Smoking, lack of exercise linked to breast, lung, colon, endometrial cancers

Issue: June 25, 2011

Results from a prospective study of several lifestyle factors demonstrated that long-term smoking and low levels of physical activity were associated with a variety of cancers. However, the same results showed that drinking was not associated with increased risk.

Compared with women who did not smoke or who had shorter smoking histories, the risks for invasive breast, lung and colon cancers were significantly higher in women who had smoked for 15 to 35 years, and even higher for those who had smoked for at least 35 years. Researchers also found a strong correlation between a lack of exercise and endometrial cancer risk, said Stephanie R. Land, PhD, research associate professor in the department of biostatistics in the Graduate School of Public Health at the University of Pittsburgh.

Land discussed the results during a press conference in advance of the 2011 ASCO Annual Meeting.

“An increase in breast cancer risk associated with cigarette smoking had not been established until recently. Our study demonstrated larger effects that were reported in those recent studies,” Land said. “This might suggest that for women who are already at high risk for breast cancer, smoking is even more dangerous than for other women in the population.”

She said these are the third set of results from a large prospective study to show a strong association between smoking and breast cancer, and the first to show that smoking increased cancer risk in women already at high risk for breast cancer.

Land and colleagues analyzed the risk for a variety of common cancers in 11,064 women at elevated risk for breast cancer as part of the National Surgical Adjuvant Breast and Bowel Project’s Breast Cancer Prevention Trial. Participants self-reported smoking history, alcohol use and physical activity. At baseline, 54% said they were inactive or had low levels of leisure-time fitness activity; 20.5% were nondrinkers, 65.8% had no more than one drink daily and 13.3% had more than one drink per day. About 13% said they were current smokers.

Compared with nonsmokers, women who smoked for 15 years to 35 years had a 34% higher risk for invasive breast cancer. The risk was 59% higher for women who smoked for at least 35 years. There was no increase in risk for breast cancer for women who smoked fewer than 15 years.

The risk for developing colon cancer for women who smoked at least 35 years was more than five times that of nonsmokers. Women who smoked for 15 years to 35 years had a 7% higher risk for colon cancer.

Alcohol use was not associated with breast cancer risk, and women who had up to one drink per day had a 65% reduced risk for colon cancer compared with nondrinkers. This result contradicts previous findings, and Land said that could be because there were fewer heavy drinkers enrolled in this study compared with other trials. Plus, the results of this study are based on a one-time self-report of alcohol drinking habits and may not be fully accurate.

Low physical activity was associated with a 72% increased risk for endometrial cancer. Land said that could be attributed to the association between fitness and obesity, which was also a risk factor for endometrial cancer. Physical activity was not associated with breast, lung or colon cancer risk.

“This study is good news because most of the other major factors known to cause breast, colon, endometrial and lung cancer are not something women can control, but healthy lifestyle choices provide women a way to reduce their risk for these four major cancers,” Land said. – by Jason Harris

For more information:

Land SR. #1505. To be presented at: 2011 ASCO Annual Meeting; June 3-7, 2011; Chicago.

This study was originally developed to look at a treatment that would prevent breast cancer, but certainly one of the major outcomes of this study is the incredible importance of lifestyle factors. We need to perhaps think less about drugs going forward, but think a great deal about whether we might prevent cancer just by making simple changes in what a woman does on a day-to-day basis.

– George W. Sledge Jr., MD
ASCO President and Ballve-Lantero Professor of Oncology,
and Professor of Pathology and Laboratory Medicine,
Indiana University School of Medicine

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