Stage IA includes: IA (T1a, N0, M0); IA1 (T1a1, N0, M0); IA2 (T1a2, N0, M0). T1a: Invasive carcinoma diagnosed only by microscopy. Stromal invasion with a maximum depth of 5.0 mm measured from the base of the epithelium and a horizontal spread of 7.0 mm or less. Vascular space involvement, venous or lymphatic, does not affect classification. T1a1: Measured stromal invasion 3.0 mm or less in depth and 7.0 or less horizontal spread. T1a2: Measured stromal invasion more than 3.0 mm and not more than 5.0 mm with a horizontal spread 7.0 mm or less. N0: No regional lymph node metastasis. M0: No distant metastasis. (AJCC 6th and 7th eds.) [from NCI]