The molecular pathogenesis of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are clinically diagnosed by positive immunohistochemical staining of KIT, a type III receptor tyrosine kinase. Most GISTs contain gain-of-function, ie, oncogenic mutations in c-KIT or in platelet-derived growth factor receptor-alpha (PDGFR-alpha), which appears to be the major initiating event that drives the pathogenesis for GIST. Furthermore, mutations in either of these genes appear to be required for tumor growth and progression. This scenario can be thought of as "oncogenic addiction" and is one of the major reasons why some GISTs respond significantly to therapies that target these mutant receptors. In addition to mutations in c-KIT or PDGFR-alpha, genomic alterations contribute to disease progression. Moreover, GISTs that harbor different c-KIT or PDGFR-alpha mutations have different molecular signatures at the level of gene expression, which further contributes to the complexity of GIST biology and variable responses to treatment. This article will discuss the molecular basis of pathogenesis and genetic and genomic alterations that contribute to GIST tumorigenesis and disease progression as well as the heterogeneity of this disease.     

Imaging gastrointestinal stromal tumors.

BACKGROUND: Because of the recent reclassification of mesenchymal tumors, which was based on a better understanding of the genetics and immunophenotype of gastrointestinal stromal tumors (GISTs), only a limited number of studies have described the radiologic appearance of GISTs. METHODS: This study reviews the imaging characteristics of GISTs, with an emphasis on differentiating benign and malignant tumors using positron emission tomography (PET), computed tomography (CT), and magnetic resonance imaging (MRI). We reviewed the data from 53 cases of GISTs treated at our institute. The imaging studies from these cases, which were recorded at our institute from January 1998 through June 2003, included PET, CT, and MRI. RESULTS: Of the 53 GIST cases, stomach and small bowel tumors accounted for 80% of the tumors. Malignant lesions were larger and more heterogeneous, had ulcerations, and were PET positive. Peritoneal and liver metastases were most common. CONCLUSIONS: PET, CT, and MRI appear to be useful in differentiating nonmetastasizing from malignant GISTs.     

Single-cell transcriptome analysis revealed the heterogeneity and microenvironment of gastrointestinal stromal tumors

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the human gastrointestinal tract. In this study, we performed single-cell RNA sequencing (RNA-seq) on intra- and peri-tumor tissues from GIST patients with the aim of discovering the heterogeneity of tumor cells in GIST and their interactions with other cells. We found four predominating cell types in GIST tumor tissue, including T cells, macrophages, tumor cells, and NK cells. Tumor cells could be clustered into two groups: one was highly proliferating and associated with high risk of metastasis, the other seemed “resting” and associated with low risk. Their clinical relevance and prognostic values were confirmed by RNA-seq of 65 GIST samples. T cells were the largest cell type in our single-cell data. Two groups of CD8⁺ effector memory (EM) cells were in the highest clonal expansion and performed the highest cytotoxicity but were also the most exhausted among all T cells. A group of macrophages were found polarized to possess both M1 and M2 signatures, and increased along with tumor progression. Cell-to-cell interaction analysis revealed that adipose endothelial cells had high interactions with tumor cells to facilitate their progression. Macrophages were at the center of the tumor microenvironment, recruiting immune cells to the tumor site and having most interactions with both tumor and nontumor cells. In conclusion, we obtained an overview of the GIST microenvironment and revealed the heterogeneity of each cell type and their relevance to risk classifications, which provided a novel theoretical basis for learning and curing GISTs.     

Biology of gastrointestinal stromal tumors.

Once a poorly defined pathologic oddity, in recent years, gastrointestinal stromal tumor (GIST) has emerged as a distinct oncogenetic entity that is now center stage in clinical trials of kinase-targeted therapies. This review charts the rapid progress that has established GIST as a model for understanding the role of oncogenic kinase mutations in human tumorigenesis. Approximately 80% to 85% of GISTs harbor activating mutations of the KIT tyrosine kinase. In a series of 322 GISTs (including 140 previously published cases) studied by the authors in detail, mutations in the KIT gene occurred with decreasing frequency in exons 11 (66.1%), 9 (13%), 13 (1.2%), and 17 (0.6%). In the same series, a subset of tumors had mutations in the KIT-related kinase gene PDGF receptor alpha (PDGFRA), which occurred in either exon 18 (5.6%) or 12 (1.5%). The remainder of GISTs (12%) were wild type for both KIT and PDGFRA. Comparative studies of KIT-mutant, PDGFRA-mutant, and wild-type GISTs indicate that there are many similarities between these groups of tumors but also important differences. In particular, the responsiveness of GISTs to treatment with the kinase inhibitor imatinib varies substantially depending on the exonic location of the KIT or PDGFRA mutation. Given these differences, which have implications both for the diagnosis and treatment of GISTs, we propose a molecular-based classification of GIST. Recent studies of familial GIST, pediatric GIST, and variant forms of GIST related to Carney's triad and neurofibromatosis type 1 are discussed in relationship to this molecular classification. In addition, the role of mutation screening in KIT and PDGFRA as a diagnostic and prognostic aid is emphasized in this review.     

Immunohistochemical and molecular genetic analyses of multiple sporadic gastrointestinal stromal tumors

A 77-year-old Japanese male patient was admitted to our hospital complaining of general fatigue and melena. A gastroduodenal endoscopic examination revealed no definitive localized lesions. However, both a large amount of cruor and blood flow from the small intestine into the ascending colon was observed during the colonoscopic examination. At least three tumors, believed to originate from the small intestine, were detected by abdominal computed tomography. Based on these findings, multiple and hemorrhagic small intestinal tumors were diagnosed and surgical treatment of the tumors planned. During the celiotomy, twelve tumors were found in the small intestine. Intestinal wedge or partial resection was applied. All excised specimens demonstrated morphology of a submucosal tumor and the largest tumor had a delle with coagulation on the mucosal face. In the histological findings, hematoxylin and eosin staining showed spindle cell morphology. The immunohistochemical examination revealed that the tumor cells were diffusely positive for KIT and CD34. The myenteric plexus layer of the small intestine was focal-positive for KIT and showed no intestinal cells of Cajal hyperplasia. The tumor sequencing results revealed an identical missense mutation in codon 642 of c-kit exon 13 leading to the replacement of lysine by glutamic acid and a silent germ-line mutation in exon 12 of the PDGFRA gene concerning whole blood, normal mucosa and tumors. We concluded that the current subject was categorized as having multiple sporadic-type gastrointestinal stromal tumor with identical mutational types. Although the patient did not receive any adjuvant chemotherapy, there has been no sign of recurrence over the 3 years since the surgery.     

Surgery including liver resection for metastatic gastrointestinal stromal tumors or gastrointestinal leiomyosarcomas

BACKGROUND: In recent years, imatinib mesylate (STI 571), a tyrosine kinase inhibitor, has shown short-term clinical usefulness for gastrointestinal stromal tumor or gastrointestinal leiomyosarcoma (GIST). The value of surgical resection, including hepatectomy, for metastatic GIST remains unknown. Our aim was to evaluate the outcome of surgical resection, including hepatectomy, for metastatic GIST at a single institute. METHODS: Eighteen patients who underwent hepatectomy for metastatic GIST were identified and the clinicopathological data of these patients were analyzed retrospectively. RESULTS: The primary site of GIST included stomach in 10, duodenum in five, ileum in two and esophagus in one patient. A hemihepatectomy or greater resection was undertaken in eight patients. Six patients underwent simultaneous resection for primary and hepatic disease. There was no in-hospital mortality in this series. The post-hepatectomy 3- and 5-year survival rates were 63.7 and 34.0% respectively, with a median of 36 (17-227) months. Recurrence after the initial hepatectomy was documented in 17 patients (94%), and metastatic mass of the remnant liver developed in 15 of these 17 patients (88%). Three patients survived >5 years after the initial hepatectomy who underwent multiple surgical resections during this period. No clinicopathological characteristic was a significant predictive factor for survival. CONCLUSIONS: Multiple surgical resections, including hepatectomy, may contribute to important palliation in selected patients with metastatic GIST. Surgical cure seems to be difficult due to the high frequency of repeat metastasis to various sites. Therefore, adjuvant therapy must be required in the treatment of metastatic GIST.     

Advanced or metastatic gastrointestinal stromal tumors: systemic treatment options

Gastrointestinal stromal tumor (GIST), the most common sarcoma arising in the gastrointestinal tract, typically expresses the tyrosine-kinase receptor, C-KIT, and contains activating mutation in the c-kit or platelet-derived growth factor receptor (pdgfr) gene. Recently, development of small molecules that inhibit the kinase activity of mutant C-KIT and PDGFR proteins has radically changed treatment and prognosis of patients diagnosed with advanced GIST as this molecularly "targeted" therapy has demonstrated remarkable high-level of activity in this disease.     

Imatinib resistance in gastrointestinal stromal tumors

Conventional chemotherapeutic drugs are ineffective in treatment of gastrointestinal stromal tumors (GISTs). Imatinib (STI571, Gleevec, Glivec; Novartis Pharmaceuticals, East Hanover, NJ), a selective inhibitor of KIT, ABL, BCR-ABL, PDGFRA, and PDGFRB, represents a new paradigm of targeted cancer therapy and has revolutionized the treatment of patients with chronic myelogenous leukemia and GISTs. Unfortunately, imatinib resistance has emerged. The reported mechanism of imatinib resistance in GISTs involves missense mutation in the kinase domain of KIT, including Thr670Ile, Tyr823Asp, and Val654Ala. The established mechanisms and potential mechanisms of imatinib resistance in GISTs, the imaging studies indicative of early development of imatinib resistance, and the management of imatinib-resistant GISTs are discussed.     

Pediatric gastrointestinal stromal tumors and leiomyosarcoma

BACKGROUND: With the introduction of molecularly targeted therapy for gastrointestinal stromal tumors (GISTs), it became important to distinguish GISTs from leiomyosarcomas (LMSs). The authors sought to characterize the clinicopathologic features of these tumors in pediatric patients. METHODS: The authors reviewed the medical records of 11 patients for whom GIST or LMS was diagnosed between March 1962 and July 2002 at St. Jude Children's Research Hospital and reclassified the tumors according to current histologic and immunophenotypic criteria. The authors also reviewed the literature pertaining to pediatric GISTs and LMSs. RESULTS: Seven patients had GISTs, and four had LMS. The median age of the patients at diagnosis was 11.5 years. At diagnosis, metastases were present in one patient with GISTs and in another with LMS. Unlike the focal distribution of CD117 (KIT) in LMS, diffuse and strong immunostaining was observed in GISTs. Only GISTs expressed CD34. Six patients underwent complete resection (four with GISTs and two with LMS), four patients underwent incomplete resection (three with GISTs and one with LMS), and one patient (with LMS) underwent a biopsy only. Radiotherapy or chemotherapy was used to treat one patient with GISTs and three patients with LMS. One patient with a high-risk GIST (largest dimension of 32 cm and high mitotic count) was treated with adjuvant imatinib mesylate outside the preferred setting of a clinical trial, due to concerns regarding the high risk of tumor recurrence. Four patients with GISTs and two with LMS survived median disease-free a median of 10.4 years and 4.3 years after diagnosis, respectively. Tumors in all but one survivor were completely resected. CONCLUSIONS: KIT staining helped to distinguish GISTs from LMSs. Surgery was the treatment of choice for both entities, and tumor resectability was a key prognostic factor.     

DOG1与胃肠道间质瘤

胃肠道间质瘤(gastrointestinal stromal tumors,GISTs)是最常见的胃肠道间叶源性肿瘤,在遗传学上存在频发性c-kit或血小板源性生长因子受体alpha(platelet-derived growth factor receptor alpha,PDGFRα)基因突变,在免疫表型上95%表达KIT蛋白(CD117)阳性,但仍有5%的GISTs缺乏KIT表达.DOG1(discovered on GIST 1)是一种新型的更加敏感而特异的标志物,选择性高表达于GISTs,且其表达并不依赖于KIT或PDGFR α基因突变状态,而与CD117的总体敏感性几乎相同,在GISTs的诊断中加入DOG1将使患者更加受益,本文就DOG1在GISTs中的表达及意义作一综述.     

胃肠间质瘤的外科治疗问题

 靶向治疗的问世使得胃肠间质瘤（GIST）的治疗发生了革命性的变化，但依然应强调外科原则和技巧在治疗GIST中的重要性。对位于食管、胃肠道、结直肠的GIST病例的治疗经验进行了总结。术中外科医师应尽可能完整切除肿瘤，如果术中无法完整切除，可予伊马替尼治疗。由于GIST甚少经淋巴途径转移，故不必常规行淋巴结清扫术。     

Pathologic,radiologic and PET scan response of gastrointestinal stromal tumors after neoadjuvant treatment with imatinib mesylate

AimThe aim of this study is to review the radiologic, PET scan and pathologic response and the outcome of patients with advanced GIST treated with neoadjuvant IM followed by surgical resection.Materials and methodsWe report a case and review 36 patients reported in MEDLINE with advanced GIST treated with neoadjuvant IM followed by surgical resection.ResultsThirty-seven patients with a median age of 56 years (range, 32–76 years) at presentation were treated with neoadjuvant IM. Radiologic response accurately predicted pathological response in 31/36 patients, whereas PET scan was accurate in predicting treatment response in only 6/23 patients.ConclusionThis study demonstrates that the pathologic response of GIST to IM is usually incomplete and does not correlate with the complete response seen on PET scan. This finding suggests that surgical resection will continue to play a vital role in the treatment of patients with advanced disease responding to IM treatment.     

Molecular response prediction in gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are rare tumors of mesenchymal origin that develop along the gastrointestinal tract. Over ten years ago, their management dramatically changed following the discovery of an activating mutation of the KIT oncogene, which led to the use of small molecule inhibitors to therapeutically target these mutant kinases. Patients with advanced GIST, who were once a subset of sarcoma with poor prognosis due to their lack of chemosensitivity, may now survive more than 5 years following treatment with tyrosine kinase inhibitors (TKI) such as imatinib mesylate (IM) and sunitinib malate (SU). After ten years of active clinical and preclinical research, it has become clear that, although relatively homogeneous compared to other solid malignancies, there is still some heterogeneity in GISTs and most notably in regard to response to therapy. Here, we review the current data regarding molecular prediction of response in this disease.     

New therapeutic options in gastrointestinal stromal tumors

Gastrointestinal stromal tumors have until recently had a uniformly poor prognosis with lack of effective drug therapies. These tumors usually have activating mutations in either KIT or PDGFR-alpha tyrosine kinase receptors. Over the past decade, imatinib (Gleevec), a selective tyrosine kinase inhibitor has become the standard of care for the first-line treatment of patients with unresectable and metastatic disease. For patients with imatinib-resistant disease or intolerant to the side effects of imatinib, sunitinib (Sutent), a multitargeted tyrosine kinase inhibitor was recently approved. For earlier-stage disease, status post-complete surgical excision, preliminary data seem encouraging for the role of adjuvant imatinib in prolonging patients' disease-free interval. The impact of neoadjuvant drug therapy needs to be further classified and explored. With additional evaluation of other tyrosine kinase inhibitors and novel therapies against other molecular markers, the treatment paradigm for this malignancy should continue to evolve.     

Surgical resection in metastatic gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are rare mesenchymal tumors of the gastrointestinal tract. Traditionally, surgery has been the primary treatment modality for these tumors, with only modest results. The recent development of kinase inhibitors (most notably, imatinib mesylate) has provided a new paradigm for the treatment of this disease. Response rates approaching 60% have been seen in studies in patients with advanced disease. Previously, chemotherapy played little role in the treatment of this disease. Now, however, treatment with kinase inhibitors can increase the number of patients who may potentially benefit from surgical intervention. Many questions regarding the use of kinase inhibitors remain. Most importantly, the optimal duration of treatment before surgical intervention and following both complete and incomplete tumor resection remains to be elucidated. Ongoing prospective trials have the potential to provide some of these answers in the near future.     

Clinical and molecular characteristics of gastrointestinal stromal tumors in the pediatric and young adult population

Gastrointestinal stromal tumors (GISTs) typically occur late in life; however, there also are reports of pediatric and young adult patients. This rare subset of GISTs has clinicopathologic and molecular features distinct from their adult counterparts. Most pediatric GIST patients are female and often present with multifocal tumors that are epithelioid in nature. Although these young patients often have metastatic disease, it progresses slowly. Most pediatric GISTs lack the gain-of-function mutation in KIT or PDGFRA commonly found in adult cases. Expression profiling and genomic studies of pediatric GISTs show distinct molecular signatures, suggesting a unique origin as compared with adult GISTs. We and others have shown that the insulin-like growth factor 1 receptor may have a prominent role in driving KIT/PDGFRA mutation-negative adult and pediatric GISTs, and clinical trials are currently being designed to exploit these types of discoveries.     

A clinicopathologic and immunohistochemical study of gastrointestinal stromal tumors.

The clinicopathologic and immunohistochemical features in 120 cases of gastrointestinal stromal tumor (GIST) were reviewed. Excluding 24 cases of gastric schwannoma, 96 cases of GIST consisting of 62 benign tumors and 34 sarcoma (low grade, 17; high grade, 17), with 9 cases arising in the esophagus, 57 in the stomach, 28 in the small intestine, and 2 in the colon, were studied. All esophagus and colon tumors were benign and resembled a conventional leiomyoma histologically. However, the gastric and small intestine benign tumors mostly showed histologic features of cellular or epithelioid leiomyoma. Immunohistochemically, desmin caused a positive reaction in all esophagus and colon tumors, but only 26% of gastric and small intestine tumors. However, muscle-specific actin (HHF35) caused a positive reaction in most GIST (92%). The 10-year survival rates of the patients with gastric sarcoma and those with intestinal sarcoma were 74% and 17%, respectively. These results showed that histologic and immunohistochemical features were distinctly different, depending on the location in the gastrointestinal tract; that most GIST, excluding schwannoma, had smooth muscle differentiation; and that sarcomas had a more favorable prognosis when they occurred in the stomach rather than the intestine.