Thyroid peroxidase immunodetection as a tool to assist diagnosis of thyroid nodules on fine-needle aspiration biopsy.

In a previous work we have reported the presence in 96.9% of malignant and 4.2% of benign thyroid tumors of an immunological abnormality of the enzyme thyroid peroxidase, impeding the fixation of the anti-thyroid peroxidase monoclonal antibody termed "MoAb47". The present study has been designed to establish the ability of thyroid peroxidase immunodetection to assist the diagnosis of malignancy in fine-needle aspiration of thyroid nodules. The fixation of anti-thyroid peroxidase monoclonal antibody was investigated by immunohistochemistry on fine-needle aspirates of 150 surgically removed thyroid nodules (20 papillary carcinomas, five follicular carcinomas, 90 colloid adenomas, nine fetal adenoma, 13 atypical adenomas, five oncocytic adenomas, six Hashimoto's thyroiditis and two Graves' disease). The percentage of positive cells has been compared to the final histological diagnosis. In samples from 113/125 benign nodules 80-100% cells presented a positive immunoreaction, whereas all samples from malignant tumors yielded less than 80% positive cells. Benign nodules exhibiting less than 80% positive cells corresponded to three degenerative colloid nodules, five atypical follicular adenomas, two oncocytomas and two thyroiditis. According to results obtained in this series, with the value of 80% as the limit for discrimination between benign and high-risk nodules, the sensitivity of thyroid peroxidase staining for diagnosis of malignancy would be 100%, its specificity 90% and its overall accuracy 92%. Thyroid peroxidase staining with monoclonal antibody MoAb47 on fine-needle aspirates is a useful adjunct to conventional cytology for the investigation of patients with thyroid nodules.