LAUSR

423Background: 5-FU, IRI, and nab-paclitaxel (NP) are active in advanced GI cancers; the combination (FOLFIRABRAX) has not been evaluated. UGT1A1 clears SN-38, the active metabolite of IRI. UGT1A1*28 polymorphism reduces enzymatic activity and predisposes to severe IRI toxicity. Dose adjustment in patients with this allele may be warranted. Primary objective: to determine the dose-limiting toxicity (DLT) rate of FOLFIRABRAX with genotype-guided dosing of IRI. Secondary objectives included determining objective response rates (ORR) in GI cancers. Methods: Pts with previously untreated GI cancers and ECOG performance status 0/1 received FOLFIRABRAX with prophylactic pegfilgrastim Q14 days. CT scans were obtained Q8 weeks. UGT1A1 *1/*1, *1/*28, and *28/*28 patients (pts) received initial IRI doses of 180, 135, and 90mg/m2, respectively. 5-FU 2400mg/m2 over 46 hours (no bolus), leucovorin 400mg/m2, and NP 125mg/m2 were given IV Q14 days. DLT during cycle 1 was defined as Grade (Gr) 3/4 febrile neutropenia (FN...