Objective: To assess the frequency of amyloid deposits in adrenal gland pheochromocytomas.
Design: We evaluated 22 pheochromocytomas using routine hematoxylin-eosin and Congo red stains, polarization microscopy, and electron microscopy. Cases with amyloid were further characterized immunohistochemically.
Results: Congo red and polarization microscopy revealed characteristic apple-green birefringence, not abolished by potassium permanganate incubation, in only one neoplasm. In a subset of the remaining tumors, yellow or yellow-green birefringence not characteristic of amyloid was found. We performed electron microscopy on the tumor with characteristic apple-green birefringence and six other neoplasms with abundant yellow or yellow-green birefringence. Amyloid was identified in two tumors, including the Congo red-positive tumor, while the remaining five neoplasms contained collagen. Immunohistochemically, the amyloid deposits were reactive with component P and immunoglobulin kappa- and lambda-light chains in both tumors. Adsorption studies using human urine with monoclonal immunoglobulin kappa- or lambda-light chains abolished reactivity, consistent with specific immunostaining for both light chains. Transthyretin was present in one tumor. The neoplastic cells expressed chromogranin, neuron-specific enolase, and [Leu5]-enkephalin, although the amyloid was not reactive.
Conclusions: We conclude that amyloid is infrequent in pheochromocytomas. Electron microscopic examination is more sensitive than Congo red stain and, in our opinion, is the best technique for the demonstration of amyloid deposits.