Young female smokers who have not had children appear to face an increased risk of developing breast cancer, Reuters reported July 16.

Researchers studied 56,042 women taking part in a long-term study and found that the risk of breast cancer rose in relation to how much women smoked before giving birth to their first child. For example, women with children who had smoked for 10 "pack years" (the number of packs smoked daily times the number of years smoked) before having their first baby were 78 percent more likely to develop breast cancer than nonsmokers.

"Our results are consistent with the biologic data indicating that the female breast is sensitive to tobacco carcinogens before first childbirth," the study by Mina Ha of Dankook University College of Medicine in Cheonan, Korea and colleagues concluded.

Girls who smoked before starting menstruation may be at even higher risk, the researchers added; the study suggests that breast tissue may be more vulnerable to carcinogens while it is still developing. Researchers found no link between pack-years smoked and breast cancer after a first child was born.

The study appears in the July 1, 2007 issue of the American Journal of Epidemiology.