Gastrointestinal stromal tumors and leiomyosarcomas in the colon: a clinicopathologic, immunohistochemical, and molecular genetic study of 44 cases

Coexistence of gastrointestinal stromal tumor (GIST) and colorectal adenocarcinoma: A case report

Background

Gastrointestinal stromal tumors (GIST) represent the most common mesenchymal tumors of the digestive tract. Over the last ten years the management of GISTs has dramatically altered but their coexistence with other gasrointesinal tumors of different histogenesis presents a special interest. The coexistence of GISTs with other primaries is usually discovered incidentally during GI surgery for carcinomas.

Case presentation

We present here, a case of a 66-year-old patient with intestinal GIST and a synchronous colorectal adenocarcinoma discovered incidentally during surgical treatment of the recurrent GIST. Immunohistochemical examination revealed the concurrence of histologically proved GIST (strongly positive staining for c-kit, vimentin, SMA, and focal positive in S-100, while CD-34 was negative) and Dukes Stage C, (T3, N3, M0 according the TNM staging classification of colorectal cancer).

Conclusion

The coexistence of GIST with either synchronous or metachronous colorectal cancer represents a phenomenon with increasing number of relative reports in the literature the last 5 years. In any case of GIST the surgeon should be alert to recognize a possible coexistent tumor with different histological origin and to perform a thorough preoperative and intraoperative control. The correct diagnosis before and at the time of the surgical procedure is the cornerstone that secures the patients' best prognosis.

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

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

Tumor do estroma gastrintestinal: achados clínicos, radiológicos e anatomopatológicos

OBJETIVO: Investigar e descrever os achados clínicos, radiológicos e anatomopatológicos dos tumores do estroma gastrintestinal. MATERIAIS E MÉTODOS: De dezembro de 2000 a março de 2006, 16 pacientes foram operados por tumores do estroma gastrintestinal em nossa instituição. As variáveis analisadas foram sexo e idade dos pacientes, sinais e sintomas na consulta inicial, localização e tamanho do tumor, achados radiológicos, características anatomopatológicas e a ocorrência de metástases. RESULTADOS: A população em estudo constou de nove homens e sete mulheres. Os locais de origem dos tumores primários foram o estômago (n = 5), o reto (n = 4), o intestino delgado (n = 3), o mesentério (n = 3) e o cólon sigmóide (n = 1). Tomografia computadorizada foi o principal método radiológico empregado. Massa circunscrita, de contornos lobulados e que sofre realce heterogêneo pelo meio de contraste foi o principal achado por imagem. Em nosso estudo, nove pacientes (56% dos casos) apresentaram metástases ao diagnóstico ou recorrência do tumor num período médio de dois anos e oito meses. CONCLUSÃO: O tumor do estroma gastrintestinal acomete adultos de meia-idade e idosos e deve ser lembrado no diagnóstico diferencial das massas abdominais. Diagnóstico precoce, tratamento correto e acompanhamento rigoroso são fundamentais, pois, como demonstrado em nosso trabalho, essas neoplasias apresentam alta tendência à malignidade.

Gastrointestinal stromal tumour

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

A subset of colorectal carcinomas express c-KIT protein independently of BRAF and/or KRAS activation

c-KIT is a tyrosine kinase receptor found to be overexpressed in several tumours, namely, GISTs, breast, lung, prostate, ovarian and colorectal carcinomas (CRC). We aimed at determining the frequency of c-KIT expression and mutations in a series of 109 CRC cases (73 primary tumours and 36 lymph node metastases) characterised for KRAS and BRAF mutations. We also aimed at analysing the cellular effects of STI571/Gleevec in CRC-derived cell lines displaying c-KIT expression and KRAS or BRAF mutations. By immunohistochemistry, we found c-KIT overexpression in 15% (11/73) of primary tumours and in 14% (5/36) of metastasis; however, cases showing overexpression did not show c-kit mutations in hotspot regions. The majority (64%) of primary tumours with c-KIT overexpression had mutations at KRAS-BRAF genes. The same was true for 60% of the metastases. We treated CRC cell lines with STI571/Gleevec and verified that it inhibits proliferation and induces apoptosis in all cell lines. In conclusion, overexpression of c-KIT is observed in a subset of primary and CRC metastases in the absence of c-kit mutations. STI571/Gleevec increases apoptosis in CRC cell lines independently of its genetic profile, suggesting that STI571/Gleevec is likely to be an alternative drug for the clinical trials of CRC.

Distinguishing gastrointestinal stromal tumors from their mimics: an update

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

Gastric GIST malignancy evaluated by 18FDG-PET as compared with EUS-FNA and endoscopic biopsy

OBJECTIVE

The usefulness of 18F-fluoro-2-deoxyglucose positron emission tomography (18FDG-PET), whose high rate of FDG accumulation indicates high metabolism and malignant potential, has already been reported. The aims of this study were to evaluate the malignancy of primary gastrointestinal stromal tumour (GIST) in the stomach by 18FDG-PET and to correlate the FDG uptake values with known risk factors as determined by histology after EUS-guided fine needle aspiration (EUS-FNA) or endoscopic biopsy.

MATERIAL AND METHODS

Of 29 patients with histologically proven GI-mesenchymal tumours, 21 with gastric GISTs underwent 18FDG-PET. Tumour size, mitotic index, Ki-67 labelling index (LI) and cellularity of the tumour tissue were compared with the standardized uptake value (SUV) of FDG.

RESULTS

Strong correlations were found between the SUV of FDG and EUS size, and mitotic index of EUS-FNA specimens (tumour size versus SUV, p=0.004, r=0.542; number of mitotic cells versus SUV, p=0.0078; n=21). Moreover, we examined the association between SUV and risk categories based on EUS-FNA findings using ROC curves. The cut-off values of FDG SUV were 2.2, 4.2 and 6.5 for the very low-, low-, intermediate- and high-risk groups, respectively.

CONCLUSIONS

18FDG-PET may be used to assess malignancy of GISTs. This image modality helps us determine the management strategy for these patients and complements the information on the biological behaviour and cellular proliferation of the tumours.

Occurrence of other malignancies in patients with gastrointestinal stromal tumors

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

KIT and PDGFRA mutations in gastrointestinal stromal tumors (GISTs)

Mutually exclusive KIT and PDGFRA mutations are central events in GIST pathogenesis, and their understanding is becoming increasingly important, because specific treatment targeting oncogenic KIT and PDGFRA activation (especially imatinib mesylate) has become available. KIT mutations in GIST are clustered in four exons. Most common are exon 11 (juxtamembrane domain) mutations that include deletions, point mutations (affecting a few codons), and duplications (mostly in the 3' region). The latter mutations most often occur in gastric GISTs. Among gastric GISTs, tumors with deletions are more aggressive than those with point mutations; this does not seem to hold true in small intestinal GISTs. Exon 9 mutations (5-10%) usually are 2-codon 502-503 duplications, and these occur predominantly in intestinal versus gastric GISTs. Lesser imatinib sensitivity of these tumors has been noted. Kinase domain mutations are very rare; GISTs with such mutations are variably sensitive to imatinib. PDGFRA mutations usually occur in gastric GISTs, especially in the epithelioid variants; their overall frequency is approximately 30% to 40% of KIT mutation negative GISTs. Most common is exon 18 mutation leading Asp842Val at the protein level. This mutation causes imatinib resistance. Exon 12 and 14 mutations are rare. Most mutations are somatic (in tumor tissue only), but patients with familial GIST syndrome have consitutitonal KIT/PDGFRA mutations; >10 families have been reported worldwide with mutations generally similar to those in sporadic GISTs. GISTs in neurofibromatosis 1 patients, children, and Carney triad seem to lack GIST-specific KIT and PDGFRA mutations and may have a different disease mechanism. Secondary mutations usually occur in KIT kinase domains in patients after imatinib treatment resulting in resistance to this drug. Mutation genotyping is a tool in GIST diagnosis and in assessment of sensitivity to kinase inhibitors. This is a US government work. There are no restrictions on its use.

Gastrointestinal stromal tumors: differential diagnosis

Availability of KIT tyrosine kinase inhibitors for specific treatment of GISTs has magnified the importance of accurate differential diagnosis of GIST from other tumors occurring in the GI tract and abdomen. The general problems in this distinction include histological mimicry of other mesenchymal tumors with GIST, occasional KIT-negativity of GIST, and KIT-positivity of non-GISTs. Up to 5% to 10% gastric GISTs and <2% of intestinal GISTs can be KIT-negative. The identification of these tumors as GISTs is based on knowledge of the spectrum of GIST morphology, and can be supported by molecular diagnosis of KIT and PDGFRA mutations (the latter pertain to gastric tumors). True smooth muscle tumors (rare in GI tract except in esophagus and colon) can be separated from GISTs by the eosinophilic tinctorial quality of tumor cells, positivity for smooth muscle markers, and negativity for KIT. Desmoids can form large GIST-like masses, but are composed of spindled or stellate-shaped cells in a densely collagenous stroma. Negativity for KIT and nuclear positivity for beta-catenin are differentiating features. GI schwannomas, melanoma, and rare primary clear cell sarcoma are S100-positive, usually with characteristic histology. The latter two can be KIT-positive. KIT-positive non-GISTs include some sarcomas, especially angiosarcoma and Ewing sarcoma, extramedullary myeloid tumor, seminoma, and a few carcinomas, notably small cell carcinoma of lung. Spurious KIT-positivity, seen with some polyclonal KIT antibodies, has been a source of confusion leading to probable false-positive results in fibroblastic tumors and occasional other sarcomas, such as leiomyosarcomas. Integration of histological features with carefully standardized immunohistochemistry, supported by KIT and PDGFRA mutation analysis, is the cornerstone of state-of-the art differential diagnosis of GIST. To comprehensively capture all GISTs, KIT immunostains should be performed on all unclassified epithelioid and mesenchymal tumors of the abdomen. This is a US government work. There are no restrictions on its use.

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.

True smooth muscle neoplasms of the gastrointestinal tract: morphological spectrum and classification in a series of 85 cases from a single institute

BACKGROUND AND AIM

True smooth-muscle neoplasms of the GI tract have been only rarely studied in the KIT era. Their incidence among other GI mesenchymal tumours and their clinicopathological spectrum have not been sufficiently analysed.

MATERIALS AND METHODS

We reviewed all GI mesenchymal lesions at the Pathology Institute of the Nuremberg Clinic Centre from 1994 through 2005.

RESULTS

Among 262 lesions, there were 142 GISTs (54%) and 85 true smooth muscle neoplasms (32%). Smooth muscle neoplasms comprised 72 polypoid leiomyomas (78%, 5 oesophageal and 67 colorectal), 10 intramural leiomyomas (11%, 5 oesophageal, 4 gastric and one ileal), two intramural leiomyosarcomas in the sigmoid colon and ileum (2%) and one polypoid leiomyosarcoma involving the stomach, descending colon and the retroperitoneum concurrently. None of the leiomyomas with available follow-up have recurred or metastasised.

CONCLUSION

Smooth muscle neoplasms are the second most common mesenchymal neoplasms in the GI tract after GISTs. They may arise either from the muscularis mucosae or proper muscle layer forming polypoid and intramural lesions, respectively. Polypoid leiomyomas are more common in the rectosigmoid, while intramural ones mainly arise in the vicinity of the oesophagogastric junction. Polypoid leiomyomas are sufficiently treated by endoscopic resection, and local surgical excision is the treatment of choice for intramural leiomyomas. Intramural leiomyosarcomas are rare high-grade sarcomas that commonly have infiltrated into the surrounding tissue or metastasised by the time of diagnosis.

Expressions of sonic hedgehog, patched, smoothened and Gli-1 in human intestinal stromal tumors and their correlation with prognosis

AIM: To investigate the role that the hedgehog (Hh) signaling pathway, which includes sonic hedgehog (Shh), Patched (Ptc), Smoothened (Smo) and Gli-1, plays in human gastrointestinal stromal tumors (GISTs).

METHODS: Surgically resected specimens from patients with GISTs, leiomyomas and schwannomas were examined by immunohistochemical staining for aberrant expression of hedgehog signaling components, Shh, Ptc, Smo and Gli-1, respectively.

RESULTS: In GISTs, 58.1% (18 of 31), 77.4% (24 of 31), 80.6% (25 of 31) and 58.1% (18 of 31) of the specimens stained positive for Shh, Ptc, Smo and Gli-1, respectively. In leiomyomas, 92.3% (12 of 13), 92.3% (12 of 13), 69.2% (9 of 13) and 92.3% (12 of 13) stained positive for Shh, Ptc, Smo and Gli-1, respectively. In schwannomas, 83.3% (5 of 6), 83.3% (5 of 6), 83.3% (5 of 6) and 100% (6 of 6) stained positive for Shh, Ptc, Smo and Gli-1, respectively. Immunohistochemistry revealed that the expressions of Shh and Gli-1 were significantly higher in leiomyomas than in GISTs (P < 0.05, respectively). Shh expression strongly correlated with the grade of tumor risk category and with tumor size (P < 0.05, respectively). However, the expressions of Ptc and Smo did not correlate with histopathological differentiation.

CONCLUSION: These results suggest that the Hh signaling pathway may play an important role in myogenic differentiation and the malignant potential of human intestinal stromal tumors.

Outcome following surgical therapy for gastrointestinal stromal tumors

We have pursued an approach of complete resection for patients with gastrointestinal stromal tumors (GISTs), including multivisceral resection, for patients with disease involving adjacent organs. We have also extended the limits of resection to include patients with metastatic disease who were treated with imatinib mesylate. The aim of this study is to report the outcomes and prognostic factors associated with this clinical approach. Study subjects were identified using the pathology database at our institution; for inclusion in the study group, patients must have undergone surgical resection for a KIT-positive gastrointestinal stromal tumor between January 1992 and March 2004. We calculated survival by using the Kaplan-Meier method. Univariate and multivariate analysis was performed using log-rank analysis and the Cox proportional hazards model. Thirty-four patients met the study criteria. Fifty-nine percent of patients had GISTs of gastric origin, 20.6% had duodenal GISTs, and the remainder was comprised of a variety of other sites. Twenty-two (64.7%) patients underwent single-organ resection, and 12 patients (35.3%) underwent multivisceral resection. Estimated actuarial survival at 5 years was 65.2%. Seven patients (five patients with metastases, one patient with locally advanced disease, and one patient with organ-confined disease) received imatinib mesylate. Independent predictors of poor survival included incomplete resection, metastatic disease at presentation, and high mitotic index. Mitotic index and the presence of metastases remain the primary predictors of postoperative survival. Complete surgical resection, even if multivisceral resection is required, is associated with improved survival.

[A gastrointestinal stromal tumor--case report]

INTRODUCTION

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. They frequently occur in the stomach and small intestine, but they rarely occur in the colon and rectum.

CASE REPORT

This is a case report of a patient with a GIST involving the cecum, and acute obstruction of the small intestine. A 47-year-old male patient was admitted to the emergency surgery department with abdominal pain and distension lasting for a few days. Clinical examination revealed tenderness in the right iliac fossa. Routine hematologic testing revealed anemia, and abdominal x-ray multiple air-fluid levels in the small intestine. Based on the clinical findings, we decided to perform an explorative laparotomy. A large cecal tumor was detected. The proximal parts of the small intestine were severely distended.

DISCUSSION AND CONCLUSION

GISTs are more common in the stomach (60-70%) and the small intestine (25-35%), than in the colon, rectum and esophagus. The most frequent complications associated with GISTs are obstructions and hemorrhages. Surgical resection is the primary treatment of GISTs. Radiotherapy and chemotherapy are generally ineffective. Continuous postoperative follow-up is necessary, because most recurrences occur within the first 2 years after complete surgical resection. In the past few years, surgical resection was followed by adjuvant tyrosine kinase inhibitor therapy.

Clinical, pathologic, and immunohistochemical characteristics of gastrointestinal stromal tumors of the colon and rectum: implications for surgical management and adjuvant therapies

INTRODUCTION

This study was designed to review the clinical characteristics of surgically treated gastrointestinal stromal tumors of the colon and rectum, evaluate their immunohistochemical and pathologic features based on the current National Institutes of Health criteria, and correlate clinicopathologic findings with the subsequent clinical course.

METHODS

Patient and disease characteristics at presentation, pathologic features, surgical management, and clinical outcomes of 18 patients with gastrointestinal stromal tumors (4 colon and 14 rectum) diagnosed and primarily treated at our institution between 1979 and 2004 were evaluated.

RESULTS

Tumors were classified on basis of size and mitotic rate according to current National Institutes of Health recommendations: 67 percent (n = 12) were high-risk, 5 percent (n = 1) were intermediate-risk, 17 percent (n = 3) were low-risk, and 11 percent (n = 2) were very low-risk gastrointestinal stromal tumors. Fifteen of 18 tumors were KIT-positive. The three KIT-negative tumors were platelet-derived growth factor receptor alpha positive. All patients with colonic gastrointestinal stromal tumors (n = 4) underwent segmental resection, whereas patients with rectal gastrointestinal stromal tumors had local excision (n = 5) or radical resection (n = 9). Sixty-six percent (8/12) of patients with high-risk colorectal gastrointestinal stromal tumors developed metastases. None of the patients (n = 6) with intermediate-risk, low-risk, or very low-risk gastrointestinal stromal tumors died of their disease after a median follow-up of 65 (range, 15-266) months.

CONCLUSIONS

The majority of gastrointestinal stromal tumors of the colon and rectum are high-risk. Patients with high-risk colorectal gastrointestinal stromal tumors have a significant likelihood of developing metastases that is associated with poor prognosis. These patients need to be closely followed for an extended period and should be considered for adjuvant therapy with tyrosine kinase inhibitors.

Gastrointestinal stromal tumor (GIST)

Gastrointestinal stromal tumors (GISTs), the most common nonepithelial neoplasms of the gastrointestinal (GI) tract, occur most commonly in the stomach. These neoplasms were previously classified as smooth muscle tumors, but it has become apparent that they represent distinct clinicopathologic entities. All GISTs should be considered as having malignant potential, although they display varying degrees of aggressiveness. Although usually asymptomatic, large GISTs may present with pain or bleeding. Definitive diagnosis is made by immunohistochemical staining of the tissue for CD117, also known as KIT protein, a cell membrane receptor with tyrosine kinase activity. Size and mitotic activity are predictive of malignant behavior. Primary treatment for GISTs with high malignant potential is surgical resection. Specific therapy targeting the KIT receptor with imatinib has resulted in improved outcomes for patients with unresectable, metastatic, and recurrent disease.

Evaluation of biological potential of smooth muscle tumours

Smooth muscle tumours (SMTs) have been traditionally divided into benign leiomyomas (LM) and malignant leiomyosarcomas (LMS) based on cytological atypia, mitotic activity and other criteria. In most instances, this dichotomous approach works, but in some instances the biological potential cannot be determined with certainty. This is often because some, but not all criteria for malignancy have been met or because the tumours are occurring in unusual settings for which there are sparse substantive data. Tumours falling into the latter categories are often designated as 'smooth muscle tumours of uncertain malignant potential'. For most non-hormonally influenced SMTs, the presence of significant atypia plus mitotic activity equates with a diagnosis of LMS. However, not all tumours classified as LMSs have a similar prognosis, as a number of other factors, including tumour size, depth, grade and resectability, affect outcome. For example, cutaneous SMTs, regardless of mitotic activity and atypia, have potential largely limited to local recurrence, whereas subcutaneous and deep LMSs have a definite metastatic potential. Angioleiomyoma is the most common SMT of peripheral soft tissues, but deep peripheral LMs are distinctly rare and should be approached with caution. Hormonally influenced oestrogen- and progesterone receptor-positive uterine and extrauterine SMTs in women have unique criteria, including the allowance of higher mitotic activity for the benign LM designation. SMTs of female genital tract can be assessed with criteria similar to uterine tumours. Because of the rarity of these tumours, experience is more limited, and more caution is needed to assess the potential of tumours with mitotic activity and atypia. This review summarizes the current knowledge, guidelines, prognostic data and controversies for the classification of SMTs of soft tissue and most visceral sites.

Expression of Ets-1 proto-oncoprotein in gastrointestinal stromal tumors, leiomyomas and schwannomas

AIM: Gastrointestinal stromal tumors (GISTs) are rare. GISTs differ from other mesenchymal tumors of the gastrointestinal tract (e.g. leiomyomas and schwannomas). The purpose of this study was to investigate the role of Ets-1 in the growth and differentiation of GISTs.

METHODS: Twenty-eight GISTs, nine leiomyomas and six schwannomas were examined by immunohistochemical staining method for Ets-1 in this study. Specimens were selected from surgical pathology archival tissues at Nagasaki University Hospital.

RESULTS: Ets-1 protein was expressed in the cytoplasm of cells in all of these tumors. Immunohistochemical staining revealed that 27 GISTs (96.4 %), six leiomyomas (66.7 %), and five schwannomas (83.3 %) were positive for Ets-1. Ets-1 expression was statistically different between GISTs and leiomyomas (P < 0.005). However, there was no correlation between Ets-1 expression and clinical risk categories.

CONCLUSION: Ets-1 plays an important role in the growth and differentiation of GISTs, leiomyomas and schwannomas.

Small gastrointestinal stromal tumor concomitant with early gastric cancer: A case report

The term gastrointestinal stromal tumors (GISTs) is defined diagnostically as the main group of mesenchymal tumors with spindle or epithelioid cells arising from the wall of the gastrointestinal tract with immunohistochemical reactivity for CD117 antibody. Previous studies revealed that cells in GISTs express a growth factor receptor with tyrosine kinase activity (termed c-kit), which is the product of the c-kit proto-oncogene. The most specific and practical diagnostic criteria for GISTs are: immunohistochemically determined c-kit (CD117) expression; mitotic score; and tumor size. A small GIST concomitant with early gastric cancer is rarely encountered clinically. Herein we have reported a case of a 1.1-cm GIST detected by esophagogastroduodenoscopy concomitant with a IIc type of early gastric cancer (signet ring cell type). It was detected during a routine physical health examination. To our knowledge, this is the first report of a small GIST concomitant with a signet ring cell type of early gastric cancer.

Differential diagnosis of gastrointestinal leiomyoma versus gastrointestinal stromal tumor

INTRODUCTION

Strategies for the diagnosis of tumors arising in the intestinal muscular wall are rapidly evolving. Immunoreactivity for CD117 (KIT) usually supports the diagnosis of gastrointestinal stromal tumor (GIST), but a small subset of GISTs lacks KIT expression. In these cases the differential diagnosis of KIT-negative GIST versus one of their morphological mimics is difficult and bears critical implications for therapeutic management.

CASE REPORT

Here, we report a case of a KIT-negative smooth muscle cell tumor of the colon in a 21-year-old man with the clinical appearance of GIST. Mutations of the KIT and platelet-derived growth factor receptor alpha (PDGFRA) gene could be ruled out. No chromosomal imbalances characteristic of GIST were found. However, cytogenetic analysis revealed losses at 7q, which has previously been reported in cases of uterine leiomyoma.

DISCUSSION

We discuss current approaches to the differential diagnosis of true gastrointestinal smooth muscle cell tumor versus GIST.

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.

Polypoid pleomorphic sarcoma of the colon

In contrast to common colonic epithelial neoplasms, polypoid mesenchymal tumors of the colon are extremely rare. The majority of uncommon gastrointestinal mesenchymal tumors are associated with the so-called gastrointestinal stromal tumors (GIST). We present a case of a rare colonic pleomorphic sarcoma, macroscopically mimicking a common epithelial colonic polyp, which did not match the criteria of GIST. In this case report we discuss the clinical and pathological characteristics of a rare polypoid-shaped, pleomorphic colonic sarcoma and refer a mark-off to other rare mesenchymal neoplasms of the gut.

Gastrointestinal stromal tumors in Iceland, 1990-2003: the icelandic GIST study, a population-based incidence and pathologic risk stratification study

Gastrointestinal stromal tumor (GIST) is a newly defined clinical and pathologic entity. This study examines the whole population-based incidence of GIST as well as pathologic risk stratification schemes. All patients diagnosed in Iceland with a gastrointestinal mesenchymal tumor over the years 1990-2003 were evaluated with an immunohistochemical panel including staining for c-kit. The age-adjusted incidence of GIST was calculated. Size, mitotic rate per 50 HPF and various other pathologic parameters were evaluated. Each tumor was categorized into 1 of 4 recently defined NIH risk stratification categories. Fifty-seven of the mesenchymal gastrointestinal tumors were positive for c-kit and therefore categorized as GIST. The annual incidence for the study period is 1.1 per 100,000. The median age of patients was 65.8 years and median tumor size was 4.6 cm. Only 2 of 35 gastric tumors fall into the NIH high-risk category while half of the nongastric tumors (11 of 22) fall into this high-risk category. Eight of the 57 tumors (14%) metastasized, 7 of which were nongastric. The positive predictive value for malignant behavior of the high-risk category is 46%. The negative predictive value of low- and very-low-risk NIH category is 100%. Pathologic predictors of malignant behavior are tumor size, mitotic rate, mucosal disruption, necrosis and high cellularity. Nongastric GISTs are clearly at much higher risk of a malignant behavior than gastric GISTs. This population-based GIST study estimates the incidence of GISTs at 1.1 per 100,000 and furthermore supports the NIH consensus categories for the prediction of malignant behavior of GISTs.

Intestinal perineuriomas: clinicopathologic definition of a new anatomic subset in a series of 10 cases

Benign peripheral nerve sheath tumors are uncommon in the gastrointestinal tract, and perineuriomas have not previously been reported to occur at this anatomic location. In this study, we analyzed the clinicopathologic and immunohistochemical features of 10 perineuriomas arising in the intestine. Eight patients were female and 2 male (median age, 51 years; range, 35-72 years). Eight of the lesions were intramucosal perineuriomas presenting as small sessile polyps detected during colonoscopy; 6 of these 8 patients were asymptomatic and undergoing colorectal cancer screening. The remaining 2 cases were submucosal masses, one each located in the colon and jejunum. Of the mucosal polyps, six were located in the rectosigmoid or sigmoid colon and one each was detected in the descending colon and transverse colon. The polyps ranged from 0.2 to 0.6 cm (median, 0.4 cm) in greatest dimension. The colonic and jejunal masses measured 3 cm and 4.5 cm, respectively. Histologically, the intramucosal perineuriomas were composed of uniform bland spindle cells having ovoid to elongated nuclei and pale indistinct cytoplasm, with no cytologic atypia, pleomorphism, or mitotic activity. The lesions had a fine collagenous stroma, demonstrated irregular borders with the adjacent lamina propria, and entrapped colonic crypts. Five cases exhibited hyperplastic changes in the adjacent or entrapped epithelium. The colonic submucosal tumor was microscopically well circumscribed, whereas the jejunal perineurioma showed focal infiltration through the muscularis propria into the subserosa. The stroma was collagenous in the colonic tumor and predominantly myxoid in the jejunal tumor. The spindle cells in the submucosal perineuriomas demonstrated tapered nuclei and elongated bipolar cytoplasmic processes. All tumors except one were positive for epithelial membrane antigen (EMA); 4 of 10 expressed claudin-1 and 2 of 10 expressed CD34. All tumors were negative for S-100 protein, glial fibrillary acidic protein, neurofilament protein, smooth muscle actin, desmin, caldesmon, KIT, and pan-keratin. Electron microscopy was performed on the tumor lacking EMA expression, revealing typical features of perineurioma, namely, spindle cells with long bipolar cytoplasmic processes and prominent pinocytotic vesicles, surrounded by discontinuous basal lamina. Clinical follow-up was available for 4 patients (median, 34 months; range, 8-53 months). No tumor recurred. In summary, perineuriomas may arise in the intestine, most often as intramucosal lesions detected as colorectal polyps with distinctive histologic features including entrapment of colonic crypts. Distinguishing perineuriomas from other spindle cell neoplasms of the gastrointestinal tract can be facilitated by immunostaining for EMA and claudin-1.

Colorectal mesenchymal tumor: a clinicopathologic study of 25 cases

BACKGROUND

It is important to distinguish gastrointestinal stromal tumors (GISTs) from other gastrointestinal mesenchymal tumors (GIMTs), because of the malignant potential of GISTs and the availability of molecular targeted therapy. GISTs represent the most common subgroup of GIMTs, and rarely occur in the colon and rectum. The first objective of our retrospective study was to reclassify colorectal mesenchymal tumors, from files collected over 20 years, to determine if, based on immunohistologic features, the lesions were truly GISTs. The second objective was to identify the relationship between clinicopathologic features and prognostic factors of GISTs in the colon and rectum.

METHODS

We evaluated all cases of colorectal mesenchymal tumor identified from the database of the Department of Surgical Pathology at Taichung Veterans General Hospital for the period 1983-2001. For 25 patients, clinical data, and information about tumor characteristics, surgical procedures, and survival outcomes, were obtained and analyzed. Histopathologic evaluations, and appropriate immunohistochemical markers, were used to distinguish between various GIMT subtypes. The relationship between KIT expression and clinicopathologic features was investigated.

RESULTS

The following variables were significantly associated with different CD117 results: symptomatic presentation, location, gross features, tumor size, mitotic count, cellularity, and type of surgery. Only 18 tumors were identified as GISTs. For these, the following variables were significantly associated (by univariate analysis) with increased lethality: tumor size (p = 0.049); mitotic count (p = 0.019); nuclear atypia (p = 0.019); and tumor necrosis (p = 0.045). However, only mitotic activity showed a significant difference in the survival analysis (p = 0.0304; log-rank test).

CONCLUSION

Two clinicopathologically different categories were identified from our colorectal mesenchymal tumors: intramural GISTs and polypoid submucosal leiomyomas. Our study suggests that GIST is a better categorization than smooth muscle tumor because of the malignant potential. Prognosis is strictly related to the number of mitoses. However, tumor size, nuclear atypia and tumor necrosis are probably also significant predictive factors of lethality. Future studies with DNA analysis and larger patient numbers are essential to evaluate the prognostic significance of our findings.

Gene expression profile analysis of mouse colon embryonic development

During late embryogenesis, the mouse colon develops from a pseudostratified, undifferentiated endoderm to a single-layered columnar epithelium with accompanying mesenchymal maturation. To identify regulatory genetic programs underlying these morphological changes, we profiled gene expression of the developing mouse colon by microarray from embryonic day (E)13.5 to E18.5. Unbiased cluster analysis of 13,484 cDNA elements revealed two distinct groups of genes whose expression changes reflect the dynamic morphological events of the epithelium and mesenchyme during this period. Additional analyses revealed two subsets of genes whose expression is either upregulated or downregulated over the same developmental period. Of those genes whose expression increases from E13.5 to E18.5 (n = 158), known functions include acquisition and/or maintenance of colonic differentiation. Genes whose transcription is downregulated over this period (n = 49) have demonstrated roles in nuclear organization, transcriptional regulation, and cell proliferation. These results provide the basis for a molecular portrait of colonic development during late embryogenesis and should be a valuable resource for investigators interested in colonic development and neoplasia, as well as comparative organogenesis.

Gastric GI stromal tumors (GISTs): The role of surgery in the era of targeted therapy

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasm arising in the stomach. These tumors were previously classified as smooth muscle tumors, but in recent years it has become clear that they are clinically, pathologically, and molecularly distinct from other tumors and are much more common than previously appreciated. Historically, patients with primary localized or advanced GIST have been managed surgically, as there was no proven role of other treatment modalities such as radiation or chemotherapy. However, the field of GIST was revolutionized with the 1998 discovery that the vast majority of these tumors have oncogenic gain-of-function mutations of the KIT receptor tyrosine kinase. Follow-up studies have confirmed that KIT is both a useful diagnostic marker and an excellent therapeutic target. Imatinib, an inhibitor of KIT kinase activity, is now the standard front-line therapy for patients with advanced GIST. In this review, we discuss pathological and molecular features of gastric GISTs and review the historic and current roles of surgery in the treatment of patients with primary or metastatic GIST. The importance of a multi-disciplinary approach using both surgery and imatinib therapy is emphasized.

Biology of gastrointestinal stromal tumors

Once a poorly defined pathologic oddity, in recent years, gastrointestinal stromal tumor (GIST) has emerged as a distinct oncogenetic entity that is now center stage in clinical trials of kinase-targeted therapies. This review charts the rapid progress that has established GIST as a model for understanding the role of oncogenic kinase mutations in human tumorigenesis. Approximately 80% to 85% of GISTs harbor activating mutations of the KIT tyrosine kinase. In a series of 322 GISTs (including 140 previously published cases) studied by the authors in detail, mutations in the KIT gene occurred with decreasing frequency in exons 11 (66.1%), 9 (13%), 13 (1.2%), and 17 (0.6%). In the same series, a subset of tumors had mutations in the KIT-related kinase gene PDGF receptor alpha (PDGFRA), which occurred in either exon 18 (5.6%) or 12 (1.5%). The remainder of GISTs (12%) were wild type for both KIT and PDGFRA. Comparative studies of KIT-mutant, PDGFRA-mutant, and wild-type GISTs indicate that there are many similarities between these groups of tumors but also important differences. In particular, the responsiveness of GISTs to treatment with the kinase inhibitor imatinib varies substantially depending on the exonic location of the KIT or PDGFRA mutation. Given these differences, which have implications both for the diagnosis and treatment of GISTs, we propose a molecular-based classification of GIST. Recent studies of familial GIST, pediatric GIST, and variant forms of GIST related to Carney's triad and neurofibromatosis type 1 are discussed in relationship to this molecular classification. In addition, the role of mutation screening in KIT and PDGFRA as a diagnostic and prognostic aid is emphasized in this review.

Clinicopathologic, phenotypic, and genotypic characteristics of gastrointestinal mesenchymal tumors

BACKGROUND & AIMS

Variability in the frequency of KIT mutations in gastrointestinal mesenchymal tumors has been reported in the literature, and their prognostic value remains uncertain. This retrospective multicenter study included 276 patients with gastrointestinal mesenchymal tumors.

METHODS

We detected c-kit and CD34 protein expression by immunohistochemistry. Mutations in exons 11 and 9 of KIT and exons 12 and 18 of PDGFR were detected by length analysis of polymerase chain reaction products and direct DNA sequencing.

RESULTS

Eighty-seven percent of the tumors analyzed were c-kit positive, with gastric tumors expressing CD34 more frequently than other tumors (86% vs. 52%; P < 0.001). KIT exon 11 mutations were detected in 90 of 179 (50.3%) of c-kit-positive and 12% of c-kit-negative tumors. These mutations showed variation in their length and location. Mutations were heterozygous in 94% of cases. Mutations were more frequent in CD34( +) tumors than in CD34( -) tumors ( P < 0.01), and 9% of tumors had a second mutation in exon 11. Mutations in exon 9 of KIT were present in 5.1% of the gastrointestinal stromal tumors, and mutations of the PDGFR were present in 11% of the KIT -nonmutated tumors. Patient's age, the primary location, size, necrosis, and mitotic counts of tumors were associated with metastases in c-kit-positive tumors. However, mitotic activity was the only independent factor identified in multivariate analysis ( P < 0.001). KIT mutations were slightly more frequent in metastatic than in nonmetastatic tumors (61% vs. 46%; P = 0.06). Deletions of codons 562-579 were more strongly associated with metastases than were deletions of codons 550-561 ( P = 0.0001).

CONCLUSIONS

Mutations in KIT or PDGFR were detected in 58.4% of the c-kit-positive and also in some c-kit-negative tumors.

Differential diagnosis of gastrointestinal stromal tumor and other spindle cell tumors in the gastrointestinal tract based on immunohistochemical analysis

To confirm the usefulness of an immunohistochemical panel of antibodies for KIT (c-kit/CD117), CD34, desmin, smooth-muscle actin (SMA), h-caldesmon (HCD), S-100 protein, neuron-specific enolase (NSE), and beta-catenin, 297 mesenchymal and peripheral nerve-sheath tumors of the gastrointestinal tract and intra-abdominal locations including 211 gastrointestinal stromal tumors (GISTs), 12 leiomyomas, 18 leiomyosarcomas, 17 solitary fibrous tumors (SFTs), 14 schwannomas, and 25 desmoid-type fibromatoses (DTFs) were analyzed immunohistochemically. Consistent (100%) immunoreactivity for KIT, CD34, desmin and S-100, and nuclear accumulation of beta-catenin were detected in GISTs, SFTs, smooth-muscle tumors, schwannomas, and DTFs, respectively. Immunoreactivity for SMA, HCD, and NSE was observed in a wide range of these tumors. In addition, 418 bone and soft tissue tumors were enrolled in this study for KIT immunostaining. As a result, a limited number of these tumors were KIT positive, including synovial sarcoma that showed morphological similarity to GISTs. These findings suggest that KIT, CD34, desmin, S-100, and beta-catenin are key markers for clinical diagnosis of GISTs and other spindle cell tumors that may involve the gastrointestinal tract, whereas SMA, HCD, and NSE have only limited value.

c-kit and PDGFRA mutations in extragastrointestinal stromal tumor (gastrointestinal stromal tumor of the soft tissue)

Extragastrointestinal stromal tumor (EGIST) is a unique tumor that occurs outside the gastrointestinal tract. EGIST shows a c-kit expression and histologic appearance similar to those of gastrointestinal stromal tumor (GIST). Most GISTs have gain-of-functional mutation of the c-kit gene, and some have mutation of the platelet-derived growth factor receptor-alpha (PDGFRA) gene. However, the frequency of mutation of those genes in EGISTs remains unclear. We examined the clinicopathologic features, prognostic factors, and c-kit and PDGFRA mutation in 39 cases of EGIST. Tumors with high mitotic counts (>or=5/50 high power fields) or a high Ki-67 labeling index (>or=10%) were significantly correlated with worse prognoses. The c-kit mutation was found in the juxtamembrane domain (exon 11) and the extracellular domain (exon 9) in 12 of 29 cases (41.4%) and 2 of 29 cases (6.9%), respectively. The PDGFRA gene mutation was found at the juxtamembrane domain (exon 12) and the tyrosine kinase domain (exon 18) in one case each. The pattern of kit and PDGFRA mutation in EGIST was essentially similar to that in GIST. Our results suggest that the c-kit and PDGFRA mutations play an important role in the tumorigenesis of EGIST. High mitotic counts and a high Ki-67 labeling index may be useful for predicting the aggressive biologic behavior in EGIST. Furthermore, STI-571, targeting c-kit and PDGFR tyrosine kinase, seems to be a possible therapeutic strategy for EGISTs, especially advanced cases.

Benign Fibroblastic Polyps of the Colon

Mesenchymal proliferations presenting as mucosal polyps are relatively uncommon and are represented by gastrointestinal stromal tumors, smooth muscle and neural tumors, and inflammatory fibroid polyps. In this report, we describe the clinicopathologic features of a distinctive type of mucosal polyp composed of cytologically bland spindled cells with fibroblastic features. Fourteen cases with histologic features of"fibroblastic polyps" were identified from our case files from January 2000 to December 2003. The clinical and endoscopic findings were reviewed. Immunohistochemistry using a panel of antibodies (vimentin, smooth muscle actin, desmin, CD31, CD34, Bcl-2, c-Kit, S-100, and epithelial membrane antigen) was performed in all cases, and electron microscopy was performed in two cases. The lesions were solitary in all cases and not associated with an identifiable polyposis syndrome. Associated adenomata and/or hyperplastic polyps at different sites were present in 10 cases and hyperplastic polyps were seen in close association in 3 cases. These polyps were characterized by a monomorphic spindle cell proliferation in the lamina propria, without necrosis or mitotic activity. The lesions were intimately associated with the muscularis mucosae and resulted in wide separation and disorganization of the colonic crypts. Immunohistochemical analysis revealed strong and diffuse positivity for vimentin only. Weak and focal reactivity was noted in 2 cases for CD34 and smooth muscle actin, while staining for other antibodies was negative. Electron microscopy revealed sparse cytoplasmic organelles and many intermediate filaments. The histology and ultrastructural and immunohistochemical findings are suggestive of fibroblastic differentiation of these spindle cells. In summary, these lesions represent a distinctive type of colonic mucosal polyp that should be distinguished from other stromal polyps of the gastrointestinal tract.

Expressions of parathyroid hormone-related protein (PTHrP) and PTH/PTHrP-receptor (PTH/PTHrP-R) in gastrointestinal stromal tumours (GISTs), leiomyomas and schwannomas

BACKGROUND

Gastrointestinal stromal tumours (GISTs) are rare, c-kit and CD34 positive, and different from other mesenchymal tumours of the gastrointestinal tract (e.g. leiomyomas and schwannomas). The purpose of this study was to investigate the roles of parathyroid hormone-related protein (PTHrP) and parathyroid hormone/parathyroid hormone-related protein-receptor (PTH/PTHrP-R) in the growth and differentiation of GISTs.

METHODS

Nineteen GISTs, six leiomyomas and five schwannomas were examined in this study.

RESULTS

All of the GISTs and leiomyomas, and four of the schwannomas (80.0%) were positive for PTHrP. Immunohistochemical staining revealed that all of the leiomyomas, 90% of the GISTs and 80% of the schwannomas expressed PTH/PTHrP-R. Furthermore, both PTHrP and PTH/ PTHrP-R were expressed in the cytoplasm of identical cells in all of these tumours.

CONCLUSION

Our results suggest that both PTHrP and PTH/PTHrP-R play an important role in the growth and differentiation of GISTs, leiomyomas and schwannomas.

Primary malignant gastrointestinal stromal tumor of the liver

We report the case of a malignant, primary, hepatic gastrointestinal stromal tumor (GIST) that was resected from the liver of a 79-year-old woman. To our knowledge, this is the first primary, hepatic GIST on record. The tumor expressed CD117 (c-Kit protein) and vimentin and had the ultrastructural features of GISTs. Sixteen months after partial hepatectomy and resection of the tumor, a hilar lymph node metastasis was found. The metastatic tumor had the same morphologic features as the primary tumor, but in addition it contained numerous multinucleated giant cells. This case shows that GIST can occur as a primary liver tumor, and accordingly, we point out that not all hepatic tumors with a GIST phenotype should be automatically considered to be metastases from a primary gastrointestinal site.

Deletion of Trp-557 and Lys-558 in the juxtamembrane domain of the c-kit protooncogene is associated with metastatic behavior of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) typically express high levels of the Kit-receptor. The majority of GISTs carry mutations in the c-kit protooncogene clustering in exon 11. The significance of c-kit mutations for the biological behavior of GISTs is still under discussion. We evaluated 55 sporadic GISTs with available follow-up data for c-kit mutations in the juxtamembrane domain and detected mutations in 35 cases (63.6%). We found a mutational hotspot in codons 557 (tryptophan) and 558 (lysine) preferentially in histomorphologically malignant tumors. In the group of GISTs carrying c-kit mutations, 16 of 21 malignant, but only 3 of 8 benign GISTs and 3 of 6 lesions with uncertain malignant potential, carried mutations of Trp-557 and/or Lys-558. We investigated whether mutations in these 2 amino acids had an impact on biological behavior. Trp-557 and/or Lys-558 were mutated in all 15 metastatic GISTs carrying c-kit mutations but only in a minority of nonmetastatic tumors. A combined deletion of Trp-557 and Lys-558 occurred exclusively in 8 metastatic GISTs. We conclude that in addition to histomorphological evaluation determination of mutations in exon 11 may be an additional parameter for predicting the metastatic risk of GISTs and may be important for the decision that patients will need close clinical follow-up or further adjuvant treatment with kit antagonists.

The proto-oncogene c-kit is expressed in leiomyosarcomas of the uterus

OBJECTIVE

The proto-oncogene c-kit encodes for a 145-kDa transmembrane tyrosine kinase receptor. Interaction with its ligand, stem cell factor, is essential in the development of hematopoietic stem cells, mast cells, gametocytes, melanocytes, and interstitial cells of Cajal. C-kit expression has been identified in a number of different neoplasms that includes mastocytosis/mast cell leukemia, acute myeloblastic leukemia, seminoma/dysgerminoma, and gastrointestinal stromal tumors. This study examines c-kit expression in uterine endometrial stromal sarcomas, leiomyomas, and leiomyosarcomas using immunohistochemistry.

METHODS

Archival tissue from 38 patients with the uterine mesenchymal tumors (16 leiomyosarcomas, 8 leiomyomas, 11 low-grade endometrial stromal sarcomas, and 3 high-grade endometrial stromal sarcomas) was stained with polyclonal antibody for c-kit. Modified avidin biotin (ABC) immunoperoxidase method was employed for antibody detection. Individual tumors were considered positive if more than 10% of the cells comprising the neoplasm displayed immunoreactive staining. Staining intensity was graded 1+ to 3+ and distribution graded as focal (10-30% of the cells), intermediate (30-60% of the cells), or diffuse (>60% of the cells).

RESULTS

C-kit was positive in 12 (75%) of the 16 leiomyosarcomas. The staining was 3+ and diffuse in the majority of the positive tumors. C-kit expression was not detected in any of the 8 leiomyomas. Two of the 3 high-grade endometrial stromal sarcomas displayed c-kit positivity. Staining was diffuse and 3+ in both of these tumors. Expression of c-kit was observed in only 3 of the 11 low-grade endometrial stromal sarcomas.

CONCLUSIONS

C-kit is expressed in uterine leiomyosarcomas and endometrial stromal sarcomas. Adjunctive diagnostic studies using c-kit may be useful in distinguishing leiomyosarcomas from benign leiomyomas in uterine tumors that offer uncharacteristic features. Furthermore, studies should investigate the prospect of treating these malignant tumors with tyrosine kinase inhibitors.

[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.

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.

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.

Malignant stromal tumor of the colon in an infant: diagnostic difficulties and differential diagnosis

Gastrointestinal stromal tumor is a rare pathology in childhood. It may occur anywhere along the alimentary tract and represents with a wide spectrum of signs and symptoms according to location. An infant with malignant colonic stromal tumor that has presented with a huge abdominal mass and lower gastrointestinal bleeding is reported to discuss the difficulties in diagnosis and differential diagnosis of this unusual tumor.

Malignant gastrointestinal stromal tumor: distribution, imaging features, and pattern of metastatic spread

PURPOSE

To investigate and describe the anatomic distribution, imaging features, and pattern of metastatic spread of malignant gastrointestinal stromal tumors (GISTs).

MATERIALS AND METHODS

The medical records of all patients at our institution with a histologic diagnosis of GIST were reviewed. Two radiologists with knowledge of the diagnosis reviewed the radiologic findings by means of consensus. Sixty-seven patients underwent computed tomography, and scans of the primary tumor were available in 38 patients.

RESULTS

One hundred sixteen patients with malignant GISTs were identified (76 men and 40 women; mean age, 54.6 years +/- 13.5 [SD]). The primary tumor locations in descending order of frequency were the small bowel (n = 49), stomach (n = 43), colon (n = 7), rectum (n = 6), other (n = 3), and not specified (n = 8). Mean primary tumor size was 13 cm +/- 6. Tumors were typically well defined (31 of 36 [86%]), with a heterogeneous rim of soft tissue with lower signal intensity than that of the contrast material-enhanced liver. Central fluid attenuation was seen in 24 of 36 (67%) patients. Metastases were seen in 23 of 38 (61%) patients at presentation and in 53 of 61 (87%) patients during follow-up. Spread was usually to the liver or peritoneum. Visceral obstruction rarely occurred, even in the presence of extensive peritoneal metastatic disease. Ascites was an unusual finding.

CONCLUSION

Malignant GISTs are typically large, well-circumscribed, heterogeneous, centrally necrotic tumors that arise in the wall of the small bowel or stomach. They rarely obstruct viscera, despite their large size and propensity to metastasize to the liver and peritoneum.

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.