What is the TNM (Tumor, Node, Metastasis) staging for adenocarcinoma of the lung?

TNM Staging for Lung Adenocarcinoma

Lung adenocarcinoma staging follows the 8th edition IASLC/AJCC TNM classification system, which provides more granular T-stage subdivisions based on 1-cm tumor size increments and refined M-stage categories based on the number and location of metastatic sites. 1

T Stage (Primary Tumor)

The T descriptor is determined by tumor size, location, and invasion of adjacent structures 1:

Size-Based Classification

• Tis (AIS): Adenocarcinoma in situ 1
• T1mi: Minimally invasive adenocarcinoma ≤3 cm with ≤0.5 cm invasion 1
• T1a: Tumors ≤1 cm 1
• T1b: Tumors >1 cm to 2 cm 1
• T1c: Tumors >2 cm to 3 cm 1
• T2a: Tumors >3 cm to 4 cm 1
• T2b: Tumors >4 cm to 5 cm 1
• T3: Tumors >5 cm to 7 cm 1
• T4: Tumors >7 cm 1

Critical Measurement Rule for Part-Solid Tumors

For part-solid adenocarcinomas, measure only the solid (invasive) component for T-stage assignment, though the total tumor size including ground-glass opacity should also be recorded. 1 This represents a major change from prior editions and provides better prognostic discrimination 2.

Additional T2 Features (regardless of size)

• Endobronchial tumor involving main bronchus at any distance from carina (without carinal involvement) 1
• Atelectasis or obstructive pneumonitis extending to the hilum 1
• Visceral pleural invasion 1

T3 Features

• Invasion of chest wall, phrenic nerve, parietal pleura, or pericardium 1
• Ipsilateral satellite nodule in the same lobe as primary tumor 1

T4 Features

• Invasion of carina, diaphragm, vertebral body, mediastinum, heart, trachea, esophagus, or recurrent laryngeal nerve 1
• Ipsilateral satellite nodules in a different lobe from primary tumor 1

N Stage (Regional Lymph Nodes)

The N stage is based on anatomic location of metastatic lymph nodes 1:

• N0: No regional lymph node metastases 1
• N1: Metastasis in ipsilateral peribronchial and/or hilar lymph nodes, including involvement by direct extension 1
• N2: Metastasis in ipsilateral mediastinal and/or subcarinal lymph nodes 1
• N3: Metastasis in contralateral mediastinal, contralateral hilar, ipsilateral or contralateral scalene, or supraclavicular lymph nodes 1

Lymph nodes >10 mm in short-axis diameter are considered abnormal, with 30% prevalence of metastasis for nodes 10-15 mm and 67% for nodes >15 mm. 1

M Stage (Distant Metastasis)

The 8th edition subdivides metastatic disease based on number and location 1, 3:

• M0: No distant metastasis 1
• M1a: Separate tumor nodule(s) in contralateral lobe; pleural or pericardial nodules; malignant pleural or pericardial effusion 1
• M1b: Single extrathoracic metastasis in a single organ 1, 3
• M1c: Multiple extrathoracic metastases in one or several organs 1, 3

Stage Grouping

The complete stage grouping according to the 8th edition 1:

Early Stages

• Stage 0: Tis, N0, M0 1
• Stage IA1: T1a(mi)/T1a, N0, M0 1
• Stage IA2: T1b, N0, M0 1
• Stage IA3: T1c, N0, M0 1
• Stage IB: T2a, N0, M0 1
• Stage IIA: T2b, N0, M0 1

Locally Advanced Stages

• Stage IIB: T1a-c/T2a-b, N1, M0 or T3, N0, M0 1
• Stage IIIA: T1a-c/T2a-b, N2, M0 or T3, N1, M0 or T4, N0-1, M0 1
• Stage IIIB: T1a-c/T2a-b, N3, M0 or T3-4, N2, M0 1
• Stage IIIC: T3-4, N3, M0 1

Metastatic Stages

• Stage IVA: Any T, Any N, M1a or M1b 3
• Stage IVB: Any T, Any N, M1c 3

Special Considerations and Pitfalls

Multiple Ground-Glass Nodules

Multiple synchronous ground-glass or part-solid nodules representing adenocarcinoma in situ, minimally invasive adenocarcinoma, or lepidic-predominant adenocarcinoma should be classified as separate primary lung cancers, not intrapulmonary metastases. 1 Stage according to the highest T category with the number of lesions indicated in parentheses 1.

Pneumonic-Type Adenocarcinoma

For invasive mucinous adenocarcinoma presenting with consolidation: T-stage based on size if single lesion, T3 if entire lobe involved, T4 if multiple ipsilateral lobes, M1a if bilateral involvement 1.

Common Staging Pitfalls

• Do not use total tumor size for part-solid lesions—only the solid component determines T-stage 1
• Lymph node size alone is insufficient—histologic or cytologic confirmation required for nodes 10-15 mm before denying surgery 1
• Diaphragmatic invasion is now T4, not T3 as in prior editions 1
• Endobronchial location is now T2a regardless of distance from carina (as long as carina not involved) 1