Expression of p21^cip1, p27^kip1, and p16^INk4a Cyclin-Dependent Kinase Inhibitors in Papillary Thyroid Carcinoma: Correlation with Clinicopathological Factors

In a variety of human malignancies, aberrant expression of proteins involved in the control of cell-cycle progression has been reported. In this study, p21^cip1, p27^kip1, and p16^INk4a cyclin-dependent kinase inhibitors were analyzed to evaluate their usefulness in clinical management of papillary thyroid carcinoma (PTC). Archived material derived from 46 cases of PTC was analyzed immunohistochemically. Protein expression was ascertained on tissue microarrays, and results were correlated with clinicopathological features of the patients. Positive immunostaining was observed in 14 (30,4%) p21^cip1, 26 (56,5%) p27^kip1, and 14 (30,4%) p16^INk4a cases. No significant correlation between p21^cip1 or p27^kip1 and clinical factors was found. In contrast, p16^INk4a expression showed a significant correlation with initial extension of the disease. Therefore, 45.8% of patients with loco-regional extension were p16^INk4a positive, whereas overexpression was only seen in 15.7% of cases with intrathyroid disease (p < 0.05). Moreover, all patients with simultaneous p16^INk4a positivity and lack of p27^kip1 staining (four patients) presented lymph node metastases. In contrast, only 12 (28.5%) of the remaining patients showed lymph node tumor involvement. In conclusion, p16^INk4a expression suggests extrathyroid neck extension of PTC. This effect is enhanced when p27^kip1 is negative. We think that their analysis by immunohistochemistry could be useful in the management of patients with PTC.