AIMS

To study the expression of cytokeratin 19 (CK-19), HBME-1 and Ret in follicular-patterned thyroid tumors, and their significance for the diagnosis of the follicular variant of papillary thyroid carcinoma.

MATERIALS AND METHODS

111 well-differentiated follicular tumors were examined by immunohistochemistry: 59 papillary carcinomas (43 of the follicular variant), 40 follicular adenomas (among which 11 atypical adenomas), 10 oxyphil cell tumors and 2 follicular carcinomas.

RESULTS

CK-19 was diffusely expressed in all the papillary carcinomas, and was also expressed in 2/4 oxyphil cell carcinomas and 4/11 atypical adenomas. 90% of the follicular adenomas (26/29), the six oxyphil cell adenomas and the two follicular carcinomas showed at best a focal staining of dystrophic areas. 78% of the papillary carcinomas and 3/11 atypical adenomas were stained with HBME-1, whereas 26/29 adenomas (90%) and the 10 oxyphil cell tumors were negative. 34% of the papillary carcinomas expressed Ret (most of them were of the usual type (14/20)). The staining was often weak and focal (13/20). The other tumors were all negative for Ret.

CONCLUSIONS

CK-19 is a sensitive (100%) and specific (82.5%) marker of papillary carcinomas, which can be helpful in the diagnosis of its follicular variant. HBME-1 can improve this specificity when associated with CK-19. The Ret protein expression is of limited practical interest.