Smoking ups risk for less favorable breast cancer

Women who smoke may be at increased risk of developing breast cancers that respond less favorably to treatment, according to a joint Swedish and Danish research team. In their study, the investigators analyzed breast cancer tissue samples from 268 women out of a group of more than 10,000 women who had participated in a study in Sweden. The women were followed for about 12 years.

From questionnaire data, the researchers determined that 35% of the women were current smokers, according to the report published in the current International Journal of Cancer. Women who smoked or had quit smoking at the time of the study had about 2.2 and 2.7 times the risk, respectively, of developing estrogen receptor-negative tumors compared with women who had never smoked.

"We conclude that smoking is associated with an increased occurrence of hormone receptor-negative tumors," writes lead author Jonas Manjer of Malmö University Hospital and colleagues at Arhus University in Denmark. Hormone receptor-negative tumors are generally believed to be less responsive to treatment. Conversely, tumors that have estrogen receptors are associated with a more favorable prognosis.

In the study, researchers identified whether the tumor samples had receptors for estrogen or progesterone. Estrogen receptor-positive tumors often respond to the anti-cancer drug tamoxifen, which acts by limiting the tumor's supply of growth-promoting estrogen. "Why smoking would be associated with an increased occurrence of (estrogen/progesterone receptor-negative) tumors can only be speculated. Smoking exerts an anti-oestrogenic effect. Furthermore, tobacco smoke contains several carcinogenic substances which, in animal experiments, have been shown to cause breast cancer," the researchers write. Further investigation is needed to resolve the question, they conclude.