[Large-cell eosinophilic tumors of the thyroid gland]

Problems surrounding malignancy of large-cell oxyphilic thyroid tumors, frequently but not quite correctly designated as Hürthle-cell tumors, are still under discussion. Whether a reliable histopathological diagnosis of malignancy can already be made on the primary lesion was tested in a series of 55 large-cell oxyphilic tumors of the thyroid seen at the Department of Pathology of the University of Zurich between 1962 and 1973, hence with a follow-up period of at least 10 years. One case was excluded due to insufficient histological slides. 34 of the remaining 54 neoplasms were reclassified histopathologically as carcinomas, 15 as adenomas and 5 as borderline tumors with doubtful malignancy. In 16 of the 35 carcinoma patients the clinical course or later pathological findings were in accordance with the histopathological diagnosis of malignancy. 6 patients had local recurrences and in 7 cases the clinical data were insufficient. Only 5 of the 34 cancer cases definitely showed no further signs of malignancy. On the other hand, only one of the 7 adenoma patients developed lung metastases, 15 years after thyroidectomy, though in this case only one histological slide could be re-examined, which is obviously an insufficient number to exclude malignancy. 3 of the 5 patients with borderline lesions followed up over a period of at least 10 years developed no signs of malignancy. In the light of these results, some 2/3 of large-cell oxyphilic thyroid tumors must be classified as carcinomas (mainly follicular) provided that only isolated tumors and not large-cell oxyphilic nodules of adenomatous goiters are considered. Benign large-cell oxyphilic tumors of the thyroid do, however, exist. Histopathologically it is quite possible to diagnose a primary lesion accurately as malignant or benign, if it is screened very carefully for capsular perforation and vascular invasion, the most reliable signs of malignancy in such tumors apart from metastases.