Breast cancer survivors whose families have a history of breast cancer gain more weight than women who are cancer-free, according to a study by Johns Hopkins Kimmel Cancer Center researchers. The research is troubling because previous studies suggest that breast cancer survivors who gain weight are more likely to have a recurrence of their disease.

In addition, the study found that the type of treatment cancer survivors were given also has an effect on weight gain — women who were treated with chemotherapy tended to gain more weight.

For the study, which was published in Cancer Epidemiology, Biomarkers & Prevention, researchers gave questionnaires to 303 breast cancer survivors and 307 cancer-free women. All were enrolled in a long-term study of women with a family history of breast or ovarian cancer. Four years later, they answered a follow-up questionnaire.

Over four years, breast cancer survivors gained an average of 3.6 pounds more than cancer-free women. Among 180 survivors diagnosed with breast cancer during the past five years, 21 percent gained at least 11 pounds over the four-year study compared to 11 percent of the cancer-free women.

"Our study suggests that chemotherapy may be one of the factors contributing to weight gain among survivors," says Kala Visvanathan, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health. "Women who completed chemotherapy within five years of the study were 2.1 times as likely as cancer-free women to have gained at least 11 pounds during the study."

Women who had a family history of breast cancer or carried the BRCA1 or BRCA2 gene mutations for breast cancer were more likely to be overweight than women who didn't have a family history. Of those who carried BRCA1 or BRCA2 gene mutations, 46.9 percent of cancer survivors and 55.1 percent of cancer-free women were overweight or obese.

In addition, those breast cancer survivors in the study with invasive disease that was diagnosed five years before the study began, and who lacked receptors for estrogen, gained an average of 7.26 pounds more than women who were cancer-free.

Statins also played a role in weight gain. Breast cancer survivors who took statins and were treated with chemotherapy gained an average of 10 pounds more than either cancer-free women who used statins or cancer-free women who didn't take them.

"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," said Amy Gross, a doctoral candidate in epidemiology at the Bloomberg School of Public Health.

Some scientists believe that chemotherapy increases inflammation and insulin resistance, disrupting metabolism and causing weight gain. Part of the answer could also be that patients treated with chemotherapy may be less active and therefore more likely to gain weight.

The American Cancer Society estimates there will be about 231,840 new cases of invasive breast cancer diagnosed in 2015 along with 62,290 new cases of non-invasive carcinoma in situ (CIS). It's the second leading cause of cancer deaths in women, after lung cancer, and will kill about 40,290 women this year.