This is a Phase III, a randomized, double-blind, parallel , multi-center trail to evaluate the efficacy and safety of TQB3616 capsules plus fulvestrant compared to placebo plus fulvestrant in participants with estrogen receptor-positive, HER2-Negative Advanced Breast Cancer. Approximately 287 women will be randomized to either TQB3616 plus fulvestrant or TQB3616-matching placebo plus fulvestrant. Randomization will follow a 2:1 randomization ratio,the experimental is 191; the Placebo Comparator is 96.

Inclusion Criteria:

• 1 The subjects voluntarily joined the study and signed the informed consent, with good compliance.
• 2 Age: 18-75 years old (upon signing the informed consent);ECOG PS score: 0~1; Expected survival ≥3 months.
• 3 participants with estrogen receptor-positive, HER2-Negative Advanced Breast Cancer were identified by pathological testing.
• 4 Patients at the relapse/metastatic stage were allowed to receive no more than 1 line of rescue chemotherapy or rescue endocrine therapy.
• 5 Confirmation of at least one measurable lesion according to RECIST1.1 criteria.
• 6 The main organs are functioning well and meet the following criteria: Routine blood examination criteria (no blood transfusion or hematopoietic stimulus drug correction within 7 days before screening) : a) hemoglobin (Hb) ≥100g/L; b) neutrophils absolute value (NEUT) ≥1.5×10^9/L; c) Platelet count (PLT) ≥90×10^9/L.

Biochemical tests should meet the following criteria: a) Total bilirubin (TBIL) ≤2.5 times the upper limit of normal (ULN); b) Alanine transferase (ALT) and aspartate transferase (AST) ≤2.5×ULN.ALT and AST≤5×ULN with liver metastasis. c) Serum creatinine (Cr) ≤1.5×ULN, or creatinine clearance rate (CCR) ≥60ml/min.

The blood coagulation function test should meet the following criteria: prothrombin time (PT), activated partial thromboplastin time (APTT), international standardized ratio (INR) ≤1.5×ULN (no anticoagulant therapy); Cardiac ultrasound evaluation: left ventricular ejection fraction (LVEF)≥50%.

Exclusion Criteria:

• 1 Complicated diseases and medical history:

  1. Has had other malignant tumors within 3 years or currently has other malignant tumors;
  2. Have a variety of factors that affect oral medication (such as inability to swallow, chronic diarrhea, and intestinal obstruction);
  3. Unmitigated toxicity above CTCAE1 grade due to any prior treatment;
  4. Severe infections (≥CTCAE2 grade) that were active or uncontrolled before the study treatment started;
  5. Cirrhosis, active hepatitis；
  6. Have a history of immunodeficiency, including HIV positive or other acquired or congenital immunodeficiency diseases, or have a history of organ transplantation;

• 2 Tumor-related symptoms and treatment:

  1. Clinical evidence or history of central nervous system metastases (CNS) and/or cancerous meningitis or pneumomeningeal disease;
  2. Had received chemotherapy within 3 weeks prior to the start of study treatment, and had received radiotherapy (except palliative radiotherapy for non-target lesions), hormone therapy, or other anti-tumor therapy within 2 weeks prior to the start of study treatment (washout period was calculated from the end of last treatment);
  3. Uncontrolled pleural effusion, pericardial effusion, or ascites that still require repeated drainage (as determined by the investigator).

• 3 Known to be allergic to fluvestone, TQB3616 or any excipient.

• 4 Participated in clinical trials of other antitumor drugs within 4 weeks prior to the initiation of study therapy.

• 5 Has other conditions that make it inappropriate for the patient to be enrolled based on investigator's opinion.