Application of an immunodiagnostic method for improving preoperative diagnosis of nodular thyroid lesions

Background: Thyroid cancer is the most common endocrine malignant disease, but preoperative diagnosis remains a challenge. Fine-needle aspiration cytology has greatly improved the clinical management of thyroid nodules, but the preoperative characterisation of follicular lesions is very difficult. Many patients are thus referred to surgery more for diagnosis than for therapeutic necessity. We undertook an international multicentre study to assess the usefulness of immunohistocytochemical staining for two potential markers of malignant thyrocytes. Methods: Expression of galectin-3 and CD44v6 was tested on 1009 thyroid lesions (tissue specimens and cytological cell-blocks) and 226 fresh cytological samples obtained preoperatively by ultrasound-guided fine-needle aspiration of thyroid nodules (prospective analysis). The test used monoclonal antibodies specific for CD44v6 and galectin-3, the indirect avidin-biotin complex immunoperoxidase method, and 3-amino-9-ethyl-carbazole as substrate. Findings: The sensitivity, specificity, positive predictive value, and diagnostic accuracy of this test method (for coexpression of the two markers) in the prospective analysis were 88%, 98%, 91%, and 97%, respectively. The sensitivity and specificity of galectin-3 immunodetection alone in discriminating benign from malignant thyroid lesions were more than 99% and 98% respectively, and the positive predictive value and diagnostic accuracy were 92% and 99%. Interpretation: The integration of galectin-3 immunostaining with conventional cytomorphological and clinical diagnostic procedures represents a sensitive and reliable diagnostic approach for preoperative identification of thyroid carcinomas. This test method improves the diagnostic accuracy of conventional cytology and provides the molecular basis for a new nosological assignation of the not yet classified thyroid neoplasms of indeterminate malignant behaviour.