Dipeptidyl aminopeptidase IV in the cytologic diagnosis of thyroid carcinoma.

Recently, the demonstration of DAP IV activity in thyroid cells aspirates has been proposed as an useful tool for the diagnosis of malignancy. We have studied the enzymatic activity of DAP IV, using the modified method of Lodja, in a series of 336 selected aspirates of the thyroid gland with the following cytologic diagnosis: 236 nodular hyperplasias, 60 follicular proliferations, eight Hashimoto's thyroiditis, eight Hürthe-cell proliferations, 20 papillary carcinomas, two anaplastic carcinomas, and two medullary carcinomas. The results were subjectively evaluated on the basis of staining intensity and extension in a minimum of 200 cells. Strong-to-moderate enzymatic activity with an extension of more than 40% of the cells were exclusively seen in follicular-cell derived carcinomas (papillary carcinoma, Hürthle-cell carcinoma, and follicular carcinoma). Medullary carcinoma, anaplastic carcinoma, and benign conditions were negative or weakly stained. Cytohistologic correlation in 88 patients operated on showed the following results: 26 nodular hyperplasia (18 nodular hyperplasia and eight follicular adenomas), 36 follicular proliferation (24 nodular hyperplasia, six, adenomas, three papillary carcinomas, three follicular carcinomas), two Hürthle-cell proliferation (one Hürthle-cell adenoma and one Hürthle-cell carcinoma), 20 papillary carcinomas, two medullary carcinomas, and two anaplastic carcinomas. DAP IV staining was moderate to strong and extensive in all malignant tumors initially diagnosed as follicular or Hürthle-cell proliferations. We conclude that DAP IV activity is present in malignant differentiated thyroid tumors of follicular cells (papillary carcinoma, follicular carcinoma, Hürthle-cell carcinoma), but it is identified neither in medullary carcinoma nor in anaplastic carcinoma. Therefore, its usefulness is restricted to the diagnosis of follicular-cell malignancies.