To investigate the benefits and risks of maintenance chemotherapy (MCT), maintenance endocrine therapy (MET) and none maintenance therapy after first-line treatment of metastatic breast cancer (MBC).

There are several options for MBC patients who are responding to chemotherapy, to continue treatment with a fix number of cycles or until disease progression which also known as maintenance chemotherapy (MCT), to stop chemotherapy and take a watch and wait strategy, or to stop chemotherapy and start the maintenance endocrine therapy (MET) for hormone receptor (HR) positive patients. Since the role of maintenance therapy in prolonging the overall survival (OS) and progression-free survival (PFS) of MBC was controversial in previous studies, the investigators performed a systematic review of randomized controlled trials to detect the association of survival with maintenance therapy in patients with MBC after first-line chemotherapy. And the investigators further performed a multi-center retrospective real-world study to evaluate these two maintenance modalities.

Inclusion Criteria:

• Patients with pathologically clear invasive breast cancer between 2003 and 2018;
• Female,18-75 years old;
• Measurable metastatic lesion according to RECIST 1.1 evaluation criteria;
• The first-line chemotherapy regimen is a breast cancer combination or single-agent chemotherapy regimen recommended by the NCCN guidelines;
• First-line chemotherapy is effective (according to RECIST1.1 evaluation criteria, the efficacy is evaluated as complete response (CR), partial response (PR), or steady state (SD));
• After the last cycle of first-line chemotherapy, patients should still be in a state of no progress for at least 4 weeks;
• Patients' Karnofsky performance status (KPS) scores were ≥70.

Exclusion Criteria:

• Unmeasurable metastatic lesion according to RECIST 1.1 evaluation criteria.

This is a multi-center real world study to compare maintenance chemotherapy (MCT), maintenance endocrine therapy (MET) and observation in patients with HR-positive MBC who achieved disease control after first-line chemotherapy. Patients were retrospectively enrolled from 3 different medical center.