Malignant APUDoma (carcinoid) of the anterior mediastinum. Simplified methods of demonstrating biogenic amines in endocrine neoplasms.

Endocrine neoplasms of the thymus and mediastinum are uncommon. This report describes such a carcinoma and the difficulty in determining its true nature. A simple modification of the technique for formaldehyde-fume-induced fluorescence (FIF) demonstrated biogenic amines in the cells. Electron microscopy and histochemical findings confirmed the close relationship of these neoplasms with neural-crest cells capable of amine precursor uptake and decarboxylation (APUD). The FIF technique is also a more sensitive method of detecting these tumors, since it has less of the sampling problems of electron microscopy, and the fluorescent granules are more easily seen than those stained by the usual methods. The techniques are simple enough for screening all poorly differentiated carcinomas in this area to determine a more accurate incidence figure.