Women who gain weight in adulthood face a greater lifetime risk of all types of breast cancer even if they do not take hormone replacement therapy after menopause, US research suggests.
The study reveals that the greater the weight gain as an adult, the greater the risk for all histological types, tumor stages, and grades of breast cancer, particularly advanced malignancies.
The most extremely obese women were up to three times more likely to have regional or distant metastases than women with less weight gain.
Breast cancer risk is linked to increased lifetime levels of circulating estrogen. Fat tissue increases circulating estrogen, thereby adding to the risk.
American Cancer Society researchers investigated the risk between weight gain and type of invasive breast cancer among 44,161 postmenopausal women who were not taking hormone therapy.
They found that the greater the weight gain, the greater the risk for all types, stages, and grades of breast cancer.
Compared to women who gained 20 pounds or less during adulthood, women who gained over 60 pounds were almost twice as likely to have ductal type tumors and more than 1.5 times more likely to have lobular type cancers.
The risk for metastatic disease increased for all women who gained weight, with the risk greater than three-fold for women who gained over 60 pounds.
As expected, weight gain increased the risk of estrogen receptor positive tumors, but not of tumors that did not present estrogen receptors.
The study is published in the journal Cancer.
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