Eribulin Combined With Sintilimab as First-line Treatment for Unresectable Locally Advanced or Metastatic HER2-negative Breast Cancer:A Multicenter, Single-arm,Phase II Clinical Trial

Eribulin: According to the standard dose,1.4mg/m\^2 day1、8，repeated every 3 week. After 6 cycles, the investigator decided whether to continue treatment depending on the patient's tolerance. Sintilimab: 500mg once every three weeks. The patients were treated until disease progression or intolerable side effects.