Immunohistochemical and fine structural characterization of primary carcinoid tumors of the larynx.

Carcinoid tumors belong to the group of neuroendocrine tumors of epithelial origin, i.e., neuroendocrine carcinomas. These neoplasms usually occur in the gastrointestinal tract or bronchial system but are very rare neoplasms in the larynx. Since carcinoid tumors in this latter site may appear to be undifferentiated by light microscopy, they may possibly be misinterpreted and their neuroendocrine characteristics may remain unrecognized. Using immunohistochemical methods, three carcinoid tumors were studied and showed positive immunostaining for markers of epithelial origin (cytokeratins, epithelial membrane antigen, carcino-embryonic antigen) and, in particular, for markers of neuroendocrine differentiation (chromogranin, synaptophysin, neuron-specific enolase). All tumors expressed calcitonin-, serotonin- and adrenocorticotropic-hormone-like immunoreactivity. In contrast, three poorly differentiated squamous cell carcinomas showed positive immunostaining for epithelial markers but did not show any immunoreactivity with markers of endocrine characteristics. Fine structurally, carcinoid tumor cells contained neurosecretory-type granules scattered throughout the cytoplasm. The present study demonstrated that (1) carcinoid tumors of the larynx possess distinct immunohistochemical characteristics that allow a clear classification, (2) it is advisable to use a battery of primary antibodies rather than rely on specificity and sensitivity of a single marker to establish diagnosis and (3) the fine structural demonstration of neurosecretory-type granules serves as a reliable adjunct to diagnosis.