A new study has shown that women who have higher levels of a certain antibody are less likely to develop ovarian cancer.

The findings could point the way to a vaccine to prevent the malignancy, which is too often discovered at an advanced stage, when it is difficult to cure.

Olivera Finn, chairwoman of immunology at the University of Pittsburgh School of Medicine, collaborated with scientists from Brigham and Women's Hospital and Dartmouth Hitchcock Medical Center to do the research.

"Our ultimate goal is to use cancer vaccines to prevent cancer in high-risk individuals," Finn said. But "that means you have to be convinced that by inducing an immune response to cancer, you're actually going to prevent it."

The new findings lay the foundation upon which an ovarian cancer vaccine could be built, she added.

For the study, which was published in this month's issue of the journal Cancer Epidemiology, Biomarkers, and Prevention, more than 700 healthy women and 650 ovarian cancer patients were surveyed and gave blood samples.

The researchers found that women were less likely to develop the cancer if they ever had osteoporosis and bone fracture, had a breast-feeding-related infection called mastitis, or used an intrauterine device, or IUD.

The risk was reduced also with pelvic surgery, such as a Caesarean section or tubal sterilization, oral contraceptive use and avoidance of talc in genital hygiene.

"The more of these events you had, the greater the reduction of risk," Finn said. A woman who had more than four factors had about one-third of the risk, she added.

A look at the blood samples confirmed what the researchers suspected: Women with the protective factors had antibodies to a protein called human mucin, or MUC1.

Antibodies to MUC1 can be produced after a bone fracture, pelvic surgery and the other risk-reduction factors. Ovarian tumors also produce a form of it in large amounts.

The reduced risk of ovarian cancer in some women therefore may be a consequence of an earlier bone fracture or other event that generated the antibodies and, in the process, immunologically primed their bodies to fend off a developing tumor, Finn explained.

So, a vaccine that produces MUC1 antibodies might be able to prevent ovarian cancer. The knowledge that some healthy women already have the antibodies suggests that "every woman at risk could be safely vaccinated," Finn said.

Dr. Roberta Ness, an ovarian cancer expert and chairwoman of epidemiology at the University of Pittsburgh, called the study "provocative," but cautioned that it will take years of additional study to confirm and clarify the findings.

Some of the findings, such as fractures and mastitis being associated with reduced cancer risk, are entirely new.

"People haven't found this previously and they haven't looked at it previously," Ness said. "It's intriguing, but needs to be reproduced."

For Finn and her collaboraters, the next step is to get blood samples from women who are in the process of having an IUD inserted, or getting pelvic surgery to look for changes in MUC1 antibody levels.