CD44 immunostaining of thyroid fine-needle aspirates differentiates thyroid papillary carcinoma from other lesions with nuclear grooves and inclusions.

Although nuclear grooves and inclusions are considered to be characteristic cytologic features of thyroid papillary carcinoma, a variety of other thyroid lesions may on occasion display these features in fine-needle aspiration specimens. The authors evaluated the immunocytochemical staining of 16 fine-needle aspirations of thyroid papillary carcinoma and 14 aspirations of thyroid lesions confirmed to be other than papillary carcinoma but that included cells with nuclear grooving and/or inclusions, comprised of multinodular goiter (four cases), follicular adenoma (two cases), Hurthle cell adenoma (two cases), pure thyroiditis (three cases), and thyroiditis with nodular hyperplasia (three cases). CD44 previously has been shown to be selectively expressed in thyroid papillary carcinoma. Of 16 surgically confirmed cases of thyroid papillary carcinoma featuring nuclear grooves and inclusions on fine-needle aspiration, 14 (88%) stained intensely for CD44 in a membranous pattern. Of the 14 nonpapillary thyroid carcinoma cases, only 1 (7%), a Hürthle cell adenoma, featured membranous CD44 staining. The difference in the proportion of cases with CD44 staining between the two groups was statistically significant (chi-square test, P < 0.001). The authors conclude that immunostaining for CD44 can readily be performed on thyroid fine-needle aspiration specimens and that, for specimens featuring nuclear grooves and inclusions, the presence or absence of staining for CD44 may be of value in the distinction between thyroid papillary carcinoma and other lesions that may share some of the cytologic features of papillary carcinoma.