Inclusion Criteria:  Male or female of ≥ 18 years old; Histology or cytology diagnosed extensive-stage small cell lung cancer ( ES-SCLC ) : Patients who plan to receive carboplatin combined with etoposide: naïve with systemic treatment (such as chemotherapy or combined immunotherapy) in the past Patients planning to receive topotecan : previously received 1/2 line chemotherapy or combined immunotherapy except for topotecan. At least one measurable lesion without radiotherapy that meets RECIST1.1 standard; Hemoglobin ≥ 90 g/L ; Neutrophil count ≥ 1.5 × 109 /L ; Platelet count ≥100 × 109 /L ; Creatinine ≤ 15 mg /L or creatinine clearance (CrCl) ≥ 60 mL/min (Cockcroft-Gault formula ) ; Total bilirubin ≤ 1.5 × upper limit of normal (ULN) ; Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 × ULN or ≤ 5 × ULN (patients with liver metastases) ; Albumin ≥ 30 g/L ; ECOG PS score:0-2 ; Expected survival time ≥ 3 months ; Contraception : Women: Women with potential fertility must have a negative serum pregnancy test result at Screening, and take reliable contraceptive measures from signing informed consent to 3 months after the last administration ; Male: If a female partner has potential fertility, reliable contraceptive measures must be taken after signing the informed consent to 3 months after the last administration. Understand and sign the informed consent form.  Exclusion Criteria:  Symptomatic brain metastases that require local radiotherapy or hormone therapy; Other history of malignant cancer, except for: (1) clinically cured basal cell or squamous cell tumors; (2) curable: a) cervical cancer, B) prostate cancer, C) superficial bladder cancer; or ( 3 ) any solid tumor that it is clinically cured for 3 years or above; Uncontrolled ischemic heart disease or congestive heart failure with clinically significance (NYHA Class III or IV) ; Stroke or cardiovascular and cerebrovascular events within 6 months before enrollment ; Severe active infection; Potential inadequate compliance from psychological or other social factors; Other uncontrolled severe chronic disease or condition, which considered by Investigator as unsuitable for study participation; Known HIV infection, active hepatitis B (defined as HBV DNA positive) and hepatitis C (HCV RNA positive); Received radiotherapy within 2 weeks before enrollment ; Received cytotoxic or investigational drug treatment within 4 weeks, or non-cytotoxic anti-tumor treatment within 2 weeks before enrollment; For Part 1 patients, concomitant administration of strong or moderate inducer of CYP3A4 within 4 weeks before study drug, or strong inhibitor of CYP3A4 within 2 weeks before study drug; Recovery from previous toxicity of anti-tumor treatments to Level 0 or 1 (except for hair loss); Allergy to the study drugs or any of their components (Trilaciclib, etoposide, carboplatin, topotecan); Unable to act independently by legal restrictions or in the legal sense; Women who are pregnant or breastfeeding ; Other patients who are considered unsuitable to participate in the study. -