Although it is nearly impossible to memorize the staging rules for all the different kinds of tumors, there are several basic principles common to all. The TNM stage of a tumor is determined by the tumor size and extent (T for tumor), lymph node involvement (N for nodes), and metastasis (M for metastasis). N0 always means no lymph nodes are involved. An NI lesion has positive nodes, and only 2nd choice, positive bronchial lymph nodes, changes the patient's nodal status. Involvement of the chest wall is a feature of tumor size and extent-thus, it is a component of the T in TNM-staging. T2 lesions involve the chest wall. Histological features of the tumor, such as small cell morphology , are not considered in tumor stage, but rather in tumor grade. Small cell tumors are considered high-grade carcinomas. Tumor extending to the carina reflects the tumor size and extent-thus, it is a component of the T in TNM-staging: T3 lesions involve the carina . Ref: Wyatt C., Butterwoh IV J.F., Moos P.J., Mackey D.C., Brown T.G. (2008). Chapter 4. Neoplasia. In C. Wyatt, J.F. Butterwoh IV, P.J. Moos, D.C. Mackey, T.G. Brown (Eds), Pathology: The Big Picture.