Racial differences in the pattern of hematologic toxicity in the treatment of colorectal cancer.

679 Background: 5-fluorouracil (5-FU), a synthetic fluoropyrimidine, is a critical component of chemotherapy in many cancers. Its metabolites inhibit Thymidylate Synthetase (TS) causing cessation of DNA synthesis and are misincorporated into DNA and RNA causing ineffective DNA repair and faulty mRNA splicing. The rate limiting step in the catabolism of 5-FU is by the Dihydropyrimidine Dehydrogenase enzyme (DPD) which catabolizes over 80% of 5-FU. Patients with near total DPD enzymatic deficiency develop life threatening toxicity after a single administration and those with less severe deficiency will have delayed elimination of 5-FU and slowly accumulate active metabolites leading to toxicities. Methods: We conducted a pilot retrospective cohort study of African American (AA) and Caucasian patients treated for colorectal cancer over a 9 year period, 2000 – 2008, in this IRB approved study. The primary outcome of interest was the rate of development of grade 3 or 4 neutropenia (Absolute Neutrophil Count <1...