Diagnostic role of markers dipeptidyl peptidase IV and thyroid peroxidase in thyroid tumors.

Background: In seeking to improve the differential diagnosis between malignant and benign thyroid tumors of follicular cell origin, we assessed the expression of dipeptidyl peptidase IV (DPP IV) and thyroid peroxidase (TPO). DPP IV is a membrane peptidase expressed in many human tissues, excluding the normal thyroid gland. However, aberrant expression has been described in thyroid carcinomas. TPO is an essential enzyme in the biosynthesis of thyroid hormones with various types of expression in pathological thyroid lesions.
Materials and Methods: A total of 151 thyroid glands were examined: 24 malignant tumors, 29 benign tumors, 98 benign lesions and 5 normal glands. DPP IV expression was analyzed by a histochemical technique in both frozen sections and imprint/aspirate smears. TPO was assessed immunohistochemically in paraffin-embedded specimens.
Results: DPP IV sensitivity in frozen section was 56% and its specificity was 99%, in both cases with a 50% threshold. In cytology, the sensitivity was 68% and the specificity was 98% using the 50% threshold. TPO sensitivity and specificity was 64% and 99%, respectively. The sensitivity and specificity of both markers was 92% and 94%, respectively.
Conclusion: We recommend adding DPP IV and TPO to the list of diagnostic tumor markers for malignant thyroid tumors of follicular cell origin.