LUNG CANCER STAGING
In 2010, the International Union Against Cancer (UICC) and the American Joint Committee on Cancer (AJCC) published the revised seventh edition of the TNM (tumor, node, metastasis) staging system. This seventh edition was developed on the basis of the International Association for the Study of Lung Cancer (IASLC) and proposed changes to the classiﬁcation from analysis of more than 67,000 cases of non–small cell lung cancer from around the world. This was the largest data set ever analyzed for the purpose of developing and validating a new staging system. The proposed new TNM staging system has also been validated for small cell carcinoma and bronchial carcinoid tumors. The primary determinant of each T, N, and M descriptor, as well as the overall stage grouping, was based on survival. Detailed algorithms were used to identify unique stages in the simplest way with the least overlap. Stages were internally and externally validated for out-comes across the various databases and geographic regions from which the data were gathered.
There were a number of substantial changes made to the former (sixth) staging system:
1. T1 tumors were divided into T1a (tumors ≤2 cm in greatest diameter) and T1b (tumors >2 cm but ≤3 cm in greatest dimension).
2. T2 tumors were divided into T2a (tumors >3 cm but ≤5 cm in greatest diameter) and T2b (tumors >5 cm but ≤7 cm in greatest dimension).
3. Tumors more than 7 cm in greatest dimension are classiﬁed as T3.
4. Tumors with additional nodule(s) in the same lobe are classiﬁed as T3.
5. Tumors with additional nodule(s) in another ipsilateral lobe are classiﬁed as T4.
6. Pleural dissemination (malignant pleural or pericardial effusions, pleural nodules) is classiﬁed as M1a.
7. The lymph node classiﬁcation remained the same, with N1 as intrapulmonary or ipsilateral hilar, N2 as ipsilateral mediastinal or subcarinal, and N3 as contralateral mediastinal or supraclavicular.
8. Incorporated proposed changes to T and M (affects T2, T3, T4, and M1 categories).
9. Reclassify T2aN1 tumors (≤5 cm) as stage IIA (from IIB).
10. Reclassify T2bN0 tumors (>5 cm to 7 cm) as stage IIA (from IB).
11. Reclassify T3 (tumor >7 cm) N0M0 as stage IIB (from IB).
12. Reclassify T4N0 and T4N1 as stage IIIA (from IIIB).
13. Reclassify pleural dissemination (malignant pleural or pericardial effusions, pleural nodules) from T4 to M1a.
14. Subclassify M1 by additional nodules in contralateral lung as M1a.
15. Subclassify M1 by distant metastases (outside the lung/pleura) as M1b.
Because of the addition of new T and M descriptors, the staging deﬁnitions have clearly become more complex. However, the new system now provides a more validated system for deﬁning prognosis. In addition, the system also allows common terminology to be used across the world to describe similar patients, which is critical for accurate communication across the medical community and the conduct of worldwide clinical trials. A future goal is the further reﬁnement of the classiﬁcation system to include the biologic behavior of lung tumors, not just anatomic location, which should promote understanding of tumor biology and provide guidance toward more speciﬁc therapies.