Immunohistochemical Analysis of Insular Carcinoma of the Thyroid Gland

ABSTRACT

BACKGROUND: Insular thyroid carcinoma (ITC) is a relatively infrequent thyroid carcinoma that has distinctive histologic features. ITC shows an aggressive clinical course and the predominant presence of an insular component, which has been reported to be an independent factor of a poor prognosis. We retrospectively examined clinical details of the nine ITC patients, which represented 9 years of experience with ITC, and investigated the expressions of variable neuroendocrine and other immunohistochemical markers associated with well-differentiated thyroid carcinomas. METHODS: We adopted an immunohistochemical approach and studied the expressions of synaptophysin, chromogranin A, CD56, NSE, S-100, RET, PPARgamma, calcitonin, galectin-3, and thyroglobulin in formalin-fixed, paraffin embedded tissue array slides of the 9 ITC patients, and investigated clinical features. Seven cases of follicular carcinoma and 4 cases of medullary carcinoma were also included as controls. RESULTS: ITCs were positive for synaptophysin (44%, 4/9), CD56 (11%, 1/9), NSE (89%, 8/9), S100 (67%, 6/9), calcitonin (22%, 2/9), galectin-3 (78%, 7/9), and thyroglobulin (100%, 9/9), but completely negative for chromogranin A, RET, and PPARgamma. CONCLUSION: ITCs express neuroendocrine markers in variable proportions and appear not to be associated with the oncoproteins of conventional thyroid carcinomas. Notably, its differential diagnosis from medullary carcinoma is required in cases showing focal calcitonin positivity.