Impact of Smoking on Breast Cancer Risk Greater Than Thought

Roxanne Nelson

May 24, 2011

May 24, 2011 — The impact of smoking on breast cancer might be larger than previously assumed. A large prospective study of healthy women at higher risk for breast cancer confirmed — as had been previously reported — the cancer risk associated with smoking and fitness, but found that the impact of smoking was even greater than had been demonstrated in other studies.

The results of the study, which were presented at a press briefing held in advance of the American Society of Clinical Oncology (ASCO) 2011 Annual Meeting, found that not only was the risk for invasive breast cancer higher in smokers than in nonsmokers, but that it increased according to years of cigarette smoking.

Lead author Stephanie R. Land, PhD, explained that women who smoked for between 15 and 35 years had a 34% higher risk for breast cancer than women who never smoked. Women who smoked for at least 35 years had a 59% higher risk, whereas those who smoked for less than 15 years had no increased risk for breast cancer.

For women who are already at high risk for breast cancer, smoking is even more dangerous.

"An increase in breast cancer risk associated with cigarette smoking had not been established until recently," said Dr. Land, who is research associate professor, Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh, Pennsylvania. "Our study demonstrated larger effects than were reported in those recent studies. 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."

Dr. George Sledge

George W. Sledge Jr., MD, ASCO president and comoderator of the briefing, noted that the 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."

"Going forward," he added, "we may need to perhaps think less about drugs in many cases, 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."

More Evidence for Breast, Colon, and Lung Cancer Risk

Dr. Land pointed out that this is the third large prospective study to report a strong association between smoking and breast cancer, and the first to show additional risk in women who are already at higher risk for the disease.

As previously reported by Medscape Medical News, one large study of nearly 80,000 postmenopausal women found that current smokers had a 16% increase in breast cancer risk and that former smokers had a 9% increase in risk.

A second study found that current and former smokers had a 39% higher rate of dying from breast cancer than women who had never smoked.

Dr. Land and colleagues found that in addition to breast cancer, long-term smokers had significantly higher risks for lung cancer (P < .001) and colon cancer (P < .001) than nonsmokers or those who had shorter smoking histories.

Heavier Smoking Equals Increased Risk

As part of the National Surgical Adjuvant Breast and Bowel Project's Breast Cancer Prevention Trial, Dr. Land and colleagues analyzed the risk for invasive cancer of the breast, endometrium, lung, and colon in 11,064 women at elevated risk for breast cancer. The analyses accounted for assignment to tamoxifen and considered other known factors that contribute to risk.

Participants self-reported cigarette smoking, alcohol use, and physical activity. At baseline, 54% of women reported low levels of physical activity or inactivity, 45.7% reported moderate to heavy physical activity, 20.5% reported being nondrinkers, 65.8% reported consuming no more than 1 drink daily, and 13.3% reported consuming more than 1 drink per day. In addition, 12.8% reported current use of tobacco.

After a median of 8.7 years of follow-up, 395 women had been diagnosed with breast cancer, 66 with lung cancer, 35 with colon cancer, and 74 with endometrial cancer.

Cigarette smoking was associated with a higher risk for colon cancer and, not surprisingly, lung cancer. The risk for colon cancer was up to 5-fold higher in women who had smoked for 35 years than in women who had never smoked; the risk was 7% greater for those smoked for 15 to 35 years.

The risk for lung cancer was even greater; women who smoked more than 1 pack of cigarettes per day for more than 35 years had a risk that was 30 times higher than those who had never smoked. Women who smoked less than 1 pack per day for more than 35 years had a 13-fold increase in lung cancer risk.

The authors found that low physical activity was associated with a 72% increased risk for endometrial cancer, but physical activity was not significantly associated with the risk for other cancers.

Does Alcohol Lower Colon Cancer Risk?

Additional findings, in contrast to results from some other studies, were that alcohol use was not associated with breast cancer risk and that it appeared to lower the risk for colon cancer. Women who consumed no alcohol had a 21% lower risk for colon cancer, whereas those who had up to 1 drink per day had a 65% reduced risk for colon cancer. No significant difference was observed for other cancers, and more than 1 drink per day was not associated with an increased cancer risk.

Some previous studies have found associations between alcohol consumption and cancer risk, Dr. Land noted, suggesting that one reason for the differences in results might be the lack of heavy drinkers enrolled in this trial.

Dr. Land has disclosed no relevant financial relationships. Coauthor Donald Lawrence Wickerham, MD, reports serving as a consultant or in an advisory role for Lilly, and receiving honoraria from AstraZeneca.

American Society of Clinical Oncology (ASCO) 2011 Annual Meeting: Abstract 1505. To be presented June 6, 2011.

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