Lung Cancer Stages 1 Through 4: What Do They Mean? (2026 Update)

Lung cancer staging uses the TNM system to classify disease from Stage 1 to Stage 4 based on tumor size and location, lymph node spread, and distant metastasis—and the stage determines which combination of surgery, radiation, chemotherapy, targeted therapy, and immunotherapy is used.

Key Takeaways

• Non-small cell lung cancer staging uses the TNM system (tumor size, lymph nodes, metastasis) to classify disease from Stage 1 to Stage 4.
• Stages 1–2 mean the tumor is confined to the lung, with no lymph node spread or spread limited to lymph nodes near the lung.
• Stage 3 means the cancer has spread to mediastinal lymph nodes or invaded nearby structures, while Stage 4 means it has spread to the opposite lung, brain, bone, liver, or other distant sites, or caused fluid buildup in the pleura.
• For small cell lung cancer, treatment planning broadly divides cases into those confined to one side of the chest and surrounding area versus those that have spread beyond it.
• Korea's 5-year relative survival rate for lung cancer is 42.5% (National Cancer Registry Statistics, 2019–2023); note this is a nationwide average, not a figure from any single hospital.

How Is Staging Determined?

• Staging is a classification system based on combined imaging and biopsy results, and it serves as the foundation for treatment planning.
• PET-CT is used to check for lymph node involvement and distant metastasis, while brain MRI checks for brain metastasis. Whether the mediastinal lymph nodes are involved is the key factor determining whether surgery is possible, so endobronchial ultrasound may be used to directly sample lymph nodes when needed.
• The TNM system evaluates the size and extent of the primary tumor (T), spread to nearby lymph nodes (N), and spread to other body parts (M). Once a stage is assigned at diagnosis, the cancer continues to be referred to by that original stage even if it later progresses—the initial stage does not change.
• For advanced or metastatic non-small cell lung cancer, genetic alterations such as EGFR, ALK, ROS1, BRAF, KRAS, MET, RET, and NTRK, along with PD-L1 expression, must be checked alongside stage to select the appropriate drug.

How Does Treatment Differ by Stage?

• For Stages 1–2, the standard approach is surgical removal of the affected lung lobe along with nearby lymph nodes, typically via video-assisted thoracoscopic surgery (VATS) or robotic surgery. For early-stage cancers where surgery isn't feasible, stereotactic body radiation therapy (SBRT) can complete treatment in just a few days.
• Stage 3 is the most complex category. When surgery appears feasible, the emerging standard is to shrink the tumor first with preoperative chemotherapy and immunotherapy before operating. When surgery is not feasible, concurrent chemoradiotherapy is given, followed by immunotherapy.
• Stage 4 treatment centers on systemic therapy. If a targetable mutation such as EGFR or ALK is present, oral targeted therapy is the starting point. Without a target, treatment is chosen based on PD-L1 expression and histologic type, starting with immune checkpoint inhibitors alone or combined with chemotherapy; radiation therapy to specific sites is added for brain or bone metastases.
• For small cell lung cancer confined to one side of the chest, concurrent chemoradiotherapy is used, and prophylactic brain radiation may be considered if the response is good. If the disease extends beyond that area, treatment starts with a combination of chemotherapy and immunotherapy.

What Is the Sequence From Diagnosis to Treatment?

• Step 1: Chest CT is used to identify a suspicious lesion.
• Step 2: Tissue is obtained using bronchoscopy, CT-guided needle biopsy, or surgical biopsy—whichever method fits the lesion's location—to confirm the cancer type and histology.
• Step 3: PET-CT and brain MRI are used to determine the stage, with endobronchial ultrasound used to check lymph nodes if needed.
• Step 4: Biomarker testing (including NGS) for EGFR, ALK, and other markers determines drug selection.
• Step 5: Treatment begins with a combination of surgery, radiation, chemotherapy, targeted therapy, and immunotherapy tailored to the stage and biomarker results, followed by regular imaging and blood tests at set intervals to monitor progress.

FAQ — Is Treatment Difficult If There Is Brain Metastasis?

Having brain metastasis does not mean treatment options are limited. Some targeted therapies penetrate the brain effectively, and stereotactic radiation therapy can be applied separately to the metastatic site. The written opinion will lay out the recommended order of these treatments.

FAQ — Why Do Outcomes Differ Even Among Stage 4 Patients?

Both Korea's 5-year relative survival rate of 42.5% (National Cancer Registry Statistics, 2019–2023) and the SEER rate of 29.5% (2016–2022) are nationwide averages, and individual outcomes vary widely depending on stage, histologic type, biomarkers, and overall health status. Even among Stage 4 patients, the choice of drugs and the course of disease differ depending on whether a target such as EGFR or ALK is present and whether PD-L1 expression is high.

Sources and Disclaimer

• This article was written based on National Cancer Registry Statistics 2019–2023 (Korea Central Cancer Registry, National Cancer Center), SEER 2016–2022, the National Cancer Information Center, and NCCN patient guidelines.
• This content is intended for general medical information purposes only. Diagnostic and treatment methods, as well as outcomes, may vary depending on individual conditions. Accurate diagnosis and treatment should always be determined through consultation with a medical professional.