Role of p53, CD44V6 and CD57 in differentiating between benign and malignant follicular neoplasms of the thyroid.

The distinction between follicular adenoma (FAD) and follicular carcinoma (FCA) of the thyroid can be particularly challenging in routine practice of diagnostic surgical pathology. It often requires examination of several histologic sections in order to identify the presence of unequivocal capsular and/or vascular invasion. To investigate the role of immunohistochemical markers in the differential diagnosis of follicular lesions of the thyroid, we studied the pattern of expression of p53, Bcl-2 and of the adhesion molecules CD44V6 and CD57, in 20 FADs and 21 FCAs of the thyroid. Ninety percent of FCAs exhibited strong nuclear p53 expression. p53 stain was seen in only 15% of FADs (p<0.0001), and it was weak. Bcl-2 cytoplasmic immunoreactivity was observed in 57% of FCAs and 60% of FADs (p=1.00). Similarly, membranous CD44V6 staining was seen in 81% of FCAs, but in only 20% of FADs (p=0.0001). CD57 was present in the cytoplasm of 71% of FCAs and 15% of FADs (p=0.0004). None of the markers studied correlated with tumor size. The results of this study indicate that immunohistochemical detection of p53, CD44V6 and CD57 may have practical utility in the differential diagnosis of FCAs from FADs in routine surgical pathology. Follicular carcinoma of the thyroid (FCA) comprises approximately 5% of all thyroid cancers. This tumor, usually unifocal, is microscopically composed of a follicular