Immunohistochemical and immunoelectron microscopic demonstration of chromogranin A in formalin-fixed tissue of Merkel cell carcinoma.

Abstract

Chromogranin A (CGA) is the major protein of neurosecretory granules (NSG) of cells of the diffuse neuroendocrine system, and the amount of CGA corresponds to the number of NSGs. Because formalin fixation may destroy NSGs, a study was performed to examine the presence of CGA in Merkel cell carcinoma (MCC) to determine whether CGA depends on the presence of intact NSGs. Formalin-fixed, paraffin-embedded tissue of 15 MCCs was investigated by immunohistochemistry and immunoelectron microscopy for the presence of CGA and NSGs. CGA was demonstrated in 12 of 15 MCCs by immunochemistry and in 6 of 10 MCCs by immunoelectron microscopy although intact NSGs could not be discerned in all cases. CGA remains demonstrable even when no morphologically intact NSGs are present, which suggests that CGA is not exclusively responsible for the electron density of NSGs.