Obese Breast Cancer Patients Often Get Reduced Doses of Chemo

UR Study Warns that Systematic Undertreatment Threatens Survival

June 14, 2005

Jennifer Griggs, M.D., M.P.H.

In a study of 9,672 women treated across the country for breast cancer, University of Rochester doctors report in the current Archives of Internal Medicine that overweight and obese women received intentionally reduced doses of chemotherapy, which may contribute to poorer prognosis.

The issue of chemotherapy dosing is increasingly important as more Americans struggle with obesity, according to lead author Jennifer Griggs, M.D., MPH, a breast cancer specialist at the university’s James P. Wilmot Cancer Center.

Current standards call for doctors to figure chemotherapy doses based on body surface area (BSA), calculated by height and weight and expressed in square meters. But due to concerns that this formula might provide too much medication to large women and cause toxic side effects, some doctors typically make adjustments in three ways: Either they reduce the dose by some estimated amount (15 percent, for example), or they calculate the dose on the patient’s ideal body weight rather than the actual body weight, or they cap the dose at 2.0 meters. Practices vary among physicians and geographic areas.

Some doctors also make adjustments to the treatment schedule by reducing the dose in the first cycle of four planned rounds of chemotherapy, and then adding one or two additional cycles. While this strategy may boost the total amount of medication a woman receives, it does not achieve the intensity of four full doses, the study says.

Adjuvant chemotherapy is given to breast cancer patients whose disease has not spread but who are at risk for a recurrence. Large studies suggest that the benefits of chemotherapy are diminished when patients do not receive the full dose.

Griggs and colleagues researched the treatment given for Stage I, II, or III breast cancer patients who received chemotherapy between 1990 and 2001 at 901 oncology practices across the country. Obesity is both a known risk factor and a negative prognostic factor: Women who are 20 percent to 25 percent over their ideal body weight tend to suffer recurrences more often than lean women. Most patients in the study were otherwise healthy, but 62 percent were overweight, obese or severely obese.

Among the findings: First-cycle dose reductions of 10 percent or more were administered to 9 percent of the healthy-weight women, 11 percent of the overweight, 20 percent of the obese, and 37 percent of the severely obese women.

Furthermore, although doctors reduce doses out of concern for a patient’s safety and to decrease possible side effects such as fever and low white blood counts, the study found that when overweight or obese women are given full-weight doses, they are no more likely than thinner women to be admitted to the hospital for serious side effects. In fact, severely obese women were less likely to require hospitalization to treat chemotherapy side effects.

“Although many patients received reduced doses, most did not. It is clear there is some uncertainty among doctors on how best to dose chemotherapy in heavy patients,” Griggs says. “This study adds to other research by demonstrating that dosing chemotherapy using actual body weight is safe and may help address some of the uncertainty. We have here an opportunity to improve the quality of all aspects of cancer care.”

The James P. Wilmot Cancer Center funded the study. Amgen Inc., a California manufacturer of drugs that boost white blood cells, funded the initial data collection.

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