Guest Editorial: Two Proposals Regarding the Terminology of Thyroid Tumors

To THE EDITOR: We have been reviewing the pathological findings in several hundred cases of thyroid tumors from children and young adults exposed to fallout from the Chernobyl accident. We will be reporting our detailed findings in due course, but we would like to draw attention to some of the problems that have arisen in applying the WHO classification [1] to this material and to the solutions we have adopted. Diagnostic difficulties have mostly arisen in encapsulated tumors with a follicular architecture. There are two separate problems: deciding whether minor nuclear changes of the type seen in typical papillary carcinomas justify a diagnosis of follicular variant of papillary carcinoma (PTC-FV) and deciding whether minor degrees of capsular penetration justify a diagnosis of malignancy. There is no doubt that nuclear changes play a major role in the diagnosis of papillary carcinoma [2]. However, since the recognition of the follicular variant of papillary carcinoma [3] we believe that there has been a gradual extension of the category to include lesions with minor nuclear changes. Many pathologists will have faced this problem, and it has occurred on a number of occasions in the present study. We suggest that it is more appropriate to recognize this difficulty than to arbitrarily place well-differentiated encapsulated tumors with a follicular architecture where minor nuclear changes are the only indicator of a papillary carcinoma in a definite malignant or definite benign category. We refer to these tumors simply as well differentiated, without specifying either follicular or papillary, and use the terms welldifferentiated tumor of uncertain malignant potential (WDT-UMP) when there is no definite evidence of invasion, and well-differentiated carcinoma not otherwise specified (WDC-NOS) when invasion is present. The latter term has already been proposed in the Third Series AFIP Fascicle of Tumors of the Thyroid Gland [4]. The second problem applies to encapsulated tumors that lack any indication that they are papillary,