THE IMMUNOHISTOCHEMICAL LOCALIZATION OF S100 IN THE DIAGNOSIS OF PAPILLARY CARCINOMA OF THE THYROID

In general, the diagnosis of papillary carcinoma of the thyroid is rea dily achieved based on a defined aggregate of histopathologic features . A papillary architecture is an important but not pivotal component o f the diagnosis. The recognition of classic nuclear features is the es sential diagnostic element, However, both the architectural and cytolo gical hallmarks may be encountered in other conditions and produce pro blems in histopathologic interpretation. A papillary architecture may be encountered in hyperplastic areas of follicular neoplasms, multinod ular goiter, and Graves' disease. Moreover, there may be scattered cel ls within several thyroid lesions that display some of the nuclear cha racteristics of papillary carcinoma, The distinction of these lesions from papillary carcinoma has important implications for clinical manag ement. Thus, the availability of supportive diagnostic evidence would be helpful. In the authors' experience, the strong expression of S100 is of value in identifying papillary neoplasia and distinguishing it f rom examples of papillary hyperplasia. It is of supportive but not con clusive use in distinguishing follicular adenoma from the follicular v ariant of papillary carcinoma. The authors stress that the overwhelmin g factor in the distinction remains the identification of the nuclear characteristics of a papillary carcinoma. However, the authors have en countered several cases wherein the latter are either focal or absent for reasons addressed previously and have found immunohistochemistry a valuable adjunct to diagnosis. In examining papillary foci within Gra ves' disease, caution must be exercised; S100 expression is a phenomen on of the hyperplastic, hyperfunctional state. Copyright (C) 1996 by W .B. Saunders Company.