Abstract
3601 Background: CET-induced hMg was reported as an early predictor of improved clinical outcomes in advanced colorectal cancer (ACC) [Vincenzi, 2010]. We explored this relationship in a prior clinical trial of CET plus BSC versus BSC in patients with pretreated ACC, in which magnesium (Mg) was prospectively collected at baseline and monthly. Methods: End of month 1 (EM1) hMg grade and percent reduction (≥20% vs <20%) of Mg from baseline was correlated with patient characteristics and outcomes (by landmark analysis). Results: The baseline median Mg was 0.83 (range 0.33-1.29) and 0.83 mmol/L (range 0.55-1.05) for patients on CET (N=260) and BSC (N=251) respectively, and decreased to 0.77 mmol/L (0.27-1.04) and 0.82 (0.51-1.06) respectively at EM1. The median % Mg reduction at EM1 was respectively 10% (-42.4 to 63.0%) for patients on CET and 0% (-21.1 to 25%) on BSC [p<0.0001]. Mg reduction ≥20% occurred in 32 (15.6%) patients on CET and 1 (0.7%) on BSC [p<0.0001]. The OS by Mg grade and reduction from baseline for CET patients are shown in the table. Grade ≥1 hMg or ≥20% reduction from baseline at EM1 was associated with worse OS (aHR 1.61; 95% CI 1.12 - 2.33, p=0.01 and 2.08; 95% CI 1.32 - 3.29, p=0.002, respectively) in multivariate analysis including grade of rash (0 or 1 v 2+). Dyspnea was higher in patients with ≥20% Mg reduction (68% vs. 45%; p=0.02). Dose intensity did not differ based on grade or % reduction of Mg. Quality of life data will be presented. Conclusions: In contrast to prior reports, grade ≥1 (and ≥20% reduction from baseline) CET-induced hMg was associated with poor OS, even after adjustment for grade of rash. Mg Median OS Adjusted HR (aHR) N Months 95% CI HR 95% CI p All Grade 0 163 8.0 6.6-9.8 0.63 0.43-0.91 0.01 >0 53 3.7 3.0-5.0 Reduction <20% 172 7.6 6.4-9.5 0.50 0.32-0.78 0.003 ≥20% 31 3.8 2.7-4.9 Wild type KRAS Grade 0 73 9.9 8.3-11.6 0.45 0.22-0.91 0.03 >0 17 4.4 2.3-9.8 Reduction <20% 75 9.8 8.0-10.9 0.43 0.18-1.04 0.06 ≥20% 9 6.5 5.0-9.8 Mutated KRAS Grade 0 45 5.6 4.8-8.2 0.44 0.22-0.91 0.03 >0 17 3.5 2.1-5.5 Reduction <20% 49 5.9 4.2-8.2 0.53 0.21-1.35 0.18 ≥20% 10 3.3 2.0-4.8
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