MKI67 and medullary thyroid gland carcinoma: There is now broad agreement that neuroendocrine tumors (NETs) of many sites can be graded on the basis of the simple factors of mitotic count and Ki67 proliferative index, with the addition of tumor necrosis for NETs arising in certain sites such as pulmonary carcinoids.8,9 The IMTCGS therefore brings the grading of MTC in line with the grading of other NETs.