Cytoplasmic accumulation of alpha-catenin in thyroid neoplasms.

Alpha-catenin (alpha-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 alpha-cat in tumors is associated with aggressive behavior. In this study, we evaluated the expression of alpha-cat in various thyroid tumors by immunohistochemical analysis. Fifty 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 (+++). Staining 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 alpha-cat staining patterns. Cytoplasmic expression of alpha-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 alpha-catenin in the aggressive biology of ACA.