This study was a multicenter, prospective, controlled trial involving 120 breast cancer patients receiving T-DXd-based therapy. Participants were randomly assigned to either the experimental group (NEPA plus megestrol acetate) or the control group (NEPA plus dexamethasone), with 60 patients in each group. The intervention was administered over two treatment cycles. During this period, the onset time, frequency, and severity of nausea and vomiting were recorded and subjected to statistical analysis.

The primary objective of this study was to evaluate the efficacy and safety of netupitant/palonosetron capsules (NEPA) combined with megestrol acetate compared to the standard triple antiemetic regimen (NEPA plus dexamethasone) in preventing chemotherapy-induced nausea and vomiting (CINV) in breast cancer patients undergoing T-DXd-containing regimens. The findings aim to generate clinical evidence to support optimal antiemetic management, minimize the risk of dose reduction or treatment discontinuation due to gastrointestinal adverse events, and ultimately improve patient quality of life.

Inclusion Criteria:

1. The patient is at least 18 years of age;
2. The patient has a histologically or cytologically confirmed diagnosis of breast cancer;
3. The patient is receiving full-dose trastuzumab deruxtecan (T-DXd) monoclonal antibody therapy for the first time;
4. The patient has an Eastern Cooperative Oncology Group (ECOG) performance status score of 2 or lower;
5. The patient voluntarily agrees to comply fully with the study protocol requirements and has provided written informed consent.

Exclusion Criteria:

1. The patient is currently taking medications that may interfere with the assessment of nausea or vomiting, including but not limited to other 5-HT3 receptor antagonists, NK1 receptor antagonists, psychotropic agents, or opioid analgesics;
2. The investigator determines that the patient's nausea or vomiting is highly likely attributable to anti-tumor treatments not involving antibody-drug conjugate (ADC) therapy;
3. The patient is deemed unsuitable for glucocorticoid or progesterone use;
4. The patient has a history of hypersensitivity to netupitant, palonosetron, or any excipient in the capsule formulation;
5. The patient has significant gastrointestinal conditions affecting oral drug absorption, such as dysphagia, chronic diarrhea, or intestinal obstruction;
6. The patient has a severe psychiatric disorder or difficulties understanding the study procedures, completing questionnaires, or communicating effectively in Chinese;
7. The investigator identifies any other condition that may compromise the conduct of the clinical study or the interpretation of its results.