Efficacy and Safety of Ribociclib in Combination With NSAI Versus Physician's Choice of Chemotherapy Sequential Endocrine Therapy in HR+/HER2- Advanced Breast Cancer

Inclusion Criteria:

1. Patient is an adult female ≥ 18 years old at the time of informed consent.
2. ECGO rating 0-2.
3. Histologically confirmed recurrent or metastatic breast cancer, including patientsinitially diagnosed as stage IV or locally advanced inoperable patients.
4. Patient has a histologically and/or cytologically confirmed diagnosis ofestrogen-receptor positive and/or progesterone receptor positive breast cancer basedon the most recently analyzed tissue sample and all tested by local laboratory. ERshould be more than 10% ER positive by local laboratory testing.
5. Patient has HER2-negative breast cancer defined as a negative in situ hybridizationtest or an IHC status of 0, 1 + or 2 + If IHC is 2 +, a negative in situ hybridization (FISH, CISH, or SISH) test is required by local laboratory testing and based on themost recently analyzed tissue sample.
6. Determination by the physician that the patient is in a rapid disease progressionsituation:

• Symptomatic visceral metastases
• Rapid progression of disease or impending visceral compromise.
• Markedly symptomatic non visceral disease if the treating physician opt to givechemotherapy for rapid palliation of patients symptoms.

7. Patient hasn't received systemic anti-cancer therapy at the stage ofrecurrence/metastasis.
8. Patient must have at least one measurable lesion (according to RECIST 1.1 criteria)
9. Postmenopausal or pre/perimenopausal female patients are eligible for enrolment; preor perimenopausal female patients must be willing to receive LHRHa during the studyperiod.
10. All patients were required to meet the following laboratory biochemical values priorto enrolment:

• Haematology: Hb ≥90 g/L, WBC ≥3.5×109/L, ANC ≥1.5×109/L, PLT ≥100×109/L;
• Renal function: serum creatinine ≤ upper limit of normal value;
• Liver function: for those without liver metastases, AST, ALT, ALP ≤2.5 times theupper limit of normal values, and ≤1.25 x the upper limit of normal values fortotal bilirubin; for those with liver metastases, AST, ALT, ALP ≤ 5 times theupper limit of normal value, and total bilirubin ≤ 1.5 x upper limit of normalvalue.

Exclusion Criteria:

1. Patient has received systemic anti-cancer therapy at the stage ofrecurrence/metastasis.
2. Those who have been treated with CDK4/6 inhibitors in the neoadjuvant/adjuvant phase.
3. Patients those with symptomatic CNS metastases.
4. Patient has a history of clinically symptomatic cardiovascular, hepatic, respiratory,renal and haemato-endocrine system or neuropsychiatric disorders.
5. Patient has a serious concomitant disease, such as an infectious disease; has multiplefactors that affect the oral administration and absorption of the drug.
6. Pregnant or lactating women (women of childbearing age must have had a negativepregnancy test within 14 days prior to the first dose; if positive, pregnancy must beruled out by ultrasound).
7. Patients in poor general condition who cannot tolerate chemotherapy treatment.
8. The investigator considers the patient unsuitable for entry into this study.