Evaluation of combinational effect of Aprepitant on nausea and vomiting induced by chemotherapy (moderate risk) in patients with Gastric Cancer or Colorectal Cancer

Interventions: Group A: * 1st course : Conventional therapy (Palonosetron 0.75 mg i.v. on 1st day + Dexamathasone 9.9 mg i.v. on 1st day, 8 mg p.o. on 2nd day and 3rd day) * 2nd course : Conventional therapy (Palonosetron 0.75 mg i.v. on 1st day + Dexamathasone 4.95 mg i.v. on 1st day, 4 mg p.o. on 2nd day and 3rd day) plus Aprepitant (125 mg p.o. on 1st day, 80 mg p.o. on 2nd day and 3rd day) Group B: * 1st course: Conventional therapy (Palonosetron 0.75 mg i.v. on 1st day + Dexamathasone 4.95 mg i.v. on 1st day, 4 mg p.o. on 2nd day and 3rd day) plus Aprepitant (125 mg p.o. on 1st day, 80 mg p.o. on 2nd day and 3rd day) * 2nd course : Conventional therapy (Palonosetron 0.75 mg i.v. on 1st day + Dexamathasone 9.9 mg i.v. on 1st day, 8 mg p.o. on 2nd day and 3rd day) Primary outcome(s): * Frequency of vomiting * Severity of nausea Study Design: Cross-over Randomized