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Obesity makes treating HER-2 positive breast cancer more difficult

Kathleen Blanchard's picture
Mayo Clinic researchers find obesity can worsen HER-2 breast cancer outcomes.

Obese women fighting HER-2 positive breast cancer are found by Mayo Clinic researchers to have worse outcomes, compared to normal or overweight women.

The finding is important for women being treated for human epidermal growth factor receptor 2 breast cancer that is aggressive.

According to the study author, one out of 3 breast cancer tumors makes an excess of HER2, which manufactures a protein that promotes growth of tumors

Jennifer Crozier, M.D., a medical resident led the study.

"While other studies have looked at the effect of body weight on treatment outcome for estrogen receptor-positive breast cancer, no one has examined this variable in the HER2-positive subtype, which accounts for about one-third of all breast cancers," says Dr. Crozier.

In the study, presented at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium, the researchers analyzed breast cancer outcomes among 3,017 patients.

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They looked at breast cancer survival in women given 3 treatments in the North Central Cancer Treatment Group N9831 study - chemotherapy alone; chemotherapy and then Herceptin for a year; and chemotherapy plus Herceptin, followed by Herceptin for a year.

The findings showed obese women had worse outcomes in all but the third ARM of the study - chemotherapy plus Herceptin, followed by Herceptin for a year.

Disease free survival rates were not significantly different for women whose BMI was normal compared to those with BMI greater than 30.

The finding say the researchers, means women who are obese may have worse outcomes from breast cancer treatment. The chemotherapy drug Herceptin was powerful enough to compensate for high body mass index. Obesity is also linked to larger tumors and more invasive disease.

Senior study investigator Edith Perez, M.D., director of Mayo Clinic's breast program in Florida said, "We are continually searching for approaches that will help our patients have the best outcome possible after their diagnosis of breast cancer, and this study suggests that excess body weight may make a difference.”

Herceptin, or trastuzumab, is a monoclonal antibody given to fight breast cancer that has spread to other parts of the body, in conjunction with other medications.

Some of the side effects can be serious, making it desirable for women with breast cancer to do all they can to avoid the need for strong chemotherapeutic agents and prolonged treatment.

The findings from the Mayo Clinic researchers show obesity can affect outcomes for women being treated for HER-2 positive breast cancer that occurs in 1/3 of women diagnosed with the disease.