Effect of obesity on the leukocyte nadir in women treated with adjuvant cyclophosphamide, methotrexate, and fluorouracil dosed according to body surface area.

Chemotherapy doses are sometimes reduced because of obesity in patients. This study examines the effect of parameters reflecting the body size, body weight and height, body mass index (BMI), and body surface area (BSA) on the depth of the blood leukocyte nadir in breast cancer patients receiving adjuvant chemotherapy, when drug dosing was based on the BSA. Three hundred and forty patients with node positive breast cancer without distant metastases were treated with 6 cycles of adjuvant postoperative CMF (cyclophosphamide 600 mg/m2, methotrexate 40 mg/m2, and 5-fluorouracil 600 mg/m2 i.v. every 3 weeks). Patients within the highest BMI had the highest leukocyte nadir values (Spearman correlation coefficient 0.3, p < 0.001). A high body weight and a large BSA were also associated with high leukocyte nadirs. We conclude that when the blood leukocyte nadir is used as a surrogate marker for the drug effect, obese patients receiving intravenous CMF have higher leukocyte nadirs than the lean ones. Therefore, the drug doses should not be reduced because of obesity, and even when obese patients are treated according to the scheduled doses they may remain slightly underdosed.