Among women who have had cancer in one breast, drinking alcohol may increase risk of developing cancer in the other breast, study findings suggest. However, this association was not seen with smoking.

Women with a history of cancer in one breast have increased risk of developing cancer in the second breast, but few investigations have assessed associated, potentially modifiable risks, such as alcohol and cigarette use, Dr. Julia A. Knight and colleagues report in the American Journal of Epidemiology.

This led Knight, from Mount Sinai Hospital in Toronto, Ontario, and her co-investigators to compare patterns of alcohol drinking and cigarette smoking among women with a history of cancer in one breast who had (708 women) or had not (1399 women) subsequently developed cancer in their second breast.

Their findings suggest this is “a 30-percent higher risk in those who (ever) drank alcohol compared to those who did not,” Knight told Reuters Health.

The researchers used tumor registries in the United States and Denmark to identify women, younger than 55 years old, who were diagnosed with localized primary invasive breast cancer from 1985 through 2000.

Knight’s team matched the women with a second new breast cancer with the women with cancer in one breast by birth year, diagnosis year, registry region, race, and radiation treatment. The researchers then compared the women’s self-reported history of alcohol consumption and cigarette smoking.

As noted, they found no significant increased risk associated with cigarette smoking, while regular alcohol consumption conferred a 30-percent elevated risk of developing cancer in the second breast. Compared with non-drinkers, longer duration alcohol consumption appeared to increase risk for contralateral breast cancer.

Knight calls for further investigations to increase knowledge of how drinking patterns over time affect risk, and whether factors such as genetics or other lifestyle habits also alter the effect of alcohol.

“Based on what we know now, though, it is better for women to avoid drinking a lot in general,” Knight said.

SOURCE: American Journal of Epidemiology, April 15, 2009.