Small Intestinal Stromal Tumors With Skeinoid Fibers

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

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

Gastrointestinal stromal tumors with BRAF gene fusions. A report of two cases showing low or absent KIT expression resulting in diagnostic pitfalls

Although most gastrointestinal stromal tumors (GISTs) exhibit activating mutations in either KIT or PDGFRA, rare cases have shown to be driven by gene fusions involving kinases, mainly involving NTRK3, and rarely BRAF or FGFR1. BRAF gene rearrangements have been described in only two patients to date, as separate case reports. In addition, BRAF V600E mutation is an uncommon but established oncogenic pathway in GIST. In this report, we describe two new GIST cases harboring novel BRAF fusion genes, arising in two young-adult women (37 and 40 years of age) in the small bowel and distal esophagus, both with a spindle cell phenotype. The small bowel GIST measured 2.8 cm and showed a high cellularity and a mitotic rate of 20/50 HPFs, while the esophageal lesion measured 7 cm and 1/50 HPFs. Immunohistochemically, both tumors showed diffuse reactivity for DOG1, while KIT/CD117 was weakly positive in the small bowel GIST and completely negative in the esophageal tumor. Based on these findings, the latter case was misinterpreted as a low-grade myxoid leiomyosarcoma, as it showed a myxoid stroma, reactivity for SMA and focal positivity for desmin. Archer FusionPlex revealed a fusion between BRAF with either AGAP3 or MKRN1 gene partners. Moreover, MSK-IMPACT DNA targeted sequencing confirmed both fusions but did not identify additional mutations. In one case with available material, the BRAF gene rearrangement was also validated by FISH. The recognition of BRAF fusion-positive GISTs is critical as it may be associated with a low level of KIT expression and may result in diagnostic challenges with significant impact on therapeutic management. The clinical benefit with KIT inhibitors, such as imatinib, remains to be determined.

Surgical Pathology of Gastrointestinal Stromal Tumors: Practical Implications of Morphologic and Molecular Heterogeneity for Precision Medicine

Gastrointestinal stromal tumor (GIST), the most common mesenchymal neoplasm of the gastrointestinal tract, exhibits diverse histologic and clinical manifestations. With its putative origin in the gastrointestinal pacemaker cell of Cajal, GIST can arise in association with any portion of the tubular gastrointestinal tract. Morphologically, GISTs are classified as spindled or epithelioid, though each of these subtypes encompasses a broad spectrum of microscopic appearances, many of which mimic other histologic entities. Despite this morphologic ambiguity, the diagnosis of GIST is aided in many cases by immunohistochemical detection of KIT (CD117) or DOG1 expression. The natural history of GIST ranges from that of a tumor cured by surgical resection to that of a locally advanced or even widely metastatic, and ultimately fatal, disease. This clinicopathologic heterogeneity is paralleled by an underlying molecular diversity: the majority of GISTs are associated with spontaneous activating mutations in KIT, PDGFRA, or BRAF, while additional subsets are driven by genetic lesions-often inherited-of NF1 or components of the succinate dehydrogenase enzymatic complex. Specific gene mutations correlate with particular anatomic or morphologic characteristics and, in turn, with distinct clinical behaviors. Therefore, prognostication and treatment are increasingly dictated not only by morphologic clues, but also by accompanying molecular genetic features. In this review, we provide a comprehensive description of the heterogenous molecular underpinnings of GIST, including implications for the practicing pathologist with regard to morphologic identification, immunohistochemical diagnosis, and clinical management.

Gastrointestinal Autonomic Nerve Tumor of the Colon

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

Diagnosis value of CD117 and PDGFRA, alone or in combination DOG1, as biomarkers for gastrointestinal stromal tumors

BACKGROUND

To explore the diagnostic values of CD117 and PDGFRA protein expressions, used alone or in combination with DOG1 protein, for gastrointestinal stromal tumors (GIST).

METHODS

The CD117, PDGFRA and DOG1 protein expressions in 99 GIST specimens and 25 non-GIST specimens were retrospectively determined, and the potential correlations were analyzed.

RESULTS

The positive rates of CD117, PDGFRA, and DOG1 expressions were 93.94% (93/99), 53.54% (53/99), and 90.91% (90/99) in GIST group and 4.00% (1/25), 4.00% (1/25), and 12.00% (3/25) in non-GIST group (all P<0.05). The expressions of CD117, PDGFRA, and DOG1 had no significant correlation with clinicopathological parameters including gender, age, tumor diameter, tumor location, histotype, and risk degree (all P>0.05). The sensitivities of CD117, PDGFRA, DOG1, CD117 + DOG1, PDGFRA + DOG1, and CD117 + PDGFRA + DOG1 were 0.989, 0.981, 0.968, 0.960, 0.933, and 0.961 in judging GIST, respectively, and the specificities were 0.800, 0.343, 0.710, 0.840, 0.947, and 0.955, respectively. The areas under the ROC curve (AUC) in these six groups were 0.945, 0.748, 0.895, 0.895, 0.840, and 0.975, respectively.

CONCLUSIONS

The populations that may benefit more from the detection of CD117, PDGFRA, and DOG1 protein expression for GIST need to be further identified. Detection of CD117 and PDGFRA protein, alone or in combination with DOG1, may increase the accuracy of GIST diagnosis.

Histopathological and clinical characteristics of duodenal gastrointestinal stromal tumors as predictors of malignancy

Background

Although gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract, they are very rare. This study evaluated clinical and histopathological characteristics of duodenal GISTs to identify factors useful in predicting prognosis for patients with these tumors.

Methods

A retrospective study was performed on 20 patients who had undergone surgery between 1987 and 2009 for duodenal GISTs. Clinical, histopathological, and immunohistochemical data were evaluated. Survival analyses were conducted using Kaplan-Meier estimates.

Results

In 12 patients (60%), duodenal GISTs were diagnosed incidentally. Eight cases (40%) were classified as high risk grade GISTs. Skeinoid fibers (SkF), which are eosinophilic globular hyaline deposits in the extracellular interstitium of the tumor, were found in 12 patients. Skeinoid fibers were not recognized in 8 cases, and these included 3 cases (37.5%) where tumors recurred after surgery and the patient died. Tumors without SkF were larger (81 ± 92 vs. 23 ± 8 mm, P < 0.001) and had a higher mitotic count (224.0 ± 336.6 vs. 0.0 ± 0.0 /50 high-power field, P < 0.001) than those with SkF. Survival time was shorter in patients with tumors lacking SkF (52.9 ± 50.7 vs. 108.9 ± 86.5 months, P = 0.019).

Conclusions

We have identified clinical and histopathological characteristics that were useful in predicting the prognosis of patients with duodenal GISTs. In this study, 60% of the tumors were found incidentally, SkF were not recognized in tumors from 40% of patients, and all cases of post-operative tumor recurrence and death occurred in this subgroup of patients.

Neurofibromatosis 1 presenting with multiple duodenal GISTS associated with a somatostatin-producing D cell neoplasm

The co-existence of a duodenal somatostatin-producing D cell neoplasm and multiple duodenal gastrointestinal stromal tumours (GISTs) in a 61-year-old woman with neurofibromatosis type 1 is reported. Histologically, the D cell neoplasm showed a glandular pattern with psammoma bodies and was metastatic to regional lymph nodes and liver at the time of surgery. Tumour cells were monomorph and showed intense and diffuse immunoreactivity for somatostatin, focal positivity for calcitonin, while were negative for other gastroenteropancreatic hormones including insulin, glucagon, pancreatic polypeptide, serotonin and gastrin. Four submucosal and subserosal GISTs, ranging from 5 to 15 mm in diameter, were composed of uniform spindle-shaped cells lacking mitoses and contained numerous skeinoid fibres. The tumours were positive for CD117, DOG1, vimentin and CD34 and did not have KIT or PDGFRA mutations. The clinical and pathological importance of this unusual association is discussed.

Gastrointestinal Stromal Tumor in the Cecum of a Horse

Gastrointestinal stromal tumors (GISTs) are defined as specific CD117-(Kit, stem cell factor receptor) expressing tumors of the gastrointestinal (GI) tract. They are believed to originate from the interstitial pacemaker cells of Cajal (ICC) or their progenitor cells. In horses only a few cases of GISTs are described in the literature. In the present paper the macroscopical, histological, immunohistochemical, and ultrastructural features of an equine cecal GIST are described.

Histopathology of gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST), generally driven by oncogenic KIT or PDGFRA mutations, is the most common mesenchymal tumor of the gastrointestinal (GI) tract. GIST is most common in the stomach (60%) and small intestine (30%), but can occur anywhere in the GI-tract and the intra-abdominal soft tissues. GIST can show spindle cell or epithelioid morphology, and mitotic count and tumor size are most important prognostic parameters. GISTs in NF1 patients and children are distinctive clinicopathologic groups. Immunohistochemical testing for KIT and sometimes for DOG1/Ano 1 is essential in confirming the diagnosis.

Gastrointestinal stromal tumours: an update

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

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

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

Cellular Fibromatous Neoplasms of the Ovary

Many ovarian tumors composed primarily of fibroblastic cells are fibromas of usual type, and generally do not pose diagnostic difficulty. These tumors can be diagnosed accurately in most instances based on morphology without needing immunohistochemistry. Approximately 10% of fibromatous neoplasms, however, exhibit increased cellularity and mitotic activity, and, in the presence of the former or both features, are classified as cellular fibroma or mitotically active cellular fibroma. Distinguishing these entities from fibrosarcoma, an exceptionally uncommon ovarian malignancy, is important. This article reviews fibromatous ovarian tumors, emphasizing cellular fibromas and their differential diagnosis.

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.

Stromal Elements for Tumor Diagnosis: A Brief Review of Diagnostic Electron Microscopic Features

Tumor diagnosis mainly depends on the appearance of the tumor cells in recapitulating the appearance of primordial cells from which they arise. However, certain tumors may present with specific stromal changes that may assist/enhance the diagnosis. In this presentation, diagnostic stromal features have been reviewed. The cytoplasm is enclosed by a unit membrane, which serves as a barrier to, as well as an interface with, surrounding structures. Epithelial cells usually show characteristic basal-apical orientation. In mesenchymal tissue, different types of interface can be found in different types of mesenchymal tissue. External lamina can be defined as an anatomic structure, which encloses anatomic functional units. In epithelial tissue, cells in a functional unit are enclosed within a well-defined external lamina (EL). In malignant epithelial tumors, EL can become increasingly indistinct as tumors become less differentiated, and one has to look for it diligently. Within the external lamina, epithelial cells are closely packed with closely apposed cell membranes and cell attachment junctions. In contrast to epithelial tissue, mesenchymal tissue is usually characterized by the stromal elements they produce. Individual cells are embedded in the stroma, and individual mesenchymal cells represent the functional unit. Vascular endothelial cells are an exception since their relationship to stroma resembles to that of epithelial cells. Thus, tumors deriving from mesenchymal cells known to have external lamina such as muscle cells and Schwann cells tend to show total enclosure of cells by external lamina. In malignant muscle tumors, external lamina production can be focally present and found only by diligent search. In Schwann cell tumors, the presence of EL is prominent in low-grade tumors and more irregular and variable in malignant tumors. In the latter, stromal aggregation of scrolls of external lamina can be characteristic. Similar features are seen in ossifying fibromyxoid tumors. Fibronexus junctions (composed of extracellular fibronectin fillements linking intracellular 5-nm filaments) is claimed to be typical of myofbroblasts. Finding them in spindle cell tumors justifies a diagnosis of myofibroblastomas. There have been several stromal changes diagnostic for certain tumors found only by electron microscopy. Fibrous long-spaced collagen (known as Luse bodies) is diagnostic for peripheral nerve sheath tumors, but they can rarely be found in other tumors. Luse bodies usually appear as focally as crystallized aggregates apart from the regular collagenous interstitial stroma. They should be distinguished from other nonspecific long-spaced collagen changes. The changes are diffusely stromal in contrast to Luse bodies. Spiny collagen and amianthoid fibers are interesting collagen fibrils and their diagnostic value is questionable. Skeinoid fibers (SF) are short-spaced collagen of 41- to 45-nm banding so-named because of their peculiar appearance by electron microscopy simulating skeins of yarn. They were originally described in neurogenic tumors and small intestinal stromal tumors with features of gastrointestinal autonomic nerve tumors (GANT). Although there have been a few sporadic case reports of the presence of skeinoid fibers in nonneurogenic tumors, the frequent presence of SF in spindle cell tumors signifies their neurogenic nature in this authors' experience. An exception to this is that SF can be a constant element of rare ciliary body tumors known as ciliary mesectodermal leiomyomas, in which tumor cells show some resemblance to smooth muscle as well as Schwann cells. In addition to SF, several other types of peculiar crystallized collagen were observed in GANT tumors, particularly those with multiple tumor syndromes such as neurofibromatosis and Carney's triad. They simulate the appearance of railroad tracks or centrosomes. The reason for this is not known. The authors speculate that such collagen crystallization may be caused by genetic alterations involving collagenosis. Further studies will be necessary to clarify their pathogenesis. Another peculiar stromal change is electron-dense stromal filamentous aggregates with extra-long banding of > 250-nm periodicity previously described in Ewing sarcomas. This stromal change simulating a tiger skin pattern is also seen in primitive neuroectodermal tumors and malignant melanomas. In view of continually new discoveries of stromal changes that can be used for the differential diagnosis of tumors, the importance of close evaluation of stromal elements of tumors, and diligent application of electron microscopy in tumor diagnosis cannot be overemphasized.

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.

[Leiomyomatosis of the colon: case report and literature review]

We present the findings of a 67 year old male patient with an intestinal leiomyomatosis localized in the rectum. To our knowledge, this is the fifth case of intestinal leiomyomatosis reported so far. The most characteristic findings of this rare disease include a cuff-like tumorous proliferation of smooth muscle within the bowel wall which may extend into extramural tissue and result in a stenosis of a longer bowel segment. Because of severe obstructive symptoms over 5 years, the patient had to undergo surgery with resection of the rectum. The histological examination revealed a morphology and immunophenotype comparable to usual leiomyomas with the exception of hyalinosis-like changes in the blood vessels, apparently a special feature of leiomyomatosis. A novel finding in our case was the occurrence of skeinoid fibers which have so far only been reported in gastrointestinal stromal tumors.

Gastrointestinal stromal tumors: pathology and prognosis at different sites

Gastrointestinal (GI) stromal tumors (GISTs) are the most common mesenchymal tumors specific to the GI tract, generally defined as KIT (CD117)-positive tumors with a characteristic set of histologic features. These tumors, derived from Cajal cells or their precursors, most commonly occur at the age >50 years in the stomach (60%), jejunum and ileum (30%), duodenum (4-5%), rectum (4%), colon and appendix (1-2%), and esophagus (<1%), and rarely as apparent primary extragastrointestinal tumors in the vicinity of stomach or intestines. Their overall incidence has been estimated as 10 to 20 per million, including incidental minimal tumors. GISTs are rare in children (<1%) and almost exclusively occur in stomach. They are common in patients with neurofibromatosis 1, who have a predisposition to (multiple) small intestinal GISTs. GISTs contain a spectrum from minute indolent tumors to sarcomas at all sites of occurrence. Their gross patterns are diverse, including nodular, cystic, and diverticular tumors. External involvement of pancreas and liver can simulate primary tumor in these organs. In general, gastric tumors have a more favorable prognosis than the intestinal ones with similar parameters. Gastric GISTs < or =10 cm and < or =5 mitoses per 50 HPFs have a low risk for metastasis, whereas those with >5 per 50 HPFs and >5 cm in diameter have a high risk for metastasis. In contrast, all intestinal GISTs >5 cm independent of mitotic rate have at least moderate risk for metastases, and all >5 mitoses per 50 HPFs have a high risk for metastases. Intestinal GISTs < or =5 cm with < or =5 mitoses per 50 HPFs have a low risk for metastases. Gastric GISTs can be divided into histologic subgroups including 4 spindle cell and 4 epithelioid variants. Intestinal GISTs are a histologically more homogeneous group and often contain distinctive extracellular collagen globules, skeinoid fibers. Immunohistochemical demonstration of KIT, CD34, or protein kinase theta positivity helps to properly identify these tumors.

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

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

Gastrointestinal stromal tumors: review on morphology, molecular pathology, prognosis, and differential diagnosis

CONTEXT

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. They are believed to originate from interstitial cells of Cajal or related stem cells.

OBJECTIVE

To review current clinicopathologically relevant information on GIST.

DATA SOURCES

Literature in Medline and authors' own experience.

CONCLUSIONS

GISTs usually occur in older adults (median age 55-60 years) and rarely in children in the second decade (<1%) throughout the gastrointestinal tract: 60% in stomach, 35% in small intestine, and less than 5% in rectum, esophagus, omentum, and mesentery; most GISTs in the latter 2 sites are metastatic. Five percent of GISTs occur in patients with neurofibromatosis type 1 syndrome (multiple small intestinal tumors) and in Carney triad (gastric epithelioid GISTs in young females). Familial GISTs occur in patients with inheritable germline Kit or platelet-derived growth factor receptor alpha (PDGFRA) mutations. Histologically GISTs vary from spindle cell tumors to epithelioid and pleomorphic tumors. Most GISTs (95%) express Kit (CD117), CD34 (70%), and heavy caldesmon (80%), whereas 25% are positive for smooth muscle actin and less than 5% for desmin. Tumor size and mitotic activity are best predictive prognostic features; small intestinal tumors behave more aggressively than gastric tumors with similar parameters. Mutually exclusive gain-of-function Kit or PDGFRA mutations occur in a majority of GISTs representing in-frame deletions, point mutations, duplications and insertions. Mutations in Kit juxtamembrane domain (exon 11) are the most common in GISTs of all sites, whereas rare Kit extracellular domain (exon 9) Ala502-Tyr503 duplication is specific for intestinal GISTs. Mutations in PDGFRA have been identified in juxtamembrane (exon 12) and tyrosine kinase domains (exons 14 and 18), nearly exclusively in gastric GISTs, mostly in epithelioid variants. Some Kit and PDGFRA mutations have a prognostic value. Kit/PDGFRA tyrosine kinase inhibitor imatinib has been successfully used in the treatment of metastatic GISTs for more than 5 years. However, primary and acquired secondary resistance linked to certain types of Kit and PDGFRA mutations is limiting long-term success necessitating the use of alternative treatments.

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

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

Gastrointestinal stromal tumors of the jejunum and ileum: a clinicopathologic, immunohistochemical, and molecular genetic study of 906 cases before imatinib with long-term follow-up

Gastrointestinal (GI) stromal tumors (GISTs), the specific KIT- or PDFGRA-signaling driven mesenchymal tumors, are the most common mesenchymal tumors of the GI tract. This study analyzed 1091 tumors originally classified as smooth muscle tumors of the small intestine (including jejunum or ileum and excluding duodenum), and found that 906 (83%) of these were GISTs. The GIST patients had 55:45 male-to-female ratio with a median age of 59 years (range, 13-94 years). Only 0.6% of tumors occurred before the age of 21 years and 13.6% before the age of 40 years. The tumors varied from 0.3 to 40 cm (median, 7.0 cm) and most commonly presented with GI bleeding or acute abdomen; 18% were incidentally detected. Histologically, the tumors were relatively monotypic with spindle cell (86%), epithelioid (5%), or mixed patterns (9%). Skeinoid fibers were present in 44% of cases, and their presence was associated with a favorable course. Most epithelioid tumors were malignant, and this morphology sometimes emerged from less cellular and less mitotically active spindle cell tumors, suggesting that it represented a transformation. KIT was immunohistochemically detected in 98%, CD34 in 40%, smooth muscle actin in 34%, desmin in 0.2%, and S-100 protein in 14% of the tumors tested. Outcome was strongly dependent on tumor size and mitotic activity, with an overall 39% tumor-related mortality, twice that for gastric GISTs. Only <3% of tumors <5 cm and < or = 5 mitoses/50 HPF metastasized, whereas 86% of tumors >10 cm and >5 mitoses/50 HPF metastasized. In stark contrast to corresponding gastric tumors, tumors >10 cm with mitotic activity < or = 5/50 HPF and those < or = 5 cm with mitoses >5/50 HPF had a high metastatic rate (>50%); tumors >5 cm < or = 10 cm with low mitotic rate had a 24% metastatic rate. The median survival times of patients with low mitotic rate tumors who died of disease decreased by increasing tumor size. KIT exon 11 mutations were detected in 90 cases, exon 9 mutation in 17 cases, and exon 17 mutation in 1 case; the presence of mutation or mutation type was not prognostically significant. There were no PDGFRA exon 12 or 8 mutations. Systematic data on prognosis of small intestinal GISTs of various size and mitotic activity categories can be helpful in management and surveillance of patients with these tumors.

[Gastrointestinal stromal tumors: definition, histological, immunohistochemical, and molecular features, and diagnostic strategy]

Gastrointestinal stromal tumors (GISTs) are the most frequent mesenchymal tumors of the gastrointestinal tract. Major advances in their definition and classification and the understanding of their molecular mechanisms have recently been made. These advances have resulted in the delineation of a treatment that has become a model of targeted therapy in oncology. GISTs are defined as tumors of the gastrointestinal tract, but also of the mesentery and peritoneum, constituted by a proliferation of usually spindle-shaped, rarely epithelioid cells, usually, but not consistently expressing the KIT protein. Most GISTs are associated with molecular abnormalities in two target genes: KIT (which encodes the KIT protein) and PDGFRA (which encodes the A chain of the PDGF receptor). The diagnosis of GIST relies on histological arguments (proliferation of spindle-shaped cells in 70% of cases, of epithelioid cells in 20%; histological variants are rare and sometimes misleading) and on immunohistochemical arguments (expression of KIT in 95%, usually associated with CD34 expression in 60%-70% of cases). The demonstration of mutations in target genes is required only in cases that are histologically suggestive but KIT-negative; beyond this indication, this is only undertaken in research protocols. The differential diagnosis of GIST includes the other mesenchymal tumors of the gastrointestinal tract, such as leiomyomas and leiomyosarcomas, and the digestive locations of some sarcomas; it relies on both histological and immunohistochemical arguments. The evaluation of the prognosis is essential. According to the current concept, every GIST carries a risk of malignancy, which may vary from very low to very high. Prognosis is based on a simple algorithm using two histoprognostic parameters, i.e., tumor size and mitotic index. The treatment of localized GIST is surgical resection, which must be complete; that of advanced or unresectable GIST is based on the use of a targeted therapy, imatinib, which is a pharmacological antagonist of the KIT protein. Proper understanding and utilisation of the diagnostic criteria and classification of GIST by pathologists are essential for good patient management.

Pathology of gastrointestinal stromal tumors

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

Gastrointestinal stromal tumors in patients with neurofibromatosis 1: a clinicopathologic and molecular genetic study of 45 cases

Gastrointestinal stromal tumors (GISTs), the specific KIT- or PDFGRA-signaling driven mesenchymal tumors, most commonly occur sporadically, but there seems to be some increased tendency for these tumors to develop in patients with neurofibromatosis 1 (NF1). The clinicopathologic profile, KIT, and PDGFRA mutation status and long-term prognosis of patients with GIST in NF1 are incompletely characterized. In this study, we analyzed 45 patients who had NF1 and GIST. There were 26 females and 19 males with a median age of 49 years (10 years lower than the median age of GIST patients in general). A great majority of tumors occurred in the jejunum or ileum, with multiple tumors occurring in 28 cases. Ten patients had a duodenal and one had a gastric GIST. The most common presentations were gastrointestinal bleeding and anemia, and many patients had intermittent bleeding over several years. The majority of the tumors were small and mitotically inactive; only 7 had mitotic activity >5/50 HPFs and 15 tumors were >5 cm. Associated Cajal cell hyperplasia was common. One patient had an intraabdominal peri-intestinal neurofibroma. Five of 35 patients with follow-up died of metastatic disease; all of these had a tumor >5 cm, mitotic rate >5/50 HPFs, or both; three of these tumors were located in the duodenum. The presence of multiple small tumors was not associated with progressive disease. Most patients with long-term follow-up enjoyed a good prognosis; 2 died of other NF1-associated tumors (malignant peripheral nerve sheath tumors, brain tumor). None of the 16 tumors from 15 patients had a KIT exon 9, 11, 13, or 17 or PDGFRA exon 12 or 18 mutation as is typically seen in sporadic GISTs, indicating that GISTs in NF1 patients have a different pathogenesis than sporadic GISTs.

The comparative roles of electron microscopy and immunohistochemistry in the diagnosis of soft tissue tumours

Electron microscopy has contributed to the diagnosis of soft tissue tumours for four decades, and immunohistochemistry for two. Because of its relative ease of use and interpretation, the latter technique has become extensively and routinely applied to identify lines of differentiation in benign soft tissue tumours and in sarcomas. The use of electron microscopy has declined but retains a role because few antibodies are wholly specific or fully sensitive, some tumours are polyphenotypic or divergent in differentiation, and others have no specific antigens. Immunohistochemistry is superior in diagnosis of smooth muscle tumours, small round cell tumours, sarcomas with epithelioid morphology, and most synovial sarcomas. Electron microscopy is of particular value for peripheral nerve sheath tumours, marker-negative synovial sarcomas, pleomorphic sarcomas and mesotheliomas. As with all adjunctive techniques, immunohistochemistry and electron microscopy should be used in a complementary fashion according to the nature of the diagnostic problem.

Gastrointestinal stromal tumours: an update

Recently, there has been intense interest in the study of gastrointestinal stromal tumour (GIST); one might call it a virtual GIST revolution. This is due largely to the realization that most GISTs express KIT and harbour activating c-KIT (KIT) or platelet-derived growth factor receptor-alpha (PDGFRA) receptor tyrosine kinase mutations that can be targeted by small molecule pharmacological inhibitors. Pathologists have benefited greatly from this revolution, mainly in the form of an improved ability to classify GISTs and, even more recently, in understanding the molecular underpinnings that underlie many fascinating clinical and pathological correlations. It is the purpose of this review to summarize recent developments in GIST classification and the molecular pathogenesis of GIST.

Differential expression of connexin 43 in gastrointestinal stromal tumours of gastric and small intestinal origin

Gastrointestinal stromal tumours (GISTs) are considered to originate from interstitial cells of Cajal (ICCs). ICCs are classified into several subtypes according to their location or roles. Several reports indicate that GISTs of the small intestine appear to have different clinical and pathological characteristics from gastric GISTs. We previously found using a cDNA expression chip that connexin 43, a component of gap junctions, is expressed specifically in small intestinal GISTs but not in gastric GISTs. To confirm the specificity of connexin 43 expression, we analysed 10 small intestinal GISTs and 15 gastric GISTs by northern blotting, western blotting and immunohistochemistry in this study. Northern blotting was performed in five small intestinal GISTs and five gastric GISTs, and revealed connexin 43 mRNA expression in all of the five small intestinal GISTs, but in none of the gastric GISTs. By western blotting, bands corresponding to connexin 43 were easily detected in all of the five small intestinal GISTs studied but were absent in all five gastric GISTs analysed. Immunohistochemistry showed that all of the 10 small intestinal GISTs were positive for connexin 43 but only one of 15 gastric GISTs, which exhibited a mutation in exon 9 of the KIT gene, was connexin 43-positive. We also examined the localization of connexin 43 in the normal stomach and small intestine. Immunoreactivity for connexin 43 was present in both normal gastric and small intestinal circular muscle layers, but it was unclear which cell type was positive. These results suggest that GISTs are divided into at least two groups, namely the gastric subtype and the small intestinal subtype, through phenotype but not location. Furthermore, these data indicate that the gastric and the small intestinal subtypes of GIST may originate from different subtypes of ICC.

Gastrointestinal stromal tumors metastatic to the ovary: a report of five cases

Five cases of gastrointestinal stromal tumor metastatic to the ovary are reported. The average patient age was 59 years (range, 44-81 years). The primary tumor was in the small bowel or its mesentery (4 cases) or stomach (1 case). The primary and metastatic tumors were discovered synchronously in 3 cases. In the other 2 cases, the ovarian tumors were discovered 18 months before a gastric tumor was identified and 27 years after a small bowel tumor had been resected. The ovarian tumors (three of which were bilateral) were usually solid, tan, and lobulated. Microscopically, three tumors had a pure spindle cell morphology, and two both spindle and epithelioid cell components. The diagnosis in all 5 cases was confirmed with positive c-kit (CD117) and negative desmin immunostaining. Variably positive immunoreactivity for either or both h-caldesmon and smooth muscle actin was seen in all 5 cases, and 3 cases were CD34-positive. Four patients died between 1 and 6.5 years (mean, 2.8 years) from the time of ovarian tumor diagnosis. The main differential diagnostic consideration was leiomyosarcoma; the most important features to help exclude this diagnosis were an absence of tumor in the uterus, low histologic grade, and a desmin-negative, c-kit-positive immunophenotype. Other differential considerations, including endometrial stromal sarcoma and fibrosarcoma, are discussed. Most of the ovarian tumors in this series were initially diagnosed as tumors of other types, a misdiagnosis with significant therapeutic and prognostic implications because of the specific therapy now available for gastrointestinal stromal tumors.

Small bowel gastrointestinal stromal tumours and ampullary cancer in Type 1 neurofibromatosis

BACKGROUND

Type 1 neurofibromatosis (NF-1) is an autosomal dominant disorder with variable penetrance; approximately 50% of cases present as new mutations

CASE REPORT

We report a case of a 56 year-old man with Von Recklinghausen's disease, carcinoma of the ampulla of Vater and incidental benign gastrointestinal stromal tumours of the jejunum.

CONCLUSIONS

Coexistence between ampullary carcinoid, ectopic pancreatic tissue in the jejunum and neurofibroma of the jejunum in NF-1 has been previously described however; the association of synchronous carcinoma of the ampulla of Vater and gastrointestinal stromal tumour of the jejunum in NF-1 has not been previously reported.

Epithelioid variant of gastrointestinal stromal tumor: Diagnosis by fine-needle aspiration

Epithelioid gastrointestinal stromal tumors (GISTs) may cause significant diagnostic confusion on fine-needle aspiration (FNA) with carcinomas, neuroendocrine tumors, and melanoma, particularly when metastatic. This study characterizes the cytologic features of nine cases of epithelioid GISTs that were obtained by computerized tomographic guidance in five, by endoscopic ultrasound in three, and from an excised liver tumor in one. Six cases presented as liver masses, one as a perisplenic mass, one as an abdominal mass, and one as a gastric mass. The aspirates revealed mainly single or small clusters of epithelioid cells with a moderate amount of granular to clear cytoplasm, small uniform nuclei with mild to marked nuclear envelope irregularities. Binucleation and intranuclear inclusions were frequent findings. Collagenous stroma was seen in most cases. In three cases, a neuroendocrine tumor was the initial diagnosis. Immunocytochemical staining for c-kit (CD117) was performed on cellblocks in six cases and was positive in five cases. On the subsequent surgical specimen, CD117 was positive in the c-kit-negative cytology case. The diagnosis of GIST should be considered in aspirates of the gastrointestinal tract, liver, mesentery, or abdominal wall mass lesions when epithelioid cells are the predominant cell type. Ancillary studies such as immunohistochemical stains are usually helpful in making a definitive diagnosis.

[Small intestinal stromal tumors with skenoid fibers. Clinicopathological study of three cases]

Gastrointestinal stromal tumours (Gist) are mesenchymal tumour with uncertain prognosis occurring in the gastrointestinal tract wall. For clinicians, these tumours raise two problems: to establish the diagnosis and to determinate the future behaviour for the choice officient therapeutics. For the diagnosis the new marker c-KIT is useful. A new treatment with an inhibitor of c-KIT has given encouraging results. currently there is no consensus on specific cut-points to distinguish as low or high risk (i.e., malignant) Gist. For metastases-free Gist, the prominent histopronostic markers are size, mitotic index and localization of the tumour. The small intestine Gist have the reputation to be more aggressive than in other localization. Skenoid fibers in small intestine Gist could be a marker of good prognostic. The authors reported three cases of small intestine Gist with skenoid fibers. The discussion point out the significance of this particular morphological aspect.

Gastrointestinal stromal tumors, intramural leiomyomas, and leiomyosarcomas in the duodenum: a clinicopathologic, immunohistochemical, and molecular genetic study of 167 cases

In this study we analyzed the clinicopathologic features of duodenal smooth muscle or stromal tumors, including 156 GISTs, 6 leiomyomas (LMs), and 5 leiomyosarcomas (LMSs) from the files of the Armed Forces Institute of Pathology and the Haartman Institute of the University of Helsinki. GISTs were documented as KIT positive (n = 109); 47 tumors were also included because of their histologic identity to KIT-positive cases. GIST-specific c-kit gene mutations were documented in exon 11 in 9 of 30 cases (30%) and exon 9 in 4 of 30 cases (13%). The GISTs occurred in patients with an age range of 10-88 years (median 56 years); 54% were male. Ten patients had neurofibromatosis type I; six of them had multiple GISTs. The GISTs ranged from small asymptomatic intramural or external nodules to large masses that extended into the retroperitoneum (median size 4.5 cm). They were mostly spindle cell tumors; three malignant GISTs had an epithelioid morphology, and 81 cases had skeinoid fibers. The tumors often coexpressed CD34 and KIT (54%) and were variably positive for smooth muscle actin (39%) and S-100 protein (20%) but never for desmin. A total of 86% of patients with tumors >5 cm with >5 mitoses/50 high power fields (HPF) (n = 21) died of disease, whereas no tumor <2 cm with <5 mitoses/50 HPF (n = 12) recurred or caused death. Long latency was common between primary operation and recurrences or metastases; either one occurred in 49 of 140 patients with follow-up (35%). No formula could accurately predict metastases, which occasionally developed even if mitotic activity was <5/50 HPF and size <5 cm. Metastases were in the abdominal cavity, liver, and rarely in bones and lungs but never in lymph nodes. Four actin- and desmin-positive and KIT-negative benign intramural LMs were similar to those more often seen in the esophagus. There were five LMSs, one of which formed a polypoid intraluminal mass; all were actin positive and KIT negative. The great majority of duodenal mesenchymal tumors are GISTs, which have a spectrum from small indolent tumors to overt sarcomas. LMs and LMSs are rare.

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

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

Gastrointestinal stromal tumors: radiologic features with pathologic correlation

Gastrointestinal stromal tumors (GISTs) are unique neoplasms that occur throughout the gastrointestinal tract, mesentery, omentum, and retroperitoneum. They are the most common mesenchymal neoplasm of the gastrointestinal tract and are defined by their expression of KIT (CD117), a tyrosine kinase growth factor receptor. The expression of KIT is important to distinguish GISTs from other mesenchymal neoplasms such as leiomyomas, leiomyosarcomas, schwannomas, and neurofibromas and to determine the appropriateness of KIT-inhibitor therapy. The series described herein was accumulated over 2 years and includes 64 pathologically proved GISTs (28 gastric, 27 small intestinal, six anorectal, one colonic, one esophageal, and one from the small bowel mesentery). Radiologic features of GISTs vary depending on tumor size and organ of origin. Since most GISTs arise within the muscularis propria of the stomach or intestinal wall, they most commonly have an exophytic growth pattern and manifest as dominant masses outside the organ of origin. Dominant intramural and intraluminal masses are less common radiologic manifestations. GISTs occurring in the gastrointestinal tract and mesentery characteristically have hemorrhage, necrosis, or cyst formation that appears as focal areas of low attenuation on computed tomographic images. Although the radiologic features of GISTs are often distinct from those of epithelial tumors, criteria to separate GISTs radiologically from other nonepithelial tumors have not yet been fully developed.

Gastrointestinal stromal tumors (GIST): C-kit mutations, CD117 expression, differential diagnosis and targeted cancer therapy with Imatinib

Gastrointestinal stromal tumors (GISTs) have been recognised as a biologically distinctive tumor type, different from smooth muscle and neural tumors of the gastrointestinal tract. They constitute the majority of gastrointestinal mesenchymal tumors. They are defined and diagnosed by the expression of a protooncogene protein called CD117 detected by immunohistochemistry. It is now believed that GISTs originate from gastrointestinal pacemaker cells known as interstitial cells of Cajal, that control gut motility or from a precursor of these cells. The identification of mutations mostly in exon 11 and to a lesser extent in exons 9 and 13 of the c-kit protooncogene coding for c-kit (CD117) in many GISTs, has resulted in a better understanding of their oncogenic mechanisms. The finding of remarkable antitumor effects of the molecular inhibitor, imatinib (Glivec trade mark ) in metastatic and inoperable GISTs, has necessitated accurate diagnosis of GISTs and their distinction from other gastrointestinal mesenchymal tumors. To achieve this, pathologists need to be familiar with the spectrum of histological appearances shown by GISTs and have a high index of suspicion for these tumors. This review summarises recent advances in knowledge regarding the histogenesis, pathology, molecular biology, genetics and differential diagnosis of GISTs and the basis for the novel targeted cancer therapy with imatinib.

Pathology and diagnostic criteria of gastrointestinal stromal tumors (GISTs): a review

Gastrointestinal stromal tumor (GIST) is the designation for the specific c-kit expressing and Kit-signaling driven mesenchymal tumors, many of which have Kit-activating mutations. The specific identification of GIST has become increasingly important because a Kit-selective tyrosine kinase inhibitor, imatinib (Glivec, formerly known as STI571, Novartis Pharma AG, Basel, Switzerland), has shown promise as an effective adjuvant therapy treatment. GISTs are the most common mesenchymal tumors of the gastrointestinal (GI) tract. We estimate the frequency of malignant GISTs as 20% to 30% of the frequency of all soft-tissue sarcomas, but small benign tumors, often found incidentally during unrelated surgery or autopsy, are probably much more common. Older adults are most at risk for GIST; very rarely, GIST occurs in children and young adults (sometimes connected with Carney's triad), or on a familial basis. GISTs have been documented in all parts of the GI tract. A great majority of them occur in the stomach (60% to 70%) and small intestine (25% to 35%), with rare occurrence in the colon and rectum (5%), esophagus (<2%) and appendix. Some GISTs are primary in the omentum, mesentery or retroperitoneum, and are unrelated to the tubular GI tract. GISTs can be histologically identified as highly cellular spindle cell or epithelioid mesenchymal tumors, and morphology is somewhat site-dependent. However, common to all these tumors is expression of Kit (CD117 antigen), which is a major diagnostic criterion. Few other Kit-positive mesenchymal tumors of the GI tract are likely to be confused with GISTs; exceptions are metastatic melanoma and related tumors and malignant vascular tumors. Additional diagnostic criteria include common positivity for CD34 (70%), variable expression of smooth muscle actins (20% to 30%) and S100 protein (10%) and almost uniform negativity for desmin (only 2% to 4% of GISTs are positive). Although the prediction of malignancy in this tumor group is notoriously difficult, tumors that have mitotic activity counts exceeding 5 per 50 high power fields (HPF) or those larger than 5 cm have a high frequency of intra-abdominal recurrence and liver metastasis. In contrast, tumors smaller than 2 cm and those with mitotic activity counts <5 per 50 HPF are likely to be benign. These diagnostic criteria leave an inevitable gray area in the separation of benign and malignant tumors. Kit-activating mutations can be detected in at least 60% to 70% of GIST cases. Most of the mutations, in-frame deletions of several codons, are located in the juxtamembrane domain (exon 11) of the gene. Less commonly, mutations have been detected in the extracellular domain (exon 9), and tyrosine kinase domains (exons 13 and 17). Functional analysis of the different c-kit mutations and their impact on the response to tyrosine kinase inhibitors are under intense investigation.

Gastrointestinal stromal tumor: consistent CD117 immunostaining for diagnosis, and prognostic classification based on tumor size and MIB-1 grade

Gain-of-function c-kit gene mutations and immunoreactivity of the c-kit protein CD117 in many gastrointestinal stromal tumors (GISTs) seem to support the idea that GISTs form a biologically distinct entity. In this study, the clinicopathologic features of 171 cases of GIST at a single institution were investigated for accurate diagnosis, and their relative risk for mortality was estimated by multivariate analysis. A GIST was defined diagnostically as a mesenchymal spindle or epithelioid cell lesion arising in the wall of the gastrointestinal tract with consistent immunoreactivity for CD117. The 171 patients with GISTs comprised 96 males (56.1%) and 75 females (43.9%), with a mean age of 59.4 years. One hundred and forty-five tumors (84.8%) occurred in the stomach, 18 (10.5%) in the small intestine, 6 (3.5%) in the rectum, and 2 (1.2%) in the esophagus. The median tumor size was 4.5 cm (range, 1.2 to 38 cm). Spindle-cell GISTs were present in 132 cases (77.2%); mixed GISTs, in 25 cases (14.6%); and epithelioid GISTs, in 14 cases (8.2%). Ten cases (55.6%) of spindled small intestine GIST contained eosinophilic skeinoid fibers. Immunoreactivity for CD34, h-caldesmon, alpha-smooth-muscle actin (SMA), desmin, and S-100 was observed in 156 (91.2%), 131 (76.6%), 46 (26.9%), 7 (4.1%), and 14 (8.2%) tumors, respectively. The percentage of CD34 positivity (38.8%) was low, in contrast with the high percentage of reactivity for SMA (77.8%) and S-100 (44.4%) in small intestine GISTs. By our histologic grading system using tumor differentiation, MIB-1 score, and necrosis, 129 tumors (75.4%) were classified as low grade and 42 tumors (24.6%) were classified as high grade. With a median follow-up period of 83.5 months for 122 living patients, the 5-year and 10-year survival rates were 81.7% and 67.4%, respectively. Multivariate analysis showed that both tumor size >10 cm and high grade were significantly associated with a poor outcome. As a result, GISTs >10 cm or high grade, 5 to 10 cm and low grade, and < or =5 cm and low grade were regarded as high risk, intermediate risk, and low risk for mortality, respectively. In conclusion, it is important to recognize GISTs that have a specific molecular pathogenesis and to separate them from other mesenchymal tumors with optimal immunostaining for CD117 when making a diagnosis and prognostic classification based on tumor size and MIB-1 grade.

Diagnosis of gastrointestinal stromal tumors: A consensus approach

As a result of major recent advances in understanding the biology of gastrointestinal stromal tumors (GISTs), specifically recognition of the central role of activating KIT mutations and associated KIT protein expression in these lesions, and the development of novel and effective therapy for GISTs using the receptor tyrosine kinase inhibitor STI-571, these tumors have become the focus of considerable attention by pathologists, clinicians, and patients. Stromal/mesenchymal tumors of the gastrointestinal tract have long been a source of confusion and controversy with regard to classification, line(s) of differentiation, and prognostication. Characterization of the KIT pathway and its phenotypic implications has helped to resolve some but not all of these issues. Given the now critical role of accurate and reproducible pathologic diagnosis in ensuring appropriate treatment for patients with GIST, the National Institutes of Health convened a GIST workshop in April 2001 with the goal of developing a consensus approach to diagnosis and morphologic prognostication. Key elements of the consensus, as described herein, are the defining role of KIT immunopositivity in diagnosis and a proposed scheme for estimating metastatic risk in these lesions, based on tumor size and mitotic count, recognizing that it is probably unwise to use the definitive term "benign" for any GIST, at least at the present time.

Gastrointestinal stromal tumors: an ultrastructural study

Gastrointestinal stromal tumors (GISTs) represent an enigmatic group of lesions of uncertain phenotype and biologic potential. Although earlier studies suggested smooth muscle cells, schwann cells, or neuronal differentiation, more recent evidence indicates that these tumors show phenotypic features that are similar to the interstitial cells of Cajal. Recently, investigators have begun to evaluate these lesions in a site-specific manner and have found that, in addition to morphologic differences between them, their biologic behavior also appears to be linked to their anatomic location. Many of these studies have emphasized the histologic and immunophenotypic features of GISTs in relation to their sites of origin, however, their site-specific ultrastructural characteristics have received little attention in the literature. In this study, we evaluated 34 GISTs (15 gastric, 12 small intestinal, 4 colonic, and 3 omental) for a variety of ultrastructural features in an effort to identify site-specific similarities and differences. Tumors predominantly composed of epithelioid cells were more commonly seen in gastric (60%) and omental (67%) tumors than in those of the small intestine (33%) and colon (0%). Cytoplasmic filaments and intercellular junctions were commonly seen in tumors from all locations, the filaments frequently forming paranuclear aggregates in the epithelioid cells. Tumors from all sites were composed of cells with surface filopodia and interdigitating cell processes, but in tumors of the stomach and omentum the filopodia were usually short and minimally intertwined, whereas those of small and large intestinal GISTs were characteristically long and complex. Basal lamina, though poorly formed, was present only in tumors of gastric and omental origin (13% and 67%, respectively). Pinocytotic vesicles were also seen in tumors from these sites (33% of gastric tumors and 67% of omental lesions) as well as those of the small intestine (17%) and the colon (25%). None of the gastric or omental tumors had microtubules; they were, however, seen in small intestinal (33%) and colonic (25%) stromal tumors. Skenoid fibers were seen in 33% of small intestinal GISTs and 1 metastatic gastric GIST. Overall, gastric and omental tumors have better developed features of myogenic differentiation and have blunt filopodia and minimally intertwined cell processes. Indeed, these 2 groups are indistinguishable ultrastructurally, raising the possibility that the genesis of omental GISTs is similar to that of gastric stromal tumors. Small intestinal stromal tumors have characteristic interdigitating cell processes and numerous elongate filopodia-like structures harboring intercellular junctions as well as microtubules and extracellular skenoid fibers. The constituent cells in colonic stromal tumors, while more reminiscent of small intestinal stromal, were frequently more primitive in appearance. In conclusion, GISTs from different anatomic locations share many overlapping ultrastructural characteristics; however, a few features are distinctive. It is hoped that these findings will aid in their recognition and contribute to the classification of this heterogeneous group of neoplasms.

Diagnosis of gastrointestinal stromal tumors: a consensus approach

As a result of major recent advances in understanding the biology of gastrointestinal stromal tumors (GIST), specifically recognition of the central role of activating KIT mutations and associated KIT protein expression in these lesions, and the development of novel and effective therapy for GISTs using the receptor tyrosine kinase inhibitor STI-571, these tumors have become the focus of considerable attention among pathologists, clinicians, and patients. Stromal/mesenchymal tumors of the gastrointestinal tract have long been a source of confusion and controversy with regard to classification, line(s) of differentiation, and prognostication. Characterization of the KIT pathway and its phenotypic implications has helped to resolve some but not all of these issues. Given the now critical role of accurate and reproducible pathologic diagnosis in ensuring appropriate treatment for patients with GIST, the National Institutes of Health (NIH) convened a GIST workshop in April 2001 with the goal of developing a consensus approach to diagnosis and morphologic prognostication. Key elements of the consensus, as described herein, are the defining role of KIT immunopositivity in diagnosis and a proposed scheme for estimating metastatic risk in these lesions, based on tumor size and mitotic count, recognizing that it is probably unwise to use the definitive term benign for any GIST, at least at the present time.

Multiple small intestinal stromal tumours in a patient with previously unrecognised neurofibromatosis type 1: immunohistochemical and ultrastructural evaluation

Neurofibromatosis type 1 could be associated with multiple gastrointestinal stromal tumours, although their presence is not considered among the major diagnostic criteria. We present here a case of a 50-year-old female complaining of abdominal pain, with about 100 small intestinal stromal tumours. This finding prompted us to suspect a neurofibromatosis which was clinically confirmed afterwards. Light microscopy examination revealed a low-grade stromal tumour with skeinoid fibres. Mixed neural-interstitial cells of Cajal origin or, alternatively, neural differentiation of interstitial cells of Cajal are discussed on the basis of immunophenotype (CD117+, CD34+) and ultrastructure. A 2-year follow-up did not indicate an aggressive course in the case of this neoplasm.

Cytologic diagnosis of gastrointestinal stromal tumors of the stomach by endoscopic ultrasound-guided fine-needle aspiration biopsy: cytomorphologic and immunohistochemical study of 12 cases

Gastrointestinal stromal tumor (GIST) is an uncommon tumor, which was usually diagnosed by endoscopic biopsy or surgical resection. This study evaluated the efficacy and accuracy of endoscopic ultrasound (EUS) -guided fine-needle aspiration (FNA) biopsy in the diagnosis of GIST and reported its cytomorphologic features. Twelve patients with gastric GIST were diagnosed through EUS-guided FNA. Immediate on-site evaluation and cytologic diagnoses were given in nine cases (75.0%) with an average of three passes. Cell blocks provided diagnostic material in three cases (25.0%). Spindle cells were present in the cytologic material in all cases. Two patients had subsequent surgical resections. Immunohistochemical (IHC) studies performed in cell blocks and two surgical specimens all supported the original diagnoses. In the two cases with surgical resections, IHC results in cell blocks were similar to that in the resected specimens. This study demonstrated that when combining smears and cell blocks, EUS-guided FNA is accurate and efficient in the diagnosis of GIST. IHC reactivity in cell blocks correlated with that of the main tumors.

Gastrointestinal stromal tumors in the appendix: a clinicopathologic and immunohistochemical study of four cases

Mesenchymal tumors of the appendix are very rare, and specific stromal tumors (i.e., gastrointestinal stromal tumors, GISTs) have not been reported in this location to date. Four GISTs were identified in the review of primary mesenchymal tumors of the appendix from the files of the Armed Forces Institute of Pathology from 1970 to 1998. There were also one benign schwannoma, one diffuse neurofibroma with neurofibromatosis 1, one leiomyosarcoma in a child with HIV infection, and one inflammatory fibroid polyp. The four appendiceal GISTs occurred in adult males 56-72 years of age (mean 63 years). Two tumors occurred in patients who had surgery for appendicitis-like symptoms: one was an incidental finding during surgery for a malignant gastric epithelioid GIST and one was an incidental autopsy finding. Only one of the two appendices operated for symptoms had acute inflammation, and a polypoid GIST projected outward from the proximal part of appendix. Three tumors were partially obliterating nodules, eccentrically expanding the appendiceal wall. All four were spindle cell tumors, and three of them contained extracellular collagen globules (skeinoid fibers); none had atypia or mitotic activity (<1/50 high power fields). Immunohistochemically, two tumors studied were positive for CD117 (KIT), and two were positive for CD34. The tumors were negative for alpha-smooth muscle actin and S-100 protein. Follow-up revealed death from cardiovascular disease in one case (4 years after appendectomy) and liver failure because of malignant gastric epithelioid GIST metastatic to liver in another case 15 years after the appendectomy. This report documents the rare occurrence of CD117-positive GISTs as primary appendiceal tumors.

Gastrointestinal stromal tumors, intramural leiomyomas, and leiomyosarcomas in the rectum and anus: a clinicopathologic, immunohistochemical, and molecular genetic study of 144 cases

Gastrointestinal stromal tumors (GISTs), the specific KIT-positive mesenchymal tumors of the gastrointestinal tract, have been sporadically reported in the rectum, but there are few clinicopathologic series. In this study we analyzed the clinicopathologic features of 133 anorectal GISTs, 3 intramural leiomyomas (LMs), and 8 leiomyosarcomas (LMSs) from the files of the Armed Forces Institute of Pathology and the Haartman Institute of the University of Helsinki. Ninety-six GISTs were documented as KIT-positive and three additional ones as CD34-positive. Thirty-four tumors were included by their histologic similarity to KIT- or CD34-positive cases. GIST-specific c-kit gene mutations, mostly in exon 11, were documented in 18 of 29 cases (62%). The GISTs occurred in adults with the age range of 17-90 years (median 60 years) with a significant male predominance (71%). The tumors ranged from small asymptomatic intramural nodules to large masses that bulged into pelvis causing pain, rectal bleeding, or obstruction. They were mostly highly cellular spindle cell tumors; four tumors had an epithelioid morphology. The tumors coexpressed CD34 and KIT and were rarely positive for smooth muscle actin or desmin and never for S-100 protein. Seventy percent of patients with tumors >5 cm with more than 5 mitoses/50 high power fields (HPF) (n = 31) died of disease, whereas only one tumor <2 cm with <5 mitoses/50 HPF (n = 21) recurred and none caused death. Long latency was common between primary operation and recurrences and metastases; either one occurred in 60 of 111 patients with follow-up (54%). Distant metastases were in the liver, bones, and lungs. Three benign actin- and desmin-positive and KIT-negative intramural LMs, similar to those seen in the esophagus, were identified. There were eight LMSs, six of which formed a polypoid intraluminal mass and were actin-positive and KIT-negative. Despite high mitotic counts, only one LMS patient died of disease. A great majority of rectal smooth muscle and stromal tumors are GISTs, which have a spectrum from minimal indolent tumors to overt sarcomas. Intramural LMs are exceptional, and true LMSs are rare, and similar to colonic ones, often present as intraluminal polypoid masses that appear to have a better prognosis than GISTs with similar mitotic rates.

Intra-abdominal spindle cell lesions: a review and practical aids to diagnosis

Intra-abdominal spindle cell lesions are uncommon and often present a diagnostic challenge. An important group of such lesions are the gastrointestinal stromal tumours. Other intra-abdominal spindle cell lesions include fibromatosis, various sarcomas-in particular, leiomyosarcoma, liposarcoma, and malignant peripheral nerve sheath tumour-and, in women, endometrial stromal sarcoma. Less common lesions are inflammatory myofibroblastic tumours, the mesenteric spindle cell reactive lesions, retroperitoneal fibrosis, and solitary fibrous tumour. A variety of intra-abdominal tumours of nonmesenchymal origin may have a spindle cell/sarcomatoid morphology; these include sarcomatoid carcinoma, malignant melanoma and, in women, sarcomatoid granulosa cell tumour. Finally, metastatic sarcomas from pelvic or extra-abdominal organs need also be considered. A set of practical aids to the diagnosis of intra-abdominal spindle cell lesions is presented to assist pathologists dealing with such lesions, particularly with regards to the consideration of differential diagnoses.

Relationship between skeinoid fibers and stromal matrix in gastrointestinal stromal tumors: morphometric analysis with quick-freezing and deep-etching method

Our previous study of a gastrointestinal autonomic nerve tumor with skeinoid fibers (SF) using the quick-freezing and deep-etching method, suggested that the distance between one radix and a neighboring radix (DRNR) in pre-existing meshwork structures around the tumor cells is consistent with the periodicity of the SF. Therefore, measurement of the DRNR in the meshwork could clarify the significance of the pericellular matrix for SF development. In the present study, we analyzed the meshwork in three cases of gastrointestinal stromal tumor (GIST), which showed different immunohistochemical stainings, but confirmed to have smooth muscle differentiation (SMD) by immunohistochemistry and/or electron microscopy. The DRNR from the three cases of GIST showed similar histogram patterns (a peak of 20-30 nm, mean values of 28.02, 25.74 and 26.45 nm), which were significantly shorter than the periodicity of SF (a peak of 40-45 nm, mean value of 42.14). Although we need further studies with additional GIST cases, we speculate that the pericellular matrix of GIST with SMD is not suitable for SF development.