[Problems in the classification of thyroid tumors. Their significance for prognosis and therapy].

Standardized nomenclatures of tumors are mandatory for epidemiological investigations as well as for the correct interpretation of pathological diagnoses by the clinician. Not least thanks to the activity of the World Health Organization (WHO), uniform tumor nomenclatures in worldwide use have been adopted for most organs. This applies also for the thyroid, even in Switzerland, where many pathologists had formerly been convinced that only the special and rather complicated nomenclature of Langhans, adapted by Wegelin, was consistent with the special tumor situation in Switzerland, a former endemic goiter area. The simplified classification of WHO is demonstrated for the group of malignant tumors of the thyroid and the problems concerning their classification are discussed. Difficulties of classifications arise in well differentiated tumors rather than in undifferentiated, anaplastic forms. For example, it is not possible to assess unequivocally the malignancy of strongly encapsulated forms of highly differentiated follicular tumors. They are then called, rather evasively, "atypical adenomas". The difficulties do not lie in the system of classification but in the tumor's specific manner of growth, and the clinician should be aware of this. Otherwise he may overstrain the diagnostic potentialities of his pathologist.