Inclusion Criteria:  Voluntarily sign the informed consent form; 18-75 years old; The expected survival period is ≥12 weeks; Eastern Cooperative Oncology Group (ECOG) score [0-2] points; The diagnosis of invasive carcinoma by histology or cytology; Estrogen receptor (ER) positive (defined as >1% nuclear ER staining); HER2 negative (defined as IHC 0 or 1+, or HER2(2+) with HER2 FISH detection no amplification); Inoperable or recurrent/metastatic breast cancer patients with aromatase inhibitor treatment failure; In the state of disease progression before enrollment; Measurable disease according to RECIST version 1.1 or only bone metastasis; Adequate hematological, hepatic and renal function; NYHA class I or II and Left ventricular ejection fraction (LVEF) ≥50%. The diagnosis of invasive carcinoma by histology or cytology: Hormone receptor (HR) positive (defined as >1% nuclear estrogen receptor staining); HER2 positive (defined as IHC 3+, or HER2 FISH detection amplification); In the state of disease progression before enrollment; Have lesions able to and agree to perform tissue biopsy at the time requested in the study; Treatment ≥1 line after recurrence/metastasis, or relapse within 12 months after completing trastuzumab-based adjuvant therapy or during trastuzumab adjuvant therapy; Previously received trastuzumab for anti-HER2 therapy; Measurable disease according to RECIST version 1.1.  Exclusion Criteria:  Allergic to the ingredients of Inetetamab, cyclophosphamide or similar drugs; Concomitant diseases/conditions that is not controllable, and any other major illness that, in the investigator's judgment, will substantially increase the risk associated with the patient's participation in this study; Patients who cannot accept drugs orally; Women who are pregnant or breastfeeding or planning to give birth; Patients with currently symptomatic brain or meningeal metastasis; History of other primary malignancy; Resistant to steroidal or nonsteroidal aromatase Inhibitor; Have used Inetetamab; Patients with life-threatening, symptomatic, metastatic visceral disease.