Diagnostic utility of cytokeratin 19 expression in multinodular goiter with papillary areas and papillary carcinoma of thyroid.

The most common benign lesion of thyroid, multinodular goiter, may mimic papillary carcinoma if it contains papillary areas. Although it is usually not very difficult to distinguish between these benign and malignant lesions, some cases may be problematic in differential diagnosis. In these cases, we decided to use cytokeratin 19 (CK19), which is shown to be effective in discriminating papillary carcinoma from follicular carcinoma of thyroid, and we also evaluated the immunoreactivity of CK19 in follicular adenomas. Twenty-five cases of multinodular goiter showing papillary formations, 25 cases of papillary thyroid carcinoma, and 15 cases of follicular adenoma were selected from archives of our institution. Immunohistochemical staining for CK19 was performed on deparaffinized sections. Diffuse and intense CK19 positivity was found in the cells of all papillary carcinomas. In the multinodular goiter group, 20 of 25 cases showed no staining while the remaining 5 were focally reactive with CK19. Three of the five were thought to be false positive owing to hemorrhage. Weak and focal CK19 staining was seen in some follicular adenomas. Our observations suggest that the staining features of CK19 may be helpful in differential diagnosis between papillary carcinoma and multinodular goiter showing papillary areas. Focal and pale staining for CK19 may be seen in multinodular goiter with papillary formations, and this feature should be considered in evaluation.