MKI67 and medullary thyroid gland carcinoma: In high-grade MTC (characterized by a mitotic index ≥ 5/2 mm2, tumor necrosis, or a Ki-67 proliferation index ≥ 5%) the Ctn doubling time is significantly shorter, averaging 8.51 ± 3.22 months compared to 38.42 ± 11.19 months in lower-grade MTC patients (96).