A 2 cm resectable non-small cell lung cancer without atelectasis, pleural effusion, nodal spread or metastasis is (T1N0M0) is a stage IA disease. We stage all malignancies to select appropriate treatment for them and divine their prognosis. The staging scheme for non-small cell lung cancers comprising adenocarcinoma, squamous cell carcinoma, and large cell carcinoma relies on the size of the tumor (T), the presence of nodal disease (N), and identification of metastasis (M), the TNM scheme. The scheme excludes small cell cancer, which typically has extrathoracic disease at presentation and is rarely resectable. Small cell cancer of the lung is said to be limited when it is confined to the thorax and extensive when there is extrathoracic spread.

In the TNM scheme, non-small cell cancers are T1 or T2 if they spare the chest wall, the diaphragm, and the mediastinum depending on their size and the presence of associated complications like atelectasis.

Nodal disease is considered with respect to the site of the tumor: N0, for no nodal spread; N1, when the ipsilateral lobar or hilar nodes are affected; N2, when there is ipsilateral mediastinal or subcarinal nodal spread; N3 when there is contralateral mediastinal or ipsilateral supraclavicular or scalene nodal spread.

When there is metastasis, the patient is said to have M1 disease, and if there is none they are classified as M0.

The stage of a patient’s disease is assigned by jointly considering their tumor, node, and metastasis status, which the tables below summarize:

TNM Classification of Lung Cancer (explained)
T1	Tumor is less than 3 cm and surrounded by lung tissue.
T2	Tumor is 3 cm or more, spares the chest wall, diaphragm, and the mediastinum; it causes atelectasis.
T3	Tumor invades the chest wall, mediastinum, or diaphragm, but is resectable. E.g., tumor within 2 cm of carina without carinal involvement or tumor invading the pericardium but not the heart.
T4	Tumor invades the chest wall, mediastinum, or diaphragm, and is non-resectable. E.g., tumor invades the carina or trachea or the heart. Malignant pleural effusion and satellite nodules in the same lobe as the primary disease are also T4 disease.
N0	No nodal disease. (Tumor is resectable by simple lobectomy.)
N1	Ipsilateral lobar or hilar adenopathy. (Tumor resectable but may require pneumonectomy.)
N2	Ipsilateral mediastinal or subcarinal adenopathy. (In many centers, tumor is non-resectable.)
N3	Contralateral mediastinal or ipsilateral supraclavicular or scalene adenopathy. (Tumor is non-resectable.)
M0	No metastasis.
M1	Metastasis present.

Staging of Lung Cancer using the TNM Classification (explained)
Stage IA	T1N0M0 : tumor is less than 3 cm; no nodal disease; no metastasis or secondary effects, e.g., atelectasis
Stage IB	T2N0M0: tumor is 3 cm or more and touches no vital structures; no nodal disease; no metastasis
Stage IIA	T1N1M0: tumor is less than 3 cm; there is ipsilateral lobar or hilar adenopathy.
Stage IIB	T2N1M0: tumor is 3 cm or more but free of vital structures; there is ipsilateral lobar or hilar adenopathy. OR T3N0M0: tumor reaches vital structures but is resectable; there is no nodal disease or metastasis.
Stage IIIA	Any T3 except T3N0M0 (see IIB) or N2: Ipsilateral mediastinal or subcarinal adenopathy.
Stage IIIB	Any T4 or N3: Non-resectable tumor or contralateral mediastinal or supraclavicular and scalene adenopathy.
Stage IV	M1: Metastasis is present.

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