Thyroperoxidase immunodetection for the diagnosis of malignancy on fine-needle aspiration of thyroid nodules

We have previously demonstrated that in 95.6% of malignant thyroid tumors the enzyme thyroid peroxidase (TPO) presents antigenic changes detectable by a monoclonal antibody termed MoAb47. The aim of this study was to investigate the interest of TPO immunodetection for the diagnosis of malignancy on fine-needle aspiration biopsy (FNAB) of thyroid nodules. The study was performed on 300 patients. Slides of FNAB aspirate were air-dried and stained by anti-TPO-MoAb47. According to the percentage of TPO-positive epithelial cells, patients were divided into two groups: benign (<80%) and malignant (<80%). In 279 cases additional slides were available for Giemsa stain and standard cytology. All the patients were operated on, and the final diagnosis was recorded as benign in 248 cases (183 macrofollicular nodules, 23 microfollicular adenomas, 18 atypical adenomas, 11 oncocytomas, 11 thyroiditis, 2 Graves' disease) and malignant in 52 cases (44 papillary carcinomas and 8 follicular carcinomas). Samples from 215 of 248 benign nodules yielded 80% to 100% TPO-positive cells, whereas samples from all malignant tumors yielded less than 80% positive cells. The sensitivity of TPO staining for diagnosis of malignancy was thus 100%, its specificity 86.7%, and its overall accuracy 89%. With conventional cytology, sensitivity, specificity, and accuracy were 91.6%, 79.2%, and 81.0%, respectively. We conclude from this study that TPO staining with MoAb47 should become an essential adjunct in the preoperative cytologic diagnosis of thyroid nodules.