Stage I includes: IA: (T1a, N0, M0); IB: (T1b, N0, M0); (T2a, N0, M0). T1a: Tumor measuring less than 0.8 mm in thickness. Ulceration status: Without ulceration. T1b: Tumor measuring less than 0.8 mm in thickness with ulceration, or 0.8-1.0 mm with or without ulceration. T2a: Tumor measuring more than 1.0 and equal to or less than 2.0 mm in thickness. Ulceration status: Without ulceration. N0: No regional lymph node metastasis detected. Presence of in-transit, satellite, and/or microsatellite metastases: No. M0: No evidence of distant metastasis. LDH level is not applicable. (AJCC 8th ed.) [from NCI]