The Diagnostic Validity of TROP-2 in Recognizing Papillary Thyroid Carcinoma

Abstract
Background: Thyroid cancer is currently the third fastest rising cancer diagnosis in the United States and represents 80.3% of endocrine neoplasms and 2.6% of total malignancies in Egypt with male to female ratio is 1:2. Papillary thyroid carcinoma (PTC) represents the most common histologic type of thyroid carcinoma in Egypt representing 83.3%. Diagnosis of papillary thyroid carcinoma is not always straight forward because some lesions exhibit equivocal nuclear features making the distinction of benign from malignant lesions is difficult. So it is necessary to use ancillary diagnostic tools to reach accurate diagnosis. TROP-2 is a trans-membranous glycoprotein, was originally identified in human trophoblast and choriocarcinoma cell lines and was subsequently reported to be over-expressed in a variety of human carcinomas. Few studies have verified the diagnostic power of TROP2 in PTC suggesting that it could be a potential novel immunohisto-chemical marker for identification of both classic and follicular variants of PTC
Aim of Study: The aim of this study is to review the diagnostic value of TROP-2 in papillary thyroid carcinoma (PTC) in English literature.
Material and Methods: From Medline databases (PubMed, Medscape and Google scholar) and also materials available on the Internet from 2014 to 2017.
The initial search presented 5 articles that studied the diagnostic role of TROP-2 in differentiating PTC from non malignant thyroid lesions and were performed on histological specimens only (cytological specimens were excluded).
If the studies did not fulfill the inclusion criteria, they were excluded. Study quality assessment included whether ethical approval was gained, eligibility criteria specified, appropriate controls, and adequate information and defined assessment measures.
A structured systematic review was performed with the results tabulated.
Results: TROP-2 sensitivity in total papillary thyroid carcinoma cases ranged from 50% to 86.8% passing through 58.3% to 81.5% and 81.6%. Regarding TROP-2 specificity it was 100% in 4 out of 5 articles and 89.3% in the remaining one. Four articles showed 100% of positive predictive value (PPV) and one article demonstrated 84.6%. The negative predicitive value (NPV) ranged from 74.1% to 92.4% and the diagnostic accuracy ranged from 79.4% to 94.3%. As regard non follicular variant PTC (non FVPTC) TROP-2 sensitivities ranged between 81.5% and 98.7%. The NPV ranged between 84% and 99.6%, while diagnostic accuracy ranged between 88.6% and 99.7%. The PPV was 100% in four articles and 82.4% in one article.
Conclusion: TROP-2 could be considered as a reliable immunostaining marker in diagnosing papillary thyroid car-cinoma especially non follicular variant owing to its high specificity and sensitivity. TROP-2 is a specific rather than sensitive as its specificities in 4 studies revealed 100%. Ther-efor it is expected to be negative in benign and non-neoplastic thyroid lesions reducing the overdiagnosis of PTC and dis-criminating it from many mimickers.