To validate the predictive value of transcriptome-based molecular subtyping of extensive stage small cell lung cancer (SCLC) for the efficacy of programmed death-1(PD-1)/programmed death-ligand1(PD-L1) inhibitor in the first line setting; to explore the differences of immune microenvironment between different SCLC subtypes to reveal the mechanisms of immunotherapy resistance of SCLC

This retrospective observational study examines the predictive value of transcriptome-based molecular subtyping of extensive stage SCLC for PD-1/PD-L1 inhibitor efficacy and explores immune microenvironment differences between subtypes to uncover immunotherapy resistance mechanisms. Patients with extensive stage SCLC receiving first-line standard treatment are enrolled, and baseline tumor tissue and peripheral blood samples are collected for transcriptome sequencing and immunohistochemistry (IHC). Based on results, patients are classified into four molecular subtypes, and treatment efficacy and safety are recorded. The study compares the efficacy between SCLC subtypes to determine if molecular typing predicts immunotherapy efficacy and investigates immune microenvironment differences between subtypes to uncover resistance mechanisms. Treatment regimens follow first-line extensive stage SCLC guidelines, including cisplatin+etoposide or carboplatin+etoposide and PD-(L)1 inhibitors, with options determined by the supervising physician.

Inclusion Criteria:

• The enrolled subjects shall meet all the following conditions at the same time.

  1. Male or female, aged 18 to 100 years
  2. Patients with untreated advanced small cell lung cancer clearly diagnosed by histopathology
  3. Be able to provide tumor biopsy tissue sample for molecular analysis
  4. Eastern Cooperative oncology Group (ECOG) score: 0~2
  5. Expected survival of more than 3 months.
  6. Has at least 1 measurable or evaluable tumor lesion with a longest diameter ≥ 10 mm at baseline (in case of lymph nodes, a shortest diameter ≥ 15 mm is required) according to RECIST v1.1
  7. Received first-line chemotherapy or chemotherapy＋PD-(L)1 inhibitor and be able to provide complete treatment information and efficacy evaluation results.
  8. Voluntary signed informed consent and expected good compliance.

Exclusion Criteria:

• Those meeting any of the following conditions may not be included.

  1. Patient unable to tolerate chemotherapy.
  2. Patients unable to provide tumor tissue samples for testing
  3. Patients with other malignant tumors or a history of other malignant tumors
  4. Patients have any other reason to be unfit to participate in this study.

This study includes adults (18-100 years) with untreated advanced SCLC. Eligible patients have an ECOG score of 0~2, an expected survival >3 months, and can provide tumor biopsy samples for transcripsome testing. They must have received first-line chemotherapy or chemotherapy combined with a PD-L1 inhibitor.

Participants are divided into two arms: Chemotherapy (80-100 cases) and Immunotherapy+chemotherapy (80-100 cases). Exclusion criteria include intolerance to chemotherapy, inability to provide tumor tissue samples, presence/history of other malignant tumors, and other reasons deeming them unfit for the study.