HYALINIZING TRABECULAR ADENOMA OF THE THYROID - A REPORT OF 2 CASES WITH CYTOLOGIC, HISTOLOGIC AND IMMUNOHISTOCHEMICAL FINDINGS

ma on cytologic specimens. CASES: The fine needle aspiration biopsies (FNABs) and surgically resected specimens from two patients with HTA w ere studied. Nuclear grooves and nuclear pseudoinclusions were identif ied in both FNABs. Gross examination of the surgical specimens reveale d two nodules (0.8 an 0.5 cm in diameter) in one case and a 6-cm nodul e in the other. A thin, fibrous capsule surrounded each nodule. A pred ominant trabecular pattern was observed in the three lesions. Antibodi es to thyroglobulin, carcinoembryonic antigen (CEA), epithelial membra ne antigen (EMA), vimentin, chromogranin, synaptophysin, neuron-specif ic enolase, proliferating cell nuclear antigen (PCNA), Ki-67 and p53 w ere used to stain 10% buffered, formalin-fixed, paraffin-embedded sect ions of the surgical specimelts. No immunostaining was observed with a ntibodies against calcitonin, synaptophysin, chromogranin, EMA vimenti n or p53. Less than 5% of cells were CEA positive in one case. The Ki- 67 index was low and PCNA expression high. CONCLUSION: HTAs occur as s olitary or multiple nodules. FNABs of HTAs contain cells with nuclear grooves and nuclear pseudoinclusions but lack psammoma bodies, high ce llularity and papillary structures. Immunohistochemistry using antical citonin and antithyroglobulin antibodies is helpful in distinguishing these tumors from medullary carcinoma. The low Ki-67 index and absence of p53 immunostaining are consistent with the benign behavior of this tumor. The significance of high PCNA immunostaining is uncertain.