This is a phase II, non-randomized, open-label, single-center study to evaluate the efficacy and safety of neoadjuvant PD-1 inhibitor (Tislelizumab) + chemotherapy (cisplatin/carboplatin + etoposide) followed by radical surgery and adjuvant Tislelizumab immunotherapy as first-line treatment in patients limited-stage SCLC.

Inclusion Criteria:

1. The patient shall sign the Informed Consent Form.

2. Aged 18 ≥ years.

3. Histological or cytological diagnosis of SCLC by needle biopsy, and limited stage (local advanced) confirmed by imageological examinations.

4. Eastern Cooperative Oncology Group (ECOG) performance-status score of 0 or 1.

5. Life expectancy is at least 12 weeks.

6. At least 1 measurable lesion according to RECIST 1.1.

7. Patients with good function of other main organs (liver, kidney, blood system, etc.):

   • ANC count ≥1.5×10^9/L, platelet count ≥100×10^9/L#hemoglobin

     ≥90 g/L;

   • the international standard ratio of prothrombin time (INR) and prothrombin time (PT) < 1.5 times of upper limit of normal (ULN);

   • partial thromboplastin time (APTT) ≤1.5×ULN;

   • total bilirubin ≤1.5×ULN;

   • alanine aminotransferase (ALT) aspartate aminotransferase (AST) ≤2.5×ULN, or ALT and AST ≤5×ULN in the patients with liver metastatic tumor.

8. No systemic metastasis;

9. Expected to be completely resected;

10. Good cardiopulmonary function and can tolerate surgical treatment;

11. Fertile female patients must voluntarily use effective contraceptives not less than 120 days after chemotherapy or the last dose of Tislelizumab (whichever is later) during the study period, and urine or serum pregnancy test results within 7 days prior to enrollment are negative.

12. Unsterilized male patients must voluntarily use effective contraception during the study period not less than 120 days after chemotherapy or the last dose of Tislelizumab (whichever is later).

Exclusion Criteria:

1. Participants who have received any systemic anti-cancer treatment for SCLC, including surgical treatment, local radiotherapy, cytotoxic drug treatment, targeted drug treatment and experimental treatment;
2. Participants with cancer other than SCLC (excluding cervical carcinoma in situ, cured basal cell carcinoma, bladder epithelial tumor [including TA and tis]) within five years before the start of this study;
3. Participants with any unstable systemic disease (including active infection, uncontrolled hypertension), unstable angina pectoris, angina pectoris starting in the last three months, congestive heart failure (>= NYHA) Grade II), myocardial infarction (6 months before admission), severe arrhythmia requiring drug treatment, liver, kidney or metabolic diseases;
4. With activate or suspectable autoimmune disease, or autoimmune paracancer syndrome requiring systemic treatment;
5. Participants who are allergic to the test drug or any auxiliary materials;
6. Have or currently have interstitial lung disease;
7. Participants with active HIV;
8. Antibiotics were used to treat the infection for 4 weeks prior to the start of the trial;
9. Pregnant or lactating women;
10. Any conditions of malabsorption;
11. Participants suffering from nervous system diseases or mental diseases that cannot cooperate;
12. Other factors that researchers think it is not suitable for enrollment.

The researchers will consider whether IPD is available to other researchers only after the paper is published