But the study, which is collecting information on more than 18,000 breast cancer survivors in the U.S. and China, also had a silver lining: most won’t pack on a large number pounds, at least not so many as to put their health at risk.
“I thought it was quite impressive,” says Mary Jo Nissen, PhD, senior health services researcher at Park Nicollet Health Services in Minneapolis, Minn.
“It was sort of a ‘good news, bad news’ message, that moderate weight gain did not seem to be predictive of increased risk of recurrence or death,” says Nissen, who has also studied weight gain after breast cancer, but was not involved in the current research.
“But the bad news, of course, is that there is a real risk for those women who gain a lot of weight.”
“There have been previous reports consistent with this finding, but this seems to be a large, thoroughly analyzed study so I think it’s important,” Nissen tells WebMD.
Researchers analyzed data from the After Breast Cancer Pooling Project, which is following 18,339 breastcancer survivors from four different sites -- three in the U.S. and one in Shanghai, China.
The average weight change reported in the study in the two years following diagnosis was an increase of 3.5 pounds.
However, about one in six women in the study gained what researchers called “extreme” amounts of weight -- more than 10% of their original body weight.
Regardless of their starting weights, women who saw extreme gains had a 14% greater risk of seeing their cancer come back compared to women whose weight didn’t change during the study.
When researchers took a closer look to determine which women were most likely to see dangerous gains, they found something surprising; it was women who were thin or normal weight, with a BMI of less than 25, when they were diagnosed who were most likely to scale up a few sizes.