This is a retrospective, observational, multi-center clinical study of circulating tumor DNA (ctDNA) to guide late-line therapy in late-stage metastatic breast cancer patients.

This study aims to evaluate the feasibility of plasma ctDNA mutation in guiding late-line treatment for late-stage metastatic breast cancer patients. Meanwhile, this study tries to evaluate the curative effect of ctDNA subtype-guided late-line therapy.

Inclusion Criteria:

• Recent progression of TNBC after multiple lines of chemotherapy or of HR+ or HER2+ MBC after multiple lines of endocrine or targeted therapy;
• No available recommendation for the next treatment regimen;
• An Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2;
• An updated, available pathological HR/HER2 status for metastasis;
• According to RECIST 1.1 standard, there should be at least one measurable target lesion;
• The expected survival time is > 3 months;
• Those aged 18-70 years old;
• Liver and kidney function and blood routine test meet the following conditions: Neutrophil > 2.0g/l, Hb > 9g / L, PLT > 100g / L; ALT and AST < 2.5ULN; TBIL < 1.5ULN; Cr < 1.0ULN
• Signing informed consent;
• Those willing to accept polygenic testing.

Exclusion Criteria:

• Patients with multiple primary tumors;
• Those who are unable to obtain blood samples;
• Those with a history of immunodeficiency or organ transplantation;
• Those with abnormal cardiac function or previous history of myocardial infarction or serious arrhythmia;
• The researchers think it is not suitable to participate in this experiment.

This cohort study recruited consecutive patients with recent progression of metastatic TNBC after multiple lines of chemotherapy or of HR+ or HER2+ metastatic breast cancer after multiple lines of endocrine or targeted therapy.