Stage I includes: IA: (T1, N0, M0); IB: (T0, N1mi, M0); (T1, N1mi, M0). T0: No evidence of primary tumor. T1: Tumor measuring 20 mm or less in greatest dimension. N0: No regional lymph node metastasis is identified or isolated tumor cell clusters (ITCs) are identified only. N1mi: Tumor with micrometastases (approximately 200 cells, larger than 0.2 mm, but none larger than 2.0 mm). M0: No clinical or radiographic evidence of distant metastases. Imaging studies are not required to assign the M0 category. (AJCC 8th ed.) [from NCI]