TROP 2 immunohistochemistry: a highly accurate method in the differential diagnosis of papillary thyroid carcinoma.
We aimed to evaluate the diagnostic utility of the novel immunohistochemical marker TROP 2 on thyroid specimens (226 tumours and 207 controls) Whole slide immunohistochemistry was performed and scored by automated digital image analysis. Non neoplastic thyroid, follicular adenomas, follicular carcinomas, and medullary carcinomas were negative for TROP 2 immunostaining. The majority of papillary thyroid carcinoma (PTC) specimens (94/114, 82.5% were positive for TROP 2; however, the pattern of staining differed significantly between the histopathological variants. All papillary microcarcinomas (mPTC) PTC classic variant (PTC cv) and tall cell variant (PTC tcv) were TROP 2 positive, with mainly diffuse staining. In contrast, less than half of the PTC follicular variant specimens were positive for TROP 2, with only focal immunoreactivity. TROP 2 could identify PTC cv with 98.1% sensitivity and 97.5% specificity. ROC curve analysis found that the presence of >10% of TROP 2 positive cells in a tumour supported a diagnosis of PTC. The study of intratumoural heterogeneity showed that low volume cytological samples of PTC cv could be adequately assessed by TROP 2 immunostaining. The TROP 2 H score (intensity multiplied by proportion) was significantly associated with PTC variant and capsular invasion in encapsulated PTC follicular variant (p<0.001) None of the baseline (age, gender) and clinical (tumour size, nodal disease, stage) parameters were correlated with TROP 2 expression. In conclusion, TROP 2 membranous staining is a very sensitive and specific marker for PTC cv, PTC tcv, and mPTC, with high overall specificity for PTC.
Pathology