SYP and neuroendocrine carcinoma: NEPC tumors are histologically heterogeneous but can appear morphologically similar to other poorly differentiated neuroendocrine carcinomas such as small cell lung cancer (SCLC) and typically expresses classical neuroendocrine markers such as chromogranin A/B (CHGA/CHGB), CD56 (NCAM1; refs. 6, 7), INSM1, and/or synaptophysin (SYP; ref. 8).