Clinical Study on Using TCR to Predict the Effect of Tislelizumab + Chemotherapy in the First-line Treatment of ES-SCLC

Inclusion Criteria: * Histologically proven ES-SCLC (American Joint Cancer Commission (7th Edition) Stage IV SCLC \[any T, any N and M1a/b\]), or T3-4 patients who are unable to be included in a tolerable radiotherapy program due to wide multiple incidences or excessive tumor volume. * Patients with brain metastases must have asymptomatic or stable steroid and anticonvulsant treatment for at least 1 month before study treatment. Patients with suspected brain metastasis during screening should undergo brain CT/MRI examination before enrollment of the study. * Have at least one measurable tumour lesion according to RECIST v1.1. * aged ≥18 years * Eastern Cooperative Oncology Group (ECOG) physical status score of 0-1 Exclusion Criteria: * Have a history of chest radiotherapy or plan to undergo intensive chest radiotherapy before systemic treatment. Radiotherapy outside the chest (i.e., bone metastasis) is allowed for palliative care purposes, however, must be done before the first medication of the study drug * Previous non-infectious pneumonia requiring systemic glucocorticoid therapy or current non-infectious pneumonia combined with mild to moderate interstitial pneumonia, inactive interstitial pneumonia. * Presence of unmitigated toxicity from prior antineoplastic therapy, with unmitigated defined as failure to recover to NCI CTCAE version 5.0 grade 0 or 1 (except alopecia areata) or failure to recover to levels specified in the inclusion/exclusion criteria. * History of known allogeneic organ transplantation and allogeneic haematopoietic stem cell transplantation; history of organ or haematopoietic stem cell transplantation requiring immunosuppression. * Patients with chronic hepatitis B or chronic hepatitis B virus carriers with HBV DNA ≥500 IU/mL (2500 copies/mL), or hepatitis C patients. * Other circumstances as determined by the investigator.