Stage I includes: IA: T1, N0, M0; IB: T2a, N0, M0. T1: Tumor measuring 10 mm or less in greatest dimension. T2a: Tumor measuring more than 10 mm but 20 mm or less in greatest dimension without invasion of the tarsal plate or eyelid margin. N0: No evidence of lymph node involvement. M0: No distant metastasis. (AJCC 8th ed.) [from NCI]