AbstractBackgroundAlpha‐catenin (α‐cat) is one of the anchoring proteins of E‐cadherin. It has been shown that deviation in its function may alter the cadherin–catenin complex leading to disturbed cell–cell adhesion. Immunohistochemical studies have shown that cytoplasmic localization of α‐cat in tumors is associated with aggressive behavior. In this study, we evaluated the expression of α‐cat in various thyroid tumors by immunohistochemical analysis.MethodsFifty cases were selected:18 papillary carcinoma classic type (PTC), 9 follicular variant of PTC (FVPTC), 6 follicular carcinoma (FCA), 4 anaplastic carcinoma (ACA), 8 follicular adenoma (FA), 3 nodular goiter (NG), and 2 lymphocytic thyroiditis (LT). The staining reaction was classified as membranous, cytoplasmic, or both. The intensity of the staining was graded as negative (0), weak (+), moderate (++), and strong (+++).ResultsStaining along the cell membrane was observed in 36 (72%) and cytoplasmic expression was present in 28 (57%) cases. The cytoplasmic staining was more commonly seen in malignant lesions; it was more common in PTC (78% of all PTC) than follicular patterned lesions (FVPTC, FCA). All cases of ACA (4 of 4) showed only cytoplasmic expression. No correlation was found between lymph node involvement and α‐cat staining patterns.ConclusionsCytoplasmic expression of α‐cat is more common in (1) malignant lesions of thyroid and (2) PTC than FVPTC and FCA. The lack of membrane and presence of cytoplasmic expression suggest a role of α‐catenin in the aggressive biology of ACA. © 2001 John Wiley & Sons, Inc. Head Neck 23: 573–578, 2001.