NKX2-2 and Ewing sarcoma: NKX2.2 has high sensitivity and moderate specificity for Ewing sarcoma and is typically negative in SS, but it can be positive in a good proportion of neuroendocrine tumors, including small-cell carcinoma (80%) and well-differentiated neuroendocrine tumors (45%) [22]. The NKX2.2 positivity here is likely explained by the neuroendocrine differentiation.