More Evidence That Smoking Raises Breast Cancer Risk

Study found strongest link for women who started smoking early in life.

By Kathleen Doheny
HealthDay Reporter

THURSDAY, Feb. 28 (HealthDay News) -- Cigarette smoking appears to increase the risk of breast cancer, especially when women start smoking early in life, new research indicates.

For years, experts have questioned whether cigarette smoking is directly linked with breast cancer risk or whether the association is complicated by the fact that many women who smoke also drink alcohol, which has also been tied to breast cancer risk.

Studies have produced conflicting results. When the U.S. Surgeon General last reviewed the issue in 2004, the report concluded that there was no cause-and-effect relationship between smoking and breast cancer risk.

Now, however, researchers who took another look, analyzing data from more than 73,000 women, have found strong evidence for a link between cigarette smoking and breast cancer.

"It's not just a relationship between alcohol and breast cancer, but in fact smoking by itself is related to breast cancer," said Mia Gaudet, director of genetic epidemiology at the American Cancer Society. She led the study, which was published online Feb. 28 in the Journal of the National Cancer Institute.

The timing of the smoking appears to affect the degree of risk, she said. "It seems that women who start smoking before their first birth are at greatest risk of breast cancer," Gaudet said.

The researchers looked at data from women enrolled in a large, long-term cancer society study involving lifestyle factors and prevention. Over the follow-up of nearly 14 years, more than 3,700 cases of invasive breast cancer were found.

When the women entered the study in 1992, they were aged 50 to 74. They supplied information on smoking habits, past and present. At the start, about 8 percent smoked, about 36 percent had quit and about 56 percent never smoked.

The incidence of invasive breast cancer was 24 percent higher in current smokers and 13 percent higher in former smokers, compared to never smokers, the researchers found.

The researchers next focused on the timing of the smoking. "Women who started smoking before their first menstrual period were 61 percent more likely [to get breast cancer than nonsmokers]," Gaudet said. Women who took up the smoking habit after their period had started but 11 or more years before giving birth were at a 45 percent higher risk, compared to nonsmokers.

To analyze whether the cigarette smoking by itself -- not the combination of drinking and smoking -- affects breast cancer risk, Gaudet first looked at both smoking and drinking in the same model. ''It showed that the relationship still existed between smoking and breast cancer," she said.