Women who are 20 to 25 percent over their ideal body weight have a 1.3 times greater risk of a recurrence of breast cancer, according to background information in the article. Differences in body chemistry in overweight and obese women, including differences in estrogen and insulin levels, may account for their poorer prognosis, but, the authors suggest, there is evidence that inadequate doses of adjuvant chemotherapy may also contribute to the differences in outcome. Adjuvant chemotherapy is given to women with no measurable spread of the cancer beyond the primary tumor to improve the likelihood of disease-free and overall survival. Physicians may deliberately reduce dosage levels, which are calculated on the basis of body weight, for heavier women because of fears of toxic effects, the authors write.
Jennifer J. Griggs, M.D., M.P.H., of the University of Rochester, Rochester, N.Y., and colleagues analyzed data on patients with early stage breast cancer treated with adjuvant therapy between 1990 and 2001. They determined the quality of the therapy as measured by the use of reduced doses for the first treatment compared with standard doses, dose proportion over the course of the therapy and the relative dose intensity. There were 9,672 women from 901 practices included in the study. Of the women, 62 percent were above a healthy weight, 31 percent were overweight, 17 percent were obese and 14 percent were severely obese.
Among the severely obese women, 37 percent had a first-cycle dose reduction of at least 10 percent, compared with 20 percent of obese women, 11 percent of overweight women and nine percent of healthy weight women. The practices varied widely in their use of first-cycle dose reductions in their overweight and obese breast cancer patients. Although 60 percent of the practices reduced the doses in more than 10 percent of their overweight and obese patients, 33 percent of practices did not reduce doses for any of their overweight and obese patients.
"However, given the evidence that maintaining dose intensity improves the likelihood of overall and disease-free survival and the lack of data supporting dose reductions in overweight and obese women, it is likely that the practice variations we have observed represent 'unwarranted variation' in the adjuvant treatment of patients with breast cancer," the authors write. "The incidence of obesity, particularly severe obesity, is increasing in the United States. Eliminating unwarranted dose reductions will therefore become increasingly important in defining best practices for the care of overweight and obese women."
(Arch Intern Med. 2005; 165:1267-1273. Available post-embargo at www.archinternmed.com.)
Editor's Note: Gary H. Lyman, M.D., M.P.H., one of the co-authors, has served on the speaker's bureau for Amgen and Ortho Biotech and has received research support from Amgen and GlaxoSmithKline.
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Archives of Internal Medicine