Prevention of Delayed CINV After Autologous Transplant: Olanzapine-Containing Regimen vs. Dexamethasone-Containing Regimen

Inclusion Criteria: * Patients with multiple myeloma who are indicated for autologous hematopoietic stem cell transplantation; * Preconditioning regimen consists of melphalan at a dose of 200 mg/m²; * ECOG performance status score of 0 to 2; * Age \>18 years and \<65 years; * Expected survival time \>3 months; * Absence of intracranial hypertension, gastrointestinal obstruction, or other causes of refractory vomiting; * Ability to understand and provide written informed consent. Exclusion Criteria: * Presence of nausea or vomiting within 48 hours prior to enrollment, with prior use of antiemetic medications; * Current use or use within the past month of CYP3A4 inducers, inhibitors, or substrate drugs; * History of hypersensitivity to fosaprepitant or olanzapine; * Serum creatinine clearance \<60 mL/min; * Inability to receive treatment and follow-up at the designated study site, or inability to comprehend, comply with the study protocol, or provide informed consent.