Lung cancer (staging - IASLC 8th edition)

The IASLC (International Association for the Study of Lung Cancer) 8^th edition lung cancer staging system was introduced in 2016 and supersedes the IASLC 7^th edition. 

Standard-of-care lung cancer staging ideally should be performed in a multidisciplinary meeting using the information provided both from CT and FDG-PET/CT with further inputs from the histopathologic findings (pathologic staging). The National Comprehensive Cancer Network (NCCN) guidelines recommend that FDG-PET/CT should be offered to all patients with non-small cell lung cancer (NSCLC) and that PET-positive findings for mediastinal nodes or distant disease need histopathologic or other radiologic confirmation ⁴. 

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 directions ³. Also, the solid component of subsolid lesions should be performed on a lung or intermediate window rather than mediastinal window ³. 

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

Please note that has been no changes in the nodal involvement staging since the 7^th edition of the IASLC.

PET-CT plays an important role in staging the nodal disease. FDG uptake higher than the blood pool is suspicious, and uptake higher than the liver it is highly concerning for nodal metastases. Endobronchial biopsy of an FDG-avid node is recommended to confirm the disease highest pathologic stage ⁴.  

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, reason why it has now been staged separately
  • M1c: multiple extrathoracic metastases in one or more organs

There is a recommendation that the number of metastatic lesions, the larger diameter of individual metastatic deposits, and the number of involved organs should be stated in the radiological report ³. But, please note, that the site of the metastasis by itself is not a prognostic factor⁴. 

FDG PET/CT has a higher diagnostic value for the diagnosis of bone metastases compared to other methods. Therefore, bone scintigraphy is not recommended for staging purposes ⁴. 

It is recommended histologic diagnosis when the adrenal gland is the only site of metastatic disease, given the risk of a false-positive ⁴. 

Stage groupings

• stage 0
  • TNM equivalent: T_is, N0, M0
• stage Ia
  • TNM equivalent: T1, N0, M0
  • 5-year survival: up to 92%
• stage Ib
  • TNM equivalent: T2a, N0, M0
  • 5-year survival: 68%
• stage IIa
  • TNM equivalent: T2b, N0, M0
  • 5-year survival: 60%
• stage IIb
  • TNM equivalent: T1/T2, N1, M0 or T3, N0, M0
  • 5-year survival: 53%
• stage IIIa
  • TNM equivalent: T1/T2, N2, M0 or T3/T4, N1, M0 or T4, N0, M0
  • 5-year survival: 36%
• stage IIIb
  • TNM equivalent: T1/T2, N3, M0 or T3/T4, N2, M0
  • 5-year survival: 26%
• stage IIIc
  • TNM equivalent: T3/T4, N3, M0
  • 5-year survival: 13%
• stage IVa
  • TNM equivalent: any T, any N with M1a/M1b
  • 5-year survival: 10%
• stage IVb
  • TNM equivalent: any T, any N with M1c
  • 5-year survival: 0%