A Phase III, Randomized, Double-blind, Multi-center Trial Comparing Efficacy and Safety of Trilaciclib Versus Placebo in Participants With Limited-stage Small Cell Lung Cancer

The primary goal of this study is to evaluate the myelo-protective effect and safety of Trilaciclib in participants with limited stage small cell lung cancer (LS-SCLC) who are receiving concurrent chemo-radiotherapy. Researchers will compare Trilaciclib with placebo (a look-alike substance that contains no drug) to see if Trilaciclib works better in protecting the participant's marrow function while receiving concurrent chemo-radiotherapy.

Inclusion Criteria: * 1\. Histologically and/or cytologically confirmed small cell lung cancer (SCLC) with clinical staging confirming limited-stage disease and no evidence of distant metastasis； * 2\. Fit for concurrent chemo-radiotherapy； * 3\. Adverse reactions related to prior anti-tumor surgery have fully recovered； * 4\. Has at least one measurable lesion per RECIST 1.1 that has not been previously irradiated； * 5\. Eastern Cooperative Oncology Group （ECOG）performance status of 0 or 1; * 6\. Has adequate organ and bone marrow function, without receipt of hematopoietic growth factors, blood transfusions, or platelet transfusions within 14 days prior to the first dose of study drug； Exclusion Criteria: * 1\. Extensive-stage small cell lung cancer * 2\. mixed-type small cell lung cancer, and transformed small cell lung cancer； * 3\. Has received prior anti-tumor therapy for small cell lung cancer, including radiotherapy, chemotherapy, or immunotherapy； * 4\. Has known allergy to any study drug or its components, or has any contraindication to any study drug. * 5\. Has any active infections requiring for intravenous treatment within 14 days prior to the first dose of study treatment； * 6\. Has received any live vaccine within 28 days prior to the first dose of study drug. * 7\. Has received any major surgeries within 28 days prior to the first dose of study treatment or expects to receive major surgeries during the study; * 8\. History of another active malignancy within the past 5 years, except for localized cancers that have been cured and are considered by the investigator to be at low risk of recurrence, including basal or squamous cell skin cancer, superficial bladder cancer, or carcinoma in situ of the prostate, cervix, or breast. * 9\. With a history of active tuberculosis infection within 1 year; trial participants with a history of active tuberculosis may be eligible for enrollment if, in the investigator's judgment, there has been no evidence of active tuberculosis for more than 1 year prior to the first dose. * 10\. Active or chronic hepatitis B or hepatitis C infection; * 11\. Known human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS). * 12\. With clinically significant cardiovascular disease within 6 months prior to the first dose * 13\. History of interstitial lung disease/non-infectious pneumonitis requiring steroid treatment, or current interstitial lung disease/non-infectious pneumonitis requiring steroid treatment; * 14\. Prior allogeneic or autologous hematopoietic stem cell transplantation or history of graft-versus-host disease; * 15\. Pregnant or breastfeeding female trial participants, or female trial participants of childbearing potential. Female participants of childbearing potential may be enrolled if they have a negative blood pregnancy test within 7 days prior to the first dose and agree to use effective contraception from the time of signing the informed consent form until 6 months after the last dose of study medication or the last radiotherapy, whichever is longer. * 16\. Any other conditions that, in the investigator's opinion, make the participant unsuitable for enrollment.