Smoking women have increased risk of breast cancer, a new study reports

Women 20 - 44 years old who had smoked a pack of cigarettes per day for at least 10 years were 60 percent more likely than those who smoked less to develop so-called estrogen receptor-positive breast cancer, Fox News reports. 

Dr. Christopher Li, the study's senior author from the Fred Hutchinson Cancer Research Center in Seattle, and his team analyzed data from young women in the Greater Seattle area who were diagnosed with breast cancer between 2004 and 2010.

Of those women, 778 were diagnosed with the more common estrogen receptor-positive type and 182 had the less common but more aggressive triple-negative type.

The researchers also included information from 938 cancer-free women for comparison.

In this study, young women who had ever smoked were about 30 percent more likely to develop any type of breast cancer, compared to women who had never smoked.

When the researchers looked at each type of breast cancer separately, there was no link between smoking and triple-negative breast cancer.

And those women who reported smoking at least one pack a day for 10 years were 60 percent more likely to have that type of cancer, compared to lighter smokers.

It could be that some of the substances found in cigarettes act like estrogens, which would promote estrogen receptor-positive breast cancer, the researchers write.