15.4 Lung Staging (AJCC Version 9, 2025+): T, N2a/N2b, M1c1/M1c2 & New Stage Groups
Key Takeaways
Version 9 lung staging applies to diagnoses from January 1, 2025; T categories are unchanged from the 8th edition (T1a 1 cm or less, T1b more than 1–2 cm, T1c more than 2–3 cm, T2a more than 3–4 cm, T2b more than 4–5 cm, T3 more than 5–7 cm, T4 more than 7 cm).
N2a is metastasis in a single ipsilateral mediastinal or subcarinal station, and N2b is metastasis in multiple ipsilateral mediastinal stations, with or without the subcarinal station.
M1c1 is multiple extrathoracic metastases in one organ system, and M1c2 is multiple extrathoracic metastases in several organ systems; both remain stage IVB.
Version 9 moved T1N1 from IIB to IIA, placed T1N2a in IIB, T2N2a and T3N2a in IIIA, and T2N2b in IIIB.
For part-solid adenocarcinomas, the clinical T category is based on the size of the solid (invasive) component, not the total size including ground glass.
Primary tumor (T)
| T | Definition |
|---|---|
| TX | Primary tumor cannot be assessed, or tumor proven by malignant cells in sputum or washings but not seen by imaging or bronchoscopy (occult carcinoma) |
| T0 | No evidence of primary tumor |
| Tis | Carcinoma in situ: adenocarcinoma in situ (AIS) or squamous cell carcinoma in situ |
| T1 | 3 cm or less, surrounded by lung or visceral pleura, not more proximal than the lobar bronchus |
| T1mi | Minimally invasive adenocarcinoma |
| T1a | 1 cm or less |
| T1b | More than 1 cm to 2 cm |
| T1c | More than 2 cm to 3 cm |
| T2 | More than 3 cm to 5 cm, or any of: involves the main bronchus without involving the carina; invades visceral pleura; atelectasis or obstructive pneumonitis extending to the hilum |
| T2a | More than 3 cm to 4 cm (or a T2 feature and 4 cm or less) |
| T2b | More than 4 cm to 5 cm |
| T3 | More than 5 cm to 7 cm, or invades parietal pleura or chest wall (including superior sulcus tumors), phrenic nerve, parietal pericardium, or separate tumor nodule(s) in the same lobe |
| T4 | More than 7 cm, or invades diaphragm, mediastinum, heart, great vessels, trachea, recurrent laryngeal nerve, esophagus, vertebral body or carina, or separate nodule(s) in a different ipsilateral lobe |
Version 9 changes to T: none to the categories. The wording was clarified for invasion of structures such as the azygos vein, vagus nerve, brachial plexus and thoracic nerve roots, which stay T3 or T4 as defined.
STORE note: occult lung carcinoma is assigned TX, according to the current AJCC definition.
Measurement rules
- Part-solid (subsolid) adenocarcinoma: cT uses the size of the solid component on CT. AJCC's illustration shows a 10 mm part-solid nodule with an 8 mm solid part, which is cT1a. pT uses the size of the invasive component on pathology.
- Pure ground-glass nodules of 3 cm or less that are adenocarcinoma in situ are Tis.
- Round the size to the nearest millimeter. When the size is between two categories and uncertain, assign the lower T.
Regional lymph nodes (N)
| N | Definition |
|---|---|
| N0 | No regional lymph node metastasis |
| N1 | Ipsilateral peribronchial and/or hilar nodes and intrapulmonary nodes, including direct extension |
| N2a | Single ipsilateral mediastinal or subcarinal nodal station |
| N2b | Multiple ipsilateral mediastinal nodal stations, with or without the subcarinal station |
| N3 | Contralateral mediastinal or hilar nodes; ipsilateral or contralateral scalene or supraclavicular nodes |
Nodal stations follow the IASLC lymph node map. For example, station 7 is subcarinal and stations 2R and 4R are right upper and lower paratracheal. EBUS-TBNA and mediastinoscopy samples establish N2 or N3 (Section 10.1).
Distant metastasis (M)
| M | Definition |
|---|---|
| M0 | No distant metastasis |
| M1a | Separate nodule(s) in a contralateral lobe; tumor with pleural or pericardial nodules, or malignant pleural or pericardial effusion |
| M1b | A single extrathoracic metastasis in a single organ, including a single non-regional node |
| M1c1 | Multiple extrathoracic metastases in one organ system |
| M1c2 | Multiple extrathoracic metastases in multiple organ systems |
A pleural effusion that is cytologically negative on repeated exams, non-bloody, not an exudate, and judged unrelated to the tumor is excluded, and the case is not M1a on that basis.
Version 9 stage groups
| Stage | T and N (M0 unless shown) |
|---|---|
| Occult | TX N0 |
| 0 | Tis N0 |
| IA1 | T1mi N0; T1a N0 |
| IA2 | T1b N0 |
| IA3 | T1c N0 |
| IB | T2a N0 |
| IIA | T2b N0; T1 (a–c) N1 |
| IIB | T2a–T2b N1; T3 N0; T1 N2a |
| IIIA | T1 N2b; T2 N2a; T3 N1; T3 N2a; T4 N0; T4 N1 |
| IIIB | T2 N2b; T3 N2b; T4 N2a; T4 N2b; T1–T2 N3 |
| IIIC | T3–T4 N3 |
| IVA | Any T, any N, M1a or M1b |
| IVB | Any T, any N, M1c1 or M1c2 |
What changed from the 8th edition:
| Combination | 8th edition | Version 9 |
|---|---|---|
| T1 N1 | IIB | IIA |
| T1 N2 | IIIA | N2a IIB; N2b IIIA |
| T2 N2 | IIIA | N2a IIIA; N2b IIIB |
| T3 N2 | IIIB | N2a IIIA; N2b IIIB |
| M1c | IVB | M1c1 and M1c2 both IVB |
Multiple lung tumors and staging
Staging and the Solid Tumor Rules answer different questions. First decide the number of primaries with the lung Solid Tumor Rules (Section 14.2). For a single primary with extra nodules, AJCC's multiple-nodule concepts are:
- A separate nodule of the same histology in the same lobe is T3.
- A nodule in a different ipsilateral lobe is T4.
- A nodule in the contralateral lung is M1a.
- Multifocal ground-glass or lepidic lesions: T is based on the highest T lesion, with (m) or the number of lesions.
- Pneumonic-type adenocarcinoma: T is based on size, or T3/T4/M1a by the extent of lobes involved.
Worked cases
- A 2.6 cm right lower lobe adenocarcinoma with a positive station 7 (subcarinal) node only, on EBUS: cT1c cN2a cM0, which is stage IIB in Version 9 (IIIA in the 8th edition).
- A 3.8 cm tumor with positive stations 4R and 7: T2a N2b M0, stage IIIB.
- A 1.8 cm tumor with a hilar node positive: T1b N1 M0, stage IIA.
- Brain and bone metastases (two organ systems): M1c2, stage IVB.
- A malignant pleural effusion: M1a, stage IVA.
A lung cancer diagnosed in 2026 measures 2.4 cm with metastasis confirmed in a single ipsilateral mediastinal nodal station (4R) and no distant metastasis. What is the stage group under AJCC Version 9?
IIA
IIB
IIIA
IIIB
A lung cancer patient has multiple liver metastases and no other extrathoracic disease. How is the M category coded under Version 9?
M1a
M1b
M1c1
M1c2
A part-solid adenocarcinoma measures 2.8 cm in total on CT, and the solid component is 1.4 cm. What is the clinical T category?
cT1b
cT1a
cT1c
cTis
Sections you finish are checked off in the contents.