[Classification of thyroid gland tumors in accordance with 1974 WHO nomenclature. Histological follow-up examination of 327 malignant thyroid gland tumors].

In 1974 an international histological classification of thyroid tumours was published by the World Health torganization, Geneva (WHO). It usefulness has been tested on the surgical specimens of 353 patients with malignant or probably malignant thyroid tumours analyzed at the Institute of Pathology, University of Zürich, from 1962 to 1973. 10 out of the 353 histologically reexamined cases had to be eliminated because of insufficient material. Of the remaining 343 tumours only 30 (10%) are difficult to classify according to the WHO nomenclature. 13 of these 34 tumours can be classified as differentiated carcinomas, though a clear distinction between follicular and papillary carcinoma is not possible. In 21 of the 34 doubtful cases the problems are of definite clinical importance: in 9 of them it cannot be decided on morphological grounds alone whether the tumor is malignant or not; 7 tumours cannot definitely be differentiated from metastases in the thyroid; and in 5 tumours it is not possible to determine the grade of differentiation. Considering that 90% of our tumours are easily classifiable, the WHO nomenclature represents - for pathologists as well as for clinicians - a distinct and simple basis for the classification of thyroid cancers. There is no need to overemphasize the difficulties of differential diagnosis in about 10% of the tumours since in only 6,2% of all tumours do these difficulties have real bearing on therapeutic procedure. Moreover, these problems concern questions of malignancy or metastases and are quite indipendent of any kind of nomenclature.