For some obese women with breast cancer, cutting chemotherapy doses "should be avoided," write researchers in The Lancet.
The finding only relates to premenopausal women whose breast cancer cells are not sensitive to hormone therapies such as tamoxifen (called estrogen-receptor negative tumors). Breast cancer is more common among older women.
The report comes from researchers including Marco Colleoni, MD, of the medical oncology division of the European Institute of Oncology in Milan, Italy.
Colleoni and colleagues didn't do a new experiment. Instead, they reviewed four trials from the International Breast Cancer Study Group.
— Obese women were more likely to have their chemotherapy dose reduced than women of normal or intermediate body mass index (BMI).
— Outcomes were worse for obese women with estrogen-receptor negative tumors who had reduced chemotherapy doses.
— No such pattern was seen for obese women with estrogen-receptor positive breast cancer.
Obese women with estrogen-receptor negative tumors who had reduced chemotherapy doses had worse odds for survival and for disease-free survival.
Hormone receptor status helps predict whether cancer will come back after it has been treated (recurrence).
Receptor-positive tumors have a slightly lower chance of recurrence than receptor-negative tumors. Receptor-positive tumors can be treated with hormone therapy alone or in combination with chemotherapy, which helps reduce recurrence and improves survival after a diagnosis of breast cancer.
Hormone receptor-negative cancers are not treated with medications such as tamoxifen; they are treated with a combination of anticancer drugs.
Chemotherapy doses are usually calculated based on the surface area of a person's body or their ideal body weight.
But a patient's overall health has to be considered, along with chemotherapy's toxic effects. For those reasons, some doctors dial down the chemo dose for obese patients.
"Few data are available to lend support to these policies," write Colleoni and colleagues.
In June, another team of scientists studied the same subject. They found that overweight or obese women with breast cancer may do better with a full dose of chemo. Their report was published in the Archives of Internal Medicine.
"Given the effects seen, the issue has some urgency," write Lars Holmberg, MD, and colleagues in an editorial for The Lancet.
Calling for more studies, they write that if the interactions seen in the study are valid, "this line of research adds one more piece to the puzzle about body-mass index and tumor biology."
Holmberg works at the Regional Oncologic Centre at University Hospital in Uppsala, Sweden. He and the other editorialists did not work on Colleoni's study.
SOURCES: Colleoni, M. The Lancet, Aug. 24, 2005; online edition. WebMD Medical News: "Breast Cancer Chemo: Lower Dose for Obese?" Holmberg, L. The Lancet, Aug. 24, 2005; online edition.