Relationship Between Platinum Levels in the Blood and Neurotoxicity in Patients Who Are Receiving Oxaliplatin for Gastrointestinal Cancer

RATIONALE: Learning about the relationship between platinum levels in the blood and neurotoxicity in patients receiving oxaliplatin may help plan treatment and may help patients live more comfortably. PURPOSE: This phase IV trial is studying the relationship between platinum levels in the blood and neurotoxicity in patients who are receiving oxaliplatin for gastrointestinal cancer.