Cape doses used to treat colorectal (CRC) and breast cancer (BC) are calculated using BSA. Cape dose is 1250 mg/m2 in CRC and 1000 mg/m2 in BC. Using BSA to calculate cape dose does not consider body composition. We hypothesize that differences in cape doses between CRC and BC patients (pts) is due to body composition differences between males (M) and females (F), not cancer type. Furthermore, low skeletal muscle density (SMD) is prognostic of poor survival in advanced cancers. As a secondary objective, we set out to determine if SMD was prognostic of outcomes in early stage CRC.
We performed a retrospective study of all pts diagnosed with early stage CRC treated with adjuvant cape from 2008-2012. Data was collected on demographics and cape doses at cycles 1 and 3. SMI and SMD were calculated using baseline CT scans.
183 pts (101 M, 82 F) were identified. F received higher starting cape doses compared to M based on SMI. Mean cape/SMI dose was 5107.4 mg/cm2/m2 (SD 1113.8) for F compared to 4711.9 mg/cm2/m2 (SD 870.6) for M (p = 0.009). At cycle 3, F still had higher doses of 3875.1 mg/cm2/m2 (SD 1663.5), but did not differ statistically from M pts at 3691.6 mg/cm2/m2 (SD 1629.5) (p = 0.5). Median recurrence free survival (RFS) for low SMD pts compared to high SMD pts was 72.8 vs 76.9 months (hazard ratio [HR] 1.80; p = 0.06). Patients with lower SMD were at higher risk of death (HR 2.81; p = 0.05); median overall survival was not reached.
F received higher cape doses/SMI than M at the CRC 1250 mg/m2 dose. After adjusting cape doses for DLTs, M and F CRC pts received the same cape dose/SMI. Our results suggest differences between CRC and BC cape dosing may be a consequence of body composition differences between M and F pts. SMI may be more useful than BSA when calculating cape doses. Our study showed low SMD was prognostic for OS probability and trended towards significance for RFS in adjuvant CRC pts.
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J. Spratlin: Conducted research project funded by Roche in the past 2 years. All other authors have declared no conflicts of interest.