Role of P53 and Ki-67 in differentiating between follicular adenoma and carcinoma of the thyroid gland

The distinction between follicular adenoma and follicular carcinoma of the thyroid can be particularly challenging in routine practice of diagnostic surgical pathology. Often examination of several histologic sections is required 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 expression pattern of P53 and Ki-67 in 52 follicular adenomas and 52 follicular carcinomas of the thyroid. Thirty simple goiters were examined as a control.

Ten percent of simple goiters exhibited nuclear P53 expression. P53 positivity was seen in 55.8% and 82.7% of follicular adenomas and carcinomas respectively. Ki-67 nuclear immunoreactivity was observed in 30% of simple goiters, 51.9% of follicular adenomas and 96.2% of follicular carcinomas. Sensitivity and specificity of P53 in diagnosing follicular carcinoma in compaarison with follicular adenomas were 82.7% and 44.2% respectively. Similarly, the results for Ki-67 were 96.2% and 48.1% respectively. Using both P53 and Ki-67 markers had 82.7% sensitivity and 57.7% specificity which shows high sensitivity and a better specificity for diagnosis of follicular carcinoma (compared with follicular adenoma).

The results of this study indicate that immunohistochemical detection of P53 and Ki-67 may have practical application in the differential diagnosis of follicular carcinomas from follicular adenomas in routine surgical pathology (p<0.0005).