Young women who smoke a lot have a significantly increased risk of developing the most common type of breast cancer, a new study indicates.

While it is already known that smoking increases the overall risk of breast cancer, few studies have looked at the different subtypes of the disease. US scientists decided to investigate further.

They studied almost 800 women with oestrogen receptor positive breast cancer - the most common type of the disease - and compared them with almost 200 patients with triple negative breast cancer.

Triple negative is less common, but tends to be more aggressive.

All of the participants were aged between 20 and 44 and had been diagnosed with cancer between 2004 and 2010.

Over 900 women without cancer were also included in the study.

The scientists found that young women who had been smoking at least 20 cigarettes per day for the last 10 years, had a 60% increased risk of developing oestroegen receptor positive breast cancer.

On the other hand, smoking did not appear to increase the 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 the team from the Fred Hutchinson Cancer Research Center in Seattle.

Details of these findings are published in Cancer, the journal of the American Cancer Society.