Neuroendocrine differentiation in bronchial carcinomas of classic squamous-cell type: an immunohistochemical study of 29 cases applying the tyramide signal amplification technique.

With regard to the cellular origin of bronchial squamous-cell carcinomas, there are some clinicopathologic and experimental data indicating a link between neuroendocrine (NE) bronchial tumors and the traditionally non-NE squamous-cell carcinomas. Against this background, 29 consecutively resected bronchial squamous-cell carcinomas were examined immunohistochemically (IHC) by means of the specific NE cell marker chromogranin A (CgA), using not only conventional IHC methods, but also the technique with increased sensitivity, offered by the tyramide signal amplification (TSA) procedure. Whereas none of the 29 tumors displayed CgA immunoreactive (IR) cells using the conventional IHC procedure, 10 were found to display a fine granular CgA IR in the neoplastic parenchymal cells using the TSA technique. This incidence is higher than previously reported. However, the CgA IR cells never formed any majority cell population of the neoplastic parenchyma; when present, most of them occurred as micronodules or larger confluent areas in the peripheral most undifferentiated parts of the carcinomatous sheets. Single CgA IR cells were detected only rarely in the spinocellular or keratinized areas. It can be speculated that the observations conform with the recently proposed hypothesis that there is a reservoir of NE progenitor cells in the bronchial mucosa capable of proliferation.