A UGT1A1 genotype-guided dosing study of modified FOLFIRINOX (mFOLFIRINOX) in previously untreated patients (pts) with advanced gastrointestinal malignancies.

427Background: FOLFIRINOX improves survival compared with gemcitabine in advanced pancreatic cancer (PC), but with significant toxicity (Conroy, NEJM 2011). UGT1A1 clears SN-38, the active metabolite of irinotecan (IRI); UGT1A1*28 polymorphism reduces enzymatic activity and predisposes to severe IRI toxicity. We hypothesized that dosing mFOLFIRINOX based on UGT1A1 genotype would improve tolerability. The primary objective of this study (NCT01643499) was to determine whether genotype-guided dosing of IRI in mFOLFIRINOX is tolerable. A secondary objective was to describe objective response rates (ORR) in PC and biliary tract cancers (BTC). Methods: mFOLFIRINOX was given every 14 days. CT scans were obtained every 8 weeks. UGT1A1 *1/*1, *1/*28, and *28/*28 pts received initial IRI doses of 180, 135, and 90 mg/m2, respectively. 5-FU dose was 2400 mg/m2 over 46 hours (no bolus); leucovorin 400 mg/m2; oxaliplatin 85 mg/m2. In cohort 1 (tolerability cohort by genotype), prophylactic pegfilgrastim was not allowed...