What Is the TNM Staging System?
Most lung cancers are staged using the TNM system created by the American Joint Committee on Cancer (AJCC). This system looks at three main factors:
- T (Tumour): Describes the size of the main tumour and whether it has grown into nearby tissues. T1 means a small tumour, while T4 indicates a larger tumour that has spread into surrounding structures.
- N (Nodes): Whether the cancer has spread to nearby lymph nodes. N0 means no lymph node involvement; N3 means spread to nodes on the opposite side of the chest.
- M (Metastasis): Whether the cancer has spread to distant organs. M0 means no distant spread; M1 means metastasis is present.
These values are combined to assign an overall stage from 0 to 4. The staging in use from 2024 onwards is AJCC version 9.
Clinical vs Pathologic Stage
The clinical stage is determined before treatment using imaging scans, CT and PET-CT. The pathologic stage is confirmed after surgery, when the removed tumour and lymph nodes are examined in a laboratory. Pathologic staging is more precise.
How SCLC Is Staged
Small cell lung cancer is also staged with TNM, but doctors commonly use a two-stage system for treatment planning:
- Limited stage: Cancer is confined to one lung and possibly nearby lymph nodes, all within a field treatable with radiation.
- Extensive stage: Cancer has spread beyond one hemithorax, to both lungs, fluid around the lungs, or distant organs such as the brain. About 70% of SCLC patients are diagnosed at the extensive stage.
Stage 1 Lung Cancer
Stage 1 is confined to the lung with no lymph node involvement. Most patients have no symptoms at this stage, and the cancer is often detected incidentally on a CT scan.
Stage 1A and 1B
Stage 1A tumours are 3 cm or smaller. They are subdivided into 1A1 (≤1 cm), 1A2 (1-2 cm), and 1A3 (2 to 3 cm). Stage 1B tumours are 3 to 4 cm or have begun to affect the main bronchus, the visceral pleura, or the airway, but lymph nodes remain clear.
Stage 1 Treatment and Survival
Surgery, typically a lobectomy (removal of the affected lobe), is the standard treatment. Stereotactic body radiotherapy (SBRT) is an effective alternative for patients who cannot tolerate surgery. Adjuvant targeted therapy or chemotherapy may follow for Stage 1B to reduce recurrence risk.
The five-year relative survival rate for localised NSCLC is approximately 67%, based on SEER data from patients diagnosed between 2015 and 2021.
Stage 2 Lung Cancer
Stage 2 is still an early stage, but the disease is more advanced than Stage 1. The tumour may be larger, or the cancer may have reached lymph nodes close to the original tumour site.
Stage 2A and 2B
Stage 2A tumours are 4 to 5 cm with no lymph node spread. Stage 2B includes tumours of 5 to 7 cm without lymph node involvement, or smaller tumours that have spread to peribronchial or hilar lymph nodes on the same side as the tumour. Tumours that have grown into the chest wall or pericardium without lymph node spread also fall into Stage 2B.
Stage 2 Treatment
Surgery remains the primary treatment when the tumour can be fully removed. Adjuvant chemotherapy is recommended after surgery for most Stage 2 patients. Radiation therapy may be added if cancer cells are found at the surgical margins.
Stage 3 Lung Cancer
Lung cancer in stage 3 has locally progressed. Although distant organs have not yet been affected, the cancer has progressed to lymph nodes in the chest. There are three sub-stages within it.
Stage 3A, 3B, and 3C
Stage 3A involves spread to ipsilateral mediastinal lymph nodes (same side as the tumour). Stage 3B involves contralateral mediastinal or supraclavicular nodes (opposite side or above the collarbone). Stage 3C involves both extensive tumour invasion of critical structures and widespread nodal spread.
Stage 3 Treatment and Survival
Stage 3A may be surgically resectable in selected patients, followed by chemotherapy and radiation. For Stage 3B and 3C, concurrent chemoradiation is the standard approach. After completing chemoradiation, patients with unresectable Stage 3 NSCLC typically receive consolidation immunotherapy with Durvalumab, which has significantly extended progression-free survival.
Approximately 13% to 36% of patients with Stage 3 lung cancer survive at least five years, depending on sub-stage and treatment.
Stage 4 Lung Cancer
Stage 4 is metastatic lung cancer. In this, the cancer has spread to distant organs. It is the most common stage at diagnosis, as the disease often produces no symptoms until it has advanced significantly.
Stage 4A and 4B
Stage 4A includes spread to the opposite lung, malignant pleural or pericardial effusion, or a single metastasis in a distant organ such as the brain, liver, adrenal gland, or bone. Stage 4B involves multiple metastases in one or more distant organs.
Stage 4 Treatment
Stage 4 NSCLC is not curable in most cases, but it is treatable. Treatment depends on the results of biomarker testing performed on the tumour tissue:
- If the tumour carries an actionable mutation (EGFR, ALK, ROS1, KRAS G12C, MET, BRAF V600E), targeted therapy with an oral kinase inhibitor is the preferred first-line approach.
- If no actionable mutation is found but PD-L1 expression is high, immunotherapy such as pembrolizumab may be used alone or with chemotherapy.
- For tumours without targetable mutations or high PD-L1, platinum-based chemotherapy plus immunotherapy is standard.
- Brain metastases may be treated with stereotactic radiosurgery or whole-brain radiation.
- Palliative care alongside active treatment helps manage pain, breathlessness, and fatigue.
For Stage 4 SCLC (extensive stage), first-line treatment is platinum-etoposide chemotherapy combined with immunotherapy (Atezolizumab or Durvalumab).
Stage 4 Survival Rate
For distant-stage NSCLC, the five-year relative survival rate is approximately 12%, based on SEER data from 2015 to 2021. For distant-stage SCLC, the five-year rate is around 4%. Patients with targetable mutations treated with modern targeted therapies are increasingly achieving long-term disease control, and outcomes are continuing to improve.
How to Read Survival Statistics
Survival rates are calculated from large groups of patients diagnosed and treated years earlier. They are useful as a guide, but they do not predict what will happen in any individual case.
Other factors that influence outcome at every stage include the specific NSCLC subtype, the presence of targetable gene mutations, PD-L1 expression level, overall health and fitness, and how well the cancer responds to initial treatment. Treatments have advanced considerably in the past decade. Patients diagnosed today are likely to have better outcomes than current statistics reflect.
Conclusion
Lung cancer stage indicates the extent to which the illness has spread throughout the body. Knowing the stage enables medical professionals to choose the best course of treatment and project how the illness will likely progress. Many patients now have better treatment options and results thanks to advancements in immunotherapy, targeted medicines, and early identification. Understanding your lung cancer stage is the first step to understanding your treatment options and what to expect.
