Addition of aprepitant, an NK1 receptor antagonist to a 5-HT3 receptor antagonist and dexamethasone regimen was shown to be effective for prevention of chemotherapy-induced nausea and vomiting (CINV) with moderately emetogenic chemotherapy (MEC). Little is known about the efficacy of aprepitant when used without dexamethasone. Dexamethasone is widely used to prevent both acute and delayed nausea and vomiting induced by chemotherapy. However, multi-period use of dexamethasone could be associated with side effect, such as hyperglycemia, dyspepsia and insomnia. This randomized phase III trial studies antiemetic therapy with aprepitant and tropisetron to see how well they work compared to dexamethasone plus tropisetron in preventing chemotherapy-induced nausea and vomiting in patients with colorectal cancer receiving FOLFOX(oxaliplatin, leuvovorin and 5-fluorouracil) chemotherapy.

Inclusion Criteria:

• Diagnosis of colorectal cancer
• No prior chemotherapy and scheduled to receive FOLFOX chemotherapy (oxaliplatin,leucovorin and 5-fluorouracil)
• Age ≥18 years
• Eastern Cooperative Oncology Group (ECOG) Performance Status 0, 1 or 2
• Laboratory index: Hemoglobin ≥ 90 g/L (No blood transfusion within 14 days), Absolute Neutrophil Count ≥ 1.5×10^9/L, Platelet Count ≥ 75×10^9/L, Serum Bilirubin ≤ 1.5×ULN, ALT and AST ≤ 3.0×ULN (without liver metastases), ALT and AST ≤ 5.0×ULN (with liver metastases), Serum Creatinine ≤ 1×ULN, Endogenous Creatinine Clearance>60ml/min
• Be able to read, understand and complete the questionnaire and diary
• Be able to understand the study procedures and sign informed consent.

Exclusion Criteria:

• Treatment with any other study medicine within 4 weeks before enrollment.
• Nausea or vomiting ≤ 24 hours prior to registration
• Ongoing emesis due to obstruction of digestive tract
• Concurrent use of olanzapine, phenothiazine or amifostine
• Female with pregnancy or lactation
• Severe cognitive compromise
• Known history of CNS disease (e.g. brain metastases, seizure disorder)
• Concurrent abdominal radiotherapy
• Chronic alcoholism
• Known hypersensitivity to aprepitant, tropisetron, or dexamethasone.
• Known cardiac arrhythmia, uncontrolled congestive heart failure or acute myocardial infarction within the previous six months.
• History of uncontrolled diabetes mellitus
• Serious or uncontroled infection
• Known active HIV, viral hepatitis or tuberculosis infections