Breast Cancer Screening and Prevention

Fighting Breast Cancer Recurrence in Obese Women

Sixty percent of doctors are using chemotherapy doses that are too low for their heavier breast cancer patients, according to a recent study. This may be one reason overweight women face a greater risk of breast cancer recurrence than their thinner counterparts.

The study, published in the Archives of Internal Medicine, looked at breast cancer treatment practices to determine if discrepancies in chemotherapy doses could be the cause of the 1.3-times greater risk of cancer recurrence in overweight and obese women.

The researchers looked at data from over 9,000 women treated at over 900 practices across the United States who received adjuvant chemotherapy between 1990 and 2001. Adjuvant chemotherapy is given to women after their cancer is successfully treated and there is no evidence of metastasis, or spread of the tumor. Administering adjuvant therapy decreases the likelihood of recurrence and improves overall survival.

Generally, chemotherapy doses are determined by body surface area (BSA), which plays a role in determining how quickly a drug will be cleared from the body. BSA takes both the patient's height and weight into account, giving doctors an idea of how much chemotherapy should be used. Therefore, a greater BSA because of a high weight results in a greater calculated dose. However, many physicians are hesitant to give this higher calculated dose for fear of causing toxic side effects. The right dose must be properly balanced: give too little and the chemotherapy will be ineffective; give too much and the patient will suffer from many toxic side effects.

While the chemotherapy doses that were given to an overweight or obese woman were still higher than what is normally given a thin person, many doctors decided to lower the recommended dose because they were wary about the side effects. As such, 60 percent of the practices surveyed reduced the therapy dose by more than 10 percent.

"We're uncertain of what happens to chemotherapy drugs in the body of a heavy person," said Dr. Jennifer Griggs, lead author of the study from the University of Rochester, "And physicians feel better if something happens because of the disease, rather than from the treatment."

Despite concerns of side effects, women in the study who were given full doses of chemotherapy were subsequently found to be less likely to be admitted for neutropenia than women of normal weight. Neutropenia is serious side effect of chemotherapy where the body fails to produce enough white blood cells; a lack of white blood cells results in an inability to fight off infections.

It was shown that many doctors even add an additional round of chemotherapy for patients with reduced doses, extending the time that patients will have to cope with side effects. However, doctors have good techniques for managing the basic side effects of chemotherapy, like hair loss and nausea, and Griggs advises her colleagues not to reduce the dose, but to "give the patient support through the side effects."

In fact, previous studies have shown that using actual body weight for calculating chemotherapy doses is associated with improved survival rates in overweight and obese women. These findings suggest that the recommended doses based on BSA would not affect heavy women in an excessively negative way and may even lower the rate of recurrence.

Griggs hopes that this study will stimulate the creation of more specific guidelines for chemotherapy dosing. In the meantime, she advises overweight and obese women to insist that their doctor give them their full chemotherapy dose.