Malignant small bowel neoplasm of enteric plexus derivation (plexosarcoma). Light and electron microscopic study confirming the origin of the neoplasm

Interstitial Cells of Cajal-Origin, Distribution and Relationship with Gastrointestinal Tumors

The interstitial cells of Cajal (ICC) represent a particular network formed by some peculiar cells that were first described by the great neuroanatomist, S. Ramon y Cajal. Nowadays, the ICC have become a fascinating topic for scientists, arousing their curiosity; as a result, there is a vast number of published articles related to the ICC. Today, everybody widely accepts that the ICC represent the pacemaker of the gastrointestinal tract and are highly probable to be the origin cells for gastrointestinal tumors (GISTs). Recently, Cajal-like cells (ICLC) were described, which are found in different organs but with an as yet unknown physiological role that needs further study. New information regarding intestinal development indicates that the ICC (fibroblast-like and muscle-like) and intestinal muscle cells have the same common embryonic cells, thereby presenting the same cellular ultrastructure. Nowadays, there is a vast quantity of information that proves the connection of the ICC and GISTs. Both of them are known to present c-kit expression and the same ultrastructural cell features, which includes minimal myoid differentiation that is noticed in GISTs, therefore, supporting the hypothesis that GISTs are ICC-related tumors. In this review, we have tried to highlight the origin and distribution of Cajal interstitial cells based on their ultrastructural features as well as their relationship with gastrointestinal stromal tumors.

A ganglion-rich gastrointestinal stromal tumor: A case report

We report a case of an extremely rare type of duodenal gastrointestinal stromal tumor (GIST) that included neuronal components. Although gastrointestinal autonomic nerve tumors (GANTs), a subtype of GISTs, exhibit ultrastructural features of the nerve plexus, neuronal cells have not been observed within GANTs or GISTs. GISTs originate from interstitial cells of Cajal (ICCs), which are markedly different from the progenitor cells of neural elements and neural-crest-derived stem cells. This may explain why GISTs typically lack neuronal elements. It remains unclear that the neuronal components of this tumor are neoplastic or hyperplastic, but proliferation and survival of ICCs have recently been reported to be closely related to neurons. Although we could not find the KIT, PDGFR, and BRAF mutation as far as we examined, it may have had a rare mutation in NF1, a fusion of EVT6-NTRK3, or an as-yet-unknown KIT mutation that affected neurogenesis. Further investigation of related genetic mutations and accumulation of data from other similar cases is needed.

Gastrointestinal Autonomic Nerve Tumor: Case Report and Review of the Literature

Gastrointestinal autonomic nerve (GAN) tumor is an uncommon specialized form of gastrointestinal stromal tumor (GIST). We report the case of a 46-year-old man affected by this tumor. The neoplasm arose from the sigmoid colon. The patient underwent surgery but eight months later an omental relapse occurred. A second laparotomy was successfully performed and the patient is free of disease at 21 months of follow-up. To our knowledge this is the first case of a large bowel GAN tumor described in the literature.

Neural and neurogenic tumours of the gastroenteropancreaticobiliary tract

Neural lesions occur uncommonly in the gastroenteropancreaticobiliary tract. However, due to the growing number of screening colonoscopy procedures, polypoid neural lesions of the colon are being recognised increasingly and range from benign tumours to high-grade malignant neoplasms. Morphological variability of neural tumours can be wide, although some entities share pathological features, and, as such, these lesions can be diagnostically challenging. We review the spectrum of pathology of neural tumours in the gastroenteropancreaticobiliary tract, with the goal of providing a practical approach for practising surgical pathologists.

Gastrointestinal Autonomic Nerve Tumor of the Colon

Gastrointestinal autonomic nerve tumor (GANT) is an uncommon subtype of gastrointestinal stromal tumor that is morphologically similar to conventional stromal tumors but has ultrastructural features of neural differentiation. Of the approximately 58 cases of GANT reported to date, most have arisen in the small intestine or stomach, but none, to our knowledge, in the colon or rectum. Accordingly, we report the first case of colonic GANT and document its histologic, ultrastructural, and immunohistochemical characteristics. These were not unlike those of GANT arising elsewhere in the alimentary tract, including interlacing spindle cells, skenoid fibers, axonal cytoplasmic processes, dense core neurosecretory granules, and immunoreactivity to vimentin and NSE. The rarity of GANT in the large intestine should not preclude ultrastructural evaluation of colorectal stromal tumors for neural features.

Gastrointestinal autonomic nerve tumors: a clinical review

PURPOSE

Gastrointestinal autonomic nerve tumors (GANTs) are believed to be rare accounting for 1 % of all malignant gastrointestinal tumors. Many gastrointestinal surgeons and gastroenterologists are unaware of this entity. This review aims to highlight the salient clinical features and prognosis of GANTs.

METHODS

Using the common search engines and manual cross-referencing, a search of the English literature was conducted for "gastrointestinal autonomic nerve tumor."

RESULTS

All of the published literature on GANTs is either case reports or small case series. From 49 retrieved articles, a total of 107 GANT cases were collected with a mean age of 54 years and equal male to female preponderance. The most commonly affected site was small bowel followed by stomach. Esophageal and colorectal GANTs were less frequent. Clinical presentation was variable ranging from non-specific symptoms, abdominal pain, weight loss, iron-deficiency anemia, to obstruction and gastrointestinal bleeding. Acute presentation due to free rupture or perforation with subsequent peritonitis was extremely rare. Endoscopic and radiological investigations were valuable in tumor localization and determination of distant spread. Thirteen patients were lost to or had no follow-up, leaving 94 patients for long-term outcome analysis. All patients were treated by radical surgical resection of the involved organ as this offered the only hope of cure. Local recurrence, metastases, or both developed in 40 % of cases despite radical surgical resection. Resection for local recurrences and hepatic metastases was feasible in some selected cases. Response to adjuvant chemoradiation was poor and imatinib mesilate was effective in cases of metastatic or inoperable CD117-positive GANTs.

CONCLUSION

Radical surgical resection of GANTs is the mainstay of treatment. The aggressive behavior after radical resection coined with the poor response to adjuvant chemotherapy call for the urgent need to develop new adjuvant therapies.

Gastrointestinal autonomic nerve tumor of the stomach

Patient: Female, 32

Final Diagnosis: Gastrintestinal Autonomic Nerve Tumor (GANT)

Symptoms: anemia • anorexia • fatigue • fever • hearburn • nausea • weight loss

Medication: —

Clinical Procedure: —

Specialty: Gastroenterology and Hepatology

Schwannoma of the rectum: A case report and literature review

Schwannoma is a tumor originating from the Schwann cells. Gastrointestinal schwannomas are uncommon stromal tumors of the intestinal tract and, in particular, rectal schwannomas are extremely rare. In fact, it is well established that schwannomas appear more frequently in the stomach and in the small intestine, while location in the colon or in the rectum is uncommon. Reading the literature, only few cases of rectal schwannoma have been reported. Their diagnosis is confirmed by the immunohistochemical panel (S-100 protein). When these tumors are located in the colon and in the rectum, radical excision with wide margins is mandatory, due to their tendency to recur locally or become malignant, if left untreated. In the present study, we describe a case of a rectal schwannoma occured in a 72-year-old man, presented as a small polypoid lesion, which was successfully removed in toto by hot-biopsy, during the same endoscopy, due to the dimensons. No recurrence of the lesion was observed after 6 mo of follow-up.

Soft tissue tumors of the anorectum: rare, complex and misunderstood

Anorectal soft tissue tumors are uncommon and often present both diagnostic and therapeutic challenges. Although many of these tumors are identified with imaging performed for unrelated reasons, most present with nonspecific symptoms that can lead to a delay in diagnosis. Historically, radical surgery (abdominoperineal resection) has been the mainstay of treatment for both benign and malignant anorectal soft tissue tumors. However, a lack of proven benefit in benign disease along with changes in technology has called this practice into question. In addition, the role of radiation and/or chemotherapy remains controversial. In this manuscript, we review the history and current status of anorectal soft tissue tumor management, with a particular focus on challenges in optimizing survival.

Primary leiomyosarcomas of the gastrointestinal tract in the post-gastrointestinal stromal tumor era

Most mesenchymal neoplasms of the gastrointestinal tract are currently classified as gastrointestinal stromal tumors (GIST). Gastrointestinal stromal tumors are diagnosed by immunopositivity for CD117, CD34, and DOG1.1, with or without molecular analyses. According to the World Health Organization classification, the diagnosis of primary leiomyosarcomas of the gastrointestinal tract is so rare that there are no significant data on demographic, clinical, or gross features of this tumor. A comprehensive literature search was performed to identify gastrointestinal leiomyosarcomas. Searches were limited to the past 12 years because definitive tools to differentiate leiomyosarcomas from GIST were introduced in the late 1990s. Cases were included only if convincing data were presented. Six cases of esophageal leiomyosarcoma and 5 cases of gastric leiomyosarcoma were confirmed. Furthermore, 26 cases of leiomyosarcoma of the small bowel, 11 cases of the colon, and 8 cases arising in the rectum were identified. Finally, 28 cases of infantile and adolescent leiomyosarcoma were reviewed. Although survival analysis is precluded by small case numbers and limited survival data availability, the trend identifies that increased size and mitotic activity portends to a worse prognosis in small bowel leiomyosarcomas. Colonic leiomyosarcomas appear to be aggressive tumors, regardless of tumor size and mitotic activity. Rectal leiomyosarcomas present as smaller tumors with favorable prognosis. Leiomyosarcomas in post-GIST era are rare tumors of the gastrointestinal tract with distinctive clinicopathologic characteristics. Owing to different treatment options, it is necessary to accurately differentiate these from GIST, using a combination of histologic appearance, presence of smooth muscle antigens, and absence of specific GIST immunomarkers.

Tumor estromal gastrointestinal: análise de 146 casos do centro de referência do Instituto Nacional do Câncer - INCA

OBJETIVO: Avaliar os resultados do tratamento de GIST no INCA. MÉTODOS: Análise retrospectiva de todos os casos de GIST tratados no INCA no período de 1997 a 2009. RESULTADOS: Analisamos 146 pacientes, com média de idade de 44,5 anos e predomínio do sexo feminino. O principal sintoma foi dor abdominal. Tivemos ocorrência de segundo primário em 22% dos casos e na imuno-histoquímica, 92% foram positivos para CD117. A localização mais frequente foi estômago e predominou o grupo de alto risco. A cirurgia foi R0 (extenso) em 70% e os principais sítios de metástases foram fígado e peritônio. A sobrevida global foi, respectivamente, em dois e cinco anos de 86% e 59%. Houve significante diferença entre a sobrevida global (p=0,29) do grupo de alto risco versus os demais. CONCLUSÃO: Os nossos pacientes apresentam-se principalmente sob forma de doença de alto risco com repercussão óbvia na sobrevida. O uso de Imatinib melhorou a sobrevida dos pacientes com doença metastática e recidivada. Devemos estudar seu uso no cenário de adjuvância e neoadjuvancia visando melhorar os índices do grupo de alto risco. A criação de centros referenciais é uma necessidade para o estudo de doenças pouco frequentes.

Surgical treatment of gastrointestinal autonomic nerve tumors (GANT) in children-2 case reports

Gastrointestinal autonomic nerve tumors form an uncommon subcategory of stromal tumors of the intestinal tract although their histologic appearance is similar to other gastrointestinal stromal tumors. Our aim was to evaluate our experience in the diagnosis and therapy of these kinds of tumors. Two patients were admitted to the Pediatric Surgery Clinic in Niš with abdominal pain and a palpable mass in the abdomen. After excision, the tumor tissue was sampled, sent for histopathological diagnosis, and examined by light microscopy, immunohistochemistry, and electron microscopy. Postoperatively, both patients recovered without complications. The patient with the tumor bulk in the mesentery of the small bowel had no evidence of tumor progression 6 years after surgery. In the second case, a giant tumor was present along the greater curvature of gaster. Even with a tumor of this size, there were no signs of progression 10 years after surgery. Radical surgical resection of gastrointestinal autonomic nerve tumors seems to be the curative approach to date, and long-term survival is possible even with large tumors.

Gastrointestinal stromal tumours: an update

Purpose. To study the evolution of concepts concerning gastrointestinal stromal tumours (GISTs) over 30 years.Discussion. GISTs have been, for more than 30 years, the subject of considerable controversy regarding their line of differentiation as well as the prediction of their behaviour. Furthermore, once they spread within the peritoneal cavity, they are extremely hard to control. The recent findings of c-Kit mutations and the immunohistochemical detection of the product of this gene, KIT or CD117, in the mainly non-myogenic subset of this family of tumours, has led to a reappraisal of this group of lesions, which, with some exceptions, is now thought to be derived from the interstitial cells of Cajal, and this has facilitated a clearer definition of their pathological spectrum. In this article, we review chronologically the evolution of the concept of GIST with the gradual application of electron microscopy, immunohistochemistry, DNA ploidy analysis. We discuss the impact of these techniques on the pathological assessment and clinical management of GISTs.

Gastrointestinal stromal tumor with structures resembling intracytoplasmic lumina

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gut. It is characterized by positive immunostaining for CD117, and bears mutations in the c-kit or PDGFRA genes. Its origin remains uncertain. GISTs mainly possess primitive smooth muscle or neuronal differentiation. Although an epithelioid pattern of GIST is a common finding on light microscopy, true epithelial differentiation has never been demonstrated by either immunohistochemistry or ultrastructural study. Here the authors report an epithelioid GIST of the stomach, immunopositive for CD117, DOG1.1, CD34, and PDGFRA, with slight cytoplasmic staining for epithelial membrane antigen. One heterozygous mutation on codon 842 of exon 18 of the PDGFRA gene was also found. Ultrastructurally, tumor cells had plentiful organelles, including some membrane-bound, dense-core granules and cytoplasmic vacuoles. Intermingled thin cellular processes were also found. Unusually, there were many structures resembling glandular epithelial intracellular lumina with processes. The processes, although resembling microvilli, did not have filament cores, while the lumina were either empty or contained some dense or flocculent content of uncertain nature. True intracellular lumina are very rare in GIST and the authors present findings related to this issue, with a discussion on their nature, origin, and significance.

Laparoscopic approach to a case of appendicular schwannoma

Appendicular schwannoma is a rare tumor originating from Schwann's cells in the Auerbach plexus. The preoperative diagnosis is difficult because the clinical features are nonspecific, and it is mostly found accidentally via a radiologic image as a tumor, mimicking malignancy. We report a case of an appendicular schwannoma coexisting with an adenocarcinoma in the lung. A laparoscopic appendectomy was done with a clear resection margin, and the immunohistochemical staining showed positive S-100 protein, which confirmed the schwannoma. The patient also underwent a left upper lobectomy of the lung. The patient has been free of recurrence for the 6 months since the operation. The laparoscopic approach could be available for treatment of an appendicular schwannoma, thus avoiding an unnecessary laparotomy.

Gastrointestinal stromal tumor: an ultrastructural investigation on regional differences with considerations on their histogenesis

Gastrointestinal stromal tumor (GIST) is the most frequent spindle cell tumor in the gastrointestinal tract and may arise from esophagus to rectum. The stomach is the most frequent site, followed by small intestine, rectum, and esophagus. There have been some regional differences reported in their histopathologic and clinical presentations. The purpose of this study is to compare ultrastructural features of GIST, according to its anatomic site, in order to provide additional data to support the current concept of its histogenesis. Fifty-four GISTs (27 from stomach, 23 from small intestine, and 4 from rectum) were included in the study. Histopathologically, gastric GISTs tended to be more frequently epithelioid, particularly those in children, while small intestinal GISTs (SISTs) were mostly spindly in all but three cases. All four of the rectal GISTs were spindly. Ultrastructurally, there seem to be considerable regional differences. In the majority of gastric GISTs, in both epithelioid and spindle types, tumor cells exhibited focal features of myoid differentiation evidenced by the presence of incomplete external lamina (EL) and/or focal accumulations of thin fibers with interrupted electron densities consistent with actin filaments. However, features of myoid differentiation were exceptional for SISTs and rectal GISTs, being present in only one example in each. Some gastric GISTs, particularly those having an epithelioid appearance, showed cell borders luxuriously decorated by long filopods (anemone cell features). Anemone cell features were also present in spindle cell types of gastric GISTs as well as SISTs, albeit it was simpler and less luxuriant. Skeinoid fibers were present in the majority of SISTs and rectal GISTs, but absent in all gastric GISTs except one. These differences appeared to be too significant to propose a uniform histogenesis for all GISTs. Nevertheless, on closer analysis, certain features could be identified to explain a line of differentiation in all GISTs ranging from (1) polygonal uncommitted epithelioid mesenchymal cells with cell borders decorated by luxuriant fimbria, to (2) spindly tumor cells with less prominent fimbria, or (3) cells with or without features of minimum myoid differentiation characterized by the focal presence of cytoplasmic actin fibers or incomplete EL or skeinoid fibers, which might represent an altered product of EL protein. These findings led the author to speculate that the probable primordial cells of GIST may be the primitive mesenchymal cells, which have the potential to differentiate into myoid cells. In this regard, it is important to note that the putative primordial cell of GIST, interstitial cells of Cajal (ICC), and intestinal smooth muscle cells have been shown to develop from the common progenitor cells of the primitive gut, and c-Kit plays a crucial role in the determination of their fate to differentiate to muscle cells or ICC. The author concludes that all GISTs derive from stem cells in the gut retaining some of the differentiation potential seen in primitive gut cells. One of the likely candidates for such cells in the intestinal musculature is ICC-DMP (interstitial cells of Cajal associated with deep muscular plexus) identified as ICC having smooth muscle features identified exclusively by electron microscopy. These cells have been shown to have some of the features of muscle cells by the presence of external lamina and less well-organized cytoplasmic filaments; they also express CD117 in the cytoplasm. Furthermore, recent studies demonstrated the presence of so-called progenitor cells of ICC, similar to ICC-DMP in appearance, expressing insulin-like growth factor and CD34, indicating their stem cell nature. The author proposes that all GISTs develop from the common progenitor cells similar to primitive gut cells, which may differentiate into tumor cells with more myoid features in the stomach (similar to so-called ICC-DMP) as well as spindle cells with less myoid features (similar to ICC-MP [interstitial cells of Cajal associated with the myenteric plexus] in the small intestine and rectum). ICC-DMP have been recruited in the group of ICC by electron microscopic technique alone without methylene blue stain and it is questionable whether they are part of ICC depicted by the ICC network originally shown by Dr. Cajal more than century ago. Recent discovery of their expression of insulin-like growth factors may indicate that they represent persisting primitive gut cells (gut stem cells), which may serve as the progenitor cells to GIST. It is also pointed out that in this era of ICC and GIST pandemonium, a minority of intestinal stromal tumors with mature smooth muscle features have been totally ignored; these now appear to belong to GISTs, representing the best differentiated example among the tumors developing from the same progenitor cells.

Gastrointestinal stromal tumors: a review of the literature

Gastrointestinal stromal tumors are mesenchymal neoplasms with a spectrum of histologic appearances and biologic activity. The morphologic classification of these lesions has evolved over time, and molecular analysis has led to a better understanding of their nature. The histologic differential diagnosis for these lesions is broad and includes many spindle cell lesions of the gastrointestinal tract, including neoplasms of true smooth muscle and neural origin, proliferating fibrous lesions, metastatic neoplasms, and primary sarcomas of vascular and adipose origin. Immunohistochemical studies that include CD117 have become invaluable in the classification of mesenchymal lesions arising in the gastrointestinal tract. Treatment of gastrointestinal stromal tumors has historically been involved surgery, but the use of the chemotherapeutic agent imatinib mesylate for advanced disease has made accurate classification even more important. The molecular features have not only allowed us to understand the pathogenesis of these tumors but also have proven to be associated with response to kinase inhibitors.

Gastrointestinal neuromuscular pathology: guidelines for histological techniques and reporting on behalf of the Gastro 2009 International Working Group

The term gastrointestinal neuromuscular disease describes a clinically heterogeneous group of disorders of children and adults in which symptoms are presumed or proven to arise as a result of neuromuscular, including interstitial cell of Cajal, dysfunction. Such disorders commonly have impaired motor activity, i.e. slowed or obstructed transit with radiological evidence of transient or persistent visceral dilatation. Whilst sensorimotor abnormalities have been demonstrated by a variety of methods in these conditions, standards for histopathological reporting remain relatively neglected. Significant differences in methodologies and expertise continue to confound the reliable delineation of normality and specificity of particular pathological changes for disease. Such issues require urgent clarification to standardize acquisition and handling of tissue specimens, interpretation of findings and make informed decisions on risk-benefit of full-thickness tissue biopsy of bowel or other diagnostic procedures. Such information will also allow increased certainty of diagnosis, facilitating factual discussion between patients and caregivers, as well as giving prognostic and therapeutic information. The following report, produced by an international working group, using established consensus methodology, presents proposed guidelines on histological techniques and reporting for adult and paediatric gastrointestinal neuromuscular pathology. The report addresses the main areas of histopathological practice as confronted by the pathologist, including suction rectal biopsy and full-thickness tissue obtained with diagnostic or therapeutic intent. For each, indications, safe acquisition of tissue, histological techniques, reporting and referral recommendations are presented.

Gastrointestinal stromal tumour--evolving concepts

INTRODUCTION

GISTs are rare tumours ofthe gastrointestinal tract constituting less than 1% of all primary neoplasms. They remain the commonest mesenchymal tumours of the gut. Historically they have been confused with more common tumours of smooth muscle and neurogenic origin because they share their histological features. Only in the past two decades has the identification of immunohistochemistry marker CD 117 (c-kit) greatly enhanced their diagnosis. Considerable perplexity surrounds prediction of their malignant potential because the predictive factors used can only make an approximate measurement of their behaviour.

METHODS

Medline Pubmed and Cochrane database searches were performed and the articles found were cross referenced.

CONCLUSION

GIST has an estimated annual incidence of 12-14 per million population. Stratifying into risk group remains important for prognosis and planning further follow-up. Complete excision (Ro) remains the mainstay curative treatment. Previous dismal prognosis of recurrent or metastatic disease has only recently been improved by introduction of targeted molecular anti-receptor therapy by imatinib.

Gastrointestinal stromal tumors (GISTs): a review

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms in the gastrointestinal tract, which, over the last 10 years, have emerged from a poorly understood neoplasm to a well-defined tumor entity exhibiting particular molecular abnormalities and for which promising novel treatment modalities have been developed. GISTs probably arise from the precursor cell of the interstitial cell of Cajal, express KIT tyrosine kinase in most of the cases and harbor mutations of importance for individualized treatment. The molecular targets for therapeutic interventions are not only of importance for the treatment of GIST patients but also useful for in the development of novel drug modalities and new strategies in basic cancer therapy.

Prognostic analysis of rectal stromal tumors by reference of National Institutes of Health risk categories and immunohistochemical studies

PURPOSE

Prognostic analysis of stromal tumors focusing on the rectal area is rarely performed. This study elucidated prognostic factors by referencing biomarkers of Ki67 and p53.

METHODS

Forty-nine surgically resected rectal stromal tumors were collected from 1986 to 2006. Immunohistochemical studies were performed with antibodies of CD117, CD34, smooth muscle actin, desmin, S100, Ki67, and p53.

RESULTS

The immunoreactivities were: CD34, 83.6 percent; smooth muscle actin, 28.5 percent; S100, 4.1 percent; desmin,16.3 percent;, Ki67, 30.6 percent;, and p53 34.7 percent. Both p53+ and Ki67+ tumors were associated with increased tumor mitosis, increased tumor size, nonspindle cell type, and increased cell pleomorphism (P < 0.05). Increased National Institutes of Health risk was associated with old age, nonspindle cell types, and severe nuclear pleomorphism (P < 0.05). Survival analysis demonstrated that older patients (P = 0.0039), large tumor size (P = 0.003), high mitotic count (P < 0.001), increased risk categories (P < 0.001), high cell pleomorphism (P = 0.003), p53+ (P = 0.007), and Ki67 + (P = 0.002) were prognostic factors for poor disease-free survival. An independent prognostic factor was tumor mitotic count.

CONCLUSIONS

This study demonstrated the prognostic role of Ki67 and p53 in rectal stromal tumors. Notably, tumor mitosis was superior for prognostic prediction compared to National Institutes of Health risk categories.

Hepatoma-derived growth factor is a novel prognostic factor for gastrointestinal stromal tumors

Proliferating activity as mitotic count is generally accepted as a major prognostic indicator for gastrointestinal stromal tumors (GISTs). Hepatoma-derived growth factor (HDGF) is a novel growth factor and elevated in several types of cancer. Our study was designed to elucidate the expression and prognostic role of HDGF in GISTs. A total 178 surgically resected CD117-positive GISTs specimens were collected for immunohistochemical analysis using antibodies against HDGF. The immunoreactivities were scored as labeling index (LI) and correlated with clinicopathologic parameters of GIST patients. The HDGF immunoreactivities were detected in both nucleus and cytoplasm of GISTs tissues. Besides, the nuclear and cytoplasmic HDGF was parallely upregulated in GISTs (p < 0.001). The nuclear HDGF LI were positively correlated with that of PCNA (p < 0.001) and Ki-67 (p < 0.001), tumor mitosis (p < 0.001), tumor sizes (p = 0.007) and NIH risk categories (p < 0.001). In addition, the cytoplasmic HDGF LI were also positively correlated with that of PCNA (p = 0.031) and Ki-67 (p = 0.038), tumor sizes (p = 0.003) and tumor mitosis (p = 0.015). Patients with higher HDGF levels had earlier tumor recurrence and unfavorable outcome (p < 0.05). In addition to standard prognostic factors (NIH risk categories), the nuclear HDGF LI is an independent prognostic factor for disease free and overall survivals of GIST patients after operation. We conclude that HDGF is a novel prognostic factor for GIST patients.

Clinicopathologic study of 275 cases of gastrointestinal stromal tumors: the experience at 3 large medical centers in Mexico

It is important to distinguish gastrointestinal (GI) stromal tumors (GISTs) from other GI mesenchymal tumors (GIMTs) because of the availability of molecular-targeted therapy for GISTs. The aim of the study was to reclassify GIMTs and to determine the clinicopathologic features of GISTs in Mexico. Cases of GIMT identified from the database of 3 large diagnostic centers in Mexico between 1995 and 2004 were reclassified according to current criteria. Hematoxylin and eosin-stained sections and clinical histories were reviewed, and immunohistochemistry was performed using anti-CD117, CD34, smooth muscle actin, and S-100 protein. A total of 275 GISTs were identified. The tumors were located in the stomach (40%), small intestine (35%), colorectum (12%), abdominal cavity (11%), and esophagus (2%). There were equal numbers of men and women with a mean age at diagnosis of 61 years. The tumors ranged in size from 3.5 to 34 cm (mean, 9.1 cm); 95 tumors (34%) were larger than 10 cm. Colorectal and omental tumors were the largest. The cell types included pure spindle (68%), pure epithelioid (16%), and mixed epithelioid/spindle (14%). Whereas 17.8% of tumors were regarded as low risk, 43% of tumors were in the high-risk category. CD117 positivity was detected in most of the tumors (96%). In addition to CD117, 255 cases (92%) were positive for CD34, 82 cases (32%) were positive for smooth muscle actin, and 13 cases (4.7%) were positive for desmin. Gastrointestinal stromal tumors in Mexico have the same clinicopathologic and immunohistochemical features as those reported in other countries. It is not always easy to distinguish GISTs from other soft tissue lesions. The diagnosis can be difficult even for experienced pathologists.

Comparative ultrastructural analysis and KIT/PDGFRA genotype in 125 gastrointestinal stromal tumors

GISTs are the most common mesenchymal neoplasms of the digestive tract and are thought to originate from or differentiate toward the interstitial cell of Cajal lineage. Almost all GISTs express KIT protein and the majority show activating mutations in either KIT or PDGFRA proto-oncogenes. Ultrastructurally, these tumors have been shown to have either a smooth muscle, neuronal, dual, or null phenotype. The objective of this study was to investigate the relationship between ultrastructural features and genotype in a large series of 125 histologically confirmed and CD117 positive GISTs. PCR analysis for the presence of KIT exon 9, 11, 13, and 17 and PDGFRA exon 12 and 18 mutations was performed. There were 62 (50%) tumors located in the stomach and 45 (36%) in the small bowel. Overall, KIT mutations were detected in 93 (75%) patients: 86 (69%) in exon 11, and 7 (6%) in exon 9. A PDGFRA mutation was detected in 7 (6%) cases and 25 (19%) cases had no mutation. Ultrastructurally, skeinoid fibers were seen in 55 (44%) cases and were more common in small bowel than stomach GISTs, and occurred in only in 1 of 16 patients with an ITD (KIT) exon 11 or PDGFRA mutation. Focal actin microfilaments were identified in 82 (65%) cases and did not correlate with location or mutation type. Rare neurosecretory-type granules (NS-G) were seen in 34 (27%) of cases, but were seen in most of the cells in only 5 (4%) cases. GISTs showing both NS-G and microtubules were associated with KIT exon 11 genotype and spindle cell morphology. PDGFRA mutated cases were associated with gastric location, predominantly epithelioid morphology and lacked NS-G.

Interstitial cells of Cajal in health and disease. Part II: ICC and gastrointestinal stromal tumours

Mesenchymal tumours in the gastrointestinal tract have long been problematic in terms of diagnosis, prognosis and therapy, but recent advances in immunohistochemistry and related therapies have allowed more specific diagnosis. In particular, the recognition that both the interstitial cells of Cajal (ICC) and many gastrointestinal stromal tumours (GISTs) are positive for c-kit and CD34 and have other features similar to those of ICC has led to the use of imatinib, a novel small molecule therapy that blocks the CD117/c-kit tyrosine kinase receptor, which shows remarkable efficacy in treatment of malignant and metastatic GISTs as well as other malignancies.

Interstitial cells of Cajal (ICC) and gastrointestinal stromal tumor (GIST): facts, speculations, and myths

Interstitial cells of Cajal (ICC) is a peculiar cell network composed of cells having processes described by the eminent Spanish neuroanatomist of the 19th century, S. Ramon y Cajal. ICC became a fascinating subject to many investigators and it is estimated that there are over 100 publications yearly on the subject related to ICC, in the last three years. Now it is widely accepted that ICC are pace maker cells of the gut and probable progenitor cells of gastrointestinal stromal tumors (GIST). Lately, interstitial Cajal-like cells (ICLC) are being found in various organs and their physiological role is still to be defined. We have reviewed the literature trying to evaluate the validity of the current concept and found that there are a few salient points to be considered. 1) There has been some important departure in defining the identity of ICC from the original criteria of Cajal. In particular, ICC with myoid feafures in intestinal smooth muscle layers (ICC-DPM) do not seem to fit to the original description of interstitial cell network by Cajal. We have also pointed out that the current reports assigning a pace maker role to ICC vastly depend on the scientific data on "ICC with myoid features", not on "fibroblast-like ICC", which are more abundant and easier to identify. 2) There seem to be an overwhelming amount of data proving the relationship between ICC and GIST. Both are known to express c-Kit and the ultrastructural characteristics seen in GIST roughly parallel those of ICC including minimal myoid differentiation seen in the majority of GIST, supporting the current concept that GIST are ICC tumors. 3) According to the original description of Cajal, ICC was not limited to the gut, suggesting an existence of ICC in other organs. The list of organs reported to contain ICC (currently identified by immunohistochemistry and electron microscopy) is ever growing and further studies are needed to define their identity and pathophysiologic role. 4). Recent data concerning gut development suggest that both c-Kit expressing ICC (fibroblasts-like as well as muscle-like) and gut muscle cells derive from the common progenitor cells of the embryonic gut unifying the histogenetic concept of all GIST with heterogeneous cytomorphologic features. In this review we attempted to incorporate recent information on interstitial Cajal-like cells (ICLC) found in other organs to broaden our understanding of ICC in general in terms of their ultrastructure, physiology, and neoplasia.

Pathology of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors in the gastrointestinal tract. It was found that most GIST expressed KIT, a receptor tyrosine kinase encoded by protooncogene c-kit. In normal gastrointestinal wall, KIT is expressed by interstitial cells of Cajal (ICC), which are a pacemaker for autonomous gastrointestinal movement. Because both GIST and ICC are double-positive for KIT and CD34, and because familial and multiple GIST appear to develop from diffuse hyperplasia of ICC, GIST are considered to originate from ICC or their precursor cells. It was also found that approximately 90% of the sporadic GIST have somatic gain-of-function mutations of the c-kit gene, and that the patients with familial and multiple GIST have germline gain-of-function mutations of the c-kit gene. These facts strongly suggest that the c-kit gene mutations are a cause of GIST. Approximately half of the sporadic GIST without c-kit gene mutations were demonstrated to have gain-of-function mutations in platelet-derived growth factor receptor-alpha (PDGFRA) gene that encodes another receptor tyrosine kinase. Because KIT is immunohistochemically negative in a minority of GIST, especially in PDGFRA gene mutation-harboring GIST, mutational analyses of c-kit and PDGFRA genes may be required to diagnose such GIST definitely. Imatinib mesylate was developed as a selective tyrosine kinase inhibitor. It inhibits constitutive activation of mutated KIT and PDGFRA, and is now being used for KIT-positive metastatic or unresectable GIST as a molecular target drug. Confirmation of KIT expression by immunohistochemistry is necessary for application of the drug. The effect of imatinib mesylate is different in various types of c-kit and PDGFRA gene mutations, and the secondary resistance against imatinib mesylate is often acquired by the second mutation of the identical genes. Mutational analyses of c-kit and PDGFRA genes are also significant for prediction of effectiveness of drugs including newly developed agents.

Functioning paraganglioma and gastrointestinal stromal tumor of the jejunum in three women: syndrome or coincidence

Functioning paraganglioma and gastrointestinal stromal tumor (GIST) are uncommon tumors that occur mostly in a sporadic and isolated form, occasionally as components of multiple neoplasia syndromes, either separately or together. Separately, they occur in several inherited syndromes including multiple endocrine neoplasia 2, and the GIST, lentigines, and mast cell tumor syndrome. Together, they are variably prominent components of three syndromes: the familial paraganglioma and gastric GIST syndrome, neurofibromatosis type 1, and the Carney triad. The two former conditions are inherited as autosomal dominant traits; the latter does not appear to be inherited and affects young women predominantly. This article reports the nonfamilial occurrence of functioning paraganglioma and GIST of the jejunum in 3 women, 1 young (22 years) at initial presentation. The occurrences were unexpected because of the infrequency of the tumors. The neoplasms, respectively, did not show germline SDHA, SDHB, SDHC, and SDHD, and KIT mutations associated with familial paraganglioma and familial GIST. The paraganglioma-jejunal GIST combination may be the harbinger of a rare genetic syndrome, a variant of the Carney triad or the paraganglioma-gastric stromal sarcoma syndrome, or be coincidental.

Expression and prognostic role of molecular markers in 99 KIT-positive gastric stromal tumors in Taiwanese

AIM: To elucidate the prognostic role and relationship of three molecular markers such as tumor suppressor gene p53, proliferating cell nuclear antigen (PCNA) and Ki-67 in gastric stromal tumor.

METHODS: A total of 108 surgically resected gastric smooth muscle tumor specimens were collected from January 1987 to December 1999. Immunohistochemical studies were performed on the paraffin sections of 99 of 108 CD117-positive tumors with antibodies of p53, PCNA, and Ki-67. Immunoreactivity of three molecular markers was recorded by labeling index (LI, %) and was analyzed for clinicopathologic and survival correlation.

RESULTS: Of the 99 cases, immunostaining revealed that 52 patients (52.5%) had p53, and 37 patients (37.3%) had Ki-67 immunoreactivity (defined as >10% of LI). All patients (100%) had PCNA immunoreactivity ranging from 12% to 93% of LI, divided into high or low by median. Statistics revealed that LI of three markers positively correlate to each other (P<0.01) and to microscopic tumor mitotic counts (P <0.001). By combination, patients with ≥2 markers (positive or high) in tumors had early tumor recurrence (P <0.001) and unfavorable outcome (P <0.001). Univariate analysis indicated that patients with tumor size >5 cm (P = 0.003), tumor mitosis >5/50 HPF (P < 0.001), p53 immunoreactivity (P  = 0.001), Ki-67 immunoreactivity (P =0.026), high PCNA LI (P =0.015) and male gender (P =0.036) were six predictors for early disease recurrence. Subsequent multivariate analysis revealed that mitotic counts, tumor size, and p53 immunoreactivity were three independent prognostic factors for both disease free and overall survival of patients. By combination of three independent prognostic factors for grouping, we found higher tumor recurrence rate (P <0.001) and shorter survival (P <0.001) existed in groups with increasing factors.

CONCLUSION: We first provide the prognostic value and linkage of three molecular markers in GISTs. The combination of three factors (p53, tumor size, and tumor mitosis) provides a more powerful prediction of prognosis than any single factor does.

Sporadic Cajal cell hyperplasia is common in resection specimens for distal oesophageal carcinoma. A retrospective review of 77 consecutive surgical resection specimens

Interstitial cell of Cajal (ICC) hyperplasia has been documented in conditions associated with multiple gastrointestinal stromal tumours (GISTs) (familial GIST syndromes, Carney's triad and von Recklinghausen's disease) and rarely in the vicinity of sporadic GISTs. The incidence of sporadic ICC hyperplasia and the so-called seedling leiomyoma (SLM) of the lower oesophagus has not been studied in the KIT era. In a retrospective review of 77 consecutive, routinely processed oesophagogastric resection specimens for distal oesophageal carcinoma, we found foci of ICC hyperplasia in 7 of 77 (9.1%) cases and foci of SLM in 17 of 77 (22%) cases. Two types of ICC hyperplasia were recognized: a non-circumscribed type and a nodular expansile type with peripherally compressed myenteric neural tissues. All cases of ICC hyperplasia were vimentin+/CD34+/CD117+. SLMs were desmin+/vimentin(-)/CD34(-)/CD117(-), similar to smooth muscles of the gut wall. In a prospective study of 32 non-carcinomatous specimens from age-matched patients (mostly autopsy cases), we found SLMs in only one case, but we were unable to detect ICC hyperplasia in any of the cases. We concluded that sporadic KIT-positive spindle-cell hyperplasia and SLMs were unexpectedly common in distal oesophageal specimens harbouring carcinomas. The possible mechanisms leading to the development of these putative precursor lesions will be discussed.

Gastrointestinal autonomic nerve tumours--report of a case and review of literature

BACKGROUND

Gastrointestinal autonomic nerve tumours are uncommon stromal tumours of the intestinal tract. They can involve any part of the gastrointestinal system, but are very rarely seen in the rectum.

CASE PRESENTATION

We report a unique case of rectal schwannoma with associated synchronous adenocarcinoma of the splenic flexure and adenoma of the descending colon. A 70-year-old patient was admitted with complaint of bleeding per rectum and investigations revealed the presence of a large submucosal rectal lesion in addition to the colonic pathologies. Following panproctocolectomy with permanent spout ileostomy, histopathology and immunohistochemistry confirmed the rectal lesion to be a schwannoma.

CONCLUSION

Literature review of the few reported cases has suggested radical surgical excision to be the best approach. Prognosis tends to be favourable after resection.

Gastrointestinal stromal tumors: clinical profile, pathogenesis, treatment strategies and prognosis

Abstract Gastrointestinal stromal tumors (GIST), although the most common mesenchymal neoplasms of the gastrointestinal (GI) tract, account for <1% of all GI malignancies. Up to 94% of these tumors express the CD117 antigen. Most patients present in the fifth to seventh decade, the commonest symptom being that of an abdominal mass. Surgery is the main modality of therapy, but even after adequate resection the vast majority of GIST reoccur, and in approximately 50% the liver is the main site of the metastasis. Long-term, maybe even lifelong follow up of these patients after initial resection cannot be over-emphasized. Initial tumor size and mitotic rate are the most useful parameters to predict malignant potential. In view of high postoperative recurrence, adjuvant forms of therapy are being explored, and the tyrosine kinase inhibitor imatinib holds the most promise.

Primitive mesenteric gastrointestinal stromal tumor with autonomic nerve/ganglionic differentiation presenting as a huge mass with small synchronous nodules

We present a case of a primary mesenteric ectopic gastrointestinal stromal tumor. The pathologic characteristics of this neoplasm, autonomic nerve/ganglionic differentiation and presentation as a huge mass with small synchronous nodules, have not been previously described in the literature.

Gastrointestinal autonomic nerve tumors: A surgical point of view

AIM: Gastrointestinal autonomic nerve tumors are uncommon stromal tumors of the intestinal tract. Their histological appearance is similar to that of other gastrointestinal stromal tumors. We report two cases and performed an analysis of the literature by comparing our findings with the available case reports in the medical literature.

METHODS: Two patients were admitted with abdominal tumor masses. One occurred in the stomach with large multiple liver metastases and the second originated in Meckel´s diverticulum. The latter site has never been reported previously. Both patients underwent surgery. In one patient gastrectomy, right liver resection and colon transversum resection were performed to achieve aggressive tumor debulking. In the other patient the tumor bearing diverticulum was removed.

RESULTS: Postoperative recovery of both patients was uneventful. Histological examination, immunohistochemical analysis and electron microscopy revealed the diagnosis of a gastrointestinal autonomic nerve tumor. The patient with the tumor in Meckel’s diverticulum died 6 mo after surgery because of pneumonia. The patient with liver metastases have been alive 13 years after initial tumor diagnosis and 7 years after surgery with no evidence of tumor progression. In light of our results, we performed a thorough comparison with available literature reports.

CONCLUSION: Radical surgical resection of gastrointestinal autonomic nerve tumors seems to be the only available curative approach to date, and long term survival is possible even in large metastasized tumors.

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.

Prognostic assessment of gastrointestinal stromal tumor

The term "gastrointestinal stromal tumor" (GIST) has been applied to a collection of distinctive mesenchymal tumors occurring within the human gastrointestinal tract. As new drug therapy becomes available, data regarding the natural history of these unusual tumors are necessary to provide selection factors for treatment. Ninety-eight patients had light microscopy compatible with GIST at a single institution from 1989 to 2000. After immunostaining with c-kit and histopathologic review, 69 were judged to be GIST. All prognostic indicators were determined for gastric GIST, intestinal GIST, and all locations combined. The location of the GIST did not have a significant impact on survival. Clinically, tumor size, peritoneal cancer index, and completeness of cytoreduction had a significant impact on prognosis for GIST at all locations. Pathologically, cytologic atypia, necrosis, invasion and number of mitoses were significant prognostic indicators for GIST. Criteria to separate three pathologic groups of GIST according to the tumor size and the mitotic count were useful to evaluate the tumor behavior; in the borderline pathologic group invasion and cytologic atypia were statistically significant prognostic criteria. The cell phenotypes, as determined by immunostains, correlated with the prognosis of gastric GIST but not intestinal GIST. A correlation between the immunostain Ki-67 but not CD-34 or desmin and the prognosis was observed. It is possible to select clinical and pathologic parameters of GIST that impact on prognosis. Invasion and necrosis help to determine the prognosis with borderline tumors. The immunostain Ki-67 correlated with the prognosis and may be helpful to assess prognosis when dealing with small biopsy specimens.

Frequent occurrence of low grade cases among metastatic gastrointestinal stromal tumours

AIM

Gastrointestinal stromal tumours (GISTs) are uncommon mesenchymal neoplasms. Some metastasise, whereas others remain asymptomatic for years, but it is difficult to distinguish between them histologically. This report analyses the characteristics of seven metastasising GISTs and compares clinicopathological parameters of the metastatic and non-metastatic groups.

METHODS/RESULTS

Histology revealed typical GIST features with spindle, epithelioid, or mixed appearance. All seven cases were positive for vimentin, five for neurone specific enolase, six for c-kit, four for S-100, three for PGP-9.5, three for CD-34 and synaptophysin, but all were negative for cytokeratin, neurofilament, chromogranin A, and desmin. Four showed a focal reaction for smooth muscle actin. Three of the tumours were GI, and two each were GII and GIII. The Ki-67 index varied from 4% to 44%, the three GI cases had 4%, 10%, and 16%. Tumours from the metastatic GIST group were significantly larger than those from the non-metastatic group.

CONCLUSIONS

Three cases exhibited bland, GI histological features with moderate or low proliferative activity. Among the c-kit positive metastasising stromal tumours, some were low grade, with moderate or low mitotic and Ki-67 indices, emphasising the necessity to develop a reliable grading system for GIST to predict clinical behaviour, the importance of careful analysis of "benign looking" tumours, and the key role of c-kit status in identifying patients who could benefit from treatment with STI-571. Larger tumours had a higher chance of metastasising, and only the size of the primary tumour played a role in predicting metastatic potential.

The reappraisal of gastrointestinal stromal tumors: from Stout to the KIT revolution

For five decades gastrointestinal stromal tumors (GISTs) truly have represented one of the most confusing as well as neglected areas of both surgical pathology and clinical oncology. The recognition of the central role played by KIT expression in the development of the interstitial cell of Cajal and of the activating KIT mutations in the pathogenesis of GIST have been the keys for a more precise categorization of this long elusive clinicopathological entity. A Consensus Conference held at the National Institutes of Health in 2001 provided both an evidence-based definition and a practical scheme for the assessment of the risk of aggressive clinical behavior. This scheme is based on evaluation of the size and mitotic rate of the tumors, and its use is strongly advocated. On the basis of current data GISTs can be defined as a distinctive group of KIT-expressing mesenchymal neoplasms of the gastrointestinal tract, showing differentiation towards the interstitial cell of Cajal, also known as the gastrointestinal pacemaker cells. Metastatic GISTs have been a virtually incurable disease until the elucidation of the role of KIT mutations. STI-571 (imatinib mesylate) is a molecule that inhibits the function of various receptors with tyrosine kinase activity, such as abl, the bcr-abl chimeric product, platelet-derived growth factor receptor, and KIT. Following its successful use in the treatment of chronic myeloid leukemia, STI-571 has also proved extremely effective in targeting metastatic GIST. Data regarding the duration of the response to this therapy are not yet available, and therefore any overenthusiasm should be avoided. Nonetheless, the GIST story remains paradigmatic of a totally innovative approach to cancer therapy which until now is the most elegant translation of cancer biology experimental knowledge into clinical practice.

Three Cases of Canine Gastrointestinal Stromal Tumors with Multiple Differentiations and c-kit-Expression

Three canine gastrointestinal stromal tumors (GISTs) were examined. Histopathologically, the tumor mass in the jejunum (Case 1) consisted of the proliferation of epithelioid cells with abundant eosinophilic or vacuolated cytoplasm. Gangliocyte-like or multinucleated giant cells were scattered. The tumor cells exhibited neural natures mimicking human gastrointestinal autonomic nerve tumors, which were immunopositive for several neuronal markers. Another jejunal mass (Case 2) was composed by a solid proliferation of spindle-shaped cells, arranging in interlacing fascicles and occasional storiform pattern. The tumor seemed to be classified undifferentiated GISTs, that showed no apparent neural or muscular features by ultrastructural and immunohistochemical examinations. In the pyloric mass (Case 3), the spindle cells having eosinophilic processes and elongated nuclei were arranged in sheets. Immunohistochemically, the tumor cells showed muscular natures as regards alpha smooth muscle actin and desmin expression.

The GIST of targeted cancer therapy: a tumor (gastrointestinal stromal tumor), a mutated gene (c-kit), and a molecular inhibitor (STI571)

Although gastrointestinal stromal tumor (GIST) is the most frequent mesenchymal neoplasm of the gastrointestinal tract, until recently it has been an obscure disease. Now, there is widespread scientific and clinical interest in GIST because its principal pathogenetic defect has been identified and a specific molecular inhibitor of GIST has been developed. Most GISTs contain a gain-of-function mutation in the c-kit proto-oncogene. Mutation results in constitutive activation of the Kit receptor tyrosine kinase, which induces cellular proliferation. STI571 is an oral agent that selectively inhibits Kit. It is a landmark development in cancer treatment and marks a new era of targeted molecular therapy. Its efficacy proves that a specific inhibitor can counteract the effects of a genetic defect responsible for neoplasia. Although STI571 was first applied to GIST only 2 years ago, it has already revolutionized the treatment of patients with metastatic disease and is also currently being tested as an adjuvant therapy after the resection of primary GIST.