Stage I includes: IA (T1, N0, M0); IB (T2, N0, M0); (T1, N1, M0). T1: Tumor invades lamina propria, muscularis mucosae, or submucosa. T2: Tumor invades the muscularis propria. N0: No regional lymph node metastasis. N1: Metastasis in 1-2 regional lymph nodes. M0: No distant metastasis. (AJCC 7th ed.) [from NCI]