The study suggests that extra body fat causes hormonal changes and inflammation that may drive some cases of breast cancer to spread and recur despite treatment.

Previous studies have tied obesity to a higher chance of developing breast cancer, as well as worse outcomes in women who have already been diagnosed. These new findings also paint a bleak picture for obese or overweight women post-treatment.

Dr Joseph Sparano and colleagues from the Albert Einstein College of Medicine’s Montefiore Medical Centre in the United States, compared the health outcomes of obese and overweight patients with others who were not in a large group of women with stage I-III breast cancer who had participated in three National Cancer Institute’€“sponsored treatment trials.

Out of close to 5 000 women treated for cancer, about one-third were obese and another one-third were overweight. Over the next eight years, one in four women had their cancer come back and 891 died – including 695 from breast cancer.

Sparano and his colleagues found that, compared to women of normal weight, obese women were 40 percent more likely to have a breast cancer recurrence over the study period and 69 percent more likely to die from breast cancer than any other cause.

Even among overweight but not obese women, there was also a general trend toward a higher risk of recurrence and death with increasing weight.

The link was especially strong for women with estrogen receptor positive cancer, which accounts for two-thirds of breast cancers.

“We found that obesity at diagnosis of breast cancer is associated with about a 30 percent higher risk of recurrence and a nearly 50 percent higher risk of death despite optimal treatment,” said Sparano. “Treatment strategies aimed at interfering with hormonal changes and inflammation caused by obesity may help reduce the risk of recurrence,” he added.

Sources: EurekAlert!, Reuters Health