Association of body surface area with fat mass, free fat mass and total weight in healthy individuals, and implications for the dosage of cytotoxic drugs

Background & aims: In oncology, the dosage of anti-neoplastic drugs is generally adapted to the patient's body surface area (BSA). We investigated the potential differences between BSA and body weight (BW) in estimating the variability in body composition among individuals, especially older adults. Materials and methods: The study population included 322 community-dwelling individuals with different age and sex: 45 adult men (AM, age 18–65 years), 86 older men (OM, age >65 years), 54 adult women (AW, age 18–65 years), and 137 older women (OW, age >65 years). For each participant, we estimated the body composition with dual-energy X-ray absorptiometry, and we calculated the BSA using the DuBois and DuBois formula. The strength of relationships between fat free mass (FFM) and fat mass (FM) with BSA, BW, and BMI were expressed as correlation (r) and determination coefficients (R2). Results: Most of the included sample was normal weight (45.7%) or overweight (41.9%). FFM demonstrated a stronger association with BSA than with BW or BMI in all age/sex groups, with r ranging from 0.831 to 0.924 (p < 0.001 for all) and R2 from 0.691 to 0.853. Conversely, BW and BMI were more strongly related to FM than BSA, especially in women. For such relationship, BW, in particular, showed r ranging from 0.793 to 0.924 (p < 0.001 for all). Conclusions: This study suggests that BSA may be more appropriately used to estimate FFM, compared with BW. Instead, alternative parameters should be considered to estimate FM in patients at risk for adverse effects of lipophilic drugs, especially in older age.