Soy’s Effect on Breast Cancer Remains Uncertain

NEW YORK—“The number one question that I used to get as a clinician taking care of people with breast cancer and people worried about breast cancer was about hormone replacement therapy. Now, by far, the number one question is about soybeans,” said Larry Norton, MD, chief of Breast Medicine and head of the Division of Solid Tumor Oncology, Memorial Sloan-Kettering Cancer Center.

He spoke at a press conference convened by the Breast Cancer Research Foundation to announce a new effort to study nutrition effects on breast cancer. The foundation was established by Evelyn H. Lauder who serves as its president.

Interest in soy as potentially beneficial in preventing breast cancer springs from the observation that the Japanese, who consume a lot of it, have low rates of the disease, explained Walter C. Willett, MD, DPH, chairman, Department of Nutrition, Harvard University School of Public Health.

Soy, he added, does have estrogenic effects and is biologically active. “There’s a lot of argument about whether it is a proestrogen or an antiestrogen,” he said, “and it’s all relative to a woman’s estrogen status and the levels of other circulating estrogens. It’s an extremely complex area. I think the bottom line is that, at this time, we don’t really know what soy does.”

Dr. Willett outlined several reasons for being skeptical that high soy intake will have a major impact on breast cancer risk. In nearly all of Asia, he noted, breast cancer rates are low, but soy is eaten in only a few areas. “So, I think it’s almost certain that we can’t attribute the low rates in general of breast cancer in Asia to soy consumption,” he said, “which isn’t to say that it might not have some effect.”

A US group that consumes a lot of soy, the Seventh Day Adventists, he added, does not have lower rates of breast cancer than the general population.

The only randomized trial on the response of breast tissue to soy of which Dr. Will-ett is aware was conducted in England. Women scheduled to have biopsies of breast lumps were randomized to either a high-soy diet or ordinary meals for 4 weeks before the procedure.

Higher Proliferation

Examination of the normal tissue removed at biopsy revealed “a higher proliferation in the women who were on the soy diet than on the regular diet,” Dr. Willett said. This finding, he commented, “would raise concern that soy might be acting more like an estrogen, which can increase breast cancer risk.”

In women consuming large amounts of soy, Dr. Norton has found breasts that are “very estrogenized, which you can feel as an examiner.” This, along with the biopsy evidence cited by Dr. Willett, he said, raises concerns.

“Americans often will treat foods as medicines. Instead of adjusting to a cuisine that has evolved over hundreds or thousands of years,” he observed, “they’ll take one component, magnify the amount to an extraordinary level . . . and get pharmacologic effects. It’s really very unpredictable.”

The effect of soy, Dr. Willett said, may be related to the amount consumed. “It also may be related to the time of life that soy is consumed,” he said. “I think it is a little disconcerting because, in this country, the way soy is used is by menopausal women who take large amounts of soy, much higher amounts than are consumed in Asia. It’s conceivable that the benefit, if there is a benefit, is during the premenopausal years when it might be counteracting the high circulating levels of endogenous estrogen.”

October 12th Symposium

The effects of soy will be a major topic at a symposium on nutrition and breast cancer sponsored by the Breast Cancer Research Foundation on October 12, 2000, Dr. Norton said. “We’re going to have some people who are supporting prospective soy studies in women who had breast cancer as well as women who are at risk of breast cancer,” he said. Uniformity of opinion, he suggested, is unlikely.

The relationship of soy to breast cancer risk,  Dr. Willett concluded, “is clearly an area where we do need research. Hopefully, the foundation might help with this kind of research because there’s a potential there, and there’s also some potential harm if it’s used in the wrong way.”

Jill Rose Award

Dr. Willett will receive the Breast Cancer Research Foundation’s Jill Rose Award at the October symposium. He will also deliver the keynote address, Mrs. Lauder said at the news conference.