Diagnostic usefulness of dipeptidyl aminopeptidase IV monoclonal antibody in paraffin‐embedded thyroid follicular tumours

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Abstract
Monoclonal antibodies to dipeptidyl aminopeptidase IV (DAP IV, EC 3.4.14.5) were raised and selectively applied to paraffin‐embedded sections of thyroid carcinoma. Five monoclonal antibodies were found to stain paraffin sections of thyroid carcinomas. Using one of these antibodies (44‐4), we studied retrospectively aberrant expression of DAP IV in thyroid carcinoma to determine whether immunohistochemical staining with DAP IV antibody is useful in pathological diagnosis. In almost all cases of thyroid follicular and papillary carcinoma, tumour cells were positive (99.0 per cent) with DAP IV, whereas the cases of follicular adenoma showed a low incidence (27.1 per cent) of positive staining. Follicular adenoma with incomplete capsular invasion had a higher positive incidence (50 per cent) than follicular adenoma without incomplete capsular invasion (9.6 per cent). In positive staining cases previously diagnosed as benign tumours, 11 benign cases reacting positively with DAP IV were rediagnosed as carcinoma after re‐examinatioan of more thyroid paraffin block sections or serial sections. These findings suggest that DAP IV monoclonal antibody is very useful in distinguishing thyroid follicular carcinoma from follicular adenoma.