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.