Differential immunohistochemical reactions of carcinoid tumors

Neuron-specific enolase, S-100 protein, and Leu 7 are present in cells showing neuroendocrine differentiation. Leu 7 recognizes myelin-associated glycoprotein, and recent evidence suggests that it further recognizes a subset of neurosecretory granules. Forty-six primary and metastatic carcinoid tumors from various sites were evaluated immunohistochemically with antisera to neuron-specific enolase, S-100, and Leu 7. Only one tumor, a rectal carcinoid, failed to stain with neuron-specific enolase. The remaining cases showed four patterns of staining: nuclear, diffuse cytoplasmic, globular cytoplasmic, or mixed. The pattern of reaction did not correlate with either the embryonic origin or histologic pattern of the tumor. Two patterns of staining were obtained with anti-Leu 7: diffuse cytoplasmic, or dot or ring-like deposition of reaction product. The latter pattern was entirely confined to appendiceal carcinoids. Reactivity with S-100 was in the form of dense positivity in individual cells having a stellate outline. Less intense cytoplasmic positivity and, uncommonly, a mixture of both types of staining were also seen. These histochemical results may lend support to recent evidence suggesting the existence of identifiable subsets of neurosecretory granules in neuroendocrine tumors, including carcinoids.