50 percent chance of surviving five years. She said she realizes she may not live long enough to benefit from the vaccine, but hopes the study will someday benefit other women, including her two daughters and grandchildren, who because of familial breast cancer face an increased disease risk.

The vaccine targets a growth-stimulating protein called HER2/neu that appears on the surface of normal cells but in overabundant quantities on cancer cells in about 30 percent of women with breast cancer, Peoples said.

Cancer cells often are able to grow and spread because the body doesn’t recognize them as foreign. But the researchers concocted the vaccine from tiny bits of that protein that are the most likely to trigger a disease-fighting immune response.

The vaccine also contains an approved drug that helps boost disease-fighting white blood cell counts.

Dr. Mary Disis, director of the tumor vaccine group at the University of Washington, has had similar results with an HER2 vaccine.

Disis said in some of her patients, the vaccine-triggered immune response has lasted about five or six years. She’s investigating whether that immunity has translated into less disease recurrence.