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By Meghan Holohan

Survivors of breast cancer with a family history of the disease gain more weight than similar women without cancer, a new study finds. What’s more—there seems to be an association between weight gain and treatment.

It’s not good. There’s some evidence showing that survivors who gain weight have a greater risk of their cancer coming back.

“The breast cancer survivors gained more weight, significantly more weight, in the four year follow-up,” says Amy Gross, a Ph.D candidate at the Johns Hopkins Bloomberg School of Public Health and an author of the paper published in “Cancer Epidemiology, Biomarkers & Prevention.”

“We actually found that the women treated with chemotherapy were twice as likely to gain this weight compared to the cancer-free women [during] the same time.”

"We actually found that the women treated with chemotherapy were twice as likely to gain this weight compared to the cancer-free women."

This is one of the few studies comparing breast cancer survivors and cancer free women. It also is one of the few to explore the association between cancer treatment and weight gain.

Experts have long known that breast cancer patients and survivors gained weight, but fully didn’t understand why.

Some speculate that people feel less motivated to work out because they don't feel well and they might choose to eat what makes them feel better and not what is most healthy. Others have suggested that chemotherapy increases inflammation and makes people insulin-resistant, changing metabolism.

"It is not known, but thought to be due to metabolic changes. We are planning to evaluate some of these factors," said Dr. Kala Visvanathan, director of the Clinical Cancer Genetics and Prevention Service at Johns Hopkins, who worked on the study.

Gross and her colleagues compared 303 breast cancer survivors and 307 cancer-free women—all of whom had a family history of breast cancer. Participants answered a baseline questionnaire and at least one more between 2005 and 2013.

Within four years, cancer survivors gained an average of 3.6 pounds, more weight than the women without cancer. Of the 108 women diagnosed with cancer in the last five years of the study, 37 women—or 21 percent—gained 11 pounds while only 35 of the 307 women without cancer— or 11 percent—gained as much weight.

When the researchers controlled for other factors, including physical activity, aging, and menopause, the results remained the same. A gain of 11 pounds is significant enough to contribute to heart health problems.

“I think [the study] highlights the importance for physicians and patients to monitor their weight from diagnosis onward, for physicians to take notice if there is an increase in weight,” said Visvanathan.

“It is not just the treatment that matters when you are thinking about the diagnosis of cancer.”

Dr. Gijsberta van Londen—director of the University of Pittsburgh Medical Center’s Cancer LiveWell Survivorship Programs, who was not involved with the study—agrees that the study emphasizes the importance of lifestyle on breast cancer patients and survivors. But she urges caution.

“If their cancer … comes back they often blame themselves that they didn’t lose weight.”

“Yes it is important to live healthy for overall outcomes,” she says. “This is not an cause and effect. As far as we know it is an association.”

While she recommends that her patients eat healthily and exercise to avoid the weight gain, she knows this advice can also cause stress.

“It puts a burden on them,” van Londen says. “If their cancer … comes back they often blame themselves that they didn’t lose weight.”