[Apud-cell tumors (carcinoids)--immunohistochemical and pathomorphologic results]

47 carcinoid tumours originating from different sites were classified on a histological basis and immunohistochemically investigated by means of a modified PAP method using 10 different antisera. The biological behaviour and the extent of anaplasia were correlated. The results were compared with those described in the literature. 19 carcinoids showed a positive immune reaction with the antisera used. 5 hormone-producing tumours were poorly differentiated and in 9 cases metastases were recognized. More than one peptide hormone was detected in 7 carcinoids, 3 of which were malignant. Metastases or invasion of lymph and blood vessels were observed in 9 cases although the tumour cells showed no greater degree of cellular atypia. A good correlation between biological behaviour and cytological features was obtained in only 5 atypical carcinoids. Carcinoid tumours represent a group with complex biological, histological and immunohistochemical properties. The secreted peptide hormones might be of importance as tumour markers in some cases.