Individualized Dose Escalation of 5-FU for Gastrointestinal Cancer

Inclusion Criteria:

* Age ≥ 18 years
* Diagnosis of metastatic or locally advanced/inoperable colorectal cancer or non-colorectal gastrointestinal cancer (including cancers of the stomach, esophagus, appendix, small bowel, and ampulla)
* Clinically appropriate staging imaging of the chest, abdomen, and pelvis performed within 30 days prior to registration
* ECOG Performance Status: 0-1

Exclusion Criteria:

* Any prior receipt of oxaliplatin or fluoropyrimidine chemotherapy (other than radiation-sensitizing fluoropyrimidine chemotherapy)
* Prior receipt of systemic chemotherapy in the 6 months prior to Day 1 of Cycle 1 of FOX (other than radiation-sensitizing chemotherapy)
* Known mismatch repair deficiency or microsatellite instability-high disease
* Known dihydropyrimidine dehydrogenase (DPD) deficiency, as identified by clinically indicated screening
* Any confirmed second malignancy that is likely to require systemic therapy during the course of the six-month study period, in the opinion of the enrolling investigator
* Any of the following baseline laboratory abnormalities:

  * Absolute neutrophil count (ANC) \< 2,500/mm3
  * Platelet count \< 100,000/mm3
  * Hemoglobin \< 9 g/dL
  * Creatinine \> 1.5 x ULN
  * Total bilirubin \> 1.5 x ULN
  * AST/ALT \> 5 x ULN
  * Patients who are unable to provide informed consent
  * Patients who are pregnant or breastfeeding
  * Patients who are incarcerated, homeless, or have active substance use disorders