Anti-emetic Prophylaxis With or Without Dexamethasone

Inclusion Criteria: 1. Breast cancer patients receiving their first anthracycline/cyclophosphamide-based HEC regimen (cyclophosphamide 600 mg/m², epirubicin 90-100 mg/m²); divided doses excluded. 2. No prior chemotherapy. 3. Aged 18-70 years. 4. ECOG performance status 0 or 1. 5. Adequate organ function: (including absolute neutrophil count≥1,500/mm3, WBC count≥3,000/mm3, platelet count≥100,000/mm3, AST\< 2.5×the upper limit of normal (ULN), ALT\< 2.5×ULN, bilirubin\< 1.5×ULN, creatinine\< 1.5×ULN). 6. No nausea or vomiting within 24 hours before registration. 7. Negative pregnancy test within 7 days prior (women of childbearing potential). 8. No severe cognitive impairment. 9. No hypersensitivity to fosaprepitant, tropisetron, olanzapine, and dexamethasone. 10. No significant cardiac issues: arrhythmia, recent heart failure, or myocardial infarction within 6 months. 11. No symptomatic brain metastasis or carcinomatous meningitis. 12. No diabetes requiring insulin or oral medication. 13. No use of prohibited medications within 48 hours before registration or during treatment. 14. Informed consent obtained. Exclusion Criteria: 1. History of allergic reactions to study drugs or their analogues. 2. Nausea and vomiting requiring antiemetic treatment at registration. 3. Pregnant or nursing women, those who may become pregnant, or those not planning to use contraception. 4. Mental illness or psychiatric symptoms interfering with daily activities, making study participation difficult. 5. Diabetes treated with insulin/oral hypoglycemics or HbA1c (NGSP) ≥ 6.5% or HbA1c (JDS) ≥ 6.1% at registration. 6. Recent (within 6 months) unstable angina, myocardial infarction, cerebral hemorrhage, cerebral infarction, or active gastroduodenal ulcer. 7. Convulsive disorders requiring anticonvulsants, ascites needing therapeutic puncture, or gastrointestinal obstruction. 8. Inability to be hospitalized for up to 120 hours (Day 6) post-AC administration initiation. 9. Any other conditions deemed inappropriate for study participation.