317 Background: CDDP-based treatment is limited by AKI. We aimed to test whether a novel AKI biomarker, uCyC, measured before and immediately after CDDP administration could permit earlier identification of UC pts at risk for AKI. Methods: In a nested case-control study, pts treated with CDDP were prospectively enrolled. uCyC was measured 2 hours pre- and 3 hours post-CDDP doses, with values normalized to urine creatinine. AKI was defined as an increase in serum creatinine (sCr) by ≥50% (severe cases) or ≥0.3 mg/dL above pre-CDDP baseline. Controls were pts with no significant sCr rise (sCr change <25% and <0.3 mg/dL). A sample size of 98 patients provided 80% power to detect a true difference in biomarker change pre- and post-CDDP between cases and controls. Results: 102 pts were enrolled: 47 had UC, and 55 had other cancers; 76 were male; 82 Caucasians/15 African Americans. 4 pts not providing urine samples were excluded from analysis. For the entire cohort, average pre-CDDP sCr was 0.98 mg/dL and mean cumulative CDDP dose was 220 mg/m2. Controls were younger (mean 59.2 vs 65.9 yrs, p=0.01). 25 pts (26%) developed AKI; 15 (15%) were severe cases. UC pts had a significantly increased risk of AKI compared with non-UC pts (UC n=17 [37%] vs non-UC n=8 [16%], Relative Risk 2.2, 95% CI 1.08-4.73; p=0.03). AKI risk did not correlate with total CDDP dose received. In AKI pts, uCyC increased temporally in accordance with sCr and did not increase in controls, but immediate uCyC changes (3 hrs post-CDDP) were not detectable in cases or controls. However, in UC severe cases, pre-CDDP uCyC was consistently higher than in UC controls (183 ng/mg vs 109 ng/mg, p=0.04). Additionally, in UC AKI pts compared to UC controls, average maximum (peak) uCyC was higher (1812 ng/mg vs 244 ng/mg, p=0.04). Baseline uCyC did not correlate with age, and there were no significant differences in age or baseline sCr between UC cases and controls. Conclusions: UC pts are over two times more likely to develop AKI with CDDP chemotherapy than pts with other cancers, even when pre-CDDP sCr is normal. Pre-treatment uCyC levels may have value in predicting which UC pts are at highest risk of developing CDDP-induced renal injury.