The value of thyroperoxidase as a prognostic factor for differentiated thyroid cancer -- a long-term follow-up study

BACKGROUND Thyroperoxidase (TPO) is a membrane-bound protein essential for the production of thyroid hormones; because of this, TPO expression may be impaired in selected thyroid diseases. The goal of this study is to analyze TPO immune expression in differentiated thyroid cancer, and to determine whether TPO has any prognostic value. METHODS A total of 139 patients who required surgery due to a thyroid nodule with signs or symptoms suspicious for malignancy during their physical, ultrasound and/or cytology examination were consecutively selected for the study. A study of TPO immunohistochemical expression was carried out on these patients using the MoAb47 monoclonal antibody. In addition, cell proliferation marker Ki67 and tumor suppressor p53 were also measured for comparison. RESULTS A total of 139 cases, 43 benign tumors, 42 papillary carcinomas, 38 follicular carcinomas, 8 undifferentiated carcinomas, and 8 sporadic medullary carcinomas were analyzed. The relationship between TPO expression and disease was statistically significant (p <0.001), and decreased with tumor dedifferentiation extent. Increased TPO expression in benign lesions as compared to decreased expression in papillary carcinomas and undifferentiated tumors is outstanding. Differences in TPO expression were observed in minimally invasive follicular carcinoma (MIFC) compared to widely invasive follicular carcinoma (WIFC). TPO expression decreases in undifferentiated malignancies in contrast with p53 and Ki67 expression, which increases in that setting. TPO, p53 and Ki67 expression was significantly related to TNM stage (p <0.001). Survival rate was 72 % after a 20-year follow-up, and 100 % for subjects with higher TPO expression. CONCLUSIONS TPO may be useful in confirming or ruling out benign diseases from differentiated thyroid carcinoma, with the exception of low-risk carcinoma such as MIFC. It could be used as a prognostic factor for differentiated thyroid cancer and patient follow-up, together with other markers.