Medical Health Encyclopedia

The TNM system is defined as T (for tumor), N (for regional lymph nodes), and M (for metastasis).

T refers to the size and extension of the tumor itself.

In TX and T0, the tumor is indicated by cancer cells in sputum or lung samples but cannot be visualized.

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Tis: Carcinoma in situ. (The cells are cancerous, but the tumor does not show evidence of spreading.)

In T1, the tumor is 3 cm or less in dimension, is still contained in the lung or the membrane covering the lung (the visceral pleura), and has not reached the main airway (bronchus).

In T2, the tumor has one or more of the following features: greater than 3 cm; involves the main bronchus; 2 cm or more away from the ridge (the carina) at the lowest part of the windpipe (trachea); has invaded the visceral pleura; is associated with collapsed lung tissue (atelectasis) or obstructive inflammation of lung tissue but does not involve the entire lung.

In T3, a tumor of any size has directly invaded any of the following: chest wall, diaphragm, the membrane covering organs and structures in the chest, the outer wall of the membrane around the heart (pericardium); the tumor is in the main airway and less than 2 cm away from the carina but has not involved the trachea; the tumor is associated with atelectasis or obstructive inflammation of the entire lung.

In T4, the tumor has invaded any of the following: the area between the lungs (mediastinum), the heart, the great vessels, carina, trachea, esophagus, main portion of the spine; separate tumor nodules are present in the same lobe; the tumor is accompanied by a malignant pleural effusion (increased amount of fluid between the membrane and the lung).

N followed by 0 to 3 refers to whether the cancer has reached regional lymph nodes.

In stage N0, the regional lymph nodes are still cancer-free.

In N1, the cancer has spread to nearest lymph nodes around the airways, in the hilum (a depression in the lung where blood and lymph vessels enter), or in both. The tumor has extended directly into lymph nodes within the lung.