Stage I includes: IA: (T1, N0, M0); IB: (T2, N0, M0). T1: Tumor invades lamina propria or muscle layer. T1a: Tumor invades lamina propria. T1b: Tumor invades muscle layer. N0: No regional metastasis. M0: No distant metastasis. (AJCC 6th ed.) [from
NCI]