A major study provides new evidence for the suspected link between how much fat a woman eats and her risk of developing breast cancer.

The study, involving 56,837 Canadian women in a long-term breast cancer study, found those who had high-fat diets had about a 35 percent higher risk of developing breast cancer than the women with low-fat diets.The findings, however, conflict with results of earlier studies, indicating more research is needed to evaluate the relationship between dietary fat and breast cancer, the researchers said.

"The present analysis has provided some support for the existence of a positive association between fat intake and increased risk of breast cancer," wrote Dr. Geoffrey Howe and his colleagues at the University of Toronto in the Journal of the National Cancer Institute.

A variety of evidence has linked dietary fat to breast cancer, including studies that have shown women who live in countries where diets tend to include a lot of fat have high breast cancer rates.

But at least two major U.S. studies found no such association, and "the contradiction between the present results and the two other . . . studies requires resolution," the Canadian researchers said.

"It is clearly important to establish the true nature of any relationship between fat intake and increased risk of breast cancer," they said.

Breast cancer strikes about 175,000 U.S. women each year, killing an estimated 44,800 - making it the most common form of cancer and second leading cause of cancer death among American women.

The number of breast cancer cases has increased steadily in the United States, and the American Cancer Society estimates the disease will strike one in nine U.S. women sometime in their lifetimes.

Experts are uncertain why the disease seems to be becoming more common. But some evidence suggests the increase could be linked to women living longer, use of birth control pills or fat in the diet.

Scientists are uncertain how fat in the diet could increase the risk for breast cancer but speculate that lowering fat may decrease blood levels of estrogen, a hormone that encourages breast cancer cells to grow.

The U.S. National Cancer Institute has been debating whether to pay for the Women's Health Trial, a $107 million, 15-year study involving 24,000 women. The study is aimed at helping resolve the issue by actually seeing if cutting fat intake by women reduces their chances of developing breast cancer.

Researchers have raised a variety of questions about the proposed study, including whether it is worth the high cost and whether it is practical. In response, officials plan a $7.5 million, three-year feasibility study.