AIM: To asses the potential use of anti-Leu-7 in the differential diagnosis of thyroid tumors. MATERIALS and METHOD: We studied 73 primary thyroid neoplasms by immunohistochemistry, utilizing a commercial antibody to Leu-7. These included 37 papillary carcinomas (18 classical type, 12 follicular type and 7 tall cell variant), 8 follicular carcinomas, 5 Hurthle cell carcinomas, 3 medullary carcinomas, 1 insular and 4 undifferentiated carcinomas, and 15 follicular adenomas. Twenty metastatic carcinomas were also evaluated and compared with the primary tumor. RESULTS: All the classic type and the tall cell variant of papillary carcinomas as well as the case of insular carcinoma showed strong membranous immunostaining. Reactivity to Leu-7 was observed only in 17% of follicular variant of papillary carcinomas, in 25% of follicular carcinomas, in 33% of medullary carcinomas and in 33% of follicular adenomas. All these cases had a predominantly intracytoplasmic pattern of staining. Positive staining was also seen in 69% of metastatic papillary thyroid carcinomas and in 67% of metastatic cases from follicular carcinomas. CONCLUSION: The results of this study suggest that immunostaining with anti-Leu-7 antibody may recognize thyroid tumors with a papillary growth pattern but it is not helpful to distinguish between benign and malignant neoplasms with a follicular or solid pattern of growth.

Key words: Thyroid, Leu-7, Thyroid carcinoma, Immunohistochemistry.

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