PDNECs and neuroendocrine tumors (NETs) are defined on the basis of expression of neuroendocrine markers such as chromogranin A and synaptophysin (Figure 1) with aggressive histologic features of PDNECs illustrating as high mitotic rate >10 mitotic figures/10 HPF, extensive necrosis, nuclear atypia, and the Ki-67 proliferation index, if performed, of more than 20% (Table 4). Here, MKI67 is linked to neuroendocrine neoplasm.