Young women who smoke and have smoked a pack a day for 10 years or more have a significantly increased risk of developing the most common type of breast cancer. This is the result of an analysis published online in advance by the peer-reviewed journal of the American Cancer Society. The study suggests that the increased risk of breast cancer may lead to another health risk for young women who smoke. Most of the recent studies assessing the relationship between smoking and the risk of developing breast cancer in young women have found a correlation between smoking and increased risk of developing breast cancer; however, few studies have assessed risk according to different breast cancer subtypes. To examine this issue, Professor Christopher Li (from Fred Hutchinson Cancer Research Center, Seattle) and his colleagues conducted a population-based study that enrolled 778 patients with estrogen receptor-positive breast cancer and 182 patients with triple-negative breast cancer. Estrogen receptor-positive breast cancer is the most common subtype of breast cancer, while triple-negative breast cancer is less common but tends to be more aggressive. Patients in the trial ranged in age from 20 to 44 years and were diagnosed with breast cancer in the Seattle-Puget Sound metropolitan area between 2004 and 2010. The study also included 938 cancer-free controls. The researchers found that current or recent smokers and young women who had smoked a pack a day for at least 10 years had a 60 percent increased risk of developing estrogen receptor-positive breast cancer. In contrast, smoking was not correlated with the risk of developing triple-negative breast cancer. ”It is well known that there are many health hazards associated with smoking. The results of this study add to our knowledge about the relationship between breast cancer subtypes and smoking, and it suggests that smoking may increase the risk of developing the most common subtype of breast cancer relative to breast cancer, but does not affect the increased risk of the rarer but more aggressive subtype,” Professor Li explained.