Implementing Pharmacogenetic Testing in Gastrointestinal Cancers

Inclusion Criteria: 1. Able and willing to provide informed consent 2. Male or female, aged 18 years or older at the time of study initiation 3. Pathologically confirmed gastrointestinal malignancy for which treatment with a fluoropyrimidine and/or irinotecan is indicated 4. Willing to undergo blood or saliva sampling for PGx testing and comply with all study-related procedures 5. Life expectancy of at least 6 months Exclusion Criteria: 1. Prior treatment with irinotecan 2. DPYD or UGT1A1 genotype already known 3. Severe renal or hepatic impairment (or unacceptable laboratory values), including: * Neutrophil count of \<1.5 x 109/L, platelet count of \<100 x 109/L * Hepatic function as defined by serum bilirubin \>1.5 x upper limit of normal (ULN), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) \>2.5 x ULN, or in case of liver metastases ALT and AST\>5 x ULN * Renal function as defined by serum creatinine \>1.5 x ULN, or creatinine clearance \<60 ml/min (by Cockcroft-Gault Equation) 4. Women who are pregnant or breast feeding, or subjects who refuse to use reliable contraceptive methods throughout the study 5. Treating physician does not want subject to participate