Efficacy of Everolimus Combined With First-line Endocrine Therapy for HR+/HER2- SNF1-subtype Advanced Breast Cancer

Inclusion Criteria:

* Patients need to meet all of the following conditions

  * Patients must be ≥18 and ≤ 75 years of age;
  * Pathologically confirmed breast cancer is HR+/HER2- breast cancer (IHC ER \>10%, or/and PR\>10%, HER 0 OR +, if HER2++, FISH negative);
  * SNF1 subtype definition: SNF1 subtype confirmed by digital pathology of H\&E sections;
  * Locally advanced breast cancer (radical local therapy is not possible) or metastatic breast cancer (without using adjuvant CDK4/6 inhibitors in the past, or one year after adjuvant CDK4/6 inhibitor therapy has ended);
  * No prior therapy (chemotherapy, targeted therapy, etc.) for advanced or metastatic breast cancer;
  * Patients with at least one measurable lesion that has not previously received radiation therapy and can be evaluated repeatedly according to RECIST 1.1;
  * The functions of the main organs are basically normal, and the following conditions are met:

    1. Blood routine examination standards should meet: HB≥90g/L (no blood transfusion within 14 days); ANC≥1.5×109/L; PLT≥75×109/L;
    2. Biochemical examination shall meet the following standards: TBIL≤1.5×ULN (upper limit of normal value); ALT and AST≤3 x ULN; In case of liver metastasis, ALT and AST≤5×ULN; Serum Cr ≤1.5×ULN, endogenous creatinine clearance \> 50ml/min (Cockcroft-Gault formula);
  * ECOG performance status 0 or 1; The expected survival is more than 3 months;
  * Fertile female is required to use a medically approved contraceptive during study treatment and for at least 3 months after the last use of the study drug;
  * Patients voluntarily join the study, sign the informed consent, have good compliance, and cooperate with follow-up.

Exclusion Criteria:

* Patients with any of the following conditions were excluded from the study

  * Patients with central nervous system metastasis out of control (symptoms need to use glucocorticoids or mannitol).
  * A history of clinically significant or uncontrolled heart disease, including congestive heart failure, angina pectoris, myocardial infarction within the last 6 months, or ventricular arrhythmia;
  * Radiotherapy, chemotherapy, surgery, other targeted therapy and immunotherapy for advanced HR+/HER2- breast cancer within 4 weeks prior to first administration of drugs used in this study.
  * Pregnant or lactating patients;
  * Other malignancies within the previous 3 years, excluding cured skin basal cell carcinoma and cervical carcinoma in situ;
  * Significant comorbid medical conditions, including mental illnesses that the investigator or sponsor believes would adversely affect the patient's participation in the study;
  * Allergic physique, or known allergic history of the drug components of this program; Or allergic to other monoclonal antibodies;
  * The investigator does not consider the patient suitable for participation in any other circumstances of the study.