Immune Therapy in HR-positive/HER2-negative Metastatic Breast Cancer(ENIGMA)-BCTOP-L-M02

Inclusion Criteria: * Females ≥18 years and ≤ 75 years old; * Histologically confirmed HR + / HER2- invasive breast cancer (specific definition: immunohistochemical detection of ER\> 10% tumor cell positive is defined as ER positive, PR\> 10% tumor cell positive is defined as PR positive, ER and / or PR Positive is defined as HR positive; HER2 0-1 + or HER2 is ++ but negative followed by FISH detection, no amplification, defined as HER2 negative); * Subtype of similarity network fusion-2 (SNF-2) confirmed by the Department of Pathology and Key Laboratory of Breast Cancer of Fudan University Affiliated Cancer Hospital * Locally advanced breast cancer (incapable of radical local treatment) or recurrent metastatic breast cancer; * Measurable disease according to Response Evaluation Criteria in Solid Tumors v1.1 (RECIST v1.1); or unmeasurable lytic or mixed (osteolytic + osteoblastic) bone lesions in the absence of measurable lesions; * Has adequate bone marrow function: absolute neutrophil count \> 1.5x10ˆ9 /L; platelet count \> 75x10ˆ9 /L, hemoglobin \> 9g/dL; * Patients had received no previous chemotherapy or targeted therapy for metastatic disease * Has adequate liver function and kidney function: serum creatinine * ECOG score ≤ 2 and life expectancy ≥ 3 months; * Participants voluntarily joined the study, has signed informed consent before any trial related activities are conducted, has good compliance and has agreed to follow-up. Exclusion Criteria: * Treatment with chemotherapy, radiotherapy, immunotherapy or surgery (outpatient clinic surgery excluded) for metastatic disease * Symptomatic, untreated, or actively progressing CNS metastases(glucocorticoids or mannitol needed to control symptoms); * Significant cardiovascular disease(including congestive heart failure, angina pectoris, myocardial infarction or ventricular arrhythmia in the last 6 months); * is pregnant or breast feeding; * Malignant tumors in the past five years (except cured skin basal cell carcinoma and cervical carcinoma in situ). * History of autoimmune disease * Positive test for human immunodeficiency virus * Active hepatitis B or hepatitis C * Uncontrolled pleural effusion and ascites * Thyroid dysfunction.