Overweight or obese women with breast cancer may benefit from getting a full dose of chemotherapy, says a new study in the Archives of Internal Medicine.

However, some doctors may be reducing chemo doses for such patients, say the researchers, who included Jennifer Griggs, MD, MPH, of the University of Rochester.

“Overweight and obese women with breast cancer often receive intentionally reduced doses of adjuvant chemotherapy,” say Griggs and colleagues. Receiving a full, weight-based dose “is likely to improve the outcomes in this group of patients,” they write in the journal’s June 13th edition.

That’s especially important these days, with obesity rising in the U.S., according to the study.

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What’s Weight Got to Do With It?

Chemotherapy is widely used after breast cancer surgery. Breast cancer is the most common cancer among U.S. women, except for nonmelanoma skin cancers. More than 211,000 new cases will be diagnosed this year, says the American Cancer Society.

Obesity is a risk factor for developing breast cancer. It can also worsen the prognosis for breast cancer patients, say Griggs and colleagues. But they don’t want to oversimplify matters. Many factors are involved in the obesity-breast cancer association, they say.

Doctors may cut chemo doses for patients who aren’t in good health (apart from their cancer). Some small studies have shown that some chemotherapy drugs linger longer in the bodies of obese patients, but Griggs and colleagues say “there is little evidence to support the use of dose reductions in these patients.”

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Chemotherapy Dose-Weight Study

Griggs’ study looked at doses of two chemotherapy drugs -- doxorubicin and cyclophosphamide -- in more than 9,600 women with breast cancer treated at about 900 practices.

Most were healthy, except for their breast cancer; few had other serious medical problems. They were treated from 1990 to 2001.

More than six out of 10 women were overweight or obese (31 percent overweight, 17 percent obese, and 14 percent severely obese), says the study. Chemo doses were reduced for 37 percent of the severely obese women, 20 percent of obese women, and 11 percent of overweight women.

Overweight is defined as a body mass index or BMI of 25-29.99; a BMI of 30-39.99 is obese, and 40 or higher is morbid or severe obesity.

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Practices Vary

The practices took different approaches; some didn’t cut back at all on chemo doses for heavier patients.

More than half (about 500 practices) had at least five patients who were overweight, obese, or severely obese. A third of those practices didn’t reduce chemo doses. Another 10 percent only cut the dose in 10 percent or fewer of their patients.

However, a small percentage of practices (9 percent) reduced the first-cycle dose in more than half of their overweight or obese patients. Few patients at any of the study’s practices got higher doses after the first chemo cycle.

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Long-Term Effects Unknown

The study didn’t focus on long-term survival or cancer recurrence.

In the short-term, women who were overweight, obese, or severely obese were not more likely to be hospitalized for chemo-related drops in white blood cells (febrile neutropenia), regardless of their chemo dose. In fact, severely obese women were less likely to be hospitalized for that health problem, says the study.

Evidence is gathering that “obese patients do not experience increased toxic effects when dosed according to actual body weight,” say the researchers. Calculating chemo doses based on actual body weight is associated with “improved disease-free and overall survival in heavy patients,” they say.

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By Miranda Hitti, reviewed by Charlotte E. Grayson, MD

SOURCES: Griggs, J. Archives of Internal Medicine, June 13, 2005; vol 165: pp 1267-1273. American Cancer Society, “What Are the Key Statistics for Breast Cancer?” News release, JAMA/Archives.