This is a randomized, controlled, open-label, multicenter phase II clinical trial comparing the efficacy and safety of low-dose radiation therapy and stereotactic body radiation therapy combined with PD-1 inhibitor (sintilimab) and standard platinum-based doublet chemotherapy versus PD-1 inhibitor (sintilimab) combined with standard platinum-based doublet chemotherapy as first-line treatment in patients with locally advanced or metastatic squamous cell lung cancer.

There will be 57 subjects in the experimental group and 57 subjects in the control group, with a total of 114 subjects.

This is a randomized, controlled, open-label, multicenter phase II clinical trial comparing the efficacy and safety of low-dose radiation therapy and stereotactic body radiation therapy combined with PD-1 inhibitor (sintilimab) and standard platinum-based doublet chemotherapy versus PD-1 inhibitor (sintilimab) combined with standard platinum-based doublet chemotherapy as first-line treatment in patients with locally advanced or metastatic squamous cell lung cancer. Patients with previously untreated, locally advanced or metastatic (unresectable or not eligible for definitive chemoradiotherapy, stage IIIB-IV) squamous cell lung cancer who have signed informed consent will be screened for eligibility. Qualified subjects who meet the inclusion criteria will be randomly assigned at a 1:1 ratio to the experimental group (radiation therapy plus sintilimab and chemotherapy) or the control group (sintilimab plus chemotherapy). Based on sample size estimation according to statistical hypotheses, there will be 57 subjects in the experimental group and 57 subjects in the control group, with a total of 114 subjects. Subjects in the experimental group will receive radiation therapy. Within 1 week after radiation therapy, they will receive treatment with sintilimab combined with standard platinum-based doublet chemotherapy. Chemotherapy combined with immunotherapy will consist of a total of 4 cycles. Patients will subsequently receive maintenance therapy with sintilimab. Subjects in the control group will receive treatment with sintilimab combined with standard platinum-based doublet chemotherapy, consisting of a total of 4 cycles. Patients will subsequently receive maintenance therapy with sintilimab. The primary efficacy endpoint of this study is objective response rate (ORR), as assessed by investigators according to Response Evaluation Criteria in Solid Tumors (RECIST v1.1).

Inclusion Criteria:

1. Age ≥ 18 years old and ≤ 75 years old;
2. Histologically or cytologically confirmed squamous cell lung cancer, imaging confirmed locally advanced or metastatic disease (unresectable or not eligible for definitive chemoradiotherapy, stage IIIB-IV);
3. According to the Response Evaluation Criteria in Solid Tumors (RECIST v1.1), there is at least one imaging measurable lesion;
4. Enough to provide quality control qualified tumor tissue or cell wax blocks to detect PD-L1 expression;
5. Have not received any systemic anti-tumor treatment for locally advanced or metastatic disease in the past;

Exclusion Criteria:

1. The pathology is small cell lung cancer (SCLC), including lung cancer mixed with SCLC and non-small cell lung cancer (NSCLC)；
2. The pathology is lung adenocarcinoma, including lung cancer mixed with lung adenocarcinoma and lung squamous cell carcinoma;
3. EGFR gene sensitive mutation or ALK fusion positive or ROS1 fusion positive;
4. Previously received the following therapies: anti-PD-1, anti-PD-L1 or anti-PD-L2 drugs or another drug that stimulates or synergistically inhibits T cell receptors;
5. Pregnant or lactating women;