Genotype-Directed Study Of Irinotecan Dosing In FOLFIRI + BevacizumabTreated Metastatic Colorectal Cancer

This study involves standard combination chemotherapy treatment for colon cancer, 5-Fluorouracil (5FU), leucovorin and irinotecan (known as FOLFIRI), plus bevacizumab (Avastin). The study is designed to test the FOLFIRI regimen based on certain characteristics of a person's genetic makeup or "genes". Genes are made of DNA and determine not only inherited traits or appearance (hair and eye color, height, body type, etc.) but also play an important role in health and how the body responds to illness and treatments for those illnesses. In this study, the investigators will examine the relationship between a patient's genes (DNA), or "genotype", and how the patient's body breaks down and removes or "metabolizes" the anti-cancer drug irinotecan. Circulating blood level of irinotecan plays an important role in how well this drug works against a patient's cancer as well as the adverse side effects the patient may experience. The current standard dose of irinotecan was determined in clinical trials without knowing individual genotypes and thus does not take into account a patient's ability to metabolize irinotecan. This means that based on one genotype the current standard dose of irinotecan may be correct or based on other genotypes the standard dose could result in lower and possibly less effective blood levels and result in significant under-dosing of irinotecan. Based on genotype the patient will be assigned to one of the following doses of irinotecan: * 180 mg/m2 (standard dose) * 260 mg/m2 * 310 mg/m2 The purpose of this research study is to determine if dosing irinotecan based on genotype is effective and safe for patients with colon cancer. Patient genotype will be determined from a small sample of blood and a laboratory test or "assay" performed at University of North Carolina Laboratories. For the purpose of this study, this assay is new and considered to be "investigational". This means that the genotype assay used in this study has not yet been approved by t