Small and microscopically detected gastrointestinal stromal tumours: an overview

Gastrointestinal Stromal Tumors: A Single Institution Experience of 176 Surgical Patients

Large single-institution series of patients undergoing resection for gastrointestinal stromal tumors (GIST) are lacking. Clinicopathologic characteristics and postoperative outcomes were retrospectively collected and analyzed from patients undergoing resection for GIST from 2002 to 2011. One hundred seventy-six patients were identified; 156 underwent resection of primary nonmetastatic disease. KIT mutations were identified in 131 patients (84.0%). Of the 156 patients with primary disease, the most common site was the stomach (75.6%). Tumors were categorized as very low (24.4%), low (35.9%), intermediate (12.2%), high (24.4%), or unknown (3.2%) risk. Symptomatic patients more often had high risk (35.6 vs 9.8%; P < 0.0001) and larger tumors (7.3 vs 3.0 cm; P < 0.0001). Forty-seven patients (30.1%) underwent laparoscopic resection (LR). Compared with open surgery, LR was performed for smaller tumors (3.8 vs 6.2 cm; P = 0.002). Positive margin rates were similar (4.3% LR vs 10.2% open; P = 0.346). Median follow-up for the 156 patients with primary tumors was 32.9 months; mean overall survival was 120.9 months (median not reached). Of the 20 patients with metastatic GIST (excluded from above analysis), five patients (25.0%) died of disease with a median follow-up of 15.9 months. Most patients with resectable primary GIST have a favorable prognosis. The presence of symptoms directly related to GIST may be associated with a poor prognosis and is likely related to increased tumor size. Laparoscopic resection is well tolerated and does not appear to compromise outcomes in well-selected patients. Highly selected patients with metastatic disease may benefit from resection.

Population-based incidence of gastrointestinal stromal tumors in Puglia

INTRODUCTION

This study presents the incidence of gastrointestinal stromal tumors (GISTs) in an Italian region of over 4 million inhabitants monitored for 10 years and is the largest incidence study of this type of cancer conducted so far in Italy.

METHODS

In order to ensure the registration of all GISTs, including those with nonmalignant behavior, a cancer list was integrated with the cases found through an ad hoc data mining process that covered all the pathologic reports of Puglia. Case distributions by sex, age groups, site, and prognostic groups according to Miettinem and Lasota classification and crude and age-standardized incidence rates were produced.

RESULTS

In the 10-year period 2006 to 2015, 708 cases of GIST were recorded in Puglia. The average crude incidence rate was 1.7 per 100,000 person-years and the age-standardized incidence rate, using 2013 European standard population, was 1.8 per 100,000 person-years (95% confidence interval [CI], 1.6-1.9). Incidence was higher in men than in women: crude incidence rate was 2.0 per 100,000 person-years and age-standardized incidence rate 2.2 per 100,000 person-years (95% CI, 2.0-2.4) in men and 1.5 per 100,000 person-years and 1.4 per 100,000 person-years (95% CI, 1.2-1.6) in women.

DISCUSSION

Our incidence rates are comparable with those of other international studies and they are located in the medium to high end of the range. The comparisons are affected by a different capacity of the cancer registries to intercept and record GISTs with nonmalignant behavior. Distribution of cases for sex, age groups, sites, and prognostic risk groups are consistent with previous results.

Clinical and pathological features of "small" GIST (≤2 cm). What is their prognostic value?

INTRODUCTION

Small GIST (<2 cm) are tumors whose biological behavior is benign and frequently involutes. Despite their increasing incidence, few studies have addressed the characteristics of these GIST. The aim of this work is to clarify the management of this entity.

PATIENTS AND METHOD

The characteristics of ≤2 cm GIST were initially described, and then compared with those >2 cm. This series comprises 104 patients and they were divided according to tumor size in 4 groups: tumors which are ≤2 cm (group 1, G1), >2 and ≤ 5 cm (G2), >5 and ≤ 10 cm (G3) and >10 cm (G4).

RESULTS AND DISCUSSION

Most of small GIST were asymptomatic and incidental, and were located in the stomach. There is an association between patients with associated tumors and asymptomatic GIST. A high overall mortality rate of up to 40% is observed being disease-specific mortality 4.5%. The disease-specific mortality increases proportionally with size. The overall survival (OS) at 5 years are lower for both <2 cm (61%) and >10 cm (53%) than the rest (85-91%). When analyzing the impact of tumor association on <2 cm GIST, we observed that the OS of patients with non-associated tumors was much higher than in the associated ones (90% vs 32% at 5 years, respectively), while no differences were observed in the disease specific survival.

CONCLUSIONS

Small GIST are tumors that are very often incidentally discovered in the course of complementary examinations. Its prognosis is very good, but it depends on the associated tumor.

Population-Based Epidemiology and Mortality of Small Malignant Gastrointestinal Stromal Tumors in the USA

BACKGROUND AND AIMS

Gastrointestinal stromal tumors (GISTs) have significant variability in size and malignant behavior. Our current understanding is limited to pathological analyses, autopsy studies, and small case series. The aim of the current study is to define the risk factors, incidence, and mortality rates of GIST <2 cm in the National Cancer Institute's Surveillance, Epidemiology, and End Results database.

METHODS

Patients with histologically confirmed malignant GIST <2 cm were studied from 2001 to 2011. GIST was defined by GI tumor site codes and GIST-specific histology codes.

RESULTS

We identified 378 patients with GIST <2 cm. The average age at diagnosis was 64.0 years with equal sex distribution. The most common tumor location was the stomach (62.2 %), followed by the small intestine (23.3 %), colon (5.6 %), and rectum (3.4 %). Most patients had localized disease (79.4 %), but 11.4 % had regional/distant metastatic disease. The annual incidence rate was 4.2 per 10,000,000 (10M). This was the highest among Blacks (7.6 per 10M). Among patients with GIST and no additional cancers, the 5-year GIST-specific mortality was 12.9 %. Moreover, there was a significantly increased 5-year GIST-specific mortality in those patients who had regionally advanced (34.0 %) or metastatic GIST (34.3 %), as compared to those patients with localized GIST (5.6 %).

CONCLUSIONS

This study represents the first population-based analysis of malignant GIST <2 cm. While quite rare, these tumors have an underappreciated disease-specific mortality. Further studies are needed to define the underlying reasons for the identified racial differences, to develop novel risk assessment schema for patients with these small tumors, and to determine appropriate indications for resection and/or medical therapy.

Clinicopathological features and prognosis of small gastrointestinal stromal tumors outside the stomach

The aim of the present study was to assess the clinicopathological features and prognostic factors of primary small gastrointestinal stromal tumors (GISTs) outside the stomach. The clinical data, clinicopathological features and prognostic factors of 20 patients with a pathologically-confirmed diagnosis of non-gastric GIST that were treated at Liaoning Cancer Hospital & Institute between July 2006 and December 2013 were retrospectively analyzed. In total, 15 patients were male and 5 were female, with a median age of 58 years (range, 44–82 years). A change in bowel habits was the original symptom of rectal small GISTs in 6 out of 8 patients, while patients with small GISTs in other locations demonstrated no overt symptoms and the lesions were detected by systematic examinations of other diseases or abdominal surgical procedures performed on other organs. In total, 19 patients out of the total 20 patients underwent surgery, and 1 patient with rectal GIST received continuous oral imatinib mesylate (400 mg once a day) instead of undergoing surgery. The mean diameter of tumors was 1.55±0.54 cm (range, 0.3–2.0 cm) and the median was 1.70 cm. The pathomorphology of the lesions was mainly spindle cell, and immunohistochemistry revealed the expression rate of cluster of differentiation (CD)117, CD34 and discovered on GIST-1 were 85, 80 and 70%. According to the mitosis index, small rectal GISTs were more frequent compared with other positions (P<0.05), while the frequency of small GISTs >1 cm in size was not significantly different from the frequency of small GISTs ≤1 cm in size (P=0.995). All 20 patients were followed up, with a median follow-up duration of 49.5 months (range, 10.5–94.4 months). At the end of the follow-up period, tumor recurrence occurred in 5 patients and 1 patient succumbed following progression. According to the analysis of the tumor sites, the RFS time of patients with small rectal GISTs was significantly different than the RFS time in patients with small GISTs in other positions. The clinical symptoms of non-gastric small GISTs were not evident and were challenging to detect. Small GISTs, regardless of size, possessed malignant potential and once detected, GISTs should be surgically resected. Lesions located in the rectum demonstrated an increased degree of malignancy and were more likely to recur. The tumor size and Ki67 index could not be considered as prognostic factors of non-gastric small GISTs.

A case of diffuse infiltrating gastrointestinal stromal tumor of sigmoid colon with perforation

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract, and typically present as discrete well-circumscribed but non-encapsulated tumor masses. In this report, we describe a case of colonic perforation caused by an unusual form of GIST. A 72-year-old Japanese woman presented to the emergency department with acute abdominal pain. Under the provisional diagnosis of sigmoid colon perforation, a laparoscopic sigmoidectomy was performed. Although the tumor mass was undetectable during the preoperative examination, a spindle cell lesion with a diffuse longitudinal growth pattern replacing the muscularis propria was revealed by microscopic examination. The spindle cell lesion was exposed at the perforation, suggesting a causal relationship between the lesion and the perforation. The spindle cell lesion was KIT-positive and had a mutation in the C-KIT gene at exon 11. We diagnosed it as diffuse infiltrating GIST. We consider that the lesion would be a cause of the colonic perforation, and emphasize the importance of accurate diagnosis of the lesion by histological, immunohistochemical and genetic examinations.

Ten-year review of gastrointestinal stromal tumours at a tertiary referral hospital in New Zealand

BACKGROUND

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal tumours of the gastrointestinal tract and make up 1-2% of all gastrointestinal malignancies. Traditionally, the treatment of choice for primary disease is surgical resection; however, no single surgeon or institution gets extensive exposure to these patients so appropriate decision-making is difficult, particularly since the introduction of the tyrosine kinase inhibitor imatinib, which has become an important additional management tool.

METHOD

All patients were diagnosed and treated for GISTs in Christchurch Hospital (Christchurch, New Zealand) between 1 January 2000 and 31 December 2010. We maintain a prospective database of all patients with GISTs. Data on clinical and histopathological variables, management and survival outcomes were recorded. These were then reviewed.

RESULTS

There were 93 patients in this study. Fifty were women. Median age was 69 (interquartile range (IQR) 59-76) years. Fifty-one tumours were located in the stomach, 27 in the small bowel, six in the colon, three in the oesophagus, one in the rectum and five were extra-gastrointestinal. In total, 22 patients received imatinib therapy; four patients with metastatic disease had imatinib as sole therapy. The median follow-up was 58 (IQR 30-90) months. The 5-year overall survival and disease-free survival (DFS) for the entire study population was 69% and 64%, respectively. The 5-year DFS was higher for all patients who have localized disease when compared with those who have metastatic disease (76% versus 28%, P-value 0.001).

CONCLUSION

Surgery aiming at an R0 resection remains the mainstay of treatment. We propose the most effective way to grow the knowledge base in New Zealand is the establishment of a national register, thereby allowing better clinical decision-making by interpretation of a larger data set.

A multidisciplinary approach to the diagnosis and treatment of gastrointestinal stromal tumor

Management of patients with gastrointestinal stromal tumor (GIST) typically involves a combination of surgical, pathologic, and pharmacologic interventions. Gastroenterologists are often the first specialists to encounter patients presenting with GIST and are therefore responsible for facilitating early intervention strategies. Although patients with gastric or small-bowel GISTs typically present with symptoms, a diagnosis of GIST should be considered whenever a submucosal lesion is seen endoscopically. Visualization by standard endoscopy often can determine tumor location and size, although endoscopic ultrasound (EUS) is the most accurate imaging technique for submucosal lesions. Biopsy techniques that yield sufficient tumor samples for diagnostic studies, such as EUS-guided fine needle aspiration, are essential, although other approaches such as EUS-guided core needle biopsy may increase diagnostic yield for subepithelial lesions. Pathology assessment should include immunohistochemical staining for KIT and possibly DOG1 expression, and mutational analysis can have prognostic and predictive value for certain patients. R0 resection is the goal for patients with localized or potentially resectable tumors, which often can be accomplished by laparoscopic resection, even for larger tumors. Medical oncologists play a key role in assessing risk of recurrence after resection and optimizing tyrosine kinase inhibitor therapy in the adjuvant or metastatic setting. Cytoreductive surgery may have value for patients with recurrent or metastatic GIST who exhibit stable disease or respond to tyrosine kinase inhibitor therapy. A coordinated multidisciplinary approach over the course of the disease will serve to enhance communication among GIST team members, reduce risk of progression, and optimize outcomes.

KIT gene mutation analysis in solid tumours: biology, clincial applications and trends in diagnostic reporting

Gain-of-function mutations involving c-kit protein, a cell-surface transmembrane receptor for stem cell factor, have been identified as a key oncogenic driver in a variety of solid tumours. Coupled with the development of tyrosine kinase inhibitors such as imatinib, c-kit has emerged as a viable drug target in what seems to be a validated therapeutic concept. This review will focus on gastrointestinal stromal tumours and melanomas, two types of solid tumours most closely associated with KIT gene mutations. The biology of KIT mutations in both conditions, as well as the value of KIT mutation testing in predicting disease and treatment outcomes are discussed. Since initial response to imatinib is largely influenced by mutation status, genotyping these tumours serves to facilitate personalised oncology. We also summarise our experience with diagnostic reporting of KIT mutation analysis over a period of 3 years, and briefly survey future developments in treatment, which indeed look very promising.

Promoting role of cholecystokinin 2 receptor (CCK2R) in gastrointestinal stromal tumour pathogenesis

The cholecystokinin 2 receptor (CCK2R/CCKBR) is expressed in gastrointestinal stromal tumours (GISTs). We sought to investigate the role of CCK2R in GIST pathogenesis. Molecular characterization of CCK2R was performed on a heterogeneous cohort of 50 GISTs. In addition, CCK2R expression was evaluated by immunohistochemistry (IHC), using tissue microarray (TMA) containing 292 GISTs, two cases of hyperplasia of interstitial Cajal's cells (ICC) and six gastric microscopic GISTs. Mono-allelic loss of the CCK2R/11p15 allele was identified in 13.7% of GISTs, having no impact on the level of CCK2R transcript expression. No CCK2R mutations were found. The CCK2Ri4sv, CCK2R splice variant with retention of intron 4 was detected in six of 20 tumours analysed. Wild-type CCK2R transcripts were commonly expressed (57.1% of cases) and this expression was highly correlated with gastric primary site of GISTs (p < 0.001). At the protein level, expression of CCK2R in incidental ICC hyperplasia and early stages of gastric GIST development was documented, and its gastric association was confirmed on GIST-TMA by IHC. To explore the in vivo effect of CCK2R activation on tumour growth, gastrin versus placebo was administered intraperitoneally in nude mice carrying human GIST xenografts. The tumour volume was followed for 10 weeks. The effect of this stimulation on tumour cell proliferation/apoptosis was assessed by IHC and KIT/PKC-θ signalling was evaluated by western blotting (WB). In vivo experiments showed a two-fold increase in the volume of tumours which were exposed to gastrin in comparison with non-exposed controls (p = 0.03), with a significant increase in mitotic activity (p = 0.04) and Ki-67 proliferation index (p = 0.008). By WB, gastrin stimulation resulted in hyper-activation of KIT and PKC-θ kinases, and in evident PI3K-AKT pathway over-activation. Our results indicate a promoting role of CCK2R on GIST tumourigenesis, particularly in tumours of gastric origin.

Endoscopic management of gastrointestinal stromal tumors

Subepithelial lesions are increasingly being identified with improved endoscopic imaging technologies. Many of these lesions are now recognized as gastrointestinal stromal tumors (GISTs). Recent advances in immunohistochemistry have allowed for reliable differentiation of GISTs from other subepithelial tumors, thereby significantly improving our understanding of these lesions. The wealth of recent information and continual evolution in our understanding of GISTs has exposed some knowledge gaps pertaining to the optimal management of these lesions. In this article, we review the endoscopic management of GISTs as it relates to the identification, diagnosis and management of these lesions based on the best available literature and our own clinical experience to date.

Selected unusual tumors of the stomach: a review

Several unusual stomach tumors have been recently described. In addition, some tumors that are often encountered in other sites may rarely occur as primary gastric tumors. The diagnostic surgical pathologist needs to be aware of some of these lesions to prevent misdiagnosis. This overview discusses the key clinical features, pathology, immunohistochemistry, and relevant molecular findings of multiple minute gastrointestinal stromal tumors and interstitial cell of Cajal hyperplasia, nerve sheath tumors (schwannoma and perineurioma), gastroblastoma, granular cell tumor, glomus tumor, plexiform angiomyxoid myofibroblastic tumor, and primary clear cell sarcoma of the gastrointestinal tract that occur as primary gastric neoplasms.

Frequency, phenotype, and genotype of minute gastrointestinal stromal tumors in the stomach: an autopsy study

Gastrointestinal stromal tumors are the most common mesenchymal tumors of the human digestive tract. Up to 85% of these tumors show somatic gain-of-function mutation of the receptor tyrosine kinase c-KIT gene. A recent study has shown a high frequency (22.5%) of minute gastrointestinal stromal tumors in stomachs examined during routine autopsies. The aims of our study were to confirm the previously reported incidence of gastric gastrointestinal stromal tumors in routine autopsies and to investigate their molecular alterations. Gastrointestinal stromal tumors were collected prospectively from 578 autopsies over an 18-month period. After recording the size and location of each lesion, representative tissue samples were processed for hematoxylin and eosin staining and immunohistochemically stained for CD117 and CD34. Microdissected DNA from all identified gastrointestinal stromal tumors was studied for c-KIT and platelet-derived growth factor receptor α mutations. We identified 17 gastrointestinal stromal tumors in 578 consecutive autopsies (2.9%) located in the gastric body (47%) and fundus (47%). One tumor location was not recorded. All tumors were immunohistochemically positive for CD117 and CD34. DNA analysis showed c-KIT mutations in 11 cases. One platelet-derived growth factor receptor α mutation was found. The incidence of gastric minute gastrointestinal stromal tumors (2.9%) is higher than the reported clinical incidence. All are benign tumors, and most, including minute tumors, contain c-KIT mutations. This finding highlights the fact that c-KIT mutations are an early event in the evolution of gastrointestinal stromal tumors but are not sufficient per se for clinically relevant disease.

NCCN Task Force report: update on the management of patients with gastrointestinal stromal tumors

The standard of care for managing patients with gastrointestinal stromal tumors (GISTs) rapidly changed after the introduction of effective molecularly targeted therapies involving tyrosine kinase inhibitors (TKIs), such as imatinib mesylate and sunitinib malate. A better understanding of the molecular characteristics of GISTs have improved the diagnostic accuracy and led to the discovery of novel immunomarkers and new mechanisms of resistance to TKI therapy, which in turn have resulted in the development of novel treatment strategies. To address these issues, the NCCN organized a task force consisting of a multidisciplinary panel of experts in the fields of medical oncology, surgical oncology, molecular diagnostics, and pathology to discuss the recent advances, identify areas of future research, and recommend an optimal approach to care for patients with GIST at all stages of disease. The task force met for the first time in October 2003 and again in December 2006 and October 2009. This supplement describes the recent developments in the field of GIST as discussed at the October 2009 meeting.

Gastrointestinal Stromal Tumors: A Guide to the Diagnosis

Gastrointestinal stromal tumors (GISTs) have emerged from being a poorly understood and therapeutically refractory sarcoma to a tumor whose biology has not only provided insight into a mechanism of oncogenesis but has also led to a rational basis for therapy. Most GISTs are characterized by KIT protein (CD117) expression and constitutive activating mutations in either the c-kit or platelet-derived growth factor receptor α genes. This information can now be obtained from routine formalin-fixed and paraffin-embedded tissue. Because the correct diagnosis is the key to successful treatment of this tumor, it is incumbent on the pathologist to be familiar with the various gross and histologic patterns shown by these tumors. GISTs range from small incidental stromal nodules to large cystic and solid tumor masses. GISTs show a variety of microscopic patterns and therefore several other tumors enter the differential diagnosis. Fortunately, with an understanding of GIST histology, and with the proper use of immunohistochemistry and molecular analysis, a correct diagnosis can usually be made. In addition to the correct diagnosis, several key attributes of the tumor need to be determined because they provide the basis for proper clinical management. This article summarizes the gross, microscopic, and molecular findings of GISTs, and discusses the differential diagnosis and key attributes of this interesting group of neoplasms.

Targeted therapies of gastrointestinal stromal tumors (GIST)--the next frontiers

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal (GI) tract and are caused by activating KIT or PDGFRA mutations. GISTs can be successfully treated with the small molecule kinase inhibitor imatinib mesylate (Gleevec, Novartis) with response rates of up to 85%. However, complete responses are rare, and most patients will develop imatinib resistance over time. Recent results have shown that although imatinib effectively stimulates apoptotic cell death in sensitive GIST cells, a considerable proportion of cells does not undergo apoptosis, but instead enters a state of quiescence. Quiescence is characterized by a reversible withdrawal from the cell division cycle, during which the cells remain alive and metabolically active. It is conceivable that quiescence not only plays a pivotal role in the emergence of residual disease but also in creating a pool of tumor cells that survive continuous small molecule therapy and may hence represent the "seeds" for the outgrowth of resistant clones. This review will summarize the current knowledge about GIST biology and treatment response to imatinib including the induction of cellular quiescence in GIST. In addition, we will highlight future strategies to design more effective treatment options to overcome these problems with an aim towards cure of this hitherto untreatable tumor entity.

NCCN Task Force report: update on the management of patients with gastrointestinal stromal tumors

The standard of care for managing patients with gastrointestinal stromal tumors (GISTs) rapidly changed after the introduction of effective molecularly targeted therapies involving tyrosine kinase inhibitors (TKIs), such as imatinib mesylate and sunitinib malate. A better understanding of the molecular characteristics of GISTs have improved the diagnostic accuracy and led to the discovery of novel immunomarkers and new mechanisms of resistance to TKI therapy, which in turn have resulted in the development of novel treatment strategies. To address these issues, the NCCN organized a task force consisting of a multidisciplinary panel of experts in the fields of medical oncology, surgical oncology, molecular diagnostics, and pathology to discuss the recent advances, identify areas of future research, and recommend an optimal approach to care for patients with GIST at all stages of disease. The task force met for the first time in October 2003 and again in December 2006 and October 2009. This supplement describes the recent developments in the field of GIST as discussed at the October 2009 meeting.

Advances in pathological diagnosis of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. The pathogenesis of GIST may be associated with the mutations of oncogenic c-kit or platelet-derived growth factor receptor alpha (PDGFRA). The pathological diagnosis of GIST needs a combined approach of macropathology, histopathology, immunohistochemistry and gene testing. Preoperative diagnosis is very important for patients with GIST, especially for those needing individualized treatment. In this article, we will review the recent advances in pathological diagnosis of GIST and the consensus criteria for risk stratification of GIST. Besides, we will also summarize the molecular biological parameters used for evaluation of the biological behavior of GIST.

Gastrointestinal stromal tumors: report of an audit and review of the literature

Gastrointestinal stromal tumors (GISTs), tumors characterized by c-KIT mutations, are the most frequent mesenchymal tumors of the digestive tract. The stomach is the most commonly involved site. Localization, size and mitotic rate are reliable predictors of survival and the two milestones of GISTs treatment are surgery and imatinib. This article is aimed to report the data of an audit, carried out on the morphological and clinical aspects of the disease and to review the present knowledge on GISTs. A total of 172 patients with GISTs (M : F=1 : 1; mean age 65 years) were recruited. The stomach was the most frequently involved site. In 50% of the cases the tumor was smaller than 5 cm, whereas major symptoms were observed in 43% of the cases. Predictors of progressive disease were present only in a small percentage of cases but the disease was in the metastatic phase in over 25% of the cases at diagnosis. Familial aggregation was rare but a consistent share of the patients (21%) had other synchronous or metachronous cancers. The most frequent mutations were in-frame deletions and point mutations of c-KIT exon 11. This report confirms in part the available data on GIST in a consecutive series of patients recruited in Italy and shows that only large collaborative multicenter studies provide data sound enough to enable making reasonable clinical and therapeutic choices, and suggests that, as a measure of secondary prevention, a diagnostic definition should be obtained in all submucosal lesions of the GI tract and that GIST patients should be screened for second tumors.

[Gastrointestinal stromal tumors. Diagnosis and estimating aggressiveness]

A diagnosis of gastrointestinal stromal tumor must be considered if a mesenchymal tumor is localized in the gastrointestinal tract, especially in the stomach. In daily practice diagnosis is based on the histology (cellular features and histologic architecture) and immunohistochemistry (cellular positivity with antibodies to CD117 and often to CD34). Expression of CD117 indicates the autoactivation of a type-III-receptor tyrosine kinase mediated by mutation of the KIT gene. This is lacking in the roughly 5% of cases which instead show a mutation of the PDGF receptor alpha gene. The estimation of dignity is difficult and can be uncertain in some cases. A malignancy grading according to the procedure in soft tissue tumors is not possible. Nowadays, however, the general consensus is that size of the tumor and number of mitoses are the most important criteria for appraising tumor aggressiveness and risk of metastasis. The tumor localization was later added to these criteria. Recent years have shown that mutation analysis can also provide information for judging tumor aggressiveness and predicting possible metastasis and response to therapy.