MKI67 and neoplasm: In 2006, the European Neuroendocrine Tumor Society (ENETS) introduced the first classification for grading pNETs, which was based on the mitotic rate per 10 high-power fields (HPFs) and Ki-67 proliferative index.[4] Subsequently, the 2010 World Health Organization (WHO) classification of pNETs was based on the ENETS classification: grade 1/grade 2 (G1/G2) pNETs were classified as well-differentiated neoplasms; and grade 3 (G3) pNETs were classified as poorly differentiated.[5]