Young women who smoke are at significantly increased risk of developing the most common type of breast cancer, a new study has found.
The majority of recent studies evaluating the relationship between smoking and breast cancer risk among young women have found that smoking is linked with an increased risk, researchers said.
However, few studies have evaluated risks according to different subtypes of breast cancer.
To investigate, Christopher Li from the Fred Hutchinson Cancer Research Center in Seattle, and his colleagues conducted a population-based study consisting of 778 patients with oestrogen receptor positive breast cancer and 182 patients with triple-negative breast cancer.
Oestrogen 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 study were 20 to 44 years old and were diagnosed from 2004-2010 in the Seattle-Puget Sound metropolitan area. The study also included 938 cancer-free controls.
The researchers found that young women who were current or recent smokers and had been smoking a pack a day for at least 10 years had a 60 per cent increased risk of oestrogen receptor positive breast cancer.
In contrast, smoking was not related to a woman's risk of triple-negative breast cancer.
"The health hazards associated with smoking are numerous and well known. This study adds to our knowledge in suggesting that with respect to breast cancer, smoking may increase the risk of the most common molecular subtype of breast cancer but not influence risk of one of the rarer, more aggressive subtypes," said Li.
The findings were published in the journal Cancer.