We trialed several different systems with different cutoffs, presented in the Data Supplement, and concluded that the IMTCGS two-tiered system that defined high-grade MTCs as tumors with at least one of the following features: MI ≥ 5 per 2 mm2, Ki67 proliferative index ≥ 5%, or tumor necrosis, was optimal. This evidence concerns the gene MKI67 and neoplasm.