TNM classification system
Both the prognosis and choice of treatment depend on the extent of the disease when it is diagnosed.
The TNM classification system is used to stage lung cancer and classify the size and extent of the disease at the time of the diagnosis. "T" describes the size and extent of the local tumor. "N" (node) expresses whether there is metastasis to lymph nodes. "M" expresses the absence or presence of distant metastasis (23).
The TNM system differentiates between the clinical classification based on radiology and clinical examination (cTNM), and the pathology classification (pTNM). Only patients treated with surgery are staged according to pTNM, while patients treated by radiation therapy or chemotherapy are staged according to cTNM.
The TNM classification is critical for the choice of treatment and must be present before treatment is initiated. However, if distant metastases are present (M1), the T and N stages are of minor importance.
From 2009, the 7th edition of the TNM classification system is being used.
T - Primary Tumor
- TX – Primary tumor cannot be assessed, or tumor proven by the presence of malignant cells in sputum or bronchial washings but not visualized by imaging or bronchoscopy
- T0 – No evidence of primary tumor
- Tis – Carcinoma in situ
- T1 – Tumor ≤ 3 cm in greatest dimension, surrounded by lung or visceral pleura without bronchoscopic evidence of invasion more proximal than the lobar bronchus
- T1a – Tumor ≤ 2 cm in greatest dimension
- T1b – Tumor > 2 cm but ≤ 3 cm in greatest dimension
- T2 – Tumor > 3 cm but ≤ 7 cm or tumor with any of the following features (T2 tumours with these features are classified T2a if ≤ 5 cm)
- involves main bronchus, ≥ 2 cm distal the carina
- invades visceral pleura
- associated with atelectasis or obstructive pneumonitis that extends to the hilar region but does not involve the entire lung
- T2a – Tumor > 3 cm but ≤ 5 cm in greatest dimension
- T2b – Tumor > 5 cm but ≤ 7 cm in greatest dimension
- T3 – Tumor > 7 cm, or one of the following:
- Tumor invades the chest wall, diaphragm, mediastinal pleura, parietal pericardium, or phrenicus nerve
- Tumor in the main bronchus < 2 cm distal to the carina but without involving the carina
- Atelectasis of the entire lung
- Separate tumor in the same lobe
- T4 – One of the following:
- Tumor invades the mediastinum, heart, great vessels, carina, trachea, esophagus, vertebral body, or recurrence nerve
- Separate tumor in other lobe of the same lung
N - Regional Lymph Nodes
- NX – Regional lymph nodes cannot be assessed
- N0 – No regional lymph node metastasis
- N1 – Metastasis in peribronchial or hilar lymph nodes on the same side as the main tumor
- N2 – Metastasis in mediastinal nodes on the same side as the main tumor and/or subcarinal lymph node(s)
- N3 – Metastasis to hilar or mediastinal nodes on the opposite side of the main tumor, or to supraclavicular or scalene lymph nodes
M - Distant Metastasis
- MX – Distant metastasis cannot be assessed
- M0 – No distant metastasis
- M1 – Distant metastasis
- M1a – Distant metastasis to lung on opposite side of the primary tumor, pleural lymph nodes or malignant or pericardial effusion
- M1b – Distant metastasis
The general health condition of the patient is an important prognostic factor in line with stage division. The WHO performance status is utilized.
Non-small cell lung cancer
TX N0 M0
Tis N0 M0
TX-T4 NX-N3 M1
T2a N0 M0
T2b N0 M0
T1a-b N1 M0
T2a N1 M0
T2b N1 M0
T3 N0 M0
T1a-b T2a-b N2 M0
T3 N1-N2 M0
T4 N0-N1 M0
T4 N2 M0
TX-T4 N3 M0
The stage is the main determinant for treatment, but prognostic factors may also be of influence.
Small-cell lung cancer
Small-cell lung cancer presents more often with metastasis at the time of diagnosis than other bronchial cancers. The condition is considered systemic regardless of stage and diagnosis, but is separated into limited or extensive disease.
In limited disease (SCLC-LD), the tumor masses can be included in a thoracic radiation field. For practical purposes, this includes stage I, II, IIIA and IIIB.
Extensive disease (SCLC-ED) includes spread of malignant cells outside the thoracic radiation field or pleural effusion.
Due to the advancement in treatment options for small-cell lung cancer requiring more precise stage determination, the TNM system is also recommended for small-cell lung cancer (26,27).