• In the Sixth Edition, Stage II was subdivided into IIA and IIB on the basis of whether the primary tumor was T3N0 or T4N0, respectively, and Stage III was subdivided into IIIA (T1-2N1M0), IIIB (T3-4N1M0), or IIIC (any TN2M0). In the Seventh Edition, further substaging of Stage II and III has been accomplished, based on survival and relapse data that was not available for the prior edition.
• Expanded data sets have shown differential prognosis within T4 lesions based on extent of disease. Accordingly, T4 lesions are subdivided as T4a (tumor penetrates the surface of the visceral peritoneum) and as T4b (tumor directly invades or is histologically adherent to other organs or structures).
• The potential importance of satellite tumor deposits is now defined by the new site-specific factor Tumor Deposits (TD) that describe their texture and number. T1-2 lesions that lack regional lymph node metastasis but have tumor deposit(s) will be classified in addition as N1c.
• The number of nodes involved with metastasis influences prognosis within both N1 and N2 groups. Accordingly, N1 will be subdivided as N1a (metastasis in 1 regional node) and N1b (metastasis in 2–3 nodes), and N2 will be subdivided as N2a (metastasis in 4–6 nodes) and N2b (metastasis in 7 or more nodes).
• Stage Group II is subdivided into IIA (T3N0), IIB (T4aN0), and IIC (T4bN0). • Stage Group III:
• A category of N1 lesions, T4bN1, that was formerly classified as IIIB was found to have outcomes more akin to IIIC and has been reclassified from IIIB to IIIC.
• Similarly, several categories of N2 lesions formerly classified as IIIC have outcomes more akin to other stage groups; therefore, T1N2a has been reclassified as IIIA and T1N2b, T2N2a-b, and T3N2a have all been reclassified as IIIB.
• M1 has been subdivided into M1a for single metastatic site versus M1b for multiple metastatic sites.