Thymoma, atypical thymoma, and thymic carcinoma - A novel conceptual approach to the classification of thymic epithelial neoplasms

Primary thymic epithelial neoplasms have been the subject of much controver sy in recent years owing to the difficulties posed by these tumors for prec ise histopathologic typing and prognostication. A number of classification schemes using different terminology have been proposed, none of which has s atisfactorily managed to address all the problems and concerns related to t hese tumors. We present a proposal for a novel approach to the histologic c lassification of primary, thymic epithelial neoplasms that is based on morp hologic features of differentiation. The principle behind this classificati on scheme is that the determination of the cytologic degree of atypia and t he identification of the organotypical features of thymic differentiation m ay permit accurate classification of these neoplasms into 3 simple and repr oducible diagnostic categories: thymoma, atypical thymoma, and thymic carci noma. We further reiterate the traditional concept that tumor staging not h istopathologic typing, has a more crucial role for accurate and reliable pr ognostication for the better differentiated forms of these tumors.