This study is researching an experimental drug called fianlimab (also called REGN3767) with two other medications called cemiplimab and platinum-doublet chemotherapy, individually called a "study drug" or collectively called "study drugs", when combined in this study. The study is being conducted in patients who have resectable stage II to IIIB (N2) non-small cell lung cancer (NSCLC) that can be treated with surgery.

The aim of the study is to see how effective the combination of fianlimab, cemiplimab, and chemotherapy is in comparison with cemiplimab and chemotherapy as peri-operative therapy in participants with NSCLC.

The study is looking at several other research questions, including:

• What side effects may happen from taking the study drugs
• How much of each study drug is in the blood at different times
• Whether the body makes antibodies against the study drugs (which could make the drugs less effective or could lead to side effects)
• How administering the study drugs might affect quality of life

Key Inclusion Criteria:

1. Patients with newly diagnosed, histologically confirmed, fully resectable stage II to IIIB (N2) NSCLC as per American Joint Committee on Cancer (AJCC) version 8
2. For patients with evidence of mediastinal adenopathy on imaging, mediastinal lymph node sampling is required as defined in the protocol
3. All patients must have disease status showing no evidence of distant metastases documented by a complete physical examination and imaging studies performed within 4 weeks prior to randomization as defined in the protocol
4. A patient must have an evaluable Programmed cell death ligand-1 (PD-L1) immunohistochemistry (IHC) result as defined in the protocol
5. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
6. Adequate bone marrow, hepatic and kidney function as defined in the protocol

Key Exclusion Criteria:

1. Any evidence of locally advanced unresectable or metastatic disease as defined in the protocol
2. Patients with tumors with known Epidermal growth factor receptor (EGFR) gene mutations, anaplastic lymphoma kinase (ALK) gene translocations as defined in the protocol
3. Uncontrolled infection with human immunodeficiency virus (HIV), hepatitis B (HBV) or hepatitis C virus (HCV) infection as defined in the protocol
4. Treatment with anti-cancer therapy including immunotherapy, chemotherapy, radiotherapy, or biological therapy in the 3 years prior to randomization. Adjuvant hormonotherapy used for breast cancer or other hormone-sensitive cancers in long term remission is allowed.
5. Patients with a history of myocarditis

Note: Other protocol-defined Inclusion/ Exclusion Criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing.

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy.

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf