Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the digestive tract. The diagnosis of GIST relies mainly on clinicopathological features, tumor cell morphology and immunohistochemical marker CD117 (c-Kit). However, some tumors (about 3%-4%) have clinicopathological features of GIST but do not express CD117. To determine whether these lesions are true GIST, it is necessary to raise awareness of CD117-negative GIST. This article discusses the immunohistochemical features, gene mutations, prognosis and efficacy of targeted drugs of CD117-negative GIST. Research results suggest that CD117-negative GIST lacks KIT expression but has typical clinical, histopathological and cytogenetic features. These tumors have KIT and/or PDGFRA mutations, or are wild type. Because most KIT-negative GISTs contain PDGFRA or KIT mutation, pathologists and oncologists should not exclude GIST diagnosis based on negative immunohistochemical staining of KIT. It is known that approximately 30% of PDGFRA mutations may be sensitive to imatinib, and patients with such tumors may benefit from imatinib, so imatinib treatment should not be empirically denied in these patients.
胃肠间质瘤（GIST）是消化道最常见的间叶源性肿瘤，GIST的诊断主要依赖肿瘤细胞形态学和免疫组织化学标记CD117（c-Kit）。然而，一些肿瘤（3%~4%）具有GIST的临床病理特征但并不表达CD117，要确定这些病变是否真正为GIST，需提高对CD117阴性GIST的认识。本文围绕CD117阴性GIST免疫组化特征、CD117阴性GIST的基因突变及其预后及靶向药物疗效进行讨论。提示，CD117阴性GIST缺乏KIT表达，但具有典型的临床、组织病理学和细胞遗传学特征。这些肿瘤中有KIT突变、PDGFRA突变和野生型。鉴于大多数KIT阴性GIST含有PDGFRA或KIT突变，因此，病理学家和肿瘤学家不应该基于KIT的阴性免疫组织化学染色来排除GIST诊断。已知大约30%的PDGFRA突变可能对伊马替尼敏感，此类肿瘤的患者可能从伊马替尼中获益，故这些患者不应该经验地否定伊马替尼治疗。.
Keywords: CD117 negative; Gastrointestinal stromal tumor; Pathological diagnoses.