Immunohistologig study of thyroidal medullary carcinoma and pancreatic insulinoma

An indirect immunofluorescent antibody technique, preceded by trypsin digestion of the tissue sections, was applied to six cases of medullary carcinoma of thyroid (MCT) and three cases of insulinoma in order to examine the state of antigenic preservation of peptide hormones in tumor tissues, which had been fixed in formalin and embedded in paraffin for periods up to 18 years for MCT and 10 years for insulinomas. By this method both C-cells of normal thyroid and tumors of MCT were shown to contain calcitonin. Other types of thyroid carcinoma did not contain calcitonin, and no increase in C-cells was found in various thyroidal diseases. The tumor cells of MCT demonstrated a large amount of immunoreactive calcitonin, particularly in the medullary (solid) form, and a decreased amount in the amyloid form. Following trypsin digestion, specific immunofluorescence for calcitonin was also noted in the amyloid stroma. This might be related to the presence of entrapped secretory granules from cell debris in the amyloid substance. The immunohistochemistry can distinguish the poorly differentiated follicular carcinoma of thyroid from MCT, as illustrated in one case. Beta cells of normal pancreatic islets and tumor cells of insulinoma, but not the accompanied amyloid, were shown to contain insulin by indirect immunofluorescent stain. In the diagnosis of insulinoma, this method equals the electron microscopy for its sensitivity, and surpasses it for simplicity in technique. In general, the trypsin treated sections showed a significant improvement over the untreated preparations in the quality of immunofluorescence, thus facilitating microscopic interpretation on tumor tissues. The results did not appear to be affected by the duration of tissue preservation in the paraffin blocks. The improved immunohistologic method may be recommended for routine use in prospective and retrospective studies of certain endocrine tumors.