Research is clear that obesity increases the risk of developing breast cancer. Now, a large study suggests that women who are overweight or obese when they are diagnosed with the most common form of breast cancer have the greatest risk of an earlier death and recurrence, even when undergoing optimal treatment.
The study was published early online in the journal CANCER. Here’s the abstract.
The link was seen among women who had hormone-receptor positive breast cancer, which make up about two-thirds of breast cancers.
In all, the study included almost 7,000 women who went through treatment. The researchers pulled data from three National Cancer Institute trials that were studying the effects of chemotherapy, tamoxifen and/or other treatments on women with breast cancer. Their breast cancers ranged from the early stage to the later stage III, where the cancer could have spread to nearby lymph nodes.
The largest of the three trials tracked the women’s health for an average of 8 years; the other two followed the women for 14 years.
When the researchers looked at the women’s BMI at diagnosis, they found a link between increasing BMI and poor outcomes among women with hormone receptor–positive breast cancer. Overall there was about a 30 percent higher risk of recurrence and a nearly 50 percent higher risk of death. Obese women with estrogen-receptor positive breast cancer, a common type of hormone-related cancer, had about a 50 percent higher risk of dying from any cause or from breast cancer specifically compared to women in the other weight categories. The link was not seen among those who with breast tumors that did not have hormone receptors.
There are several ways in which extra body fat may trigger breast cancer recurrence, the authors note. Excess body fat is linked to high insulin levels and inflammation, both of which are linked to hormone positive breast cancers.
The study is an observational one, and does not show that losing weight after diagnosis can reduce risk of recurrence or an earlier death. But it does add to a growing body of evidence suggesting lifestyle can make a difference for breast cancer patients.
Along with weight, physical activity is another area researchers are looking at. We’ve written about how exercise may possibly help breast cancer survivors improve their quality of life and avoid recurrence. Here’s one Cancer Research Update article on it.
For prevention, AICR’s expert reports and its updates link excess body fat to
increased risk of post-menopausal breast cancer, along with six other
types of cancers.