MKI67 and digestive system neuroendocrine tumor, grade 1/2: We found, for the first time, that WHO tumor grade (based on mitotic index and Ki67 proliferative index) proved to be a strong predictor of survival (HR: 12.61, p < 0.001 for G2 vs G1 tumors), as demonstrated in pancreatic and other gastrointestinal NETs [34].