A comparative study of neuroendocrine carcinoma and carcinoid tumor with special reference to expression of HLA-DR antigen and PCNA.

Both carcinoid tumor (carcinoid) and neuroendocrine carcinoma (NEC) are composed of neuroendocrine cells which are positive for chromogranin. The former is a low grade malignancy but NEC is a highly aggressive malignancy. We compared histological differences of those tumors using antibodies to major histocompatibility complex (MHC) class II antigens HLA-DR, proliferating cell nuclear antigen (PCNA), Leu7 (CD57), CEA and P53. Most characteristic differences between those tumors were in the expression of HLA-DR and PCNA. HLA-DR positive capillary endothelial cells were abundant in carcinoid as well as in non-tumorous endocrine organs but sparse in NEC. On the contrary, cells positive for PCNA were 92% in NEC, but 27% in carcinoid. We concluded that carcinoid imitates an endocrine organ in both morphology and function, but NEC deviates far from it.