A study of nearly 147,000 women shows no correlation between exposure to environmental tobacco smoke and deaths from breast cancer. The study, which used data from the American Cancer Society Prevention Study II, contradicts previous studies that have shown that exposure to second-hand smoke can increase a woman's risk for breast cancer. However, because of the size and nature of this study, researchers say that the results are significant.

In the study, researchers followed 146,488 non-smoking, married women who were healthy when they enrolled in the study in 1982. After 12 years, there were 669 cases of breast cancer among the women. The researchers found no difference in the death rate from breast cancer among the women whose husbands smoked versus the women who were married to non-smokers. Taking into account the women's exposure to environmental tobacco smoke at home and work, the researchers concluded that there was no link between second-hand smoke and breast cancer deaths.

According to the American Cancer Society, this is the largest study on environmental tobacco smoke and breast cancer ever conducted. There were more participants in this study than in all of the previous studies on this topic combined. Also, unlike previous studies that often relied on women's recollections of their past exposure to tobacco, this prospective study began following the women before any of them had developed breast cancer. Therefore, there is no possibility of "recall bias" (participants inaccurately reporting previous events).

According to researcher Eugenia E. Calle, PhD, director of analytic epidemiology for the American Cancer Society, and her colleagues, the results of the study suggest that women who have been exposed to their husbands' passive smoke for 30 years or more do not have a greater risk of dying from breast cancer than women who were not exposed to second-hand smoke.

The study did find a slight increased risk of death from breast cancer among women who were married to smokers before they were 20 years of age. However, the data were too small to be statistically significant.

While the study did not show a link between second-hand smoke and breast cancer mortality (death), the researchers warn that environmental tobacco smoke has been proven to have a negative effect on a person's health. Physicians advise women, men, and children to avoid exposure to tobacco smoke.

Previous studies which investigated the link between women who smoke and their risk for breast cancer are also contradictory. Currently, the majority of studies do not show a significant increase in the risk for breast cancer among smokers. However, smoking does increase the risk for several other illnesses and diseases, including heart disease, lung cancer, and stroke. Heart disease is the number one cause of death among Americans and lung cancer is the leading cause of cancer deaths in women today. Research has also shown that smoking may interfere with the way in which the body heals from other diseases and conditions.

Further research will continue to investigate whether environmental tobacco smoke affects breast cancer risk and mortality. Other established risk factors for breast cancer include:

• Age
• Genetics
• Family history of breast cancer
• Early menstruation (before age 12)
• Late menopause (after age 50)
• Delayed childbirth (after age 30) or having no children