Immunohistochemical spectrum of GISTs at different sites and their differential diagnosis with a reference to CD117 (KIT)

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.

Immunohistochemistry in the diagnosis of soft tissue tumours

Immunohistochemistry is particularly important in the field of soft tissue tumours because of their variety and the frequent difficulty of diagnosis. The first part of this paper discusses useful or new antibodies, together with others that are no longer of use. The second part is devoted to the role of immunohistochemistry in the diagnosis of soft tissue tumours: identification of some rare or atypical benign lesions, identification of non-mesenchymal malignant tumours, and classification of sarcomas. The respective roles of immunohistochemistry and molecular biology are underlined.

Gastrointestinal stromal tumors: a spectrum of disease

The majority of gastrointestinal stromal tumors (GIST) express c-kit, a growth factor receptor with tyrosine kinase activity. Mutations in the c-kit proto-oncogene may lead to constitutive ligand-independent activation of c-kit and subsequent neoplastic transformation. Selective tyrosine kinase inhibitors target this property of GIST and have become the standard chemotherapy for metastatic or unresectable tumors. The mainstay of treatment, however, continues to be complete surgical resection. Tyrosine kinase inhibitors may prove expedient for adjuvant therapy, and are currently the focus of clinical trials conducted by the ACOSOG, RTOG, and ACRIN. It is important to distinguish GISTs from other mesenchymal tumors of the GI tract because of differences in natural history, as well as the efficacy of treatments targeting the GIST tyrosine kinase.

Expression of KIT and epidermal growth factor receptor in chemotherapy refractory non-seminomatous germ-cell tumors

BACKGROUND

The majority of patients with germ-cell tumors (GCTs) are curable with standard therapy. The molecular differences between curable and incurable disease are unknown. We have studied the expression of KIT and the epidermal growth factor receptor (EGFR) to determine their incidence in chemorefractory disease.

PATIENTS AND METHODS

We retrospectively analyzed 23 patients with chemorefractory non-seminomatous GCTs (15 late relapse and eight transformed teratomas). None of these 23 patients were cured by their initial chemotherapy and/or surgery. Immunohistochemical analysis of KIT and EGFR was performed on the most recently available specimen from a metastatic site. PCR amplimers of KIT exon 17 were screened for mutations by a combination of denaturing high-performance liquid chromatography and direct sequencing.

RESULTS

KIT was expressed (>/=10% of the tumor displaying membranous or cytoplasmic staining) in 11 of 23 GCT patients [48%; 95% confidence interval (CI) 26% to 68%]. There were no activating KIT mutations in the phosphoryltransferase domain (exon 17) in 21 patients analyzed. EGFR was expressed (1+ to 3+) in 15 of 23 GCT patients (65%; 95% CI 41% to 82%).

CONCLUSIONS

KIT and EGFR are expressed in a significant proportion of refractory GCTs. The significance of these findings will be determined by ongoing clinical trials.

[Gastrointestinal stromal tumors. A morphologic and molecular genetic independent tumor entity with new therapeutic perspectives]

Recent morphological and molecular genetic findings have greatly expanded our understanding of gastrointestinal stromal tumors (GISTs). GISTs are now defined by their overexpression of CD117 (KIT), the receptor for the stem cell factor, and can thus be discriminated from smooth muscle tumors. Cytogenetically, GISTs are characterized even in early lesions by frequent entire or partial loss of the chromosomes 14 and 22 and terminal deletions of the chromosomal arm 1p. During tumor progression further chromosomal imbalances accumulate. Following the first report on activating KIT mutations in GISTs, several studies have addressed the role of wild-type and mutant KIT in GISTs and demonstrated activating KIT mutations in the majority of cases. Moreover, KIT tyrosine phosphorylation is even present in KIT mutation-negative GISTs, implicating KIT activation as a central event in the pathogenesis of GISTs. Imatinib (STI571/Glivec) is a selective inhibitor of BCR/ABL, PDGFR and KIT receptor-tyrosine kinases. First therapeutic applications of imatinib in patients with progressive GISTs have yielded promising results. This review focuses on the morphological and molecular findings in GISTs which have opened up a new therapeutic perspective.

High prognostic value of p16INK4 alterations in gastrointestinal stromal tumors

PURPOSE

Gastrointestinal stromal tumors (GISTs) represent a distinctive (but histologically heterogeneous) group of neoplasms, the malignant potential of which is often uncertain. To determine the prognostic relevance of p16INK4 alterations in GISTs, we investigated a larger group of GISTs and correlated the genetic findings with clinicopathological factors and patient survival.

MATERIAL AND METHODS

We evaluated the methylation status of the promotor by methylation-specific polymerase chain reaction (PCR), the presence of mutations by PCR-SSCP-sequencing, the loss of heterozygosity at the p16INK4 locus (using the c5.1 marker), and the immunohistochemical expression of p16INK4 protein in 43 GISTs in 39 patients.

RESULTS

p16INK4 alterations were found in 25 of 43 GISTs (58.1%), with benign, borderline, or malignant GISTs showing no differences in the type and frequency of alteration. p16INK4 alterations were correlated with a loss of p16INK4 protein expression (P <.01). Patients who had tumors with p16INK4 alterations had a poorer prognosis than patients with tumors without such alterations (P =.02). There was a high predictive value for p16INK4 alterations only in the group of benign and borderline GISTs (P <.01) with regard to clinical outcome. Univariate Cox's proportional hazard regression analysis revealed a strong correlation between p16INK4 alterations, tumor size, mitotic index, and overall survival (P <.02), whereas multivariate Cox's analysis confirmed only p16INK4 alterations as an independent prognostic factor.

CONCLUSION

We believe that the evaluation of p16INK4 alteration status is a helpful prognosticator, particularly in the benign and borderline groups of GISTs.

Schwannomas of the gastrointestinal tract: clinicopathological features of 12 cases including a case of esophageal tumor compared with those of gastrointestinal stromal tumors and leiomyomas of the gastrointestinal tract

We analyzed the clinicopathological features of 12 gastrointestinal (GI) schwannomas and compared them with those of 37 GI stromal tumors (GISTs) and 15 leiomyomas. Grossly, the schwannomas showed rubbery to firm, yellow-white to tan, glistening, and often trabeculated cut surfaces, resembling soft tissue schwannomas. The GISTs were firm to soft or fish-flesh tan, gray-pink, or variegated tumors with a degenerative change, and the leimyomas resembled typical uterine leiomyomas. Histologically, GI schwannomas were moderately cellular tumors with focal significant nuclear pleomorphism and rare mitotic figures. A characteristic peripheral lymphoid cuff was observed in all cases, but was indistinct in two cases. The GISTs were highly cellular spindle cell, epithelioid or, occasionally, pleomorphic tumors with basophilic appearance. Leiomyomas were paucicellular tumors with eosinophilic appearance. Immunohistochemically, schwannomas were S-100 protein- and glial fibrillary acidic protein (GFAP)-positive, but were negative for c-kit, CD34, and smooth muscle actin (SMA). GISTs were all c-kit- and/or CD34-positive, but GFAP-negative. Leiomyomas were SMA-positive and were negative for c-kit, CD34, S-100 protein, and GFAP. The mean Ki-67 index of schwannoma was 0.7, and those of GIST and leiomyoma were 5.9 and 0.3, respectively. The patients with schwannomas and leiomyomas had a favorable outcome, whereas 12 patients with GISTs showed progression and died of disease. The separation of GISTs from schwannomas is clinically important because the former group has a high risk of malignant behavior. GI schwannomas differed from the conventional soft tissue schwannomas in that they had peripheral lymphoid cuffs, lacked fibrous capsule and vascular hyalinization, and rarely showed degenerative changes. GI schwannomas, however, resembled soft tissue schwannomas in many aspects, and the clinical, gross, histological, and immunohistochemical features were different from those of GISTs and leiomyomas.

Gastrointestinal stromal tumors and other mesenchymal lesions of the gut

In the past 5 years, there has been a paradigm shift in our understanding of gastrointestinal stromal tumors (GISTs). Once thought to be smooth muscle tumors, these uncommon neoplasms are now thought to differentiate along the lines of interstitial cells of Cajal, the pacemaker cells of the gut. Along with this understanding comes an exciting new drug therapy (Gleevec) that for the first time offers real hope to patients with malignant stromal tumors. Overall, approximately 60-70% of stromal tumors are from the stomach, 20-30% are from the small intestine, and <10% come from the esophagus, colon, rectum, omentum, and mesentery. Between 10 and 30% of GISTs are malignant. Stromal tumors should be studied in a site-specific fashion, as tumors from a given location in the gut have unique growth patterns and corresponding behaviors. Although the most important tool needed to diagnose a GIST is still a hematoxylin and eosin-stained section, a confirmatory CD117 stain is recommended (and may be required for drug therapy). True smooth muscle tumors, inflammatory fibroid polyps, fibromatoses, schwannomas, inflammatory myofibroblastic tumors, and solitary fibrous tumors all enter into the differential diagnosis of GISTs. This article reviews the histologic features of these tumors in the context of recent molecular genetic and immunohistochemical advances.

Reactive nodular fibrous pseudotumor of the gastrointestinal tract and mesentery: a clinicopathologic study of five cases

Although the majority of mesenchymal lesions of the gastrointestinal tract are neoplastic in nature, nonneoplastic reactive processes may involve the gastrointestinal tract and mesentery, causing diagnostic confusion with more aggressive neoplasms, such as fibromatosis or gastrointestinal stromal tumors. In this study, we report a series of fibroinflammatory lesions of the gastrointestinal tract that we think represent a relatively cohesive group of tumors and describe the clinical and pathologic features of this entity, which we have termed "reactive nodular fibrous pseudotumor." The tumors affected five patients (four male and one female patient) who ranged in age from 48 to 71 years (mean 56 years). Two patients presented with acute abdominal pain without a significant past medical history, two had incidental lesions discovered during evaluation for other medical conditions, and one was found to have an abdominal mass. Three patients had a history of abdominal surgery. The tumors were multiple in three patients and solitary in two patients. In four cases, at least one of the tumors involved the small intestine or colon, and the lesion was confined to the peripancreatic soft tissue in one case. The tumors were firm, tan-white, ranged in size from 4.3 to 6.5 cm in greatest dimension, and were grossly well circumscribed. All of the lesions were of low to moderate cellularity and composed of stellate or spindled fibroblasts arranged haphazardly or in intersecting fascicles. Three cases had microscopically infiltrative borders. The stroma was rich in collagen, which was wire-like, keloidal, or hyalinized. Intralesional mononuclear cells were sparse but were more numerous peripherally and frequently arranged in lymphoid aggregates. Immunohistochemical stains demonstrated that all of the tumors stained for vimentin, 80% stained for CD117 or muscle specific actin, 60% stained for smooth muscle actin or desmin, and none of the tumors stained for CD34, S-100 protein, or anaplastic lymphoma kinase-1. Follow-up information was available in all cases: four patients had no residual disease following surgical resection (mean follow-up 16.3 months) and one patient who had an incomplete surgical resection had stable disease at 26 months. In summary, we report a series of distinct intraabdominal fibroinflammatory pseudotumors that we have collectively termed "reactive nodular fibrous pseudotumors." These lesions are uncommon and may infiltrate the bowel wall, thereby mimicking primary bowel neoplasms or intraabdominal fibromatosis. Recognition of these nonneoplastic lesions is important, as they pursue a benign clinical course, but may be confused with other mesenchymal neoplasms that require more aggressive treatment.

An osteoclast-rich tumor of the gastrointestinal tract with features resembling clear cell sarcoma of soft parts: reports of 6 cases of a GIST simulator

Six cases are reported of an osteoclast-rich tumor of the gastrointestinal tract that should be segregated from GIST. Five of the cases were located in the small bowel and one in the stomach. The age of the patients ranged from 13 to 37 years. The tumors behaved aggressively, with metastases to regional lymph nodes, liver, and other intra-abdominal sites. Microscopically, the tumor cells were medium-sized, predominantly oval, relatively monomorphic, diffusely immunoreactive for S-100-protein, and negative for CD117, CD34, HMB-45, and Mart-1. They were admixed with scattered osteoclast-like, multinucleated giant cells which were S-100-protein negative and KP1-positive. One case studied cytogenetically had the karyotype 46XX t(12;22)(q13;q12). The cases here reported are interpreted as examples of a distinctive type of gastrointestinal neoplasm which shares some features with clear cell sarcoma of soft parts (melanoma of soft parts), including in one case the chromosomal translocation that is characteristically associated with that entity.

Secondary amyloidosis and gastrointestinal stromal tumors. A case report and discussion of pathogenesis

A 69-year-old man presented with a malignant gastrointestinal stromal tumor associated with secondary amyloidosis. The tumor had classic features of a malignant gastrointestinal stromal tumor with interlacing fascicles and whorls of spindled cells, numerous and conspicuous mitotic figures, and extensive coagulative necrosis. The cells stained diffusely for CD117 (c-Kit), confirming the diagnosis of gastrointestinal stromal tumor. The spleen, 1 adrenal gland, and part of the pancreas were removed en block with the stomach. By microscopy, the spleen and adrenal gland were partially replaced with amyloid deposits confirmed by Congo red staining, electron microscopy, and immunohistochemistry. In contrast, neither the tumor nor the surrounding vasculature showed amyloid deposition. To our knowledge, this represents only the second case of systemic amyloidosis associated with a gastrointestinal stromal tumor. This case is unique in that extensive, diffuse amyloid deposits were observed in the spleen, adrenal gland, and liver.

Fine-needle aspiration cytology and immunocytochemistry in the diagnosis of 24 gastrointestinal stromal tumors: a quick, reliable diagnostic method

The diagnosis of gastrointestinal stromal tumors (GISTs) is generally established on histopathologic examination of surgical specimens. Fine-needle aspiration (FNA), performed under the guidance of ultrasound or computed tomography, is being used with increasing frequency in an attempt to diagnose primary and/or metastatic GISTs before surgery. The present study was undertaken to characterize the cytological appearance of these tumors and to assess the role of cytology, together with immunocytochemistry (ICC), in the diagnosis of GISTs. Twenty-four GISTs diagnosed by FNA cytology at our institution have been reviewed. Immunocytochemical studies with c-kit and CD34 were performed in all cases on current or archival Papanicolaou-stained smears. All cases stained with c-kit, and 19 reacted with CD34. Cytomorphology and immunocytochemical characteristics are discussed. Our results confirm the utility of FNA together with ICC in the diagnosis of primary and/or metastatic GISTs.

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

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

Gastrointestinal stromal tumors and leiomyomas in the dog: a histopathologic, immunohistochemical, and molecular genetic study of 50 cases

Fifty canine gastrointestinal (GI) mesenchymal tumors were examined to determine the occurrence of leiomyomas (LM) and GI stromal tumors and to compare their clinicopathologic features. Twenty-one tumors (42%) were histologically reclassified as gastrointestinal stromal tumors (GISTs) and 29 tumors (58%) as LMs on the basis of their histologic similarity with homologous human tumors. The GISTs occurred equally in males and females, with a mean age of 11 years (range 5-14 years). Five GISTs (24%) were associated with clinical signs and six (29%) had metastasis in liver or abdominal cavity. The GISTs occurred in large intestine (10, 48%), small bowel (six, 29%), stomach (four, 19%), and mesentery of small intestine (one, 5%). Histologically, they were highly cellular spindle, or less commonly epithelioid tumors with mitotic rates ranging from 0 to 19 per 10 HPF. Eleven tumors (52%) were positive for CD117 (KIT); seven (33%) were positive for smooth muscle actin but none for desmin and S-100 protein. Sequences of KIT exon 11, often mutated in human GISTs, were evaluated from four GISTs. Deletion of Try556-Lys557 coexisting with duplication of Gln555 in one case of GIST and T to C transition resulting in substitution of Pro for Leu575 in another were identified. The LMs occurred predominantly in males (82%) with a mean age of 11 years (range 8-17 years). Nine tumors (31%) had associated clinical signs. They occurred in the stomach (22, 76%), esophagus (four, 14%), and intestines (three, 10%); all were paucicellular, had no mitoses, and were composed of mature smooth muscle cells. Twenty-eight (97%) were positive for smooth muscle actin and 18 (62%) for desmin but none for CD117 and S-100. Both GISTs and true LMs occur in the GI tract of dogs. Both tumors have distinctive pathologic features.

Immunohistochemical comparison of gastrointestinal stromal tumor and solitary fibrous tumor

CONTEXT

The differential diagnosis of gastrointestinal stromal tumors (GIST) and solitary fibrous tumors (SFT) may be a diagnostic challenging because of overlapping clinicopathologic features. Many studies have shown consistent immunoreactivity for CD117 (c-Kit) in GIST. However, only a few studies have evaluated CD117 expression in SFT, and these studies have used an antibody from Santa Cruz Biotechnology. In non-GIST lesions, reactivity with this antibody has been shown to differ from that with a CD117 antibody from Dako Corporation. The immunoreactivity of SFT with the Dako CD117 antibody has not been reported. Conversely, CD99 is a marker for SFT, and its expression in GIST has not been evaluated.

OBJECTIVE

To study the immunohistochemical profiles of GIST and SFT to evaluate their diagnostic overlap.

DESIGN

We studied the immunoreactivity of 27 unequivocal GIST and 19 unequivocal extra-abdominal SFT for CD117, CD34, CD99, alpha-smooth muscle actin, vimentin, CD31, S100 protein, and muscle-specific actin. All antibodies, including CD117, were from Dako Corporation.

RESULTS

We found positive immunoreactivity for CD117 in 100% of GIST and none of SFT; for CD34 in 89% of GIST, and 100% of SFT; for CD99 in 89% of GIST and 100% of SFT; for alpha-smooth muscle actin in 48% of GIST and 31% of SFT; for vimentin in 89% of GIST and 90% of SFT; and for muscle-specific actin in 22% of GIST and none of SFT. None of the GIST or SFT showed immunoreactivity for CD31 and S100 protein.

CONCLUSIONS

The major difference between GIST and SFT was strong CD117 immunoexpression in all GIST and an absence of this expression in all SFT. With the exception of muscle-specific actin, the prevalence of immunoreactivity for the markers studied did not differ substantially between these 2 tumors. We conclude that GIST and SFT show distinctly divergent immunoprofiles with respect to CD117 and muscle-specific actin.

Fine-needle aspiration cytology diagnosis of metastatic gastrointestinal stromal tumor in the liver: a report of three cases

Gastrointestinal stromal tumor (GIST) is the designation for a major subset of gastrointestinal mesenchymal tumors that histologically, immunocytochemically, and genetically differ from leiomyomas, leiomyosarcomas, and schwannomas. GISTs derive from the interstitial cells of Cajal and, in addition to variable expression of smooth muscle and neural markers, they characteristically express CD34 and CD117. The cytological appearance, including immunocytochemical and mutational analysis of c-kit gene in primary GIST has been well described. To our knowledge, only two cases of metastatic GIST diagnosed by fine-needle aspiration (FNA) have been reported. We illustrate three cases of metastatic GIST in the liver. Two cases had no prior history of gastrointestinal tumor and the third case had a 4-yr previous history of duodenal tumor. Consistent immunocytochemistry and ultrastructual studies supported the diagnosis of GIST. We emphasize that in the appropriate clinical and radiological setting, a confident diagnosis of GIST can be established by FNA of metastatic lesions.

Prognostic value of KIT mutation type, mitotic activity, and histologic subtype in gastrointestinal stromal tumors

PURPOSE

Previous studies have reported clinical correlates for KIT mutations in GISTs, but in most of those studies the KIT mutations were found in less than 50% of the GISTs. The aim of this study was to evaluate the prognostic relevance for KIT mutations in a series of GISTs in which the mutations were evaluated intensively by genomic and cDNA sequencing.

PATIENTS AND METHODS

A comprehensive clinical and pathologic analysis of 48 patients with GISTs who had snap-frozen tissue was performed. The median tumor size was 10 cm (range, 2 to 30 cm). Median follow-up for disease-free patients was 48 months. KIT genomic and cDNA was sequenced by using nucleic acid templates isolated from frozen tumors.

RESULTS

The overall 5-year recurrence-free survival was 41% +/- 6%. Five-year recurrence-free survival for patients with tumors that had mitotic counts of three mitoses or fewer per 30 high-power fields (HPF), more than three to <or= 15 mitoses per 30 HPF, and more than 15 mitoses per 30 HPF were 89% +/- 7%, 49% +/- 12%, and 16% +/- 6%, respectively (P =.0001). The 32 patients with spindle-cell histology had a 49% +/- 7% 5-year recurrence-free survival; in contrast, the 16 patients with epithelioid or mixed histology had a 23% +/- 11% 5-year recurrence-free survival (P =.01). Five-year recurrence-free survival for patients with tumors less than 5 cm, 5 to 10 cm, and more than 10 cm were 82% +/- 12%, 45% +/- 9%, and 27% +/- 8%, respectively (P =.03). Prognostic associations were found with particular KIT mutation types, and patients with missense exon 11 mutations had a 5-year recurrence-free survival of 89% +/- 11% compared with 40% +/- 8% for GISTs with other mutation types (P =.03). The independent predictors for disease-free survival were the presence of deletion/insertion exon 11 mutations (hazard ratio [HR] = 4; P =.006), more than 15 mitoses per 30 HPF (HR = 18; P =.0001), mixed histology (HR = 21; P =.0001), and male sex (HR = 3; P =.05).

CONCLUSION

In this series of KIT-expressing GISTs, tumor mitotic activity and histologic subtype were the most important prognostic features. The majority of GISTs contain KIT-activating mutations with the type/location of mutation serving as an independent predictor for disease-free survival. These results suggest that KIT mutation and activation are important in GIST pathogenesis and also may provide important prognostic information.

Use of positron emission tomography in oncology and its potential role to assess response to imatinib mesylate therapy in gastrointestinal stromal tumors (GISTs)

The reliability of established anatomical imaging techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI), is compromised in following response to certain types of treatment if metabolic improvement occurs before morphologic change is apparent. Thus, traditional imaging techniques cannot discriminate early tumor response because they are based on purely visual structural assessments. Recently, the use of positron emission tomography (PET), most commonly employing the radiotracer 18F-fluoro-2-deoxy-D-glucose (FDG), has been shown to improve the assessment of tumor behavior by highlighting early functional changes in tumor glucose metabolism that appear to correlate closely with metabolic tumor response to imatinib mesylate. Like CT and MRI, PET can identify an abnormal mass; its improvement over these techniques lies in its ability to differentiate active tumor from necrosing tissue, malignant from benign tissue, and recurrent tumor from scar tissue. Understanding and using this tool should improve our ability to accurately follow response in GIST patients treated with imatinib mesylate, and permit this new therapeutic approach to be used optimally with accurate follow-up assessments and informed therapeutic decision-making.

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.

CD117 (KIT receptor) expression in Merkel cell carcinoma

The KIT receptor tyrosine kinase (CD117 antigen) is found in a variety of normal tissue cell types and in several malignant tumors, including acute myeloid leukemia. We recently encountered two tumors initially suspected as acute myeloid leukemia cutis and expressing CD117 that showed punctate positivity for cytokeratin 20 diagnostic for Merkel cell carcinoma. We evaluated 20 additional cases of MCC and found that 21 of 22 tumors (95%) expressed CD117. Intensity of CD117 expression did not appear to correlate with aggressive behavior. While the function of the KIT receptor in MCC is not known, its pathogenic role in other malignant neoplasms suggests the possibility of a similar role in MCC.

A malignant gastrointestinal stromal tumor with osteoclast-like giant cells

Gastrointestinal stromal tumors (GISTs) are a heterogeneous group of mesenchymal tumors with a wide spectrum of histologic features and consistent expression of c-Kit. We describe an 85-year-old woman who presented with left lower quadrant abdominal pain and was subsequently diagnosed as having a malignant GIST. The tumor was composed of short fascicles of spindle cells. In addition to the presence of tumor giant cells, the tumor also demonstrated many osteoclast-like giant cells, a feature that has not been previously described in the literature. These giant cells expressed histiocytic markers CD68 and alpha(1)-antitrypsin but not c-Kit, a marker for GISTs. Electron microscopy showed no features of smooth muscle differentiation in the giant cells. The possible origin of the osteoclast-like giant cells is discussed in the context of immunohistochemical and ultrastructural characteristics.

Patterns of nestin and other intermediate filament expression distinguish between gastrointestinal stromal tumors, leiomyomas and schwannomas

The KIT-positive specific gastrointestinal stromal tumors (GISTs), leiomyomas, and schwannomas are the three most common types of primary mesenchymal tumors of the gastrointestinal (GI) tract. The intermediate filaments are abundant cytoskeletal proteins commonly used as cell differentiation markers in diagnostic immunohistochemistry. Their patterns have not been fully characterized in GI mesenchymal tumors, and could offer differential diagnostically useful parameters. Very recently, nestin, a class VI intermediate filament expressed in neuroectodermal stem cells and skeletal muscle progenitor cells, has been shown in GISTs and suggested as a marker for these tumors. In this study we immunohistochemically examined the expression of nestin and other intermediate filament proteins, including desmin, keratins (Ks), glial fibrillary acidic protein (GFAP), neurofilament, and vimentin in GISTs of different sites, esophageal leiomyomas and GI schwannomas. Nestin was nearly consistently present in GISTs of different locations whether spindle cell or epithelioid, and benign or malignant. It was also detected in 23 of 24 (96%) GI schwannomas, whereas leiomyomas were uniformly negative. Vimentin was present in both GISTs and schwannomas, whereas it was typically absent in leiomyomas (25% positive, usually focally). Desmin was present in all leiomyomas, whereas only 3% of GISTs (4 of 140) were positive, and all schwannomas were negative. K18 was detected in a minority of GISTs, leiomyomas, and schwannomas. Malignant GISTs were more commonly keratin positive than the benign ones; there was 18% K18 positivity in malignant gastric and small intestinal GISTs, but 9% K18 positivity in benign gastric and small intestinal GISTs. Moreover, K8, albeit to a lesser degree, was detected in a minority of GISTs, but K7, K14, K19 and K20 were not detected. GFAP was present in the majority of schwannomas, whereas all GISTs were negative; some leiomyomas had weak cytoplasmic positivity. These results document distinctive patterns of intermediate filament proteins in GI mesenchymal tumors. Nestin is confirmed to be consistently expressed in GISTs but it is also present in most GI schwannomas; GFAP is helpful when separating GISTs and schwannomas, since only the latter are positive. The potential presence of K8 and K18 in GISTs should not lead to the misdiagnosis of carcinoma on biopsy.

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.

Evaluation of malignancy and prognosis of gastrointestinal stromal tumors: a review

This paper reviews data on the prognosis of gastrointestinal stromal tumors (GISTs). These tumors are specific KIT-expressing and KIT-signaling-driven mesenchymal tumors, many of which have KIT-activating mutations. GISTs occur in the entire gastrointestinal (GI) tract and may also arise from the omentum, mesenteries, and retroperitoneum. They range from small benign tumors to sarcomas at all sites of occurrence. A KIT tyrosine kinase inhibitor, STI-571 (imatinib [Gleevec]; Novartis, Basel, Switzerland), has recently shown promise in the treatment of metastatic GISTs. Understanding the natural history of GIST before introduction of STI-571 will help assess the impact and position of this new treatment. The frequency of benign versus malignant GISTs varies between sites. Benign GISTs outnumber malignant GISTs in the stomach, whereas malignant GISTs are more common in the intestines. Tumors that have metastasized at presentation have a very poor prognosis. Traditionally, the 3 key prognostic factors have been mitotic rate, tumor size, and site. Tumors that are small (< or =2 cm) and show mitotic activity not exceeding 5 mitoses per 50 high-power fields (HPFs) have an excellent prognosis, probably independent of site, although this has not been shown specifically for all sites. In the stomach, most epithelioid GISTs are benign, provided that mitotic counts do not exceed 5/50 HPFs. However, a small proportion of tumors apparently lacking mitotic activity do metastasize. Tumors with a mitotic rate >5/50 HPFs usually have a malignant behavior. The Ki67 index may help identify tumors with malignant potential, but large site-specific series are not yet available. Genetic markers, including DNA-copy number changes, telomerase activity, and KIT mutation status, may be useful in more accurately identifying tumors with malignant potential.

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.

Molecular characterisation of soft tissue tumours: a gene expression study

BACKGROUND

Soft-tissue tumours are derived from mesenchymal cells such as fibroblasts, muscle cells, or adipocytes, but for many such tumours the histogenesis is controversial. We aimed to start molecular characterisation of these rare neoplasms and to do a genome-wide search for new diagnostic markers.

METHODS

We analysed gene-expression patterns of 41 soft-tissue tumours with spotted cDNA microarrays. After removal of errors introduced by use of different microarray batches, the expression patterns of 5520 genes that were well defined were used to separate tumours into discrete groups by hierarchical clustering and singular value decomposition.

FINDINGS

Synovial sarcomas, gastrointestinal stromal tumours, neural tumours, and a subset of the leiomyosarcomas, showed strikingly distinct gene-expression patterns. Other tumour categories--malignant fibrous histiocytoma, liposarcoma, and the remaining leiomyosarcomas--shared molecular profiles that were not predicted by histological features or immunohistochemistry. Strong expression of known genes, such as KIT in gastrointestinal stromal tumours, was noted within gene sets that distinguished the different sarcomas. However, many uncharacterised genes also contributed to the distinction between tumour types.

INTERPRETATION

These results suggest a new method for classification of soft-tissue tumours, which could improve on the method based on histological findings. Large numbers of uncharacterised genes contributed to distinctions between the tumours, and some of these could be useful markers for diagnosis, have prognostic significance, or prove possible targets for treatment.

Expression of KIT (CD117) in angiomyolipoma

Angiomyolipoma is a unique mesenchymal tumor postulated to arise from perivascular epithelioid cells. Immunohistochemical studies have shown that angiomyolipomas express the melanocytic markers HMB-45, MART-1 (Melan A), microphthalmia transcription factor, and tyrosinase, in addition to smooth muscle actin. KIT (CD117) is a transmembrane growth factor receptor expressed in cells of melanocytic and a variety of other cell lineages. To date, KIT immunoreactivity has not been systematically studied in angiomyolipoma. In this study we immunohistochemically analyzed a series of 21 angiomyolipomas (15 hepatic, six renal) with KIT. All were KIT positive: 14 of 21 (67%) with 3+ staining (>50% of tumor cells), 4 of 21 (19%) with 2+ staining (25-50% of tumor cells), and 3 of 21 (14%) with 1+ staining (<25% of tumor cells). In comparison, the percent of angiomyolipomas showing 3+ staining with HMB-45 was 62% and with Melan A was 52%. Positive KIT staining was detected in the epithelioid, spindle, and intermediate small round cells. Most cases showed diffuse cytoplasmic positivity. Strong perinuclear staining was present in the vacuolated clear epithelioid cells. There was focal KIT staining of fat cells. KIT was not detected in the endothelial cells lining blood vessels within the tumor. KIT may be a useful ancillary marker for the diagnosis of angiomyolipoma. Angiomyolipoma should be included in the differential diagnosis of KIT-positive tumors.

C-kit expression in pediatric solid tumors: a comparative immunohistochemical study

The stem cell factor/c-kit tyrosine kinase receptor pathway has been shown to be important for tumor growth and progression in several cancers, including mast cell diseases, gastrointestinal stromal tumor, acute myeloid leukemia, small cell lung carcinoma, and Ewing sarcoma. Studies using the oral agent STI-571 (Gleevec, Novartis), an inhibitor of the tyrosine kinases bcr-abl, c-kit, and PDGFR, have shown significant responses in patients with chronic myelogenous leukemia and gastrointestinal stromal tumor. With the aim of identifying additional groups of tumors that may use the stem cell factor/c-kit pathway and secondarily may be responsive to STI-571 treatment, this study surveyed 151 primary tumors from patients treated at St. Jude Children's Research Hospital for immunohistochemical expression of c-kit. Formalin-fixed, paraffin-embedded sections were stained with rabbit polyclonal anti-human c-kit (CD117, Dako) using standard avidin-biotin-peroxidase complex technique, antigen retrieval, and an automated stainer. Strong, diffuse staining for c-kit was seen in a proportion of synovial sarcomas, osteosarcomas, and Ewing sarcomas. Strong, diffuse staining was less common in neuroblastomas, Wilms' tumors, and rhabdomyosarcomas and was negative in alveolar soft part sarcomas and desmoplastic small round cell tumors. Tumors with strong, diffuse staining for c-kit in a pattern similar to gastrointestinal stromal tumor may represent suitable targets for new therapeutic agents.

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.

Gastrointestinal glomus tumors: a clinicopathologic, immunohistochemical, and molecular genetic study of 32 cases

Glomus tumors usually occur in the peripheral soft tissues, but similar tumors have also been reported in the stomach and occasionally in the intestines. However, the relationship of these tumors to peripheral glomus tumors and gastrointestinal stromal tumors has not been fully clarified because previous series of gastrointestinal glomus tumors predate availability of immunohistochemistry. This clinicopathologic study examined 32 gastrointestinal glomus tumors. All but one of the tumors were located in the stomach and the remaining tumor was from the cecum. The tumors occurred with a strong female predominance (23 females and 9 males) and a median age of 55 years (range 19-90 years). The gastric tumors typically presented with gastrointestinal bleeding or ulcer-like symptoms, and 14 tumors had mucosal ulceration. Five tumors were incidental findings. The tumor sizes varied from 1.1 to 7 cm (median 2 cm), and most were located in the antrum. Histologically, the tumors typically had a solid pattern of sharply demarcated, round glomus cells with prominent, mildly dilated pericytoma-like vessels. Vascular invasion and focal atypia were relatively common (seen in 11 and 13 cases, respectively), and low mitotic activity (1-4 per 50 high power fields), was seen in 10 cases. Immunohistochemically, all tumors were positive for alpha-smooth muscle actin and calponin, and nearly all had a net-like pericellular laminin and collagen type IV positivity. All tumors were negative for desmin and S-100 protein. Three tumors had focal synaptophysin positivity, but none was positive for chromogranin. All tumors lacked KIT expression and the GIST-specific mutations in the c-kit gene. Follow-up revealed one patient death of metastatic disease to liver at 50 months; this tumor had 1 mitosis per 50 high power fields, but had spindle cell foci, mild atypia, and vascular invasion. Thirteen patients were well and alive after long-term follow-up. Gastrointestinal glomus tumors occur almost exclusively in the stomach, and they have a good overall prognosis, but a small, unpredictable potential for malignant behavior exists. These tumors are phenotypically similar to peripheral glomus tumors and differ from epithelioid GISTs.

c-kit mutations in gastrointestinal stromal tumors occur preferentially in the spindle rather than in the epithelioid cell variant

Gastrointestinal stromal tumors (GISTs) coexpress CD34 and the Kit tyrosine-kinase receptor (CD117). A subset of GISTs carry gain-of-function mutations of the c-kit proto-oncogene in its juxtamembrane domain. The relationship between the mutational status and histological as well as immunohistochemical features has not been assessed in detail. 36 GISTs and 14 other gastrointestinal mesenchymal tumors were investigated for their morphology and immunophenotype as well as for the presence of c-kit mutations. DNA was extracted from formalin-fixed, paraffin-embedded tissue. Exons 9, 11, 13, and 17 of c-kit were analyzed by SSCP. Bands with altered mobility were excised, reamplified, and sequenced. C-kit mutations in Exon 11 encoding the juxtamembrane domain were identified in 19 cases (52.8%), with deletions in 12 cases, insertions in 3 cases (2 of these as duplications), and point mutations in 4 cases. The mutations clustered between Codons 553 and 561, pinpointing the critical region for deregulated Kit receptor activation. In both Exons 9 and 13, single mutations could be identified, whereas no mutations were found in Exon 17. There were c-kit mutations in 66.6% of benign GISTs (14/21), 83.3% of the malignant (5/6), and 40% of the cases of intermediate malignancy (2/5). A low frequency of mutations in benign GISTs, as reported previously by other researchers, could not be observed in our panel. Interestingly, all GISTs with c-kit mutations displayed a spindle cell phenotype, whereas mutations were absent in all 7 tumors with an epithelioid component (P =.03). This finding suggests a relationship between c-kit mutation and histological subtype in GISTs.

Immunohistochemical staining for KIT (CD117) in soft tissue sarcomas is very limited in distribution

We performed immunohistochemical analysis for KIT in 365 soft tissue sarcomas. Most tumors evaluated were completely negative for KIT, including all cases of leiomyosarcoma, rhabdomyosarcoma, myxofibrosarcoma, liposarcoma, solitary fibrous tumor, synovial sarcoma, dermatofibrosarcoma protuberans, schwannoma, malignant peripheral nerve sheath tumor, clear cell sarcoma, low-grade endometrial stromal sarcoma, and follicular dendritic cell sarcoma. Tumors showing occasional immunoreactivity for KIT included extraskeletal myxoid chondrosarcoma (2/20), Ewing sarcoma/malignant primitive peripheral neuroectodermal tumor (4/20), melanotic schwannoma (3/5), metastatic melanoma (4/20), and angiosarcoma (5/20). In most cases, staining for KIT was focal. Rare tumor cells showing KIT positivity were identified in a small number of other tumors. This study demonstrates very limited expression of KIT in soft tissue tumors other than gastrointestinal stromal tumors and underscores the discriminatory value of KIT immunohistochemical analysis for differential diagnosis. As some of these findings differ markedly from previous reports, it is evident again that variations in immunohistochemical technique can lead to major discrepancies in positive staining. Since treatment eligibility for selective tyrosine kinase inhibitors such as STI571 hinges on positive immunostaining, standardization and reproducibility of meaningful results are critically important.

Gastrointestinal stromal tumors (gists): Definition, clinical, histological, immunohistochemical and molecular genetic features and predictors of malignant potential and differential diagnosis

Gastrointestinal stromal tumors (GISTs) represent a distinct and the most important subset of mesenchymal tumors of the gastrointestinal (GI) tract GISTs occur throughout the GI tract but are usually located in the stomach and small intestine. The cellular origin, differentiation, nomenclature and prognosis of GISTs are controversial. Because GISTs, like the interstitial cells of Cajal, the GI pacemaker cells, express CD117 (c-kit protein), the origin of GISTs from the Cajal cells has recently been suggested. GISTs are also known for their wide variability in clinical behavior and for the difficulty to determine their malignant condition The most reproducible predictors of malignancy are mitotic count >1-5 per10 high-powered fields (HPF), size >5 cm, tumor necrosis, infiltration and metastasis to other sites. However, some tumors with mitotic activity <1/10 HPF may metastasize indicating some uncertainty in malignant potential of GISTs, especially those larger than 5 cm. Recently, mutations in c-kit gene (exon 11) preferentially occur in malignant GISTs and may be a clinically useful adjunct marker in evaluation of GISTs. In conclusion, the strong CD117 expression mostly defines primary GI mesenchymal tumors as GIST. Specific identification of GIST may become clinically important if therapies targeting the c-kit tyrosine kinase activation become available.

CD117 (KIT): a diverse protein with selective applications in surgical pathology

CD 117 (KIT) is a transmembrane, tyrosine kinase growth factor receptor which is expressed on numerous diverse fetal and adult cells including hematopoietic cells, mast cells, melanocytes, germ cells, and the interstitial cells of Cajal. Its expression in tumors is also diverse, but with selective use and attention to specific staining patterns, this marker is useful in the identification of gastrointestinal stromal tumors, mast cell tumors, and seminomatous germ cell tumors.

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.

Retroperitoneal leiomyomas: a clinicopathologic and immunohistochemical study of 56 cases with a comparison to retroperitoneal leiomyosarcomas

Most retroperitoneal smooth muscle tumors are believed to be malignant, and leiomyomas are considered very rare. This study was undertaken to determine the clinicopathologic features and long-term follow-up of 56 tumors diagnosed as retroperitoneal leiomyomas (LM) or smooth muscle tumors with an uncertain malignant potential (SMTUMP) in an effort to correlate their behavior and clinicopathologic features. These tumors were compared with a series of 11 cases of retroperitoneal leiomyosarcomas (excluding gastrointestinal stromal tumors). Histologic slides and immunohistochemistry for SMA, desmin, S-100 protein, HMB45, CD34, C-KIT, estrogen (ER) and progesterone (PR) receptor proteins, and MIB-1 were analyzed. All tumors diagnosed as LM and all but one SMTUMP were well-differentiated smooth muscle tumors that lacked atypia and coagulative necrosis. There was <1 mitosis per 50 high power field (HPF) in 38 tumors; no tumor had >3 mitoses/50 HPF. Most tumors had a striking resemblance to uterine smooth muscle tumors with common hyaline change and trabecular patterns. There were 51 females and 5 males ranging in age from 25 to 79 years (mean 45 years, median 43 years). These tumors were typically large, with a mean size of 16.2 cm and weight of 1600 g. Immunohistochemically, all 35 tumors studied were positive for alpha-SMA, 30 of 35 tumors were positive for desmin, and all were negative for CD117, S100 protein, and HMB45 and all but one for CD34. Steroid receptors were commonly present: ER in 20 of 29 cases and PR in 26 of 31 cases in the tumors of female patients. MIB-1 score was <2% in all of 28 cases. Long-term follow-up (mean 140 months) did not reveal metastases, but two patients had local recurrence; however, neither patient with recurrence demonstrated disease progression in follow-up. By contrast, all 11 leiomyosarcomas had at least mild atypia, and all were ER and PR negative. All cases had MIB-1-positive nuclei, but only four had >10% nuclei positive. Four patients died of disease, four were alive with recurrence, and three had no evidence of disease. A group of benign leiomyomas can be identified among retroperitoneal smooth muscle tumors. Most of these tumors resemble uterine leiomyomas by histology and positive hormone receptors, and they seem to have a good long-term prognosis with a small potential for local recurrence.

Small intestinal neoplasms

Small intestinal neoplasms are uncommonly encountered in clinical practice. They may occur sporadically, in association with genetic diseases (e.g., familial adenomatous polyposis coli or Peutz-Jeghers syndrome), or in association with chronic intestinal inflammatory disorders (e.g., Crohn's disease or celiac sprue). Benign small intestinal tumors (e.g., leiomyoma, lipoma, hamartoma, or desmoid tumor) usually are asymptomatic but may present with intussusception. Primary malignancies of the small intestine-including adenocarcinoma, leiomyosarcoma, carcinoid, and lymphoma-may present with intestinal obstruction, jaundice, bleeding, or pain. Extraintestinal neoplasms may involve the intestine via contiguous spread or peritoneal metastasis. Hematogenous metastases to the intestine from an extraintestinal primary are unusual and are most typical of melanoma. Because the small intestine is relatively inaccessible to routine endoscopy, diagnosis of small intestinal neoplasms is often delayed for months after onset of symptoms. When the diagnosis is suspected, enteroclysis is the most useful imaging study. Small bowel endoscopy (enteroscopy) is increasingly widely available and may permit earlier, nonoperative diagnosis.

Gastrointestinal autonomic nerve tumor: immunohistochemical and molecular identity with gastrointestinal stromal tumor

Gastrointestinal autonomic nerve tumor (GANT) is a gastrointestinal neoplasm that ultrastructurally recapitulates the enteric neural plexus. This study identifies and defines the features of 10 cases of this rare mesenchymal tumor and compares its clinicopathologic and molecular genetic features with the data on gastrointestinal stromal tumor (GIST). The majority of patients in this series presented at an older age (mean 64 years). Tumors arose from the stomach (6), small intestine (2), and retroperitoneum (2). Mean tumor size was 14 cm; however, four neoplasms were <6 cm. Histologically, tumors were spindled or epithelioid; one epithelioid tumor demonstrated a previously undescribed rhabdoid histologic phenotype. All tumors were positive for CD117 (KIT), while eight of 10 were positive for CD34. In contrast, only two were positive for S-100, and all were negative for actin and desmin. Five GANTs demonstrated GIST-specific gain-of-function mutations in the juxtamembrane domain of the c-kit gene (50%). Three of 10 patients died of disease in 22-30 months, one patient died in the postoperative period, and one patient died of complications of CML. The clinicopathologic, histologic, immunohistologic, and molecular features of GANT are similar to GIST, indicating that GANT merely represents a phenotypic variant of GIST.

p53 expression in gastrointestinal stromal tumors

The understanding of gastrointestinal stromal tumors (GIST) is complex because of their divergent differentiation and unpredictable behavior. However, our understanding is becoming clearer, despite some cases of tumors which are exceptions from the typical cases. Tumor size, mitotic rate and, to a lesser degree, location, are the most important predictive parameters for the behavior of GIST. In this study, expression of p53 protein was evaluated in 15 cases of GIST. Tumors were divided into three groups: (i) benign (mitotic index [MI] < 5/50 high-power fields [HPF] and size < 5 cm); (ii) borderline (MI < 5/50 HPF and size > or = 5 cm); and (iii) malignant (MI > or = 5/50 HPF, irrespective of size). The mean values of p53 expression in the three groups were significantly different (benign, 10.6%; borderline, 33.8%; and malignant, 71%). The conclusion of the present study is that p53 overexpression correlates well with the malignant potential of GIST.

Gastrointestinal stromal tumors

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. A relationship to the interstitial cells of Cajal (ICCs) has been proposed, and expression of CD117, the c-kit receptor present in ICCs, has been suggested as a marker for GISTs.

METHODS

The English literature has been reviewed with an emphasis on histogenetic features, especially the potential relationship of GISTs to ICCs.

RESULTS

GISTs are most common in the stomach (70%), followed by small intestine (20%), colon and rectum (5%), and esophagus (<5%). GISTs commonly have activating mutations in exon 11 (or rarely exon 9 and exon 13) of the KIT gene that encodes a tyrosine kinase receptor for the stem cell factor or mast cell growth factor.

CONCLUSIONS

Malignant potential is best estimated by the simultaneous evaluation of several clinical parameters. The only absolute criterion for malignancy is tumor spread beyond the organ of origin at the time of diagnosis. The remarkable clinical response of tumors that express c-kit to treatment with the tyrosine kinase inhibitor STI571 is a triumph of molecular pharmacology.