As Matin and Goldberg note, the accurate staging of non-small-cell lung cancer (NSCLC) is necessary to provide patients with correct information regarding prognosis and appropriate treatment recommendations. Therefore, physicians who treat patients with NSCLC must have a thorough understanding of the staging system and an appreciation for the sometimes subtle differences between the various TNM combinations.
In addition, correct interpretation of the medical literature requires an understanding not only of the version of the staging system utilized by individual investigators but also of any modifications they may have used. For instance, some authors consider level 10 lymph nodes to be N1 disease, while others include them in the N2 category.
Recent Changes in the Staging System
The TNM staging system was altered in 1997 in order to better group patients by therapeutic and prognostic categories. The principal changes were the subdivision of stage I into stages Ia (T1 N0) and Ib (T2 N0) and the creation of stages IIa (T1 N1) and IIb (T2 N1; T3 N0). Patients with tumors designated as T3 N0 were moved from stage IIIa (T1-3 N2) because their prognosis more closely approximates that of N1 disease than N2 disease.
In addition, T4 was redefined. Patients with more than one focus of tumor in the same lobe of the lung are now considered to have T4 disease, while the presence of cancer in any other lobe of the ipsilateral lung is classified as M1 disease.
Changes in the definition of some of the nodal levels were also made. Most importantly, level 4 extends from the aortic arch to the origin of the upper lobe bronchus (right or left). Level 10 is located distal to the pleural reflection on the anterior surface of the bronchus, adjacent to the bronchus intermedius (right) or near the bifurcation of the upper and lower lobes (left). Involvement of level 4 nodes is considered to be N2 disease, while level 10 involvement is N1 disease.
Pretreatment evaluation of the patient with NSCLC should include chest computed tomography (CT), pulmonary function tests, a complete blood count, serum chemistries, and liver function tests. Brain magnetic resonance imaging (MRI) and bone scans are reserved for patients with specific symptoms or significant weight loss or anemia.
Histologic diagnosis of a new lung mass with the radiologic characteristics of a malignancy is not necessary prior to surgery. As indicated by Matin and Goldberg, not all enlarged mediastinal lymph nodes contain tumor. Therefore, histologic proof of N2 disease is necessary before declaring a tumor to be inoperable or recommending neoadjuvant therapy.
The zeal with which the mediastinum is assessed depends to no small degree on the treatment philosophy of the attending physician. If the physician believes that no patient with N2 disease should undergo surgery (at least initially), all patients should have mediastinoscopy. If, however, the clinician thinks that the best treatment is resection of all gross disease followed, (if N2 disease is found), by radiation or chemotherapy, patients with resectable disease (including those with minimally enlarged lymph nodes) should proceed directly to operation.
In the near future, positron emission tomographic (PET) scanning may assume a prominent role in the pretreatment evaluation of patients with NSCLC. Its specificity and sensitivity are both excellent. However, PET scanning does not provide accurate anatomic information, and mediastinoscopy may still be necessary to differentiate between metastases to the ipsilat-eral mediastinal lymph nodes (N2, stage IIIa) and contralateral lymph nodes (stage IIIb).
Intraoperative Staging of the Mediastinum
Intraoperative staging of the mediastinum remains the gold standard for determining the presence or absence of mediastinal lymph node metastases. During a right thoracotomy, at least levels 4, 7, and 10 nodes should be dissected or sampled. At the time of a left thoracotomy, level 5 or 6, as well as level 7, lymph nodes should be biopsied or removed.
Mere visual inspection or manual palpation of the lymph node–containing regions is insufficient to determine the status of the mediastinal lymph nodes.[5,6] Intraoperative nodal dissection should be an integral part of any operation performed for resection of NSCLC. It requires an additional 15 to 20 minutes and is associated with minimal morbidity.