Table 7-1 Classification of Gastrointestinal Mesenchymal Tumors | |
|---|---|
|
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
Mesenchymal Tumors
Mesenchymal Tumors
INTRODUCTION
Mesenchymal tumors of the gastrointestinal (GI) tract can be classified as shown in Table 7-1. Some are unique to the GI tract (e.g., gastrointestinal stromal tumor [GIST], inflammatory fibroid polyp [IFP], etc.), but most have identical counterparts in soft tissues. GIST, the most common of the GI mesenchymal tumors, has been in the spotlight since the “KIT revolution” provided a firm framework for its diagnosis and treatment. Advances in diagnostic, molecular, prognostic, and therapeutic aspects of these tumors have been exponential. Meanwhile, the list of other mesenchymal tumors involving the GI tract continues to expand.
The increase in screening colonoscopy has seen the emergence of several new mesenchymal polypoid lesions including benign fibroblastic polyp, perineurioma, benign epithelioid peripheral nerve sheath tumor, and Schwann cell “hamartoma.” In addition, reactive nodular fibrous proliferation and heterotopic mesenteric ossification have emerged as new reactive entities.
A number of rare mesenchymal tumors are starting to be seen as GI primaries (e.g., PEComa, clear cell sarcoma, and calcifying fibrous tumor) sometimes mimicking GISTs. Molecular testing has revealed some “CD117-negative GISTs” to be synovial sarcomas and some “metastatic melanomas” to be clear cell sarcomas. The ever-changing landscape of mesenchymal tumors and the rarity of most lesions pose significant challenges to surgical pathologist. This chapter aims to provide a current view of mesenchymal tumors, offering practical approaches to diagnostic challenges and highlighting their clinical implications.
GASTROINTESTINAL STROMAL TUMORS
GISTs have evolved from poorly defined, histogenetically obscure GI mesenchymal tumors to well-defined oncogenic entities with distinctive clinical, morphologic, ultrastructural, histiogenetic, and molecular features, for which targeted therapy is available.
Histogenesis
Many tumors currently defined as GISTs were, in the past, thought to be smooth muscle or neural tumors due to their morphologic resemblance to these lesions.1, 2, 3, 4 When immunohistochemistry became available, substantial proportions were found to have neither typical smooth muscle nor neural differentiation. The noncommittal term “GI stromal tumor” to accommodate this group of tumors was coined.5 The major conceptual breakthrough came in 1998 with the discovery of activating mutations in the receptor tyrosine kinase c-kit gene6 and overexpression of its product CD1177, 8 in the vast majority of these tumors. GISTs are currently believed to arise from or differentiate along the lines of interstitial cells of Cajal (ICC) (the “pacemaker” cells of the GI tract), which they resemble at a morphologic, ultrastructural, and immunohistochemical (CD117+, DOG1+) level.7, 8
Demography and Clinical Aspects
