The IASLC (International Association for the Study of Lung Cancer) 9^th edition lung cancer staging system was introduced in 2025 and supersedes the IASLC 8^th edition. It is a TNM staging system.

There are only minor differences from the 8^th edition.

• no changes to the T staging.

• subdivision of N2 involvement into

  • N2a (single N2 station) and

  • N2b (multilevel stations)

• subdivision of M1c status into

  • M1c1 (multiple metastases in a single organ system) and

  • M1c2 (metastases in multiple organ systems).

These changes result in a rearrangement of some stage groups as shown in the next table. Several prefix can be used that specify the context of the TNM classification.

• clinical stage (c) is determined by all information available pre-treatment.

• pathologic stage (p) is defined by the results after surgical resection only, and should not be used outside this context.

• restaging (y) is used after part or all of the treatment has been given.

The full staging groups are therefore.

TNM system

T: primary tumour

• Tx: primary tumour cannot be assessed or tumour proven by the presence of malignant cells in sputum or bronchial washings but not visualised by imaging or bronchoscopy

• T0: no evidence of a primary tumour

• Tis: carcinoma in situ - tumour measuring 3 cm or less and has no invasive component at histopathology

• T1: tumour measuring 3 cm or less in greatest dimension surrounded by lung or visceral pleura without bronchoscopic evidence of invasion more proximal than the lobar bronchus (i.e. not in the main bronchus)

  • T1a(mi): minimally invasive adenocarcinoma

    • tumour has an invasive component measuring 5 mm or less at histopathology

  • T1a ss: superficial spreading tumour in central airways (spreading tumour of any size but confined to the tracheal or bronchial wall)

  • T1a: tumour ≤1 cm in greatest dimension

  • T1b: tumour >1 cm but ≤2 cm in greatest dimension

  • T1c: tumour >2 cm but ≤3 cm in greatest dimension

• T2: tumour >3 cm but ≤5 cm or tumour with any of the following features:

  • involves the main bronchus regardless of distance from the carina but without the involvement of the carina

  • invades visceral pleura

  • associated with atelectasis or obstructive pneumonitis that extends to the hilar region (involving part or all of the lung)

  • T2a: tumour >3 cm but ≤4 cm in greatest dimension

  • T2b: tumour >4 cm but ≤5 cm in greatest dimension

• T3: tumour >5 cm but ≤7 cm in greatest dimension or associated with separate tumour nodule(s) in the same lobe as the primary tumour or directly invades any of the following structures:

  • chest wall (including the parietal pleura and superior sulcus)

  • phrenic nerve

  • parietal pericardium

• T4:

  • ​tumour

    • >7 cm in greatest dimension or

    • associated with separate tumour nodule(s) in a different ipsilateral lobe than that of the primary tumour

    • or

  • invades any of the following structures

    • diaphragm

    • mediastinum

    • heart

    • great vessels

    • trachea

    • recurrent laryngeal nerve

    • oesophagus

    • vertebral body

    • carina

It is recommended that solid and non-solid lesions should be measured on the image that shows the greatest tumour dimension (on axial, coronal, or sagittal planes). Although those lesions that are part solid should be measured on both their largest average diameter and the largest diameter of the solid component, only the solid component measurement is to be used for staging ³. The solid component of subsolid lesions should be measured on a lung or intermediate window rather than mediastinal window ³. 

For those centrally located lung tumours associated with peripheral post-obstructive atelectasis, FDG-PET-CT is useful in further delineating the real tumour size and, leading to a more precise T staging and a smaller targeted volume in radiation treatment planning. 

N: regional lymph node involvement

• Nx: regional lymph nodes cannot be assessed

• N0: no regional lymph node metastasis

• N1: metastasis in ipsilateral peribronchial and/or ipsilateral hilar lymph nodes and intrapulmonary nodes, including involvement by direct extension

• N2: metastasis in ipsilateral mediastinal and/or subcarinal lymph node(s)

  • N2a (single N2 station) and

  • N2b (multilevel stations)

• N3: metastasis in contralateral mediastinal, contralateral hilar, ipsilateral or contralateral scalene, or supraclavicular lymph node(s)

PET-CT could play an important role in staging nodal disease. FDG uptake higher than the blood pool is suspicious, and uptake higher than the liver is highly concerning for nodal metastases. Endobronchial biopsy of an FDG-avid node is recommended to confirm the highest pathologic stage of disease.   

M: distant metastasis

• M0: no distant metastasis

• M1: distant metastasis present

  • M1a: separate tumour nodule(s) in a contralateral lobe; tumour with pleural or pericardial nodule(s) or malignant pleural or pericardial effusions

  • M1b: single extrathoracic metastasis, involving a single organ or a single distant (nonregional) node

    • a single extrathoracic metastasis has a better survival and different treatment choices, which is why it has now been staged separately

  • M1c: multiple extrathoracic metastases in one or more organs

    • M1c1 (multiple metastases in a single organ system) and

    • M1c2 (metastases in multiple organ systems).

Stage groupings

To be added