Stage 0 includes: Tis (HGD), N0, M0, G1, GX, Tumor location: Any. Tis: High-grade dysplasia. N0: No regional lymph node metastasis. M0: No distant metastasis. G1: Well differentiated. GX: Grade cannot be assessed-stage grouping as G1. Tumor location: Location of the primary cancer site is defined by the position of the upper (proximal) edge of the tumor in the esophagus. (AJCC 7th ed.) [from NCI]