But Zhang cautioned that larger studies with women from many medical centers are needed before scientists can say that soy may help reduce the risk of breast cancer's return.
McCullough agreed. "It's still possible that other lifestyle differences in women in China who were eating less soy" might explain their higher likelihood of getting breast cancer again, she said.
There have been concerns about the effect of soy consumption on women with estrogen receptor-positive and progesterone receptor-positive breast cancer because soy isoflavones are similar to estrogen in chemical structure, and because tumor growth is dependent on estrogen, the study authors said in a news release.
Dr. Joanne Mortimer, director of the women's cancers programs at the City of Hope Comprehensive Cancer Center in Duarte, Calif., said some doctors tell women to avoid soy, concerned that too much might be hazardous. "I think this is yet another study that confirms that soy products do not cause an increased risk of breast cancer or even recurrence," she said.
But, it's not a reason to go overboard on soy, Mortimer said. "I wouldn't tell people they should eat a lot of soy," she said. Rather, "they should eat a healthy diet and if they eat soy, this study suggests there is not harm in it."
According to current American Cancer Society guidelines, which are under review, up to three servings a day of soy foods is considered safe, McCullough said. But women are advised to avoid the high soy dose found in more concentrated sources such as soy powders and isoflavone supplements, she said.
To learn more about soy, visit the American Cancer Society.
SOURCES: Joanne Mortimer, M.D., d
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