TROP-2 expression in papillary thyroid cancer: a preliminary cyto-histological study

Objective: TROP-2 (human trophoblast cell surface marker) is a gene-related protein expressed in trophoblastic cells, which is also present in a variety of epithelial cancers and whose overexpression has been found to correlate with a poor prognosis. We analysed the possibility of using the expression of TROP-2 to detect papillary thyroid carcinoma (PTC) on cytological and histological samples, and compared it with Hector Battifora mesothelial antigen-1 (HBME-1). Methods: From 127 patients, 127 fine needle aspirates (FNAs), in which HBME-1 was detected by immunocytochemistry (ICC), were re-classified according to the Bethesda system for reporting thyroid cytopathology (TBSRTC): 20% were benign, 56% were atypical cells/follicular lesion of undetermined significance (AUS/ FLUS), 4% were follicular neoplasm/suspicious for a follicular neoplasm, 5% were suspicious for malignancy and 16% were malignant. Sufficient material to test for TROP-2 was available in 64 FNAs, 22 of which had a histological control. Including six additional cases in which the FNAs were not available, immunohistochemistry (IHC) was carried out with both markers on 94 cases. Results: Among 88 FNAs with histological control, the sensitivity of HBME-1 to predict PTC was 87.5% (28/32) and the specificity was 86% (48/56), whereas, in 22 FNAs, TROP-2 sensitivity was 100% (13/13) and specificity was 89% (8/9). In 94 histological specimens in which IHC was carried out with both markers, the sensitivity and specificity were 82% and 86%, respectively, for HBME-1 and 87% and 89%, respectively, for TROP-2. The difference between the markers was not significant. Concordance between IHC and ICC was 76% for HBME-1 and 91% for TROP-2. Conclusion: TROP-2 can be used as well as HBME-1 in thyroid cytology to detect PTC. Positivity for either or both markers could help to stratify the risk of malignancy in indeterminate FNAs. Larger studies are need to analyse its role in the behaviour of PTC and its variants.