Somatostatin type 2A receptor immunoreactivity in human pancreatic adenocarcinomas.

Somatostatin and its analogs have been included in experimental treatment protocols for advanced pancreatic adenocarcinoma based on their known antisecretory and antiproliferative properties. Somatostatin receptor type 2 (sstr2A) mediates antiproliferative actions of somatostatin and has the strongest affinity to the therapeutically used somatostatin analog--octreotide. We investigated localization of sstr2A in 27 pancreatic adenocarcinomas in relation to tumor histological features and neuroendocrine differentiation confirmed by immunoreactivity for chromogranin A (CgA), chromogranin B (CgB), or somatostatin. Immunoreactivity for sstr2A generally coincided with tumor neuroendocrine differentiation demonstrated by staining for CgA and was present on the cell membranes of pancreatic islet cells and endocrine cells occasionally present in the wall of normal pancreatic ducts. Thirteen pancreatic adenocarcinomas contained cells immunoreactive for sstr2A in numbers ranging from occasional single cells, cell clusters, or carcinoma duct segments. In two cases, cells immunoreactive for sstr2A and CgA represented more than 30 and 10% of the total tumor cell population (case 1 and 15, respectively). Case 1 fulfills the diagnostic criteria of mixed ductal endocrine carcinoma. We conclude that immunohistochemical staining for a generic neuroendocrine marker such as CgA would facilitate identification of a subgroup of pancreatic adenocarcinomas expressing sstr2A receptors. Future studies need to evaluate the responsiveness of these tumors to somatostatin analogue treatment.