Breast Cancer: A Puzzling Plague

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Study after study has explored the possibilities. Could it be the birth control pill? Probably not, since dozens of investigations into that question have produced a quagmire of contradictions. How about smoking? Again, there is no clear connection. Alcohol? Drinking seems to raise the risk of the disease slightly, but the association is too weak to account for America's prodigious rate. What about the widespread use of estrogen therapy following menopause? Studies show only a mildly elevated risk. And while food additives and even lack of sunlight have come under suspicion, there is little evidence to convict them.

THE FAT FACTOR

Instead, many researchers around the world are pointing to another component of the Western way of life: a diet rich in fat. Researchers have known for more than 40 years that high-fat diets promote the growth of mammary tumors in laboratory animals. They have also observed that the varying rates of breast cancer in various countries correlate neatly with the amount of fat in a nation's diet. The U.S., Britain and the Netherlands, which have some of the world's richest diets, also have among the highest breast-cancer rates. Meanwhile, in countries such as Japan, Singapore and Romania, where the diet is very lean, the incidence of breast cancer is one-sixth to one-half the U.S. rate.

On the theory that genetic factors might be responsible for such national variations, researchers have looked at immigrant groups. They have found that when Japanese move to the U.S., or Italians to Australia, their previously low breast-cancer mortality rate rises to match the higher rate of their adopted country within a generation or two, as diet and life-style change. "The results are too consistent to believe that the association is indirect," says Maureen Henderson, an epidemiologist at the Fred Hutchinson Cancer Research Center in Seattle. When it comes to the breast cancer-fat connection, she says flatly, "I'm sure of it."

Japanese researchers are also convinced. Breast cancer is one of the fastest-growing diseases among Japanese women, with the incidence up 58% between 1975 and 1985. "The largest factor behind the sharp rise is the Westernization of eating habits," says Dr. Akira Eboshida, chief deputy director of the Health and Welfare Ministry's Disease Control Division. "We are eating more animal fat and less fiber." Cancer of the breast is not the only ailment rising with the larding of the Japanese diet. Heart disease is also surging, as is cancer of the colon, ovaries and prostate. All have been linked to a high-fat diet. On the other hand, stomach cancer, historically the ! most common cancer in Japan, is falling as the nation moves away from its traditional diet of salty, pickled and smoked foods. "If the current trend continues," predicts Eboshida, "breast cancer will replace stomach cancer as the No. 1 killer of Japanese women in the next century."

Despite such evidence, not everyone shares the conviction that fat is the villain. Critics of this theory point out that statistical correlations are not the same as proving cause and effect. Many researchers argue that there are probably several life-style factors rather than a single culprit. "The high rates are not due to one bad habit, but to our whole way of life," says Mary-Claire King, a cancer geneticist at the University of California, Berkeley.