A substudy of the large prospective National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention Trial revealed both expected and surprising findings related to the association between lifestyle factors (cigarette smoking, alcohol, and exercise) and cancer risk. As might be expected, long-term cigarette smoking increased the risks of invasive cancers of the breast, lung, and colon. Low levels of physical activity increased the risk of endometrial cancer. Alcohol use did not increase the risk of any invasive cancer, and somewhat surprisingly, moderate alcohol consumption of up to one drink per day actually decreased the risk of colon cancer. 

“We know that smoking is a risk factor for some cancers, and it appears to be even more risky for women who are at high risk of breast cancer due to family history and other factors. These findings suggest that healthy lifestyle choices give women a way to reduce their risk of invasive cancers,” said lead author Stephanie R. Land, PhD, Research Associate Professor, Graduate School of Public Health, University of Pittsburgh, who presented the results at the ASCO Annual Meeting.¹

Study Details

The NSABP Breast Cancer Prevention Trial included more than 13,000 healthy women at increased risk of breast cancer due to age, a diagnosis of lobular carcinoma in situ, family history, or other risk factors. The main study compared 5 years of tamoxifen vs placebo and was unblinded early when it was evident that tamoxifen reduced the risk of breast cancer by 50%. The study presented at the 2011 ASCO Annual Meeting was designed to assess the risk of several common cancers based on self-reports at baseline about alcohol, cigarettes, and exercise. Median follow-up was 7 years.

The risk of invasive breast cancer was higher in smokers than in nonsmokers, and increased with longer exposure to cigarettes. Women who smoked for 35 years or more had a 60% higher risk of invasive breast cancer, and those who smoked between 15 and 35 years had a 34% higher risk, compared with those who never smoked. Women with a smoking history of less than 15 years did not have an increased risk of breast cancer.

Earlier Findings Confirmed

“This is the third large prospective study to show a strong association between smoking cigarettes and breast cancer, and it is the first to show further elevation of cancer risk in women at already high risk of breast cancer,” Dr. Land stated. The risk of colon cancer was also higher for women with longer smoking histories compared to never-smokers. Women who smoked cigarettes for more than 35 years had more than a fivefold higher risk of colon cancer vs those who never smoked. These findings confirm previous studies in women at high risk of breast cancer, and the increase in risk was even higher than in previous studies, Dr. Land noted.

As would be expected, smoking cigarettes increased the risk of lung cancer, and longer cigarette exposure increased the risk further. Women who smoked more than one pack per day for more than 35 years had a 30 times higher risk of lung cancer compared with those who never smoked. Those who smoked less than one pack per day for fewer than 35 years had a 13 times higher lung cancer risk.

Other Risk Factors

Moderate alcohol consumption (≤ 1 drink per day) was associated with a 65% decreased risk of colon cancer compared to those who did not drink. Although this finding seems to controvert previous studies, Dr. Land pointed out several factors that might explain this. Fewer heavy drinkers were enrolled in the NSABP study than in the studies that found an association with alcohol and colon cancer, and the findings are based on a single self-report of alcohol drinking habits. In addition, past studies have generally found alcohol to be a stronger risk factor for men than for women, and for rectal rather than colon cancer.

About 54% of subjects reported low levels of physical activity at baseline; among these women, the risk of endometrial cancer was increased by 70%. This finding may be related to obesity in these women, Dr. Land speculated. ■

Financial Disclosure: Dr. Land reported no potential conflicts of interest.

Reference

1. Land SR, Christian N, Wickerham D, et al: Cigarette smoking, fitness, and alcohol use as predictors of outcomes among women in the National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention Trial. 2011 ASCO Annual Meeting. Abstract 1505. Presented June 6, 2011.