The impact of sarcopenia on toxicity and pharmacokinetics of 5-fluorouracil (5FU) in colorectal cancer.
633 Background: Great heterogeneity exists in the ability of adults with cancer to tolerate treatment. Variability in body composition may affect rates of metabolism of cytotoxic agents and contribute to the variable chemotherapy toxicity observed. The goal of this study was to explore the impact of body composition, in particular sarcopenia, on the pharmacokinetics of 5-fluorouracil (5FU) in a cohort of patients receiving FOLFOX +/- bevacizumab for colorectal cancer. Methods: We performed a secondary analysis of a completed multicenter trial that investigated pharmacokinetic-guided 5FU in patients receiving mFOLFOX6 +/- bevacizumab [Patel et al. The Oncologist 2014]. Computed Tomography (CT) images that were performed as part of routine care were used to for body composition analysis. Skeletal muscle area (SMA) and density (SMD) were analyzed from CT scan L3 lumbar segments using radiological software. SMA and height (m2) were used to calculate skeletal muscle index (SMI = SMA/m2). Skeletal Muscle Gauge (SMG) was created by multiplying SMI x SMD. Differences were compared using two group t-tests and fisher’s exact tests. Results: Of the 70 patients from the original study, 25 had available CT imaging. The mean age was 59, 52% female, 80% Caucasian, and 92% with either stage III or IV disease. Eleven patients (44%) had grade 3/4 toxicity, and 12 patients were identified as sarcopenic (48%) [per Martin et al. JCO 2013]. Sarcopenic patients had numerically higher first cycle 5FU AUCs compared to non-sarcopenic patients (19.3 vs. 17.3 AUC, p= 0.43) and higher grade 3/4 toxicities (50 vs 38.5%, p= 0.70). Patients with low SMG ( < 1475 AU) had higher grade 3/4 toxicities (62 vs 25%, p= 0.11) and higher hematologic toxicities (46 v 8%, p= 0.07). Conclusions: CRC patients with sarcopenia had numerically higher first cycle AUCs of 5FU and a higher incidence of severe toxicities; however, this was not statistically significant, possibly due to limited sample size. SMG, an integrated muscle measure, was more highly correlated with toxicity outcomes than either SMI or SMD alone. Further research exploring the role of body composition in pharmacokinetics is needed with a focus on alternative dosing strategies in sarcopenic patients.