Breast cancer risk is linked to increased levels of the hormone estrogen, and fat tissue produces estrogen, adding to the risk.

A study of more than 44,000 women found that the more weight a woman gained, the greater her risk for all types, stages, and grades of breast cancer.

Compared to women who gained 10 kilograms (22 lbs.) or less during adulthood, women who gained more than 27 kilograms (60 lbs.) were almost twice as likely to have ductal type breast tumors and more than 1.5 times more likely to have lobular type cancers, Heather Spencer Feigelson of the American Cancer Society and colleagues found.

The risk of breast cancer that had spread tripled for women who gained more than 27 kilograms, they reported in yesterday's issue of the journal Cancer.

Fat Tissue Produces Estrogen

Breast cancer risk is linked to increased levels of the hormone estrogen, and fat tissue produces estrogen, adding to the risk.

"These data further illustrate the relationship between adult weight gain and breast cancer, and the importance of maintaining a healthy body weight throughout adulthood," the researchers wrote.

A study published earlier this month found that women who take estrogen-only hormone replacement therapy for 20 years or longer to treat symptoms of menopause have a higher risk of developing breast cancer.

No. 2 Cause of Cancer Deaths Among US Women

Breast cancer is the second leading cause of cancer death among US women, after lung cancer. More than 200,000 people are diagnosed and another roughly 40,000 die from it each year, according to the American Cancer Society.

Globally more than 1.2 million men and women develop breast cancer every year.