A polyclonal antiserum against chromogranin A and B--a new sensitive marker for neuroendocrine tumours.

Chromogranins A, B, and C, proteins that are co-stored and co-released with peptides and amines, have been identified in a variety of neuroendocrine tissues, both normal and neoplastic. We examined the secretion of chromogranin A and chromogranin A + B by hormone-producing tumours in patients with endocrine pancreatic tumours, carcinoid tumours, pheochromocytomas, and small cell lung cancer. The radioimmunoassay determining the plasma concentrations of chromogranin A + B showed a greater sensitivity than that determining chromogranin A alone. All patients with endocrine pancreatic tumours, carcinoids, and pheochromocytomas had increased levels of chromogranin A + B, whereas a small number of the patients (5/18 with endocrine pancreatic tumours and 1/3 with pheochromocytomas) had normal levels of chromogranin A. Also in immunocytochemical stainings, our polyclonal antiserum detecting both chromogranin A and B showed a greater sensitivity than other available antisera against chromogranin A, B and C. We have demonstrated that a polyclonal antiserum against a mixture of chromogranin A and B might be a more sensitive marker than chromogranin A alone for diagnosing neuroendocrine tumours. This is not surprising, since both chromogranins are widely distributed in neuroendocrine cells.