Thyroperoxidase (TPO) immunostaining of the solitary cold thyroid nodule

OBJECTIVE To evaluate the value of immunostaining using the monoclonal anti body (MoAB47) against thyroperoxidase (TPO) in distinguishing between benig n and malignant tumour cells in fine needle aspiration cytology (FNAC) samp les obtained from a solitary cold nodule of the thyroid gland for the purpo se of strengthening the indication for thyroid surgery. DESIGN A prospective, immunocytochemical study of FNACs taken from patients with solitary cold thyroid nodules who presented to Rigshospitalet, Copenh agen, Denmark, during the period April 1993 to May 1996. The first sample s eries was taken perioperatively in order to test the utility of the method, in the second part of the study samples were obtained preoperatively by ul trasonic guided aspiration. Tissue sections from the nodules obtained durin g a subsequent operation served as controls. PATIENTS One hundred and eighty-one patients, 150 women and 31 men, were st udied. The age range was 14-89 years with a median age of 44 years. Fifty-s even patients were excluded from the study for various reasons leaving us w ith a total of 124 nodules from 124 patients for final evaluation. METHODS FNAC cells and corresponding nodular tissue were stained by immunoc yto- and immunohistochemistry using MoAb47 and by routine staining methods. Samples were considered benign if 80% or more of the epithelial-looking ce lls of both the FNACs and the histological tissue sections of the nodule we re stained by TPO. Consequently, samples were considered malignant if more than 20% of the epithelial-looking cells failed to stain for TPO. Routinely stained tissue cells and sections served as diagnostic controls. RESULTS A pattern with negative TPO staining was found in all lesions which , by conventional histological staining, were subsequently proven to be mal ignant. A universal and reliable, positive TPO staining pattern was found i n all subsequently proven benign lesions, with the exception of one out of 26 follicular adenomas. This gave the method a sensitivity of 1.0 (negative TPO staining = malignancy in 27 out of 27) and a specificity of 0.99 (posi tive TPO staining benign lesion, in 96 out of 97). Positive and negative pr edictive values were 0.96 and 1.00 respectively. CONCLUSION Thyroperoxidase immunostaining of fine needle aspirates from sol itary, scintigraphically cold nodules of the thyroid gland has proved to be an important and reliable diagnostic tool for distinguishing between benig n and malignant nodules. Thus, patients might be spared further surgery if not otherwise indicated.