The findings held even after the researchers took into account factors that could affect breast cancer risk, such as age, smoking and a family history of breast cancer.
The results suggest that being overweight or obese may promote breast cancer through variations in this gene, the researchers said.
Previous studies have shown that obesity increases the risk of breast cancer for women after menopause.
The new study involved about 1,300 white women and 1,300 black women living in New York and New Jersey. About half of the women within each ethnic group had breast cancer. The women ranged from 20 to 75 years old, and nearly half had been through menopause. Women were considered overweight or obese if they had a BMI of 25 or greater.
A marker within the mTOR gene increased the risk of breast cancer for white women, but not for black women, suggesting that the effect of this marker varies by ethnicity.
The mTOR gene is involved in cell growth and blood-vessel formation, which are both important for cancer growth. The gene can be active by excess energy intake, or taking in more calories than you need, Cheng said.
The finding “makes sense, because, if the gene is regulated by energy intake, and women who are obese tend to have excess energy intake, then that’s going to signal the gene,” which promotes cancer growth, Cheng said.
The findings were presented this week at the meeting of the American Association for Cancer Research.