WEDNESDAY, May 18 (HealthDay News) -- Long-term smoking significantly increases the risk of invasive breast, lung and colon cancers in women with a high risk of breast cancer, a new study finds.

Researchers analyzed how smoking, drinking and physical activity affected the risk of several common cancers in 13,388 women at increased risk of breast cancer because of family history of breast cancer, age and other factors. The women were participants in the U.S. National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention Trial.

Compared to those who never smoked, women who smoked for at least 35 years had a 60 percent higher risk of invasive breast cancer and more than four times the risk of colon cancer, the investigators found.

Women who smoked for 15 to 35 years were 34 percent more likely to develop invasive breast cancer and 7 percent more likely to develop colon cancer than those who never smoked.

Women who smoked for fewer than 15 years had no increased risk of invasive breast cancer, according to the report.

Compared to those who never smoked, women who smoked more than one pack of cigarettes per day for more than 35 years were 30 times more likely to develop lung cancer, while the risk was 13 times higher for those who smoked less than one pack a day for more than 35 years.

Alcohol use was not associated with increased cancer risk, but the researchers did find that low levels of physical activity were associated with a 70 percent increased risk of endometrial cancer. This may be because women who don't exercise are more likely to be obese, a risk factor for endometrial cancer.

The study was posted online ahead of its presentation June 6 at the annual meeting of the American Society of Clinical Oncology, in Chicago.

"The NSABP study was the first large study to prospectively examine the impact of smoking in women at high risk of breast cancer," said study author Stephanie Land, a research associate professor in the department of biostatistics at the University of Pittsburgh's Graduate School of Public Health.

"Our results showed an even greater increase in risk than has been shown in previous studies, suggesting that for women who are at risk of breast cancer because of family history or other factors, smoking cigarettes is even more risky than for other women," Land said in an ASCO news release.

"It sends a very important message for women with family histories of breast cancer about the long-term risks of smoking, as well as the importance of staying physically active. We're seeing again that smoking cessation is one of the most effective tools we have for reducing risk of many cancers," she added.

Research presented at meetings is considered preliminary until published in a peer-reviewed journal.

More information

The U.S. National Cancer Institute has more about women and cancer.