Gastrointestinal stromal tumors/smooth muscle tumors (GISTs) primary in the omentum and mesentery: clinicopathologic and immunohistochemical study of 26 cases

Development and validation of a prognostic nomogram for recurrence-free survival after complete surgical resection of localised primary gastrointestinal stromal tumour: a retrospective analysis

BACKGROUND

Adjuvant imatinib mesylate prolongs recurrence-free survival (RFS) after resection of localised primary gastrointestinal stromal tumours (GIST). We aimed to develop a nomogram to predict RFS after surgery in the absence of adjuvant therapy to help guide patient selection for adjuvant imatinib therapy.

METHODS

A nomogram to predict RFS based on tumour size (cm), location (stomach, small intestine, colon/rectum, or other), and mitotic index (<5 or > or =5 mitoses per 50 high-power fields) was developed from 127 patients treated at Memorial Sloan-Kettering Cancer Center (MSKCC), New York, NY, USA. The nomogram was tested in patients from the Spanish Group for Research on Sarcomas (GEIS; n=212) and the Mayo Clinic, Rochester, MN, USA (Mayo; n=148). The nomogram was assessed by calculating concordance probabilities and testing calibration of predicted RFS with observed RFS. Concordance probabilities were also compared with those of three commonly used staging systems.

FINDINGS

The nomogram had a concordance probability of 0.78 (SE 0.02) in the MSKCC dataset, and 0.76 (0.03) and 0.80 (0.02) in the validation cohorts. Nomogram predictions were well calibrated. Inclusion of tyrosine kinase mutation status in the nomogram did not improve its discriminatory ability. Concordance probabilities of the nomogram were better than those of the two NIH staging systems (0.76 [0.03] vs 0.70 [0.04, p=0.04] and 0.66 [0.04, p=0.01] in the GEIS validation cohort; 0.80 [0.02] vs 0.74 [0.02, p=0.04] and 0.78 [0.02, p=0.05] in the Mayo cohort) and similar to those of the AFIP-Miettinen staging system (0.76 [0.03] vs 0.73 [0.004, p=0.28] in the GEIS cohort; 0.80 [0.02] vs 0.76 [0.003, p=0.09] in the Mayo cohort). Nomogram predictions of RFS seemed better calibrated than predictions made with the AFIP-Miettinen system.

INTERPRETATION

The nomogram accurately predicts RFS after resection of localised primary GIST and could be used to select patients for adjuvant imatinib therapy.

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.

Gastrointestinal stromal tumors presenting as omental masses--a clinicopathologic analysis of 95 cases

Gastrointestinal stromal tumors (GISTs), generally KIT-positive and KIT/PDGFRA mutation-driven mesenchymal neoplasms, most commonly originate from the stomach or small intestine, but in rare examples they involve the omentum. In this study, we analyzed 95 GISTs surgically designated as the omental masses. These tumors occurred in 49 males and 46 females with a median age of 60 years (range: 27 to 88 y). They formed single (n=51) or multiple masses (n=39); 5 cases were equivocal in this respect. Of the single tumors, 21 had no evidence of gastrointestinal tract involvement, 25 were attached to stomach, and 3 were attached to small intestine. Clinicopathologic parameters and prognosis of the 2 former groups were similar. Single tumor cases showed a median mitotic count of 2/50 HPFs and median tumor size was 14 cm. Their histologic features were similar to gastric GISTs in 22 cases, and to small intestinal GISTs in 6 cases. These tumors were KIT positive 38/41, CD34 positive 20/33, 8 had PDGFRA mutations, and 6 had KIT exon 11 mutations. The median survival was 129 months (range: 0 to 397 mo) and 14 patients were alive at the end of follow-up. Multiple tumor cases showed median mitotic count of 14/50 HPFs and the main tumor median size was 16 cm. The histologic features were similar to small intestinal GISTs in 21 cases and to gastric GISTs in 7 cases; small intestinal attachment or history of a previous small intestinal GIST were noted in 5 cases, whereas no tumor was attached to stomach. The multiple GISTs were KIT positive 23/24, CD34 positive 7/21, and 5 had KIT exon 11 mutations, 3 had KIT exon 9 mutations, and 2 had PDGFRA mutations. The median survival was for 8 months and all patients died. Omental GISTs are clinicopathologically heterogenous. Patients with solitary tumors usually have gastric GIST-like morphology and a better prognosis than those with multiple tumors, whose tumor usually has small intestinal GIST-like histology. Omental GISTs unattached to gastrointestinal tract often resemble gastric GISTs suggesting that they may be gastric GISTs directly extending or parasitically attached into the omentum, whereas multiple omental GISTs more often resemble small intestinal GISTs suggesting that they may be metastatic or detached from this source. KIT positive Cajal cells were not found in normal omental tissues failing to support the presence of these ancestral cells for GIST in the omentum.

Gastrointestinal stromal tumors and shock

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumor of the gastrointestinal tract. Clinically, they are associated with nonspecific symptoms, but some patients can present gastrointestinal bleeding with shock. We report two cases of GIST of the small bowel, revelated by hemorrhagic shock secondary to acute bleeding, succesfully treated by emergency surgery.

Gene expression signatures and response to imatinib mesylate in gastrointestinal stromal tumor

Despite initial efficacy of imatinib mesylate in most gastrointestinal stromal tumor (GIST) patients, many experience primary/secondary drug resistance. Therefore, clinical management of GIST may benefit from further molecular characterization of tumors before and after imatinib mesylate treatment. As part of a recent phase II trial of neoadjuvant/adjuvant imatinib mesylate treatment for advanced primary and recurrent operable GISTs (Radiation Therapy Oncology Group S0132), gene expression profiling using oligonucleotide microarrays was done on tumor samples obtained before and after imatinib mesylate therapy. Patients were classified according to changes in tumor size after treatment based on computed tomography scan measurements. Gene profiling data were evaluated with Statistical Analysis of Microarrays to identify differentially expressed genes (in pretreatment GIST samples). Based on Statistical Analysis of Microarrays [False Discovery Rate (FDR), 10%], 38 genes were expressed at significantly lower levels in the pretreatment biopsy samples from tumors that significantly responded to 8 to 12 weeks of imatinib mesylate, that is, >25% tumor reduction. Eighteen of these genes encoded Krüppel-associated box (KRAB) domain containing zinc finger (ZNF) transcriptional repressors. Importantly, 10 KRAB-ZNF genes mapped to a single locus on chromosome 19p, and a subset predicted likely response to imatinib mesylate-based therapy in a naïve panel of GIST. Furthermore, we found that modifying expression of genes within this predictive signature can enhance the sensitivity of GIST cells to imatinib mesylate. Using clinical pretreatment biopsy samples from a prospective neoadjuvant phase II trial, we have identified a gene signature that includes KRAB-ZNF 91 subfamily members that may be both predictive of and functionally associated with likely response to short-term imatinib mesylate treatment.

Primary large gastrointestinal stromal tumor of the liver: report of a case

A 30-year-old man was diagnosed to have a large intra-abdominal tumor in 1999. A histological examination of a resected liver specimen from an operation in 2002 revealed a gastrointestinal stromal tumor (GIST), diagnosed based on positive immunostaining for CD34 and c-kit. Two years after the operation, new lesions developed in the residual liver and the lesser curvature of the stomach. An immunohistological examination of both specimens showed the features of a GIST, thus matching those of the first histological examination of the liver GIST. While there were no mutations at exon 11 of c-kit in the liver GISTs resected in 2002 and 2004, the gastric lesion had a mutation at P577L (CCT to CTT) at exon 11. Therefore, the liver GIST and the gastric lesion were diagnosed to be independent. The patient already has survived for more than 9 years after receiving surgery three times and with administration of imatinib.

[A case of a primary gastrointestinal stromal tumor (GIST) found in the greater omentum of a 99-year-old woman]

We report the case of a primary gastrointestinal stromal tumor (GIST) found in the greater omentum of an extremely elderly woman. A 99-year-old woman with a history of heart failure and renal failure presented with dyspnea and disturbance of consciousness. A tumor located between the stomach and spleen had been detected by abdominal computed tomography three years previously. After admission, she received oxygen supplementation and diuretics. However she died of heart failure and disseminated intravascular coagulation on the 31st day of hospitalization. Autopsy was performed on the same day. A large mass measuring 12.5 x 7.0 x 7.5 cm was revealed, originating from the greater omentum. Histopathologically, it was composed of spindle cells with the nuclei showing a focal palisading pattern, however there were no mitoses. Immunohistochemically, the tumor was positive for c-kit. The tumor was diagnosed as a primary GIST of the greater omentum.

A single-institution experience with eight CD117-positive primary extragastrointestinal stromal tumors: critical appraisal and a comparison with their gastrointestinal counterparts

INTRODUCTION

Gastrointestinal stromal tumors (GISTs) arising from outside the gut wall also termed extragastrointestinal stromal tumors (EGISTs) are reported to be rare. Presently, their pathogenesis remains controversial, and recently, it has been proposed that EGISTs may be the result of extensive extramural growth of GISTs which lose contact with the gut wall. This study presents a single-institution experience with eight EGISTs and compares their clinicopathological features with mural GISTs in order to determine further insight to their possible origin.

METHODS

Between 1997 and 2008, 156 patients with pathologically proven CD117-positive primary GISTs were retrospectively reviewed. Eight tumors were identified as EGISTs, 104 were gastric GISTs, and 44 were small-bowel GISTs. Mural GISTs were classified as extramural or intra/transmural according to their gross pattern of growth.

RESULTS

There were five male and three female patients with a median age of 58 years (range, 42-81 years). All patients were symptomatic, and the tumors were located in the greater omentum (n = 2), lesser sac (n = 2), lesser omentum, retroperitoneum, small-bowel mesentery, and pancreas. The median tumor size was 140 mm (range, 55 to 220 mm). Seven of eight EGISTs were found to be in close association to the adjacent gut wall. Pathological examination demonstrated that two tumors demonstrated focal involvement of the muscularis propria of the adjacent gut wall. Four tumors demonstrated tumor abutting or adherent to the serosa but no muscle involvement and one tumor was separated from the serosa. Comparison between the clinicopathological features of EGISTs with extramural GISTs and intra/transmural GISTs demonstrated that EGISTs were significantly larger [140 range (55-220) mm vs 80 (5-260) mm vs 50 (15-190) mm, P = 0.049, P < 0.001 respectively].

CONCLUSION

The occurrence of true EGISTs is rare. Most cases demonstrate some form of communication or contact with the gut wall, and EGISTs are significantly larger than extramural or intra/transmural GIST. These observations suggest that most, if not all, cases of EGISTs are likely to represent mural GISTs with extensive extramural growth with eventual loss of contact with the muscle layer of the gut.

Gastrointestinal stromal tumors with pseudocystic change mimicking a pancreatic tumor: two case reports

Introduction

Cystic lesions of the upper abdomen normally develop from pancreatic tissue. The differential diagnoses include neoplastic and non-neoplastic lesions. Pseudocystic tumors that secondarily involve the pancreas are very rare and may lead to diagnostic pitfalls.

Case presentation

A 51-year-old woman and a 65-year-old man, both German, presented with abdominal cystic lesions suspected to be pancreatic pseudocysts. Both tumors were classified as gastrointestinal stromal tumors, epithelioid subtype. In one case, tumor origin in the gastric wall was confirmed by relaparotomy. In the other case, a point mutation in PDGFRalpha gene, exon 18 proved the diagnosis of gastrointestinal stromal tumor. The tumors were resected and both patients are still alive and disease-free.

Conclusions

The differential diagnosis of cystic lesions in the upper abdomen must include gastrointestinal stromal tumors with pseudocystic change. The origin of a large cystic gastrointestinal stromal tumor may be difficult to determine. Epithelioid tumor pattern, weak or absent KIT expression and detection of PDGFRalpha mutation are typical diagnostic parameters of gastric gastrointestinal stromal tumors.

Contemporary pathology of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. The vast majority of GISTs harbor a KIT or PDGFRA mutation and express KIT by immunohistochemistry. However, KIT-negative tumors and tumors showing unusual morphologic features can cause major diagnostic problems. The ability to inhibit the active KIT or PDGFRA kinase with tyrosine kinase inhibitors and alternative drugs demands more than ever accurate tumor classification and risk assessment. This article focuses on the pathology of GIST, including unusual variants and morphologic changes resulting from treatment. Parameters for risk assessment, potentially helpful new immunohistochemical markers, differential diagnosis, and the application of molecular classification schemes are discussed.

Extragastrointestinal stromal tumor arising in the rectovaginal septum: report of an unusual case with literature review

BACKGROUND

Extragastrointestinal stromal tumor (EGIST) is a rare tumor that shows features of gastrointestinal stromal tumor (GIST) outside the gastrointestinal tract, but EGIST arising in the rectovaginal septum is extremely rare.

CASE

We report a unique case of a 42-year-old woman with EGIST in rectovaginal septum. The tumor was excised locally. The patient is healthy without evidence of recurrence 11 months after surgery.

CONCLUSION

The clinical features and treatment of EGIST are not well known because few cases have been reported. Pathologically, immunohistochemistry with antibody against c-kit protein (CD117) is valuable for diagnosis of EGIST. Mitotic rate is the most reliable prognostic factor, and mutations in KIT may be a clinically useful adjunct marker in the evaluation. Surgery is the most effective treatment, and long-term follow-up is necessary.

Gastrointestinal stromal tumor of the uterus: a case report with genetic analyses of c-kit and PDGFRA genes

The author reports a very rare case of a gastrointestinal stromal tumor in the uterus. A 74-year-old woman was admitted to our hospital because of pelvic pain. Imaging modalities showed a large tumor of the posterior aspect of the uterus, and enucleation was performed. The tumor was attached to the posterior uterus, similar to subserosal leiomyoma. No attachment to the gastrointestinal organs was recognized. The tumor was soft, tan, and measured 13 x 15 x 12 cm. The tumor consisted of cellular spindle cells with focal necrotic areas. Mitotic figures were noted in 3 of 50 high-power fields. The tumor cells were positive for KIT, CD34, platelet-derived growth factor receptor alpha, and vimentin, but negative for alpha-smooth muscle actin, S100 protein, p53 protein, HMB45, and desmin. Ki-67 labeling was 3%. Five normal uteruses used as controls showed KIT-positive Cajal-like mesenchymal cell scattering in the myometrium. Genetic analyses of the c-kit gene (exons 9, 11, 13, and 17) and platelet-derived growth factor receptor alpha gene (exons 12 and 18) revealed a point mutation at codon 559 (GTT-->GAT) of exon 11 of the c-kit gene. Other exons showed no abnormalities. This case shows that gastrointestinal stromal tumor may occur in the uterus.

Gastrointestinal stromal tumors in a baboon, a spider monkey, and a chimpanzee and a review of the literature

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are believed to originate from the intestinal pacemaker cells (interstitial cells of Cajal) or their progenitor cells. Spontaneous tumors have been reported in dogs, horses, rhesus, and a chimpanzee and they have been produced experimentally in mice and rats. GISTs represent a diagnostic challenge because they cannot be differentiated from non-lymphoid mesenchymal tumors without using human c-kit (CD117) immunohistochemistry.

METHODS

Three neoplasms were incidental findings at necropsy in the stomachs of a baboon and a spider monkey and in the rectum of a chimpanzee.

RESULTS

The GISTs were initially diagnosed grossly and histologically with hematoxylin and eosin as leiomyomas. Immunohistochemical analysis revealed that all three were c-kit (CD117) positive.

CONCLUSIONS

These are the first reports of GISTs in the baboon and spider monkey and the second in a chimpanzee. The occurrence of GISTs in non-human primates may provide a unique opportunity to study these tumors.

Bilateral gluteal metastases from a misdiagnosed intrapelvic gastrointestinal stromal tumor

Background

The location of gastrointestinal stromal tumors (GIST) outside of the gastrointestinal system is a rare event.

Case presentation

A 56-year old woman presented with a GIST of the pelvis was misdiagnosed and treated as a uterine leiomyosarcoma. The diagnosis was made after the CD117 (KIT) positivity in the biopsy of the excised bowel mass four years from the first presentation. During this period she presented a bilateral muscle and subcutaneous metastasis in the gluteal area.

Conclusion

The correct diagnosis of the extra-gastrointestinal stromal tumor is a challenge even for experienced pathologists. CD117 (KIT) positivity is the most important immunohistochemical feature in the histological diagnosis. To our knowledge a metastatic EGIST (extra-gastrointestinal stromal tumor) to the skeletal muscle bilaterally has not been described previously in the English medical literature.

Primary multiple extragastrointestinal stromal tumors of the omentum with different mutations of c-kit gene

The author reports a very rare case of sporadic primary multiple extragastrointestinal stromal tumors (EGISTs) of the omentum associated with different mutations of the exon 11 of the c-kit gene in a 75-year-old man with gastric cancer. During an operation for the cancer, two solid tumors (10 mm and 8 mm) were found in the omentum. Both tumors consisted of cellular spindle cells. Mitotic figures were two and three per 50 high power fields. The tumor cells were positive for KIT, CD34 and vimentin, but negative for desmin, S100 protein, α-smooth muscle actin and p53 protein. Ki67 labeling was 2% and 3%. The larger EGIST showed a deletion of codons 552-558 of exon 11 of the c-kit gene, while the smaller EGIST had a point mutation at codon 559 (GTT←GAT) in exon 11 of the c-kit gene. Exons 9, 13, and 17 of the c-kit gene, and exons 12 and 18 of the platelet derived growth factor receptor α genes showed no mutations. The case shows that sporadic multiple EGISTs can occur in the omentum.

Minimally invasive resection of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are rare neoplasms. The advent of electron microscopy and immunohistochemistry has led to the realization that these tumors originate from a pleuropotential cell known as the interstitial cell of Cajal (ICC). The morphologic features demonstrated as most predictive of recurrence or metastases are tumor size and mitotic rate. There is oncologic justification for minimally invasive resection techniques with gross margins for GISTs. Minimally invasive resection provides advantages to patients in terms of morbidity and recovery. A variety of endoscopic, laparoscopic, and hybrid techniques are described for surgically excising GISTs in different anatomic locations.

Dose escalation of imatinib after failure of standard dose in Korean patients with metastatic or unresectable gastrointestinal stromal tumor

OBJECTIVE

We evaluated the results of imatinib dose escalation in patients with advanced gastrointestinal stromal tumors (GISTs) after disease progression on standard-dose imatinib.

METHODS

Clinical data from patients with metastatic or unresectable GISTs whose dose of imatinib was increased after disease progression on imatinib 400 mg/day were retrospectively reviewed.

RESULTS

The 24 patients studied had a median age of 52 years. Imatinib dosing was escalated to 600 mg/day in 12 patients, then to 800 mg/day in four patients. The other 12 patients had dose escalation directly to 800 mg/day. Two patients (8.3%) achieved a partial response, and seven (29.2%) had stable disease. Six-month progression-free and overall survival rates were 33.3 and 70.7%, respectively. Dose escalation to 600 or 800 mg/day was generally well tolerated.

CONCLUSION

Imatinib dose escalation is feasible and well tolerated in patients with advanced GIST who progress on standard-dose therapy, producing clinical benefit in approximately 37% of patients.

Neoplastic and non-neoplastic proliferative disorders of the perirenal space: cross-sectional imaging findings

The perirenal space, located between the anterior and the posterior renal fasciae, is shaped like an inverted cone with an apex that extends into the iliac fossa. Perirenal tumors and pseudotumors primarily originate either from the kidney or as part of a systemic disease process and have characteristic histopathologic features and biologic behavior. The lesions may be classified on the basis of their distribution and imaging features as solitary soft-tissue masses (renal cell carcinoma, lymphangioma, hemangioma, and leiomyoma), rindlike soft-tissue lesions (lymphoma, retroperitoneal fibrosis, and Erdheim-Chester disease), masses containing macroscopic fat (angiomyolipoma, liposarcoma, myelolipoma, and extramedullary hematopoiesis), and multifocal soft-tissue masses (metastases, plasma cell tumors). Because of overlap in imaging findings among these diverse perirenal lesions, a definitive diagnosis in most cases can be established only at histopathologic analysis. However, an imaging pattern-based approach may facilitate the diagnosis and optimal management of perirenal tumors and pseudotumors.

Primary extragastrointestinal stromal tumor of the transverse mesocolon without c-kit mutations but with PDGFRA mutations

The author reports a rare case of primary large cystic extragastrointestinal stromal tumor (eGIST) of the transverse mesocolon with genetic analyses of the c-kit and platelet-derived growth factor receptor-alpha (PDGFRA) genes. A 78-year-old man was found to have a large cystic tumor in the abdomen, and the tumor was resected. Grossly, the tumor was located in the transverse mesocolon, and cystic. Microscopically, the tumor consisted of epithelioid cells with atypia. Mitotic figures were noted in five of 50 high power fields. Immunohistochemically, the tumor cells were positive for KIT, CD34, PDGFRA, and vimentin, but negative for cytokeratins, neuron specific enolase, desmin, S100 protein, alpha-smooth muscle actin, p53 protein, HMB45, CD68, CEA, factor VIII-related antigen, chromogranin, and synaptophysin. Ki67 labeling was 5%. Genetically, the tumor showed a point mutation (GAC --> GTC) at codon 842 of exon 18 of the PDGFRA gene. Exon 12 of the PDGFRA gene and exons 9, 11, 13, and 17 of the c-kit gene showed no mutations. No recurrence is noted 3 years after the operation. This case shows that eGIST may occur in the transverse mesocolon.

Clinicopathological characteristics of gastrointestinal mesenchymal tumors and diagnostic value of endoscopic ultrasonography

BACKGROUND AND AIM

Gastrointestinal mesenchymal tumors (GIMTs) are tumors which arise from mesenchymal cells other than lymphocytes or epithelial cells and include gastrointestinal stromal tumors (GISTs), smooth muscle tumors, neurogenic tumors, fibroblast tumors, and liparomphalus. Here, we studied the clinicopathologic characteristics of GIMTs and determined the diagnostic value of endoscopic ultrasonography (EUS) in GIMTs.

METHODS

The morphological characteristics of 415 GIMT cases were observed using light microscopy. The expression of CD117, CD34, smooth muscle actin (SMA), S-100, and Ki-67 were detected using immunohistochemistry. EUS results were retrospectively analyzed in 76 cases.

RESULTS

Among the 415 GIMT cases, there were 229 GIST cases, 178 smooth muscle tumor cases, and eight neurogenic tumor cases. Diffuse strong expression of CD117 was observed in 202 (88.2%) GISTs and strong expression of CD34 was observed in 135 (59.0%) GISTs. SMA and S-100 expression was detected in smooth muscle tumors (leiomyomas/leiomyosarcoma) and neurogenic tumors, respectively. Of the 12 cases with GISTs, nine cases with positive ki-67 expression and accompanied with more mitosis were pathologically diagnosed as malignant GISTs. Most of the borderline and malignant tumors were found in male patients. EUS was 98.7% accurate in determining GIMT locations, 82.9% accurate in diagnosing GIMTs, and 80.3% accurate in differentiating benign from malignant tumors.

CONCLUSIONS

GISTs, rather than leiomyomas, are the most common GIMTs. Immunohistochemical markers, such as CD117, CD34, SMA, and S-100, can differentiate GISTs from smooth muscle and neurogenic tumors. The expression of Ki-67 in patients with significant karyokinesis supports a malignant tumor diagnosis. EUS is an accurate method for detecting GIMTs and differentiating between benign and malignant tumors. Use of endoscopic ultrasound-guided fine-needle aspiration biopsies may enable clinicians to make more accurate diagnoses than currently used methods.

A case of gastrointestinal stromal tumor with spontaneous rupture in the greater omentum

BACKGROUND

Although GIST generally occurs in the digestive tract, such as the stomach, and small and small intestine primarily, Omental GIST tumours are very rare.

CASE PRESENTATION

A 63-year-old male patient, who recognized an abdominal tumor 1 year before admission, had a slight expansion of the tumor, reduction of the body and malaise, was consulted to our hospital. Abdominal CT and MRI revealed a cystic lesion of 26 cm in diameter with a clear boundary from immediately below the interseptum to the pelvic cavity, and imaged the septum and cystic wall. We considered that the patient had a cystic tumor in the abdomen, of which the primary lesion was unknown, and scheduled surgery. The patient unfortunately deteriorated with shock and sudden pain in the abdomen. Wediagnosed tumor rapture, and emergency surgery was performed. The tumor, weighing 3,600 g, was mostly cystic, and filled with sanguinous fluid and clot. Histologically, the tumor was composed of spindle cells, and was positive for c-KIT (CD117), slightly positive for alpha-smooth muscle actin (SMA), and S-100 protein positive. Based on these findings, the tumor was diagnosed as GIST primarily occurring in the greater omentum.

CONCLUSION

We experienced a rare case of GIST which originated from the greater omentum. Recently, the prognosis of GIST has been improved since the treatment with Imatinib.It is necessary to consider the diagnosis of GIST on encountering a mass in the greater omentum.

Gastrointestinal stromal tumor in Brazil: clinicopathology, immunohistochemistry, and molecular genetics of 513 cases

The aim of the present study was to evaluate the clinicopathological, immunohistochemical, and molecular genetic features of gastrointestinal stromal tumors in Brazil and compare them with cases from other countries. Five hundred and thirteen cases were retrospectively analyzed. HE-stained sections and clinical information were reviewed and the immunohistochemical expression of CD117, CD34, smooth-muscle actin, S-100 protein, desmin, CD44v3 adhesion molecule, p53 protein, epidermal growth factor receptor, and Ki-67 antigen was studied using tissue microarrays. Mutation analysis of KIT and platelet-derived growth factor receptor-alpha genes was also performed. There was a slight female predominance (50.3%) and the median age at diagnosis was 59 years. The tumors were mainly located in the stomach (38.4%). Immunohistochemistry showed that CD117 was expressed in 95.7% of cases. Epidermal growth factor receptor expression was observed in 84.4% of tumors. p53 protein expression was found only in 2.6% of cases but all belonged to the high-risk group for aggressive behavior according to the National Institutes of Health consensus approach. No CD44v3 adhesion molecule expression was detected. KIT exon 11 mutations were the most frequent (62.2%). The present data confirm that gastrointestinal stromal tumors in Brazilian patients do not differ from tumors occurring in other countries.

A malignant omental extra-gastrointestinal stromal tumor on a young man: a case report and review of the literature

Background

Gastrointestinal stromal tumors (GIST) are uncommon intra-abdominal tumors. These tumors tend to present with higher frequency in the stomach and small bowel. In fewer than 5% of cases, they originate primarily from the mesentery, omentum, or peritoneum. Furthermore, these extra-gastrointestinal tumors (EGIST) tend to be more common in patients greater than 50 years of age. Rarely do EGIST tumors present in those younger than 40 years of age.

Case presentation

We report a case of a large EGIST in a 27-year-old male. An abdominal pelvic computerized tomography imaging demonstrated an intra-abdominal mass of 22 cm, without invasion of adjacent viscera or liver lesions. This mass was resected en bloc with its fused omentum and an adherent portion of sigmoid colon. Pathology results demonstrated a malignant gastrointestinal stromal tumor with positive CD117 (c-kit) staining, and negative margins of resection, and no continuity of tumor with the sigmoid colon. Due to the malignant and aggressive nature of this patient's tumor, he was started on STI-571 as adjuvant chemotherapy.

Conclusion

Stromal tumors of an extra-gastrointestinal origin are rare. Of the reported omental and mesenteric EGISTs in four published series, a total of 99 tumors were studied. Of the 99 patients in these series only 8 were under 40 years of age, none were younger than 30 years old; and only 5 were younger than 35 years old. Our patient's age is at the lower end of the age spectrum for the reported EGISTs. Young patients who present with an extra-gastrointestinal stromal tumor (EGIST), who have complete resection with negative margins, have a good prognosis. There is little data to support the role of STI-571 in adjuvant or neoadjuvant therapy after curative resection. Given the lack of data, the use of STI-571 must be individualized.

[Gastrointestinal stromal tumors: role of computed tomography before and after treatment]

Gastrointestinal stromal tumors (GIST) are the most frequent mesenchymal tumors of the gastrointestinal tract. They are generally located in the stomach or the small bowel and the potential for becoming malignant varies. Due to their expression of c-kit protein, a positive diagnosis as well as a specific targeted treatment by molecular biology (imatinib) are available. Computed tomography is the best imaging method for diagnosis, staging and follow-up of GIST. They appear as a well-defined exophytic mass with heterogeneous enhancement after intravenous injection of iodinated contrast material. They may contain areas of necrosis and/or haemorrhage and enlarged lymph nodes are exceedingly rare. Most common metastatic sites are the liver and mesentery. Large tumour size and liver or mesenteric metastases are computed tomography criteria for a high malignant potential. After treatment, decrease in tumour size, number and density of lesions and the disappearance of enhancing nodules suggest a positive response to imatinib therapy, whereas a new enhancing nodule within a mass is the usual pattern of recurrence. Positron emission tomography may be useful in specific cases when clinical data are inconsistent with computed tomography criteria.

A rare tumor in the adrenal region: neuron-specific enolase (NSE)-producing leiomyosarcoma in an elderly hypertensive patient

A 73-year-old Japanese woman was referred for examination of right flank pain and progressive hypertension. Abdominal CT incidentally detected a right adrenal mass 8 cm in size. The tumor exhibited isodensity by CT and contained high-intense lesion by T2-weighted MRI. Scintigraphy with (131) I-metaiodobenzylguanidine and (131) I-adosterol showed no abnormal uptake by whole body scan. Positron emission tomography scan with (18) F-2-fluoro-D-deoxyglucose demonstrated an exclusive uptake in the right adrenal mass. Adrenocortical hormone levels and catecholamine secretion were within normal range; however, the level of serum neuron-specific enolase (NSE) was found to be markedly high. After controlling systemic blood pressure with an alpha1-blocker, the right adrenal tumor was surgically removed, along with the right kidney and inferior vena cava which adhered to it. The tumor was pathologically proven to be leiomyosarcoma, which was immunohistochemically positive with alpha-smooth muscle actin and negative with CD57, S-100 and c-kit proteins. Notably, NSE protein was massively expressed in the resected tumor. After surgery blood pressure was controlled with regular medication and serum NSE levels have since normalized. The possibility of leiomyosarcoma should be kept in mind in adrenal incidentalomas with rapid growth and atypical radiological images. Our findings suggest that circulating NSE levels may be clinically useful for early detection of recurrence.

Extra-gastrointestinal stromal tumor of the greater omentum: report of a case and review of the literature

Background

Gastrointestinal stromal tumors (GISTs) represent the majority of primary non-epithelial neoplasms of the digestive tract, most frequently expressing the KIT protein detected by the immunohistochemical staining for the CD117 antigen. Extra-gastrointestinal stromal tumors (EGISTs) are neoplasms with overlapping immunohistological features, occurring in the abdomen outside the gastrointestinal tract with no connection to the gastric or intestinal wall.

Case presentation

We here report the clinical, macroscopic and immunohistological features of an EGIST arising in the greater omentum of a 74-year-old man, with a discussion on the clinical behavior and the prognostic factors of such lesions and a comparison with the gastrointestinal counterpart.

Conclusion

The EGISTs in the greater omentum can grow slowly in the abdomen for a long time without clinical appearance. In most cases a preoperative diagnosis is not possible, and the patient undergoes a surgical operation for the generic diagnosis of "abdominal mass". During the intervention it is important to achieve a complete removal of the mass and to examine every possible adhesion with the gastrointestinal wall. Yamamoto's criteria based on the evaluation of the mitotic rate and the MIB-1 labelling index seems to be useful in predicting the risk for recurrence or metastasis. More studies are necessary to establish the prognostic factors related to localization and size of the EGIST and to evaluate the impact of the molecular characterization as an outcome parameter related to the molecular targeted therapy. In absence of these data, an accurate follow-up is recommended.

Gastrointestinal stromal tumor

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. These form a distinct category of tumors characterized by oncogenic mutations of the KIT receptor tyrosine kinase in a majority of patients. KIT is used not only for diagnosis but also for targeted therapy of GISTs. Imatinib, a tyrosine kinase inhibitor, is widely used in the treatment of advanced and metastatic GISTs and has been recently employed in the neo adjuvant and adjuvant set-up with encouraging results. Certain specific mutations in an exon (such as in exon 9) of the KIT gene result in GISTs that are relatively unresponsive to the Imatinib treatment. New therapeutic agents like Sunitinib have now been approved for the treatment of Imatinib-resistant GIST. This review summarizes the salient features of GIST along with a detailed review of targeted multi-disciplinary approach to the treatment of these special tumors.

Extragastrointestinal stromal tumor possibly originating from the prostate

We report a case of extragastrointestinal stromal tumor possibly originating from the prostate. The patient underwent radical prostatectomy because of no metastatic evidence. No recurrence and metastasis have been found during 14 months of follow up. To our knowledge, this may be the third such case published in a report in terms of pathological type.

Sunitinib, a multitargeted tyrosine kinase inhibitor, in the management of gastrointestinal stromal tumor

Due to the remarkable advances in the understanding of the biology of gastrointestinal stromal tumors (GIST), tyrosine kinase inhibition has become the mainstay of therapy for patients with advanced GIST. Sunitinib is a tyrosine kinase inhibitor with a wide range of kinase inhibition, including KIT, platelet-derived growth factor receptor (PDGFR), vascular endothelial growth factor (VEGF), and FLT3. Sunitinib has demonstrated benefit in patients with advanced GIST who have progressed on primary therapy with imatinib. The objectives of this review are to discuss the role of sunitinib in the current management of GIST, to review the unique side effect profile of the agent, and to discuss future trends in the use of the drug as the understanding of the mechanism of GIST evolves.

Progress in molecular diagnostics of gastrointestinal stromal tumors

Gastrointestinal stromal tumor (GIST) is the most frequent mesenchymal tumor of the alimentary tract, presently being defined as a tumor composed of spindle and/or epithelioid cells presumably differentiating towards interstitial cells of Cajal. The most frequent location of gastrointestinal stromal tumor is the stomach, followed by other sites of gastrointestinal tract. Occasional sites of occurrence are mesenterium, omentum, retroperitoneum, gall bladder, urinary bladder, pancreas, prostate and the vagina. Most of these tumors are KIT-immunoreactive and almost all carry mutated KIT or PDGFRA genes encoding two transmembrane class III tyrosine kinases. These mutations not only shed light on molecular oncogenesis of GISTs, but can also serve as diagnostic markers of this type of tumor, and, last but not least, the function of the proteins encoded by the mutated genes may be influenced by small molecule tyrosine kinase inhibitors. Nevertheless, negative results of immunohistochemistry and mutational analysis do not exclude histologically proven diagnosis of GIST, and although the response to tyrosine kinase inhibitors is correlated with the presence and type of KIT and PDGFRA mutations, the molecular genetic analysis of these genes is presently not required for imatinib therapy of GISTs.

Gastrointestinal stromal tumors: computed tomographic features and prediction of malignant risk from computed tomographic imaging

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are specific, generally Kit (CD117)-positive, mesenchymal tumors of the gastrointestinal tract encompassing a majority of tumors previously considered gastrointestinal smooth muscle tumors. Our aim was to characterize the computed tomographic findings and predict malignant risk from computed tomography for the evaluation of GISTs.

METHODS

The computed tomographic images of 39 patients with pathologically and immunohistochemically proven GISTs were reviewed by 2 radiologists, and the final interpretations were reached by consensus. Images were assessed for the size, contour, growth pattern, boundary, degree of enhancement, and necrosis of the tumors. The presence of calcification within the lesions, abdominal lymphadenopathy, ascites, and bowel obstruction were also recorded. Categorical variables were compared using Fishers exact test. Univariate and multivariate logistic regression analyses were used for selection of significant predictors of high-risk malignancy. In addition, the relationships between computed tomographic features and tumor size were assessed by means of nonparametric univariate analysis with the MannWhitney U test and KruskalWallis test.

RESULTS

Both old age and larger tumor size (>or= 5 cm) were statistically significant in the univariate logistic analysis for high-risk malignant tumors (p < 0.25). However, in multivariate logistic regression, only larger tumor size (>or= 5 cm) was found to have final statistical significance for high-risk malignant GISTs (p < 0.05). In addition, more exophytic growth pattern (p < 0.01), more lobulated appearance (p < 0.01), good enhancement (p < 0.05),and more necrosis (p < 0.01) of masses were more often observed in larger GISTs than small ones on computed tomography.

CONCLUSION

Larger tumor size (>or= 5 cm) was found to have a predictive value with respect to high-risk malignant GISTs.

Mutation analysis of gastrointestinal stromal tumors: increasing significance for risk assessment and effective targeted therapy

Molecular characterization of gastrointestinal stromal tumors (GISTs) plays an increasing role not only for the patient's prognosis but also for treatment options and in the context of resistance to therapy. Several mutational subtypes in KIT or platelet-derived growth factor receptor-alpha (PDGFRalpha) have been identified to be correlated with a different clinical behavior of GISTs. In KIT exon 11, deletions in the proximal part are associated with a high metastatic risk, whereas duplications in the distal part lead to a less aggressive phenotype. GISTs of the small bowel with a duplication in KIT exon 9 are often high risk tumors. In contrast, PDGFRalpha exon 18 mutated GISTs tend to have a low malignant potential. The authors suggest to include these molecular data together with classical parameters such as mitotic count and tumor size into the risk assessment of GISTs. The first choice for treatment of GISTs is still the surgical resection. In advanced tumors, which cannot be R0 resected, the neoadjuvant treatment with the tyrosine kinase inhibitor imatinib is now well established. Furthermore, an adjuvant treatment of locally R0-resected intermediate and high risk tumors is evaluated in several international clinical trials. For metastatic disease, treatment with imatinib is still the first option, but with new upcoming substances, the molecular characterization of GISTs may become mandatory. Very recently, it has been shown that sunitinib may be especially effective in GISTs with KIT exon 9 mutation, whereas these tumors show only an intermediate response to imatinib. A European Organisation for Research and Treatment of Cancer clinical trial randomizing patients according to their mutational status is under preparation. Secondary resistance to imatinib treatment is increasing, at least partly due to secondary mutations in the tyrosine kinase domain of the KIT receptor. Once a lesion has been shown to carry such a mutation, the local excision may be useful, mean while still responding metastases are further controlled by continuing imatinib. Taken together, the molecular characterization of GISTs turns out to play a central role before and during the treatment with tyrosine kinase inhibitors, which have improved the treatment of GIST patients dramatically.

Multiple peritoneal calcifying fibrous tumors revealed by ischemic colitis

We report the case of a 41-year-old man presenting with multiple calcifying fibrous tumor (CFT) revealed by ischemic colitis. Peritoneal nodular lesions involved omental, mesenteric, mesorectal, and mesocolic serosal surfaces. Histologically, nodules were composed of dense bundles of collagen, calcifications, and lymphoplasmacytic infiltrate. These findings were diagnostic of CFTs, a rare and often asymptomatic benign fibrous process. Multiple peritoneal CFTs are very uncommon and usually occur in women. Calcifying fibrous tumors are usually cured by surgical excision. The differential diagnosis and histogenesis of this entity are discussed.

Gastrointestinal stromal tumors: diagnostic challenges and practical approach to differential diagnosis

Over the last decade, gastrointestinal stromal tumors (GISTs) have evolved from histogenetically obscure gastrointestinal mesenchymal tumors to well-defined tumors with distinctive clinical, morphologic, ultrastructural, histogenetic, and molecular characteristics, for which targeted therapy is available. This is largely attributable to the discovery of CD117 overexpression and activating mutations in c-kit or platelet-derived growth factor alpha genes in most of GISTs. The availability of specific diagnostic tests and targeted therapy for GISTs has led to an increased awareness of these tumors. At the same time, the list of potential GIST mimics has lengthened considerably and it has become increasingly important that GISTs be distinguished from their mimics because correct diagnosis has implications for both treatment and prognosis. The purpose of this review is to provide an update of the expanding differential diagnosis of GISTS, to draw attention to unusual GIST variants, to provide a practical approach the differential diagnosis of GISTs and to highlight some of the challenges faced by pathologists in resolving this differential diagnosis.

Multiple malignant extragastrointestinal stromal tumors of the greater omentum and results of immunohistochemistry and mutation analysis: A case report

To report an extragastrointestinal stromal tumor (EGIST) that occurs outside the gastrointestinal tract and shows unique clinicopathologic and immunohistochemical features. In our case, we experienced multiple soft tissue tumors that originate primarily in the greater omentum, and in immunohistochemical analysis, the tumors showed features that correspond to malignant EGIST. Two large omental masses measured 15 cm x 10 cm and 5 cm × 4 cm sized and several small ovoid fragments were attached to small intestine, mesentery and peritoneum. On histologic findings, the masses were separated from small bowel serosa and had high mitotic count (115/50 HPFs). In the results of immunohistochemical stains, the tumor showed CD117 (c-kit) positive reactivity and high Ki-67 labeling index. On mutation analysis, the c-kit gene mutation was found in the juxtamembrane domain (exon 11) and it was heterozygote. Platelet-derived growth factor receptor (PDGFR) gene mutation was also found in the juxtamemembrane (exon 12) and it was polymorphism. From above findings, we proposed that there may be several mutational pathways to malignant EGIST, so further investigations could be needed to approach this unfavorable disease entity.

Imatinib-refractory gastrointestinal stromal tumors: the clinical problem and therapeutic strategies

Treatment of gastrointestinal stromal tumor (GIST) is a paradigm for targeted therapy. These mesenchymal tumors are refractory to standard chemotherapy and radiation therapy. Targeted therapy has successfully exploited the oncologic drivers of GIST--the tyrosine kinases, KIT, and the platelet-derived growth factor receptor. Therapy with imatinib has dramatically altered the natural history of patients with advanced GIST. However, patients are developing resistance to imatinib and thus presenting with a major clinical challenge. Alternative approaches to imatinib-refractory disease are needed. Newer approaches using biologic data regarding the mechanisms of resistance are being tested alone or in combination with imatinib and are the focus of this review. Effective novel agents for imatinib-refractory GIST used as single agents or in combination with imatinib will likely become future regimens to be tested in first-line metastatic disease and in the adjuvant setting.

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.

Primary omental gastrointestinal stromal tumor (GIST)

Background

We report herein a rare case of primary omental gastrointestinal stromal tumor (GIST).

Case presentation

A 65 year-old man was referred to our hospital with a huge abdominal mass occupying the entire left upper abdomen as shown by sonography. On computed tomography (CT), this appeared as a heterogeneous low-density mass with faint enhancement. Abdominal angiography revealed that the right gastroepiploic artery supplied the tumor. With such an indication of gastric GIST, liposarcoma, leiomyosarcoma or mesothelioma laparotomy was performed and revealed that this large mass measured 20 × 17 × 6 cm, arising from the greater omentum. It was completely resected. Histopathologically, it was composed of proliferating spindle and epithelioid cells with an interlacing bundle pattern. Immunohistochemically, the tumor was positive for myeloid stem cell antigen (CD34), weakly positive for c-KIT (CD117) and slightly positive for neuron-specific enolase (NSE), but negative for cytokeratin (CK), alpha-smooth muscle actin (SMA) and S-100 protein. A mutation was identified in the platelet-derived growth factor alpha (PDGFRA) juxtamembrane domain (exon 12, codon561) and the tumor was diagnosed as an omental GIST. The postoperative course was uneventful. The patient is treated by Glevec^® and is alive well with no sign of relapse.

Conclusion

Our case demonstrated a weak immunohistochemical expression of c-kit (CD117) and a point mutation in PDGFRA exon 12 resulting in an Asp for Val⁵⁶¹ substitution. Imatinib therapy as an adjuvant to complete resection has been carried out safely. Because of the rarity of primary omental GISTs, it is inevitable to analyze accumulating data from case reports for a better and more detailed understanding of primary omental GISTs.

Gastrointestinal stromal tumors (GISTs): focus on histopathological diagnosis and biomolecular features

Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors of the gastrointestinal tract that are believed to originate from a neoplastic transformation of the intestinal pacemaker cells (interstitial cells of Cajal) normally found in the bowel wall or their precursors. Although the microscopic features have been known for a long time, the defining characteristic of GIST is the presence of the cell-surface antigen CD117 (KIT), which is demonstrated by immunohistochemistry. KIT, which is a growth factor transmembrane receptor, is the product of the proto-oncogene c-kit (chromosome 4). Surgical removal remains the only curative treatment for patients with GISTs. Tumor size, mitotic index, anatomic location, tumor rupture and disease-free interval are the classic characteristics used to predict the clinical course of patients who undergo complete gross resection. Most GISTs express constitutively activated mutant isoforms of KIT or kinase platelet-derived growth factor receptor alpha (PDGFRA) that are potential therapeutic targets for imatinib mesylate. Imatinib mesylate is a rationally designed, molecularly specific oral anticancer agent that selectively inhibits several protein tyrosine kinases central to the pathogenesis of human cancer and which has demonstrated remarkable clinical efficacy in patients with chronic myeloid leukemia and malignant GISTs. More recently Sunitinib, a new KIT/PDGFRA kinase inhibitor, has been tested in patients with GIST resistant to imatinib, with promising results.

The role of KIT in the management of patients with gastrointestinal stromal tumors

In recent years, immunohistochemical staining for KIT (CD117) has become integral to the diagnosis of gastrointestinal stromal tumors (GISTs), nearly 90% of which harbor activating mutations in the KIT receptor tyrosine kinase gene. Approximately 80% of patients with metastatic GIST show at least some clinical response to the targeted small molecule KIT inhibitor imatinib. The response to imatinib is closely correlated with the presence and type of KIT mutation. GISTs with the most common KIT exon 11 mutations have the highest response rate by far, whereas GISTs lacking mutations in KIT or the alternative receptor tyrosine kinase PDGFRA show much lower rates of response to imatinib. Less than 5% of GISTs are KIT-immunonegative; and many of these tumors have activating mutations of PDGFRA, some of which are also inhibited by imatinib. Most patients who initially respond to imatinib become resistant and eventually progress, which coincides with the selection of imatinib-resistant secondary KIT mutations in the kinase domain. Sunitinib has recently been approved for patients with GIST, principally those who fail imatinib therapy; and additional small molecule inhibitors are in the pipeline. It is becoming evident that alternative approaches to direct KIT inhibition will be required for long-term survival of patients with advanced GISTs. This review examines the role of KIT in the diagnosis and management of patients with GIST.

Gastrointestinal stromal tumour

Gastrointestinal stromal tumours are the most common mesenchymal neoplasm of the gastrointestinal tract and are highly resistant to conventional chemotherapy and radiotherapy. Such tumours usually have activating mutations in either KIT (75-80%) or PDGFRA (5-10%), two closely related receptor tyrosine kinases. These mutations lead to ligand-independent activation and signal transduction mediated by constitutively activated KIT or PDGFRA. Targeting these activated proteins with imatinib mesylate, a small-molecule kinase inhibitor, has proven useful in the treatment of recurrent or metastatic gastrointestinal stromal tumours and is now being tested as an adjuvant or neoadjuvant. However, resistance to imatinib is a growing problem and other targeted therapeutics such as sunitinib are available. The important interplay between the molecular genetics of gastrontestinal stromal tumour and responses to targeted therapeutics serves as a model for the study of targeted therapies in other solid tumours.

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.

Distinguishing gastrointestinal stromal tumors from their mimics: an update

Since the discovery of activating KIT mutations in gastrointestinal stromal tumors (GISTs) in 1998 and the subsequent demonstration that some malignant GISTs respond to targeted therapy with imatinib, it has become increasingly important for pathologists to correctly diagnose GISTs and separate them from their potential mimics in the gastrointestinal tract and abdominal cavity. Some mesenchymal tumors, such as leiomyomas of the muscularis mucosae, are easily distinguished from GIST on the basis of their anatomic location and morphologic appearance. Others, such as gastrointestinal schwannomas, can significantly overlap with GIST in their gross appearance and morphology and require a panel of immunostains for correct diagnosis. This article will review the most common mimics of GISTs: desmoid tumors, smooth muscle tumors (leiomyomas and leiomyosarcomas), gastrointestinal schwannomas, inflammatory fibroid polyps, and solitary fibrous tumors. Pertinent differences between each of these tumors and GIST in terms of gross appearance, histologic features, and immunophenotype will be emphasized. It is important to separate GISTs from these potential mimics because their treatment and prognosis can differ markedly.

Gastrointestinal stromal tumor of the stomach with a giant abscess penetrating the gastric lumen

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. In large GISTs, cystic degeneration, necrosis and focal hemorrhage that occur inside the tumor can result in gastrointestinal bleeding. We describe a case of a 74-year old male with GIST of the stomach accompanied with a giant abscess that penetrated the gastric lumen. The patient experienced undiagnosed fever for two months prior to hospitalization. Gastrointestinal endoscopy, X-ray series and computed tomography of the patient’s abdomen revealed a gastric submucosal tumor in the fornix, with a fistula to the gastric lumen that was inundated with a great deal of pus. The mass was diagnosed as a GIST from biopsy specimens. The patient was treated by endoscopic drainage of the abscess and intravenous administration of antibiotics. Eventually, a partial gastrectomy was performed. He was also administered Imanitib mesylate as adjuvant therapy. He was followed up for 2 years and no metastasis or recurrence was recognized at the follow-up examinations. This is the first report of a patient with clearly diagnosed GIST with endoscopic evidence of an abscess penetrating into the gastric lumen.

Occurrence of other malignancies in patients with gastrointestinal stromal tumors

Almost one-third of gastrointestinal stromal tumors (GISTs) are discovered incidentally during investigative or therapeutic procedures for unrelated diseases. In this regard, GISTs may coexist with different types of cancer, either synchronously or metachronously. The frequency of this association and the spectrum of neoplasms involved have not been sufficiently analyzed. We conducted a review of the literature and our own records for cases with sporadic GISTs and other malignancies, with emphasis on solid tumors. Neurofibromatosis 1 and Carney triad-associated tumors were excluded. Based on these data, there were 518 cancers in 486 GIST patients among 4813 cases with informative data. The overall frequency of second tumors in different series varied from 4.5% to 33% (mean, 13%). A total of 29 patients had multiple malignancies. GISTs of gastric location were most commonly involved with other neoplasms, reflecting their overall high frequency (60%) of all GISTs. The major types of GIST-associated cancers were gastrointestinal carcinomas (n=228; 47%), lymphoma/leukemia, (n=36; 7%), and carcinomas of prostate (n=43; 9%), breast (n=34; 7%), kidney (n=27; 6%), lung (n=26; 5%), female genital tract (n=25; 5%), and carcinoid tumors (n=13; 3%). Other cancers included soft tissue and bone sarcomas (n=15; 3%), malignant melanoma (n=12; 2%), and seminoma (n=6; 1%). Occurrence of collision tumors and metastases of carcinoma or sarcoma into a GIST (the latter noted in 4 cases) can be challenging diagnostic problems. The potential nonrandom association and causal relationship between GIST and other neoplasms remain to be investigated.