Endocrine differentiation of extra‐pulmonary small cell carcinoma demonstrated by immunohistochemistry using antibodies to PGP 9.5, neuron‐specific enolase and the C‐flanking peptide of human pro‐bombesin

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Abstract
Several recent studies have confirmed the endocrine nature of small cell carcinoma of the lung. In extra‐pulmonary sites, small cell ‘undifferentiated’ carcinomas have classical morphological features similar to their pulmonary counterpart. We therefore investigated, using immunocytochemistry, the possibility that the non‐pulmonary neoplasms may also be endocrine in nature. Sections of 29 small cell carcinomas from oesophagus, stomach, larynx, colon and urinary bladder were immunostained using antisera to protein gene product 9.5 (PGP 9.5), neuron‐specific enolase (NSE), cytokeratin, leucocyte common antigen and peptides including bombesin, the C‐flanking peptide of human probombesin, adrenocorticotrophic hormone, neurotensin, calcitonin and pancreatic polypeptide. All the tumours showed immunoreactivity for at least one of the two general endocrine markers PGP 9.5 and NSE. Twenty‐three of the 29 cases were immunoreactive for PGP 9.5, 27 for NSE. All were positive for cytokeratin and negative for leucocyte common antigen. Of the regulatory peptides, immunoreactivity was obtained with antisera to bombesin (one case), the C‐flanking peptide of human pro‐bombesin (14 cases), adrenocorticotrophic hormone (one case) and calcitonin (three cases). No PGP 9.5‐, NSE‐or peptide‐like immunoreactivity was detected in 25 control tumours from similar sites, including lymphomas and poorly differentiated tumours. These results suggest that non‐pulmonary small cell carcinoma has an endocrine character.