NSCLC TNM Staging (AJCC 8th Edition)

The AJCC 8th Edition TNM classification for non-small cell lung cancer (NSCLC), effective January 2018, introduced several important revisions from the 7th edition: subdivision of T1 into T1a (≤1 cm), T1b (>1–2 cm), and T1c (>2–3 cm); new categories for minimally invasive adenocarcinoma (T1mi) and adenocarcinoma in situ; reclassification of T2 and T3 based on size alone (≤5 cm = T2; >5–7 cm = T3; >7 cm = T4); and split of Stage IIIB/IIIC. These refinements better stratify prognosis across 11 stage groups (IA1–IVB) and directly inform resectability decisions, adjuvant therapy thresholds, and clinical trial eligibility.

T Descriptors

• TX: Primary tumor cannot be assessed; tumor proven by malignant cells in sputum or bronchial washings but not visualized by imaging or bronchoscopy. Requires further workup to localize and characterize the primary lesion.
• T0: No evidence of primary tumor.
• Tis: Carcinoma in situ: squamous cell carcinoma in situ (SCIS) or adenocarcinoma in situ (AIS) — lepidic-only growth pattern, ≤3 cm. AIS has a nearly 100% disease-specific survival with complete resection; limited resection (wedge/segmentectomy) is preferred when feasible.
• T1mi: Minimally invasive adenocarcinoma (MIA): solitary adenocarcinoma with predominantly lepidic pattern, ≤3 cm greatest dimension, with ≤5 mm invasion in any one focus. Excellent prognosis; near 100% disease-specific survival after complete resection.
• T1a: Tumor ≤1 cm in greatest dimension, surrounded by lung or visceral pleura, not in main bronchus. NCCN recommends limited resection (segmentectomy preferred over wedge) if margins allow, per JCOG 0802 data.
• T1b: Tumor >1 cm but ≤2 cm in greatest dimension, otherwise meeting T1 criteria.
• T1c: Tumor >2 cm but ≤3 cm in greatest dimension, otherwise meeting T1 criteria.
• T2a: Tumor >3 cm but ≤4 cm, OR any size tumor with: involvement of main bronchus (regardless of distance to carina); invasion of visceral pleura; or associated atelectasis/obstructive pneumonitis extending to hilar region.
• T2b: Tumor >4 cm but ≤5 cm, OR any size meeting T2 criteria as above. T2b N0 M0 = Stage IIA; adjuvant chemotherapy (and osimertinib if EGFR-mutant) is recommended for resected Stage IIA.
• T3: Tumor >5 cm but ≤7 cm; OR direct invasion of chest wall (including parietal pleura), phrenic nerve, or parietal pericardium; OR separate tumor nodule(s) in the same lobe as the primary.
• T4: Tumor >7 cm; OR invades mediastinum, heart, great vessels, trachea, recurrent laryngeal nerve, esophagus, vertebral body, or carina; OR separate tumor nodule(s) in a different ipsilateral lobe. T4 does not automatically preclude resection — selected T4 (e.g., chest wall T4, satellite nodule in different lobe) may be resectable in high-volume thoracic surgery centers.

N Descriptors

• 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).

M Descriptors

• M0: No distant metastasis.
• M1a: Separate tumor nodule(s) in a contralateral lobe; OR tumor with pleural or pericardial nodules; OR malignant pleural or pericardial effusion.
• M1b: Single extrathoracic metastasis in a single organ (including involvement of a single non-regional lymph node).
• M1c: Multiple extrathoracic metastases in a single organ or in multiple organs.

Stage Groups