The new 8th TNM staging system of lung cancer and its potential imaging interpretation pitfalls and limitations with CT image demonstrations

Abstract

The tumor, node, metastasis (TNM) staging system approved by International Association for the Study of Lung Cancer (IASLC) and the American Joint Committee on Cancer (AJCC) to stage lung cancer was recently revised. The latest revision is the 8th edition published in January, 2017. This new edition made some important changes to the previous edition, including modification of the T classification based on 1 cm increment, downstage of T descriptor including endobronchial tumor disregarding its distance from carina (T2), merging total and partial atelectasis/pneumonitis into the same T category (T2), upstage diaphragmatic invasion to T4, new classification concept of adenocarcinoma in situ and minimally invasive adenocarcinoma for pure and part-solid ground-glass nodules, and further division of extrathoracic metastasis into M1b and M1c based on the number and sites of extrathoracic metastases. Consensus is reached for debating situations not covered in the previous edition of staging system, such as the classification of pancoast tumor based on its invasion depth and staging tumors that extend directly across the fissure as T2a. Classification of multiple sites of pulmonary involvement, including multiple primary lung cancer, separate lung cancer nodules, multiple ground-glass or lepidic lesions, and consolidation, is also discussed. Even though the 8th edition of the TNM lung staging system provides us with more precise classification based on prognostic analysis of each TNM descriptors, there are still some potential limitations and clinical situations that have not yet been clarified in terms of clinical staging by imaging. It is important for radiologists to understand the major changes introduced in the 8th edition of TNM staging and to recognize the potential pitfalls and limitations of imaging interpretation to precisely classify the clinical stage of lung cancer.

Conflict of interest statement

Conflict of interest disclosure

The authors declared no conflicts of interest.

Figures

Figure 1

Chest CT showed pure ground-glass nodule of 0.8 cm in diameter (arrow) in a 45-year-old woman with frozen section showing adenocarcinoma in situ of right upper lobe of the lung without definite stromal invasion or lymphovascular permeation. In the 8th edition of TNM imaging staging, it will be staged as Tis.

Figure 2. a–e

Part-solid nodules of various sizes that correspond to different T stages. Chest CT images (a, b) of a 55-year-old female with two part-solid nodules, one found in the apical segment of the right upper lobe of the lung with total diameter of 1.0 cm and a solid component of 0.3 cm (a, arrow), and the other noted in the superior segment of the left lower lobe of the lung with a diameter of 0.7 cm and a solid component of 0.4 cm (b, arrow). Pathology proved adenocarcinoma of lung. The imaging staging was cT1mi (m), m for multiple nodules. CT image (c) of a part-solid nodule with a solid component measuring up to 0.8 cm in maximum diameter with total size of 1.8 cm (arrow), imaging staging T1a, in a 53-year-old man with pathology showing non-small cell carcinoma. Lung CT image (d) of a 62-year-old male, a case of esophageal cancer, pT2N0M0, status post thoracoscopic esophagectomy and gastric tube reconstruction. Follow-up chest CT found one part-solid nodule up to 1.8 cm with 1.2 cm solid part (arrow) in the left upper lobe without obvious lymph node and distant metastasis, imaging staging T1a (≤2 cm) in the 7th edition and T1b in the 8th edition, suspected primary lung cancer. Pathology showed moderately differentiated mixed mucinous and acinar adenocarcinoma and hilar/mediastinum lymph node metastasis. Lung CT image (e) of a 76-year-old female with incidental finding of a 2.8 cm part-solid tumor with a solid part measuring up to 2.7 cm (arrow), located at the right lower lobe of the lung. Imaging staging of AJCC 8th edition is T1c. CT-guided biopsy revealed adenocarcinoma.

Figure 3. a–c

Clinical image illustration of lung cancers that have features of T2. Squamous cell carcinoma of the right lower lobe of the lung (a) in a 57-year-old heavy smoker male. Chest CT with contrast showed the poorly enhanced, central tumor (a, arrow) measuring 4.4 cm with distal partial atelectasis/pneumonitis (arrowheads) of the right lower lobe of the lung. The stage is T2b in the 8th edition of lung cancer staging. A case of endobronchial lung cancer of the left upper lobe of the lung (b, c), involving the left main bronchus and left upper lobar bronchus with a maximum diameter of 2.7 cm (arrows). The involvement of main bronchus without touching the carina gives the cancer stage iT2a in the 8th edition of lung cancer staging.

Figure 4

A case of lung cancer (arrow) with chest wall invasion in a 65-year-old male. Chest CT showed characteristics of chest wall invasion, including destruction of the right 4th rib (arrowhead), a tumor and pleural contact length of more than 3 cm, an obtuse angle between tumor and chest wall and associated pleural thickening.

Figure 5. a, b

Lung cancer with major vessel invasions. Lung cancer at superior segment of the left lower lobe (a, arrow), with maximum tumor diameter of 4 cm, in a 71-year-old female with pathology from endobronchial ultrasound biopsy proving non-small cell carcinoma, favoring adenocarcinoma. Lung CT showed tumor invasion of descending aorta with contact length more than one fourth (90°) of the circumference of descending aorta, and thus increased the T classification to T4, according to the 8th edition of lung cancer staging. Chest CT (b) showing lung cancer (arrow), with maximum diameter of 4.9 cm, in an 83-year-old female with tumor invasion to the left pulmonary artery.

Figure 6. a–f

CT scans showing three classifications of M descriptors. Chest CT image (a) of a 51-year-old female with a mass having maximum diameter of 4.2 cm and multiple pulmonary nodules in bilateral lungs (arrows), suspected bilateral lung to lung metastasis. Biopsy pathology favored primary lung adenocarcinoma. This case was staged M1a in image staging, with intrapulmonary metastasis. Contrast-enhanced chest CT images (b, c) of a 54 year-old female with lung tumor at left upper lobe of lung and distal metastasis to a nonregional lymph node. Lung window (b) showing the 1.3 cm solid tumor nodule with spiculated margin in the apicoposterior segment of left upper lobe of lung (arrow). Soft tissue window (c) illustrating the extrathoracic lymph node metastasis at left axillary region (arrow). Since no other distant metastasis is detected, this case should be staged as M1b, a single extrathoracic metastasis in a single organ. A case of M1c classification (d–f): multiple extrathoracic metastatic lesions at multiple sites of a 61-year-old male with lung cancer in the apicoposterior segment of left upper lobe of lung with a diameter of 3.3 cm (d, arrow). Soft tissue window (e) showing poorly enhanced nodules (arrows) in segment VII, VIII and V of liver, suspected metastatic lesions. Bone metastatic osteolytic lesions were noted in T10 and T11 vertebrae (f, arrows).

Figure 7

CT scan of lymphangitis carcinomatosis. This 62-year-old male is diagnosed with adenocarcinoma of right upper lung. CT scan shows a spiculated mass in apical segment of right upper lobe of lung with a maximum dimension of 3.8 cm and extensive nodular septal thickenings (lymphangitis carcinomatosus, arrows).

Figure 8

Image illustration that likely present pleural invasion in lung cancer. Chest CT showing 2.3 cm adenocarcinoma of left upper lung with type 2 pleural tags, defined as one or more linear pleural tags with soft tissue component at the pleural end, in a 41-year-old female with pathology showing invasion to the chest wall (arrow).