Chromogranin A as a marker of neuroendocrine histogenesis of tumours: an immunoelectron microscopic study with considerations about the influence of fixation and embedding media on immunolabelling.

The ultrastructural localization of chromogranin A (Chr A) was studied in eleven neoplasias of the diffuse neuroendocrine system (3 pancreatic islet-cell tumours, 1 medullary carcinoma of the thyroid, 1 large bowel and 1 small bowel carcinoid tumours, 2 carcinoid tumours of the lung, 1 adenoma of the parathyroid gland, 2 pheochromocytomas of the adrenal gland). On account of the great influence of the technical treatment of the samples on the immunolocalization of Chr A, the effect of the following variables was studied in a case of pheochromocytoma: fixation in glutaraldehyde versus paraformaldehyde, postfixation in osmium tetroxide versus omission, embedding in epoxy resin versus acrylic resin. The method of choice for the better preservation of the antigenic character of the tissue was found to be fixation in 4% paraformaldehyde, omission of osmium postfixation and embedding in LRWhite acrylic resin; by this procedure we were able to find Chr A in the neurosecretory granules of all the studied cases, using three commercially available antibodies directed against Chr A. These findings further confirm that Chr A is a reliable marker for the study of neuroendocrine neoplasias by electron microscopy.