Prognostic Significance of the Tall Cell Variant of Papillary Thyroid Carcinoma: Expression of p53, bcl-2 & Leu-M1 proteins

ABSTRACT

Papillary carcinoma of the thyroid is a well differentiated neoplasm and usually has a good prognosis. However, a subset of morphologically distinct papillary carcinoma has bad prognoses. The tall cell variant of papillary carcinoma (TCPC), characterized by tall columnar cells with a height at least twice the width, is the one of these. In order to differentiate TCPC from usual papillary carcinoma (UPC) in terms of prognosis, we performed immunohistochemical studies for the expression of p53, bcl-2 and Leu-M1 proteins in 25 cases of TCPC, 26 cases of UPC and 14 cases of poorly differentiated, solid type papillary carcinoma (SPC) with an analysis of clinical parameters. The nuclear expression of p53 was noted in one case each of UPC and TCPC. The cytoplasmic p53 expression of TCPC, UPC, and SPC was observed in 17/25 cases (68%), 14/26 cases (54%), 3/14 cases (21%), respectively. bcl-2 expression was 19/25 cases (76%), 18/26 cases (69%), 5/14 cases (36%), and that of Leu-M1 was 21/25 cases (84%), 18/26 cases (69%), 4/14 cases(29%), respectively. There were no statistical significance in the expression of those immunoproteins among these three groups (p>0.05). The p53 protein was consistently expressed in the cytoplasm rather than nucleus in this study and was very well correlated to bcl-2 positivity (p0.05). In conclusion, TCPC can not be separated from UPC as a distinct entity in this study and the cytoplasmic expression of p53 protein provides another mechanism of p53 inactivation in tumorigenesis of the thyroid papillary carcinoma, possibly by bcl-2 related mechanism.