The purpose of this study is to investigate the association between UGT1A1 polymorphisms and neutropenia and diarrhea in Korean patients with advanced colorectal or gastric cancer treated with FOLFIRI regimen.

Inclusion Criteria:Subjects should meet all of the following criteria to participate in the trial.

• Histologically confirmed colorectal or gastric cancer patients who are chemonaive or failed to 1st line chemotherapy

• Subjects who are expected to receive toxicity test at least once after FOLFIRI treatment.

• Aged 18 years or older.

• ECOG performance status of ≤ 2.

• Anticipated life expectancy of ≥ 3 months.

• Clinically acceptable function of bone marrow, kidney and liver function as below.

  1. ANC ≥ 1500/mm3 and platelet count ≥ 100,000/mm3
  2. Serum total bilirubin ≤ 1.5 x ULN, alkaline phosphatase ≤ 2.5 x ULN, Serum ALT and AST ≤ 2.5 x ULN (Serum ALT and AST ≤ 5 x ULN, if liver metastases are present)
  3. Serum creatinine ≤ 1.5 mg/dL or CLcr > 60 ml/min

• Subjects whose written informed consent can be obtained prior to their participation in the trial.

Exclusion Criteria: Subjects who meet any of the following criteria should not be included in the trial.

• Pregnant or breast feeding women
• Serious concurrent complication, severe active infection.
• Subjects with chronic diarrhea, paralytic ileums, pulmonary fibrosis or pneumonia interstitialis
• Subjects with epilepsia or severe psychiatric disorders.
• Subjects who are regarded to be unsuitable for this trial by the investigator.
• Subjects who are participating in other clinical trials
• Subjects who have received prior chemotherapy including irinotecan.