Research Background:Subcutaneous injection is an important route of administration in targeted therapy for breast cancer, but injection pain affects patients' treatment experience. Fluctuations in injection speed during traditional manual push may be one of the factors exacerbating pain, whereas machine-driven injection can provide a constant flow rate, theoretically reducing pain; however, high-quality evidence is lacking.

Research Objective:To compare the difference in pain intensity between instrument constant-speed injection and manual injection in breast cancer patients receiving subcutaneous injection of pertuzumab and trastuzumab.

Research Methods:A randomized self-controlled design is used, with data analysis performed using paired t-tests. The study plans to enroll 40 female breast cancer patients. Each patient receives two injection methods across two treatment cycles: instrument constant-speed injection (medical infusion pump, 2 mL/min) and manual injection (a nurse uses a stopwatch to time and simulates the injection pump speed of 2 mL/min). The order of injection methods is randomly assigned by drawing lots (the injection method for the first cycle is randomly drawn, and the method for the second cycle is naturally the alternative method). The primary outcome is the patient's most severe pain during injection, measured immediately after injection using the Numerical Rating Scale (NRS, 0-10). Secondary outcomes include injection site reactions, patient satisfaction, nurse fatigue (Borg CR10 scale), patient preference, and safety indicators.

Research Significance:The results of this study will provide high-level evidence for selecting comfortable and efficient subcutaneous injection techniques in clinical practice, thereby improving patients' treatment experience.

Inclusion Criteria:

1. Female breast cancer patients histologically confirmed as HER2-positive.
2. Have completed at least one subcutaneous injection of Phesgo, with at least three planned injections remaining.
3. No history of acute allergic reactions (e.g., Grade 1-2 allergic reactions) during previous Phesgo injections.
4. Aged between 18 and 70 years (inclusive).
5. No use of pain medications, pain patches, or pain pumps for pain management within 3 days prior to injection.
6. Normal activity level (ECOG score 0-2), no limb paralysis, and able to clearly express personal feelings.
7. Signed informed consent form and voluntarily agreed to participate in this study.

Exclusion Criteria:

1. Presence of any skin diseases or conditions affecting subcutaneous injection (e.g., severe infection or dermatitis at the injection site).
2. Simultaneous participation in other clinical trials that may interfere with the results of this study.
3. Cognitive impairment or mental illness preventing completion of study questionnaires and assessments.
4. Regular use of analgesics.

This is a small - scale exploratory study focused on internal hypothesis - testing and preliminary mechanism analysis. The data is not intended for external collaboration, as it lacks sufficient generalizability to support broader scientific inferences. All findings are based on aggregated and de - identified results reported in the main publication.