ABSTRACT
Localized deposits of amyloid are commonly found in human medullary thyroid carcinoma (MTC). Heretofore, sequence analyses of this material had revealed the presence of calcitonin (CT) and/or its precursor, procalcitonin (PCT). Fibrils were extracted from 4 µm-thick sections of formalin-fixed, paraffin-embedded amyloid-laden tissue from 2 patients with MTC. The extracts were reduced and alkylated, passaged through a reverse phase-HPLC column, and the relevant peaks subjected to direct Edman degradation, as well as trypsin digestion. In immunohistochemical analyses, consecutively cut sections from each of the MTC cases were stained with Congo red, anti- calcitonin gene-related peptide II (CGRP II), anti-CT, and anti-PCT antibodies. In both, the apple green birefringent congophilic deposits were recognized only by the anti-CGRP II antibody. In contrast, there was diffuse tissue reactivity with the anti-CT and -PCT antisera and the amyloid was not immunostained by these reagents.
