The addition of dimethyldiguanide might increase the efficacy of AI treatment in metastatic breast cancer.

The addition of dimethyldiguanide might increase the efficacy of AI in patients with metastatic breast cancer after the failure of the first line endocrine therapy.

Inclusion Criteria:

• postmenopausal HR positive breast cancer patients;
• inoperable locally advanced or metastatic breast cancer patients;
• candidate for endocrine therapy;
• ECOG equal to or less than 1;
• adequate bone marrow function(Hb>=90g/L, WBC >=3.5×10^9/L,ANC>=1.5×10^9/L, PLT>=80×10^9/L; adequate renal function(Ccr<=ULN);adequate liver function(ALT,AST,AKP<=2.5*ULN,or <=5*ULN if liver metastases)
• life expectancy >=12weeks;
• no severe history disease of liver,heart,lung or kidney;
• written informed consent form;

Exclusion Criteria:

• Her-2 overexpression;
• patients who has visceral endocrisis；