Soy and Breast Cancer in Japanese Women.




Journal of the National Cancer Institute

Related Monographs

Consumer Data: Soy Isoflavones Breast Cancer
Professional Data: Soy Isoflavones Breast Cancer


The incidence of breast cancer has been increasing steadily for decades. In 1972 when President Nixon declared our national war on cancer, a woman's lifetime risk of developing breast cancer was 1 in 20. Today breast cancer rates have escalated to the point where women's lifetime risk of developing breast cancer is 1 in 8. In the year 2002, the American Cancer Society estimates that nearly 203,500 women will be diagnosed with breast cancer and approximately 39,600 women will die from the disease. This means that approximately every two and a half minutes a woman in the United States is diagnosed with breast cancer and that approximately every thirteen minutes, a woman dies from this disease. Breast cancer has become the second largest cause of cancer death in women, after skin cancer, and the leading cause of death for women between the ages of 35 and 54.

The primary sign or symptom associated with breast cancer is finding a breast lump. In a survey of post-mastectomy women, the first sign or symptom of breast cancer was identified by the patient herself 80% of the time. In 19% of cases, the first signs were picked up by health professionals. In 1% of cases, the first clues were identified by lovers. An unexpected finding was that pain was the first symptom noted by 13% of the women.1

A recent study published in the Journal of the National Cancer Institute stated that soy has been shown to inhibit breast cancer in laboratory studies, but human evidence is inconsistent. Researchers evaluated soy consumption and breast cancer risk in over 21,000 Japanese women starting in 1990. In 1999, 179 women were diagnosed with breast cancer. After reviewing dietary patterns, the results showed that intake of soy isoflavones and miso soup were associated with a lower risk of breast cancer. However, this association was not seen with consumption of soy foods. This was seen stronger in postmenopausal women. The authors concluded that in Japanese women, high intakes of miso soup and isoflavones were linked to a lower risk of breast cancer.2


1. Bullough B. Discovery of the first signs and symptoms of breast cancer. Nurse Pract. Nov1980;5(6):31-2,47.
2. Yamamoto S, et al. Soy, Isoflavones, and Breast Cancer Risk in Japan. JNCI. Jun 2003;95(12):906-913.