COMMON QUESTIONS ABOUT BREAST CANCER: IS HEREDITY A RISK FACTOR?

Heredity does appear to be a strong influence in the development of breast cancer. The risk of developing the disease increases fivefold or sixfold if at least two first relatives (mother, daughter, or sister) has had the disease. This risk is greater if the cancer was diagnosed as premenopausal or was detected in both breasts. If a second-degree relative (aunt, grandmother, cousin) had breast cancer, the risk is increased by only 1.5 times the average. Heredity, however, may involve more than the genetic predisposition to develop the disease.

Other risk factors, including dietary and environmental influences, may arbitrarily be "handed down" in families or cultures. Although there is no direct association in humans between breast cancer and a fatty diet, studies suggest that a high-fat, high-calorie diet may increase the incidence of tumor development in animals. Dietary factors also have been significantly associated with increased incidence of breast cancer in Japanese women who have emigrated to the United States. Japanese women living in Japan traditionally have had very little breast cancer; their diet is low in fat and high in fiber. Unfortunately, after emigration to the United States the incidence of breast cancer in these women has increased threefold until it has approached the rate for U.S. women. Other western cultural changes may be involved, including later pregnancies and increased exposure to environmental hazards.

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Cancer