Purpose: Obesity and breast cancer are common conditions that often coexist. Concerns of relative overdosing of chemotherapy in the large cancer patient have led clinicians to apply empiric dose reductions, 'cap' the body surface area (BSA) at 2 m2, or use ideal rather than actual body weight to calculate BSA. There are no data supporting or refuting these practices and their prevalence is unknown. We sought to determine the distribution of body size and prevalence of obesity in the breast cancer population of our cancer centre, and to determine clinician chemotherapy dosing practices in the era of modern adjuvant chemotherapy.
Patients and methods: Women with invasive breast cancer receiving systemic therapy at our institution between 1980 and 1998 were identified and their recorded height and weight were used to calculate BSA and body mass index (BMI). We reviewed the first cycle adjuvant chemotherapy dosing practices from 1990-1998. The ideal dose of chemotherapy was calculated based on calculated BSA, and then contrasted with the actual dose received at cycle one. Discrepancies were recorded and categorized, using the largest single drug reduction if more than one drug was reduced.
Results: Mean BMI in the systemic therapy population was 26.4 +/- 5.3 kg/m2, 54% were overweight, 2% severely obese and 18% moderately so. Their mean BSA was 1.7 +/- 0.2 m2 and only 5% had a BSA > or = 2 m2. In the adjuvant chemotherapy subgroup, most patients received > or = 85% of their ideal dose. The mean dose reduction was 5.3 +/- 11.3% versus 9.9 +/- 11.3% in the BSA < 2 and > or = 2 m2 groups, respectively (p = 0.02), and 4.3 +/- 8.2% versus 6.7 +/- 13.1% in the BMI < 25 and > or = 25 kg/m2 groups, respectively (p = 0.008). While only 24% of chemotherapy dose reductions of > or = 15% were in the BSA > or = 2 m2 group, 76% were in the BMI > or = 25 kg/m2 group.
Conclusions: Obesity is prevalent in this breast cancer population. BSA is not a sensitive index of large body size. We consistently detected more frequent empiric dose reductions at cycle one of adjuvant chemotherapy, with reductions of greater magnitude in the largest women (BSA > or = 2 m2) and those who were overweight (BMI > or = 25 kg/m2).