Obesity, alcohol consumption, and smoking significantly increase the risk of second breast cancers among breast cancer survivors, according to the results of a study published in the Journal of Clinical Oncology.
Approximately 200,000 women are diagnosed with breast cancer every year in the United States alone. Treatment for the disease has improved, and five-year survival rates are now greater than 90%; however, survivors have a significantly increased risk of developing a second breast cancer in the opposite breast.
Researchers from the Fred Hutchinson Cancer Research Center in Seattle conducted a study that involved 365 women who were diagnosed with an estrogen-receptor (ER) positive first primary breast cancer and then were later diagnosed with a second primary breast cancer. These women were compared to 726 matched controls who were diagnosed with only an ER-positive primary breast cancer.
The researchers reviewed medical records and conducted patient interviews to ascertain data on obesity, alcohol consumption, and smoking. The results indicated that women who were considered obese (body mass index [BMI] over 30 kg/m2) were 50% more likely to develop a second breast cancer than women who had a BMI lower than 25 kg/m2. Furthermore, women who consumed more than seven drinks per week after their first breast cancer diagnosis had a 70% higher risk of developing a second breast cancer compared with non-drinkers. Finally, women who smoked were more than twice as likely to develop a second breast cancer compared with nonsmokers.
The researchers concluded that lifestyle factors such as obesity, smoking, and drinking could significantly increase the risk of developing a second cancer. Modifying these factors might provide breast cancer survivors with a way to reduce their risk of developing a second cancer.
 Li CI, Daling JR, Porter PL, et al. Relationship between potentially modifiable lifestyle factors and risk of second primary contralateral breast cancer among women diagnosed with estrogen receptor-positive invasive breast cancer. Journal of Clinical Oncology. Published early online September 8, 2009.