The role of cytokeratin 19 in the differential diagnosis of true papillary carcinoma of thyroid and papillary carcinoma-like changes in Graves' disease.

Graves' disease is an autoimmune disease predominantly seen in females. All types of thyroid cancers may co-exist with Graves' disease but papillary carcinoma is the most frequent. Vesicular nuclei, nuclear grooves, and papillary formations that may be seen in Graves' disease may lead the pathologist to an overdiagnosis of papillary carcinoma. The differential diagnosis between a true papillary carcinoma and foci mimicking papillary carcinoma in Graves' disease may be challenging by light microscopic features only. This study is designed to determine whether CK19 is effective in the discrimination between the true papillary carcinoma of thyroid and foci resembling papillary carcinoma in Graves' disease. Twenty-five cases with papillary carcinoma and 25 cases with Graves' disease containing foci resembling papillary carcinoma were included in the study. All 25 cases with papillary carcinoma stained positive with CK19, whereas only six of 25 cases with Graves' disease showed weak staining, and the remaining 19 cases were completely negative. It is known that CK19 may show faint staining in benign thyroid lesions such as adenomas. Staining pattern with CK19 together with histopathological findings may be helpful in the differential diagnosis between foci mimicking papillary carcinoma and true papillary carcinoma in Graves' disease.