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.
Next, she looked separately at the groups of drinkers --never, former and current -- and analyzed their risk of breast cancer. For the never drinkers, smoking now or in the past was not linked with breast cancer risk. Ideally, she said, all three groups would have a similar risk to prove smoking by itself is a risk factor. However, she acknowledged, "We did not see that."
Gaudet said she is not sure why that was, but that there may be something about the combination of smoking and drinking that affects breast cancer risk. "Or the numbers [of women] may be too small to show an accurate result."
Even so, she said, the new research suggests that smoking by itself drives up breast cancer risk. The researchers found a link or association, but cannot prove cause and effect.
One cancer expert praised the study.
"This paper is another important step toward the conclusion that smoking is a risk factor [for breast cancer] on its own," said James Lacey, an associate professor of cancer etiology at the City of Hope Comprehensive Cancer Center in Duarte, Calif. He was not involved with the research.
One interesting finding, he said, is that the window before a woman has children seems to
All rights reserved