Why are breast cancer survivors prone to weight gain?

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Women who survive breast cancer are more likely to gain weight over the following years than women who have not had cancer – especially if they have a family history of the disease – according to a new study. Women treated with chemotherapy are at particular risk for weight gain, claim researchers from Johns Hopkins Kimmel Cancer Center in Baltimore, MD.

normal and overweight women
Among both the breast cancer survivors (46.9%) and cancer-free women who had a family history of breast cancer (55.1%), the study found a high prevalence of overweight participants.

Previously, studies have found that women who have survived breast cancer and go on to gain weight are at increased risk of having their cancer return. In addition, weight gains of 11 lb or more have been linked with an increased risk of cardiovascular disease.

In the new study, published in the journal Cancer Epidemiology, Biomarkers & Prevention, the Johns Hopkins team recruited 303 breast cancer survivors and 307 cancer-free women between 2005 and 2013. All women completed a questionnaire at the start of the study, and they were followed-up 4 years later. About a quarter of the women in the study were premenopausal and the majority of the participants were white.

The researchers found that breast cancer survivors gained significantly more weight during the 4-year follow-up period than women who had not had cancer. Breast cancer survivors gained an average of 3.6 lb more in weight.

Among women in the study who had been diagnosed with cancer during the last 5 years of the study period, 21% put on at least 11 lb over 4 years, while only 11% of the cancer-free women put on this much weight over 4 years.

Does chemotherapy contribute to weight-gain association?

Women who had completed chemotherapy within 5 years of the study were found to be 2.1 times as likely as women who had not had cancer to gain at least 11 lb during the study.

After taking into account other factors that may have influenced weight, such as age, menopausal status and level of physical activity, the association between cancer history and weight gain remained strong.

“Above and beyond age and menopausal status, there seems to be a weight gain associated with treatment of cancer, particularly in women having chemotherapy and those diagnosed with estrogen receptor-negative, invasive cancers,” says Amy Gross, a doctoral candidate in epidemiology at the Bloomberg School of Public Health.

Cholesterol-blocking drugs also seemed to affect weight gain among breast cancer survivors. Women who had been treated with chemotherapy and who now used statins gained an average of 10 lb more than cancer-free women using statins and women from both groups who did not use statins.

Among both the breast cancer survivors and cancer-free women who had a family history of breast cancer, the study found a high prevalence of overweight participants – 46.9% of breast cancer survivors and 55.1% of cancer-free women with a family history of breast cancer were overweight or obese. This group included women with an inherited predisposition for breast cancer, such as carrying the BRCA1 or BRCA2 gene mutations.

Kala Visvanathan, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health and director of the Clinical Cancer Genetics and Prevention Service at the Kimmel Cancer Center, says:

“There is limited data on weight change in breast cancer survivors, including those at higher risk for the disease compared to the general population. A lot of studies have focused on breast cancer survivors alone, so we don’t get a sense of whether women without cancer gain more or less weight, or whether the gain is due to the cancer or the treatment.”

The team will continue to follow-up with the group every 3-4 years to investigate the long-term weight changes of the women.

Visvanathan says that the authors are not suggesting any weight gain intervention at the time of chemotherapy. “But we are suggesting that oncologists, internists or anyone treating breast cancer survivors, including those with a family history of the disease, could help them monitor their weight over the long term,” she explains.