A prospective study first presented at the American Association for Cancer Research's 9th Annual International Conference on Frontiers in Cancer Prevention Research has reported that smoking increases risk of breast cancer-specific death, as well as death from other causes, among breast cancer survivors. Cigarette smoke has been shown to increase the ability of cancer cells to metastasize but its influence on breast cancer outcome remains poorly understood.

The study included 2,265 women diagnosed with breast cancer from 1997 to 2000 and followed for approximately nine years. The authors examined whether smoking was associated with death from breast cancer and non-breast cancer-related causes, while taking into account age, education, body mass index (BMI), tumor characteristics and treatment. A total of 164 women died from breast cancer and 120 died from other causes during the follow-up period.

Women who were current or past smokers were found to have a 39% higher rate of dying from breast cancer and a two-fold higher rate of dying from other causes than women who had never smoked. When the data was analyzed according to subgroups, the negative effect of smoking on breast cancer survival was found to be highest among women who were normal weight or underweight (BMI < 25kg/m2) (83% higher rate of breast cancer-specific death than non-smokers), whose tumors were not HER2 positive 61% higher), or who were postmenopausal (47% higher). The authors conclude that smoking was associated with important increases in risk of death from breast cancer and other causes independently of clinical, sociodemographic and other lifestyle-related factors among the women in the study.