It is noteworthy that in a previous investigation of grading on the basis of MI, Ki67, and necrosis in a small series of 44 sporadic MTCs, there was no correlation between these factors and RET or RAS somatic mutation status.12 Although assessment of mutation status may further refine risk stratification in MTC, additional multicenter studies will be required to further evaluate the relationship between mutation status, grade, and outcome. This evidence concerns the gene MKI67 and medullary thyroid gland carcinoma.