Serotonin in fore-gut carcinoids. A survey of 60 cases with regard to silver stains, formalin-induced fluorescence and serotonin immunocytochemistry.

A series of 60 fore-gut carcinoid tumours was examined with regard to serotonin content after application of three different techniques, namely: the argentaffin reaction, formalin-induced fluorescence according to Falck-Hillarp and immunocytochemistry with monoclonal antibodies to serotonin. To evaluate the staining-fluorescence of individual tumour cells, the methods were applied to identical tumour sections. Twelve tumours demonstrated serotonin-immunoreactive cells, six of which were also argentaffin. Four tumours contained argentaffin cells but no serotonin-immunoreactivity. With the use of all three techniques, three types of tumour cells occurred, namely: serotonin-immunoreactive, non-argentaffin and non-fluorescence cells, serotonin-immunoreactive, argentaffin and fluorescent cells, and non-serotonin immunoreactive, argentaffin and non-fluorescent cells. The first (serotonin-immunoreactive) cell type was most frequently found in the tumours. One gastric carcinoid in which the argentaffin cells exceeded the serotonin-immunoreactive cells, a positive reaction was found with the modified Warthin-Starry reaction for demonstrating melanin. Since none of the techniques used for visualization of serotonin in endocrine tumours is unquestionably specific and since they do not give identical results, it is indicated that for a more accurate identification of serotonin in fore-gut carcinoid tumours, a positive reaction with at least two of the applied techniques is desirable.