This phase III, multicenter, randomized, open-label trial evaluates whether aromatherapy plus standard antiemetic therapy improves complete response (CR) of CINV compared with standard therapy alone in breast cancer patients receiving highly emetogenic chemotherapy (HEC). Despite guideline-recommended triple prophylaxis (5-HT3 antagonist, NK-1 antagonist, dexamethasone), 30-50% of patients still develop delayed CINV. Aromatherapy with lemon, lavender, and peppermint essential oils may provide additive benefit through olfactory-limbic and vagal pathways, but phase III evidence is lacking. 374 patients (aged 18-80) scheduled for at least two HEC cycles will be randomized 1:1, stratified by prior CINV. On chemo day, aromatherapy starts 30 min before and continues until 2 h after chemotherapy; on days 2-5, inhalation is at least 2 h daily.Primary endpoint: complete response (no vomiting, no rescue antiemetic) over 0-120 h. Key secondary endpoints: acute and delayed CR rates, complete/total control rates, time to treatment failure, quality of life (FLIE), anxiety, depression, sleep quality, and safety. Exploratory: plasma GDF15 dynamics and predictive value.