Background: Treatment options for patients with HER2-positive breast cancer after progression on two or more lines of HER2-directed therapies are scarce. Inetetamab, a novel anti-HER2 antibody, exhibits the same binding affinity to HER2 antigen and antibody-dependent cell-mediated cytotoxicity as trastuzumab. Previous studies have demonstrated the treatment potential of PD-1 inhibitor combined with HER2-targeted therapy in HER2-positive gastric or gastroesophageal junction cancer. Utidelone, a genetically engineered epothilone analogue, has shown promising efficacy in heavily pretreated metastatic breast cancer. This study aimed to investigated inetetamab plus camrelizumab (anti-PD-1 antibody) and utidelone in patients with HER2-positive recurrent or metastatic breast cancer who had progressed after at least two lines of HER2-directed therapies with trastuzumab and tyrosine kinase inhibitors (TKIs). Methods: In this phase 2 study (NCT04681287), patients received intravenous camrelizumab (200 mg once every 3 weeks), inetetamab (8 mg/kg loading dose then 6 mg/kg, day 1), and utidelone (30 mg/m², days 1-5) until disease progression or intolerable toxicity. The primary endpoint was 3-month progression-free survival (PFS) rate according to the Response Evaluation Criteria In Solid Tumors, version 1.1. Secondary endpoints included objective response rate (ORR), PFS, overall survival, and safety. Simon’s two-stage design was adopted for this study. Results: Between April 2021 and January 2022, a total of 27 patients were enrolled. As of January 2022, 20 patients could be analyzed. The median number of previous systemic therapies for advanced disease was three. Previous HER2-targeted therapies included trastuzumab (20 [100%]), pyrotinib (17 [85%]), lapatinib (7 [35%]), pertuzumab (3 [15%]), and margetuximab (2 [10%]). The first stage required 10 patients, and 8 of them were free from progression at 3 months. The study proceeded to the second stage for another 31 patients, and the accrual is ongoing. The 3-month PFS rate in 20 patients was 75%. The ORR was 30% (6/20); one (5%) patient achieved complete response. The most common treatment-related adverse events (TRAEs) were peripheral neuropathy (19 [98%]), capillary proliferation (19 [98%]), alopecia (18 [90%]), and fatigue (7 [35%]). Grade ≥3 TRAEs included peripheral neuropathy (2 [10%]) and rash (1 [5%]). No treatment-related treatment discontinuation or deaths occurred. Conclusions: Inetetamab plus camrelizumab and utidelone showed promising efficacy and acceptable safety profile in patients with HER2-positive advanced breast cancer after progression on at least two lines of HER2-directed therapies with trastuzumab and TKIs. Clinical trial information: NCT04681287.