A new study highlights that post-menopausal women who gain weight in adulthood are at an increased risk of developing all types of breast cancer irrespective of whether they are on hormone replacement therapy (HRT). The study, which is the first of it's kind to have explored the relationship between breast cancer types and weight gain is published in the July issue of Cancer, a publication of the American Cancer Society.
The effect holds good for all types, stages and grades of breast cancer. It is particularly significant with respect to advanced malignancy/ cancer. Women who were very obese were three times more likely to develop either regional or distant metastases compared to their counterparts with insignificant weight gain.
Breast cancer risk is linked to increased lifetime levels of circulating estrogen. Fat tissue increases circulating estrogen, thereby adding to the risk. Previous studies have shown, though, that the risk can be affected by other factors. Postmenopausal women who take hormone replacement therapy actually mitigate the effects of obesity on cancer risk. Moreover, current weight as defined by body mass index is not as important as a woman's weight gain from the age of 18.
While there is much literature on the risk of obesity and breast cancer, there is no data on whether that risk is specific for the type of breast cancer. Led by Heather Spencer Feigelson, Ph.D., M.P.H of the 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.
The researchers 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.
Dr. Feigelson and her colleagues conclude that 'these data further illustrate the relationship between adult weight gain and breast cancer, and the importance of maintaining a healthy body weight through-out adulthood.'