Stage I includes: IA: (T1, pN0, M0) and IB: (T1, cN0, M0). T1: Primary tumor equal or less than 2 cm in size. pN0: No regional lymph node metastasis by pathologic examination. cN0: No regional lymph node metastasis by clinical examination. M0: No distant metastasis. (AJCC 7th Ed.) [from
NCI]