Diagnosis of gastrointestinal stromal tumors: a consensus approach

As a result of major recent advances in understanding the biol-ogy of gastrointestinal stromal tumors (GISTs), specifically recogni-tion of the central role of activating KIT mutations and associated KIT protein expression in these lesions, and the development of novel and effective therapy for GISTs using the receptor tyrosine kinase inhibitor STI-571, these tumors have become the focus of considerable attention by pathologists, clinicians, and patients. Stro-mal/mesenchymal tumors of the gastrointestinal tract have long been a source of confusion and controversy with regard to classification, line(s) of differentiation, and prognostication. Characterization of the KIT pathway and its phenotypic implications has helped to resolve some but not all of these issues. Given the now critical role of accurate and reproducible pathologic diagnosis in ensuring appropri-ate treatment for patients with GIST, the National Institutes of Health convened a GIST workshop in April 2001 with the goal of developing a consensus approach to diagnosis and morphologic prog-nostication. Key elements of the consensus, as described herein, are the defining role of KIT immunopositivity in diagnosis and a pro-posed scheme for estimating metastatic risk in these lesions, based on tumor size and mitotic count, recognizing that it is probably unwise to use the definitive term “benign ” for any GIST, at least at the presen