Dietary fat predicts breast cancer's course.

Many women who undergo surgery to remove a malignant breast tumor live in fear that cancer will return. Now, a study by a team of Swedish investigators suggests that a low-fat diet may help women avoid a recurrence of this disease, which will kill more than 46,000 women in the United States this year.

Epidemiologists have long pondered whether a low-fat diet can prevent breast cancer from appearing in the first place. Rather than focus on the cause of breast cancer, however, epidemiologist Lars-Erik Holm, then at the Karolinska Hospital in Stockholm, and his colleagues wondered if fat intake could change the course of the disease.

Holm, now at the National Institute of Public Health in Stockholm, and his co-workers studied 220 women who had surgery to remove a malignant breast tumor. At the time of surgery doctors analyzed a snippet of each patient's tumor to learn whether it had protein receptors that bind with the sex hormone estrogen. After their surgery, women in the study received adjuvant therapy such as radiation, chemotherapy, or hormonal treatment with the drug tamoxifen. Such adjuvant therapy helps reduce the risk of cancer recurrence in the breast and in other parts of the body

Next, the researchers sent a nutritionist to each woman's home. The nutritionist asked about diet and food preparation habits (such as the use of cooking oil) during the year prior to the patient's diagnosis.

The team then monitored the subjects for at least four years and noted all reappearances of cancer. A statistical analysis revealed that fat intake did influence the outcome of breast cancer treatment, but only in women who had tumors with lots of estrogen receptors.

In the Jan. 6 Journal of the National Cancer Institute, the team reports that women with estrogen-rich tumors who had eaten fatty foods before surgery (and presumably afterward) were more likely to suffer a return of the disease than women with estrogen-rich tumors who had a less fatty diet.

The team then homed in on saturated fat, the type found in foods of animal origin, such as butter. Women in the group who ate the most saturated fat ran a 20 percent higher risk of recurring cancer than those whose diets contained the least saturated fat.

The mechanism underlying fat's link to breast cancer recurrence remains a mystery, Holm says. However, high-fat diets may boost concentrations of estrogen in the blood. Estrogen fuels the growth of breast tumors, especially those that contain many estrogen receptors. Indeed, the researchers could find no association between fat intake and the risk of cancer recurrence in women whose tumors had very few or no estrogen receptors.

The study doesn't resolve the controversy regarding fat's role in the development of cancer, comments Norman F. Boyd of the Ontario Cancer Institute in Toronto. Last year, a U.S. team found no link between fat intake and the appearance of breast cancer (SN: 10/24/92, p.276). However, Boyd and others still believe that dietary fat may help cause breast cancer.

At the same time, the new findings provide convincing evidence that dietary fat affects the growth of an existing breast tumor, adds Boyd, who wrote an editorial in the same issue of the journal. The Swedish team hopes that a low-fat diet may prove beneficial, even for women who switch to less fatty foods after surgery

A low-fat diet, as well as adjuvant therapies, may increase the odds that women can avoid a second bout with cancer, Holm says. A low-fat diet causes no ill side effects and can help prevent cardiovascular disease, diabetes, and other debilitating health conditions, he adds.