KIT extracellular and kinase domain mutations in gastrointestinal stromal tumors

Systemic mastocytosis in adults: 2017 update on diagnosis, risk stratification and management

Disease overview:Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in one or more extra-cutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of morphologically abnormal MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC expression of CD25 and/or CD2, and presence of KITD816V. Risk stratification: The 2008 World Health Organization (WHO) classification of SM has been shown to be prognostically relevant. Classification of SM patients into indolent (SM), aggressive SM (ASM), SM associated with a clonal non-MC lineage disease (SM-AHNMD) and mast cell leukemia (MCL) subgroups is a useful first step in establishing prognosis.

MANAGEMENT

SM treatment is generally palliative. ISM patients have a normal life expectancy and receive symptom-directed therapy; infrequently, cytoreductive therapy may be indicated for refractory symptoms. ASM patients have disease-related organ dysfunction; interferon-α (±corticosteroids) can control dermatological, hematological, gastrointestinal, skeletal and mediator-release symptoms, but is hampered by poor tolerability. Similarly, cladribine has broad therapeutic activity, with particular utility when rapid MC debulking is indicated; the main toxicity is myelosuppression. Imatinib has a therapeutic role in the presence of an imatinib-sensitive KIT mutation or in KITD816-unmutated patients. Treatment of SM-AHNMD is governed primarily by the non-MC neoplasm; hydroxyurea has modest utility in this setting; there is a role for allogeneic stem cell transplantation in select cases. Investigational drugs: Recent data confirms midostaurin's significant anti-MC activity in patients with advanced SM. Am. J. Hematol. 91:1147-1159, 2016. © 2016 Wiley Periodicals, Inc.

Germline mutations of KIT in gastrointestinal stromal tumor (GIST) and mastocytosis

Somatic mutations of KIT are frequently found in mastocytosis and gastrointestinal stromal tumor (GIST), while germline mutations of KIT are rare, and only found in few cases of familial GIST and mastocytosis. Although ligand-independent activation is the common feature of KIT mutations, the phenotypes mediated by various germline KIT mutations are different. Germline KIT mutations affect different tissues such as interstitial cells of Cajal (ICC), mast cells or melanocytes, and thereby lead to GIST, mastocytosis, or abnormal pigmentation. In this review, we summarize germline KIT mutations in familial mastocytosis and GIST and discuss the possible cellular context dependent transforming activity of KIT mutations.

A review of imatinib mesilate in the treatment of patients with gastrointestinal stromal tumours and chronic myeloid leukaemia

Context. Imatinib mesylate (GlivecÒ, GleevecÒ, Novartis) has made a dramatic impact on the treatment available for both chronic myeloid leukaemia (CML) and gastrointestinal stromal tumours (GISTs). Both are rare diseases that have possibly been unfamiliar to many pharmacists until now.

Objective. To provide readers with a structured overview of CML and GISTs and the trial data available to support the role imatinib is playing in the treatment of these diseases.

Data sources. Published reviews and primary trial results were sourced via Medline to prepare the review. Articles published up to and including August 2002 were considered. Additionally, pertinent books were used to prepare the text and Novartis kindly supplied information currently only available on file at the company. As imatinib has only been available for a short time, all types and sizes of trials were considered for inclusion. The authors made the final decision as to the relevance and therefore subsequent inclusion of data.

Conclusions. Imatinib is a new molecularly targeted therapy for the treatment of CML and GISTs. It has provided an efficacious alternative therapy choice for physicians managing the care of patients suffering from these diseases. In the future there is the possibility that imatinib may demonstrate activity in other disease states characterized by the genetic changes targeted by imatinib. The results of randomized controlled trials in new and existing indications are awaited.

Identification of the two KIT isoforms and their expression status in canine hemangiosarcomas

BACKGROUND

KIT is a tyrosine kinase growth factor receptor. High expression of KIT has been found in several tumors including canine hemangiosarcoma (HSA). This study investigated the correlation of KIT expression and c-kit sequence mutations in canine HSAs and benign hemangiomas (HAs).

RESULTS

Immunohistochemistry (IHC) staining confirmed KIT expression in 94.4 % (34/36) of HSAs that was significantly higher than 0 % in HAs (0/16). Sequencing the entire c-kit coding region of HSAs and normal canine cerebellums (NCCs) revealed GNSK-deletion in exon 9. As for exon 9 genotyping by TA-cloning strategy, GNSK-deletion c-kit accounted for 48.6 % (68/140) colonies amplified from12 KIT-positive HSAs, a significantly higher frequency than 14.1 % (9/64) of colonies amplified from six NCCs.

CONCLUSIONS

Due to the distinct expression pattern revealed by IHC, KIT might be used to distinguish benign or malignant vascular endothelial tumors. Moreover, the high incidence of GNSK-deletion c-kit in canine HSAs implicates KIT isoforms as possibly participating in the tumorigenesis of canine HSAs.

Targeted therapy of gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GISTs) are mesenchymal neoplasms originating in the gastrointestinal tract, usually in the stomach or the small intestine, and rarely elsewhere in the abdomen. The malignant potential of GISTs is variable ranging from small lesions with a benign behaviour to fatal sarcomas. The majority of the tumours stain positively for the CD-117 (KIT) and discovered on GIST-1 (DOG-1 or anoctamin 1) expression, and they are characterized by the presence of a driver kinase-activating mutation in either KIT or platelet-derived growth factor receptor α. Although surgery is the primary modality of treatment, almost half of the patients have disease recurrence following surgery, which highlights the need for an effective adjuvant therapy. Traditionally, GISTs are considered chemotherapy and radiotherapy resistant. With the advent of targeted therapy (tyrosine kinase inhibitors), there has been a paradigm shift in the management of GISTs in the last decade. We present a comprehensive review of targeted therapy in the management of GISTs.

The clinical correlation of phosphatase and tensin homolog on chromosome 10, phosphorylation of AKT to an activated state, and odontogenic ameloblast-associated protein in gastrointestinal stromal tumors

BACKGROUND

Approximately 15% of gastrointestinal stromal tumors (GISTs) will not respond to tyrosine kinase inhibitors and drug resistance can develop over time. For refractory tumors, additional therapies are needed. Odontogenic ameloblast-associated protein (ODAM) is expressed in some epithelial malignancies and can correlate with clinical outcomes. This study evaluated ODAM and its relationship to phosphatase and tensin homolog on chromosome 10 (PTEN) and phosphorylation of AKT to an activated state (pAKT) in GISTs.

MATERIALS AND METHODS

Ninety-five distinct tumor specimens from 79 patients were identified. Morphologic features and clinical data were recorded for all tumors. Risk of recurrence was calculated using the Memorial Sloan-Kettering nomogram. Immunohistochemistry was performed using antibodies to ODAM, PTEN, and pAKT. Immunoreactivity was assessed for both cytoplasmic and nuclear expression. Staining patterns were correlated with clinical outcomes.

RESULTS

Increasing cytoplasmic ODAM staining correlated with a lower recurrence score (P = 0.002), a lower mitotic rate (P = 0.0001), and smaller tumor size (P = 0.038). Increasing pAKT cytoplasmic staining correlated with a higher recurrence score (P = 0.037) and a higher mitotic rate (P = 0.036). ODAM and pAKT expression in the nucleus was associated with tumor origin. PTEN nuclear expression increased with increasing mitotic rate. pAKT expression increased in the cytoplasm and nucleus in high-risk tumors.

CONCLUSIONS

Risk of recurrence correlated with cytoplasmic expression of ODAM and pAKT, whereas nuclear expression did not predict recurrence. The staining pattern for ODAM and pAKT in the cytoplasm may further clarify the risk of recurrence beyond the available nomograms. The increased expression of pAKT in the cytoplasm and nucleus of high-risk tumors suggests a potential target for systemic therapy.

Metastatic Liver Disease Associated with Gastrointestinal Stromal Tumors: Controversies in Diagnostic and Therapeutic Approach

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are the most frequent mesenchymal lesions of the GI tract. They are considered to originate from neoplastic transformation of either the intestinal pacemaker cells of Cajal or the precursor pluripotential stem cells. The genetic basis of GIST growth is an activating mutation of two receptor tyrosine kinases. Recent epidemiologic studies demonstrate that the GIST prevalence is approximately 20/1000000/year. Although GISTs develop in every part of the GI tract, stomach remains the most common localization. About 80 % of the patients experience tumor recurrence or hepatic metastasis after radical resection. GIST liver metastases are usually multiple, large in diameter, and localized in both lobes. In addition, GISTs are usually completely asymptomatic, discovered incidentally. Symptoms are not typical and depend on the location, size, and aggressiveness of the tumor.

DISCUSSION

Diagnostic evaluation is based on imaging techniques, such as computed tomography, magnetic resonance imaging, positron emission tomography, and endoscopic ultrasound. Despite recent research on the therapeutic strategies against GISTs, surgical resection appears the only potentially curative approach. For the advanced metastatic disease, imatinib, a tyrosine kinase inhibitor, has been proposed neoadjuvantly with the surgery performed after the adequate reduction of tumor burden. The aim of this review was to evaluate the results of surgical treatment for metastatic GIST with special reference to the extent of its histological spread and to present the recent literature in order to provide an update on the current concepts of advanced surgical management of this entity.

KIT Exon 11 Codons 557-558 Deletion Mutation Promotes Liver Metastasis Through the CXCL12/CXCR4 Axis in Gastrointestinal Stromal Tumors

PURPOSE

KIT mutations, the most prevalent genetic event in gastrointestinal stromal tumors (GIST), are associated with malignant features and poor prognosis. Aggressive GISTs possess a high propensity to spread to the liver. This study aimed to explore the role of KIT mutations in GIST liver metastasis.

EXPERIMENTAL DESIGN

A total of 170 GISTs were used to determine the association between KIT mutations and liver metastasis. Immunohistochemistry was performed to assess the correlation of KIT mutations with CXCR4 and ETV1 expression. Genetic and pharmacologic methods were used to study the regulation of CXCR4 and ETV1 by KIT mutations.

RESULTS

Codons 557 and 558 in KIT exon 11 were deletion hot spots in GISTs. KIT exon 11 deletions involving codons 557-558 were highly associated with liver metastasis. Overexpression of mutant KIT with exon 11 codons 557-558 deletion (KIT Δ557-558) increased GIST cell motility and liver metastasis. Mechanistically, overexpression of KIT Δ557-558 in GIST cells increased ETV1 and CXCR4 expression. CXCR4 knockdown counteracted KIT Δ557-558-mediated cell migration. Moreover, KIT Δ557-558-induced CXCR4 expression could be abolished by silencing ETV1. The chromatin immunoprecipitation assay showed that ETV1 directly bound to the CXCR4 promoter. After ERK inhibitor PD325901 treatment, the upregulation of ETV1 by KIT Δ557-558 was prevented. In addition, KIT exon 11 codons 557-558 deletion enhanced CXCL12-mediated GIST cell migration and invasion.

CONCLUSIONS

KIT exon 11 557-558 deletion upregulates CXCR4 through increased binding of ETV1 to the CXCR4 promoter in GIST cells, which thus promotes liver metastasis. These findings highlighted the potential therapeutic targets for metastatic GISTs. Clin Cancer Res; 22(14); 3477-87. ©2016 AACR.

Gastrointestinal (GI) leiomyosarcoma (LMS) case series and review on diagnosis, management, and prognosis

This review of 76 gastrointestinal (GI) leiomyosarcoma (LMS) cases that include 11 cases from the American University of Beirut Medical Center represents, to our knowledge, the largest number of combined GI LMS cases reported. The age range of GI LMS is variable, and the presentation is non-specific, making pathological diagnosis essential. LMSs usually lack CD117 and CD 34 mutations and are usually positive for smooth muscle cell markers. The review highlights surgery as the mainstay of treatment with negative margins attained most of the times. Adjuvant chemotherapy is used in around 7-27 % of the cases mainly for small intestinal and colorectal LMS. The relatively small number of patients is a limitation on outcome analysis. However, LMS has a risk of recurrence reaching 39-80 % and secondary metastasis reaching 55-71 % in small intestinal and colorectal cases. In light of the high frequency of recurrence and metastasis, enrolling patients in clinical randomized trials to investigate the role of chemotherapy, radiation therapy, and targeted therapy is required for better control of this rare aggressive GI tumor.

C-kit Mutations in Endometrial Cancer: Correlation with Tumor Histologic Type

OBJECTIVE

Endometrial cancer is the fourth most common cancer among women in developed countries. Affected patients may benefit from systemic chemotherapy, alone or in combination with targeted therapies if the disease is clinically diagnosed prior to expansion and metastasis to other organs.The aim of this study was to evaluate the prognostic role of c-kit mutations and comparision with tumor type and grade in human uterine endometrial carcinomas.

MATERIALS AND METHODS

Seventy five patients with endometrial carcinoma and seventy five normal controls were studied for possible mutations in exon 17 of the c-kit gene using single strand conformational polymorphisms and sequencing.

RESULTS

c-kit mutation in exon 17 appeared to be significantly different between endometrial carcinoma and normal endometrium. The pattern and frequency of the mutations was also shown to be different between tumors from different stages.

C-Kit Promotes Growth and Migration of Human Cardiac Progenitor Cells via the PI3K-AKT and MEK-ERK Pathways

A recent phase I clinical trial (SCIPIO) has shown that autologous c-kit+ cardiac progenitor cells (CPCs) improve cardiac function and quality of life when transplanted into patients with ischemic heart disease. Although c-kit is widely used as a marker of resident CPCs, its role in the regulation of the cellular characteristics of CPCs remains unknown. We hypothesized that c-kit plays a role in the survival, growth, and migration of CPCs. To test this hypothesis, human CPCs were grown under stress conditions in the presence or absence of SCF, and the effects of SCF-mediated activation of c-kit on CPC survival/growth and migration were measured. SCF treatment led to a significant increase in cell survival and a reduction in cell death under serum depletion conditions. In addition, SCF significantly promoted CPC migration in vitro. Furthermore, the pro-survival and pro-migratory effects of SCF were augmented by c-kit overexpression and abrogated by c-kit inhibition with imatinib. Mechanistically, c-kit activation in CPCs led to activation of the PI3K and the MAPK pathways. With the use of specific inhibitors, we confirmed that the SCF/c-kit-dependent survival and chemotaxis of CPCs are dependent on both pathways. Taken together, our findings suggest that c-kit promotes the survival/growth and migration of human CPCs cultured ex vivo via the activation of PI3K and MAPK pathways. These results imply that the efficiency of CPC homing to the injury site as well as their survival after transplantation may be improved by modulating the activity of c-kit.

Platelet-Derived Growth Factor Receptor-α Regulates Proliferation of Gastrointestinal Stromal Tumor Cells With Mutations in KIT by Stabilizing ETV1

BACKGROUND & AIMS

In gastrointestinal muscles, v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) is predominantly expressed by interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor-α (PDGFRA) polypeptide is expressed by so-called fibroblast-like cells. KIT and PDGFRA have been reported to be coexpressed in ICC precursors and gastrointestinal stromal tumors (GISTs), which originate from the ICC lineage. PDGFRA signaling has been proposed to stimulate growth of GISTs that express mutant KIT, but the effects and mechanisms of selective blockade of PDGFRA are unclear. We investigated whether inhibiting PDGFRA could reduce proliferation of GIST cells with mutant KIT via effects on the KIT-dependent transcription factor ETV1.

METHODS

We studied 53 gastric, small intestinal, rectal, or abdominal GISTs collected immediately after surgery or archived as fixed blocks at the Mayo Clinic and University of California, San Diego. In human GIST cells carrying imatinib-sensitive and imatinib-resistant mutations in KIT, PDGFRA was reduced by RNA interference (knockdown) or inhibited with crenolanib besylate (a selective inhibitor of PDGFRA and PDGFRB). Mouse ICC precursors were retrovirally transduced to overexpress wild-type Kit. Cell proliferation was analyzed by methyltetrazolium, 5-ethynyl-2'-deoxyuridine incorporation, and Ki-67 immunofluorescence assays; we also analyzed growth of xenograft tumors in mice. Gastric ICC and ICC precursors, and their PDGFRA(+) subsets, were analyzed by flow cytometry and immunohistochemistry in wild-type, Kit(+/copGFP), Pdgfra(+/eGFP), and NOD/ShiLtJ mice. Immunoblots were used to quantify protein expression and phosphorylation.

RESULTS

KIT and PDGFRA were coexpressed in 3%-5% of mouse ICC, 35%-44% of ICC precursors, and most human GIST samples and cell lines. PDGFRA knockdown or inhibition with crenolanib efficiently reduced proliferation of imatinib-sensitive and imatinib-resistant KIT(+)ETV1(+)PDGFRA(+) GIST cells (50% maximal inhibitory concentration = 5-32 nM), but not of cells lacking KIT, ETV1, or PDGFRA (50% maximal inhibitory concentration >230 nM). Crenolanib inhibited phosphorylation of PDGFRA and PDGFRB, but not KIT. However, Kit overexpression sensitized mouse ICC precursors to crenolanib. ETV1 knockdown reduced KIT expression and GIST proliferation. Crenolanib down-regulated ETV1 by inhibiting extracellular-signal-regulated kinase (ERK)-dependent stabilization of ETV1 protein and also reduced expression of KIT and PDGFRA.

CONCLUSIONS

In KIT-mutant GIST, inhibition of PDGFRA disrupts a KIT-ERK-ETV1-KIT signaling loop by inhibiting ERK activation. The PDGFRA inhibitor crenolanib might be used to treat patients with imatinib-resistant, KIT-mutant GIST.

Genetics of Gastrointestinal Stromal Tumors: A Heterogeneous Family of Tumors?

Approximately 85-90% of adult gastrointestinal stromal tumors (GISTs) harbor KIT and PDGFRA mutations. The remaining cases, including the majority of pediatric GISTs, lack these mutations, and have been designated as KIT/PDGFRA wild-type (WT) GISTs. Nearly 15% of WT GISTs harbor BRAF mutations, while others arise in patients with type I neurofibromatosis. Recent work has confirmed that 20-40% of KIT/PDGFRA WT GISTs show loss of function of succinate dehydrogenase complex. Less than 5% of GISTs lack known molecular alterations ("quadruple-negative" GISTs). Thus, it is important to consider genotyping these tumors to help better define their clinical behavior and therapy.

Gastrointestinal stromal tumors: treatment patterns of a population-based sample

OBJECTIVES

The National Cancer Institute (NCI) annually confirms therapy with treating physicians on a sample of patients diagnosed with a specific cancer.

METHODS

Using the NCI Patterns of Care data, treatment patterns were examined on a population-based sample of patients diagnosed with gastrointestinal stromal tumors (GIST) in 2008.

RESULTS

A random sample of 323 of 405 GIST patients registered in SEER was selected. Most patients had gastric GISTs, were ≥ 65 years, white, had private insurance, and treated in a hospital with a residency program. Surgery was primarily performed in patients with non-metastatic disease (94%), in which: 26, 12, and 36% were at low, intermediate, and high-risk of recurrence, respectively. Amongst low-risk patients, ∼ 30% received adjuvant therapy. Amongst patients at higher risk, 26-40% did not receive adjuvant therapy. Imatinib was the most common targeted therapy administered. On multivariate analysis, age and risk-group were associated with receipt of adjuvant targeted therapy.

CONCLUSIONS

Our study shows that in 2008, the majority of patients diagnosed with GIST received appropriate surgical and adjuvant therapies. However, a considerable subset may have been overtreated and undertreated. Future studies identifying factors that impact the delivery of adjuvant therapy should be conducted.

A point mutation in the extracellular domain of KIT promotes tumorigenesis of mast cells via ligand-independent auto-dimerization

Mutations in the juxtamembrane and tyrosine kinase domains of the KIT receptor have been implicated in several cancers and are known to promote tumorigenesis. However, the pathophysiological manifestations of mutations in the extracellular domain remain unknown. In this study, we examined the impact of a mutation in the extracellular domain of KIT on mast cell tumorigenesis. A KIT mutant with an Asn508Ile variation (N508I) in the extracellular domain derived from a canine mast cell tumor was introduced into IC-2 cells. The IC-2(N508I) cells proliferated in a cytokine-independent manner and showed KIT auto-phosphorylation. Subcutaneous injection of IC-2(N508I) cells into the dorsal area of immunodeficient BALB/c-nu/nu mice resulted in the formation of solid tumors, but tumor progression was abrogated by treatment with a tyrosine kinase inhibitor (STI571). In addition, the N508I mutant KIT protein dimerized in the absence of the natural ligand, stem cell factor. Structure modeling indicates that the increased hydrophobicity of the mutant led to the stabilization of KIT dimers. These results suggest that this extracellular domain mutation confers a ligand-independent tumorigenic phenotype to mast cells by KIT auto-dimerization that is STI571-sensitive. This is the first report demonstrating the tumorigenic potential of a mutation in the extracellular domain of KIT.

Hyperplasia of interstitial cells of cajal in sprouty homolog 4 deficient mice

Gastrointestinal stromal tumors, which are thought to derive from interstitial cells of Cajal or their precursors, often harbor an oncogenic mutation of the KIT receptor tyrosine kinase. Sprouty homolog 4, a known negative regulator of ERK pathway, has been identified in the interstitial cells of Cajal in the Kit^K641E murine model of gastrointestinal stromal tumors. Sprouty homolog 4 was upregulated both at the mRNA and protein level in these cells, suggesting that Sprouty homolog 4 is downstream of oncogenic KIT activation and potentially engaged in the negative feedback loop of ERK activation in this model. Here, we used Kit^K641E heterozygous and Sprouty homolog 4 knock out animals to quantify interstitial cells of Cajal in situ, using quantitative immunofluorescence for the receptor tyrosine kinase Kit and for phosphodiesterase 3a (PDE3A). In the antrum of Sprouty homolog 4 knock out mice, hyperplasia of interstitial cells of Cajal was reminiscent of the Kit^K641E heterozygous mice antrum. Additionally, the density of interstitial cells of Cajal was higher in the colon of adult Sprouty homolog 4 knock out mice than in WT littermates, although hyperplasia seemed more severe in Kit^K641E heterozygous mice. Functional transit studies also show similarities between Sprouty homolog 4 knock out and Kit^K641E heterozygous mice, as the total transit time in 9 month old animals was significantly increased in both genotypes compared to WT littermates. We concluded that the lack of Sprouty homolog 4 expression leads to hyperplasia of the interstitial cells of Cajal and is functionally associated with a delayed transit time.

Systemic mastocytosis in adults: 2015 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in one or more extracutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of morphologically abnormal MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC expression of CD25 and/or CD2, and presence of KITD816V.

RISK STRATIFICATION

The 2008 World Health Organization classification of SM has been shown to be prognostically relevant. Classification of SM patients into indolent SM (ISM), aggressive SM (ASM), SM associated with a clonal non-MC lineage disease (SM-AHNMD), and mast cell leukemia (MCL) subgroups is a useful first step in establishing prognosis.

MANAGEMENT

SM treatment is generally palliative. ISM patients have a normal life expectancy and receive symptom-directed therapy; infrequently, cytoreductive therapy may be indicated for refractory symptoms. ASM patients have disease-related organ dysfunction; interferon-α (+/-corticosteroids) can control dermatological, hematological, gastrointestinal, skeletal, and mediator-release symptoms, but is hampered by poor tolerability. Similarly, cladribine has broad therapeutic activity, with particular utility when rapid MC debulking is indicated; the main toxicity is myelosuppression. Imatinib has a therapeutic role in the presence of an imatinib-sensitive KIT mutation or in KITD816-unmutated patients. Treatment of SM-AHNMD is governed primarily by the non-MC neoplasm; hydroxyurea has modest utility in this setting; there is a role for allogeneic stem cell transplantation in select cases. Investigational Drugs: Recent data confirms midostaurin's significant anti-MC activity in patients with advanced SM.

Role of surgery in patients with recurrent, metastatic, or unresectable locally advanced gastrointestinal stromal tumors sensitive to imatinib: a retrospective analysis of the Spanish Group for Research on Sarcoma (GEIS)

BACKGROUND

Recurrent, metastatic, and locally advanced gastrointestinal stromal tumors (GISTs) can be treated successfully with imatinib mesylate. Surgery for residual disease has been suggested for nonrefractory metastatic GISTs to reduce the probability of resistant recurrent clones, although no randomized Phase III trial has been performed to answer the question about its benefit. We carried out an analysis of the outcome of patients with recurrent unresectable locally advanced or metastatic imatinib-sensitive priamary GIST in 14 institutions in Spain. We compared two cohorts: treated or not treated with surgery after partial response or stabilization by imatinib.

PATIENTS AND METHODS

Data were obtained from the online GIST registry of the Spanish Group for Research in Sarcomas. Selected patients were then divided into two groups: group A, treated initially only with imatinib, and group B, treated additionally with metastasectomy. Baseline characteristics between groups were compared, and univariate and multivariate analysis for progression-free survival and overall survival (OS) were performed.

RESULTS

Analysis was undertaken in 171 patients considered nonrefractory to imatinib. The median follow-up time was 56.6 months. Focusing on OS, the Eastern Cooperative Oncology Group performance status different than 0, extent of disease limited to one metastatic organ, and comparison between groups A or B achieved statistical difference in the multivariate analysis. Median survival was 59.9 months in group A and 87.6 months in group B.

CONCLUSIONS

Based in its benefit in OS, our study supports surgery of metastatic disease in GIST patients who respond to imatinib therapy.

Gastrointestinal stromal tumor - an evolving concept

Gastrointestinal stromal tumors (GISTs) are the most frequent mesenchymal tumors of the gastrointestinal tract. The discovery that these tumors, formerly thought of smooth muscle origin, are indeed better characterized by specific activating mutation in genes coding for the receptor tyrosine kinases (RTKs) CKIT and PDGFRA and that these mutations are strongly predictive for the response to targeted therapy with RTK inhibitors has made GISTs the typical example of the integration of basic molecular knowledge in the daily clinical activity. The information on the mutational status of these tumors is essential to predict (and subsequently to plan) the therapy. As resistant cases are frequently wild type, other possible oncogenic events, defining other "entities," have been discovered (e.g., succinil dehydrogenase mutation/dysregulation, insuline growth factor expression, and mutations in the RAS-RAF-MAPK pathway). The classification of disease must nowadays rely on the integration of the clinico-morphological characteristics with the molecular data.

Combination therapy for KIT-mutant mast cells: targeting constitutive NFAT and KIT activity

Resistant KIT mutations have hindered the development of KIT kinase inhibitors for treatment of patients with systemic mastocytosis. The goal of this research was to characterize the synergistic effects of a novel combination therapy involving inhibition of KIT and calcineurin phosphatase, a nuclear factor of activated T cells (NFAT) regulator, using a panel of KIT-mutant mast cell lines. The effects of monotherapy or combination therapy on the cellular viability/survival of KIT-mutant mast cells were evaluated. In addition, NFAT-dependent transcriptional activity was monitored in a representative cell line to evaluate the mechanisms responsible for the efficacy of combination therapy. Finally, shRNA was used to stably knockdown calcineurin expression to confirm the role of calcineurin in the observed synergy. The combination of a KIT inhibitor and a calcineurin phosphatase inhibitor (CNPI) synergized to reduce cell viability and induce apoptosis in six distinct KIT-mutant mast cell lines. Both KIT inhibitors and CNPIs were found to decrease NFAT-dependent transcriptional activity. NFAT-specific inhibitors induced similar synergistic apoptosis induction as CNPIs when combined with a KIT inhibitor. Notably, NFAT was constitutively active in each KIT-mutant cell line tested. Knockdown of calcineurin subunit PPP3R1 sensitized cells to KIT inhibition and increased NFAT phosphorylation and cytoplasmic localization. Constitutive activation of NFAT appears to represent a novel and targetable characteristic of KIT-mutant mast cell disease. Our studies suggest that combining KIT inhibition with NFAT inhibition might represent a new treatment strategy for mast cell disease.

Analysis of gene expression profiles of soft tissue sarcoma using a combination of knowledge-based filtering with integration of multiple statistics

The diagnosis and treatment of soft tissue sarcomas (STS) have been difficult. Of the diverse histological subtypes, undifferentiated pleomorphic sarcoma (UPS) is particularly difficult to diagnose accurately, and its classification per se is still controversial. Recent advances in genomic technologies provide an excellent way to address such problems. However, it is often difficult, if not impossible, to identify definitive disease-associated genes using genome-wide analysis alone, primarily because of multiple testing problems. In the present study, we analyzed microarray data from 88 STS patients using a combination method that used knowledge-based filtering and a simulation based on the integration of multiple statistics to reduce multiple testing problems. We identified 25 genes, including hypoxia-related genes (e.g., MIF, SCD1, P4HA1, ENO1, and STAT1) and cell cycle- and DNA repair-related genes (e.g., TACC3, PRDX1, PRKDC, and H2AFY). These genes showed significant differential expression among histological subtypes, including UPS, and showed associations with overall survival. STAT1 showed a strong association with overall survival in UPS patients (logrank p = 1.84 × 10(-6) and adjusted p value 2.99 × 10(-3) after the permutation test). According to the literature, the 25 genes selected are useful not only as markers of differential diagnosis but also as prognostic/predictive markers and/or therapeutic targets for STS. Our combination method can identify genes that are potential prognostic/predictive factors and/or therapeutic targets in STS and possibly in other cancers. These disease-associated genes deserve further preclinical and clinical validation.

C-kit and PDGFRA gene mutations in triple negative breast cancer

In this study, we evaluated C-kit immunohistochemical expression and C-kit and platelet derived growth factor receptor A (PDGFRA) gene mutations in triple negative breast cancer. 171 cases were analyzed by immunohistochemical staining for the expression of C-kit and 45 cases, including 10 C-kit negative cases and 35 C-kit positive cases, were performed for C-kit gene mutations in exons 9, 11, 13 and 17 and PDGFRA gene mutations in exons 12 and 18. C-kit expression was detected in 42.1% of triple negative breast cancers. Only 1 activating mutation was detected in exon 11 of C-kit gene in 1 case. No activating mutations were found in the other 44 cases. C-kit expression is a frequent finding in triple negative breast cancers; 1 activating mutation which was also found in gastrointestinal stromal tumors was detected; a few cases might benefit from imatinib.

Imatinib mesylate

Imatinib mesylate (Gleevec, Glivec [Novartis, Basel, Switzerland], formerly referred to as STI571 or CGP57148B) represents the paradigm of a new class of anticancer agents, so-called small molecules. They have a high selectivity against a specific molecular target known to be the cause for the establishment and maintenance of the malignant phenotype. Imatinib is a rationally designed oral signal transduction inhibitor that specifically targets several protein tyrosine kinases, Abl, Arg (Abl-related gene), the stem cell factor receptor (c-KIT), platelet-derived growth factor receptor (PDGF-R), and their oncogenic forms, most notably BCR-ABL. Imatinib has been shown to have remarkable clinical activity in patients with chronic myeloid leukemia (CML) and malignant gastrointestinal stroma tumors (GIST) leading to its approval for treatment of these diseases. Treatment with imatinib is generally well tolerated with a low incidence of severe side effects. The most common adverse events include mild to moderate edema, muscle cramps, diarrhea, nausea, skin rashes, and myelosuppression. Several mechanisms of resistance have been identified. Clonal evolution, amplification, or overexpression of BCR-ABL as well as mutations in the catalytic domain, P-loop, and other mutations have been demonstrated to play a role in primary and secondary resistance to imatinib, respectively. Understanding of the underlying mechanisms of resistance has led to the development of new second- and third-generation tyrosine kinase inhibitors (see chapters on dasatinib, nilotinib, bosutinib, and ponatinib).

Gastrointestinal stromal tumors: what do we know now?

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the GI tract, arising from the interstitial cells of Cajal, primarily in the stomach and small intestine. They manifest a wide range of morphologies, from spindle cell to epithelioid, but are immunopositive for KIT (CD117) and/or DOG1 in essentially all cases. Although most tumors are localized at presentation, up to half will recur in the abdomen or spread to the liver. The growth of most GISTs is driven by oncogenic mutations in either of two receptor tyrosine kinases: KIT (75% of cases) or PDGFRA (10%). Treatment with tyrosine kinase inhibitors (TKIs) such as imatinib, sunitinib, and regorafenib is effective in controlling unresectable disease; however, drug resistance caused by secondary KIT or PDGFRA mutations eventually develops in 90% of cases. Adjuvant therapy with imatinib is commonly used to reduce the likelihood of disease recurrence after primary surgery, and for this reason assessing the prognosis of newly resected tumors is one of the most important roles for pathologists. Approximately 15% of GISTs are negative for mutations in KIT and PDGFRA. Recent studies of these so-called wild-type GISTs have uncovered a number of other oncogenic drivers, including mutations in neurofibromatosis type I, RAS genes, BRAF, and subunits of the succinate dehydrogenase complex. Routine genotyping is strongly recommended for optimal management of GISTs, as the type and dose of TKI used for treatment is dependent on the mutation identified.

Identification of KIT activating mutations in paediatric solitary mastocytoma

AIMS

Mastocytosis is an abnormal mast cell proliferation involving one or more organs, in particular the skin and bone marrow. In children, disease is usually limited to the skin, with three distinct clinical presentations: urticaria pigmentosa, diffuse cutaneous mastocytosis and solitary mastocytoma. Although the KIT D816V mutation is typically found in adult-onset mastocytosis, it is less commonly seen in childhood-onset mastocytosis, and the frequency of KIT mutations in paediatric solitary mastocytoma is poorly documented.

METHODS AND RESULTS

In this study we analysed KIT exons 8, 9, 11, 13 and 17 in nine cases of paediatric solitary mastocytoma using a laboratory-developed Sanger sequencing assay. A KIT mutation was identified in six cases (67%), including three with the D816V mutation typical of adult-onset disease, and another three with an internal tandem duplication (p.A502_Y503dup) in exon 9, previously described in gastrointestinal stromal tumour.

CONCLUSIONS

Paediatric solitary mastocytoma is frequently associated with KIT activating mutations, in keeping with a clonal process. KIT mutational status appears insufficient to explain the divergent biology of childhood and adult-onset disease.

Membrane-to-nucleus signaling links insulin-like growth factor-1- and stem cell factor-activated pathways

Stem cell factor (mouse: Kitl, human: KITLG) and insulin-like growth factor-1 (IGF1), acting via KIT and IGF1 receptor (IGF1R), respectively, are critical for the development and integrity of several tissues. Autocrine/paracrine KITLG-KIT and IGF1-IGF1R signaling are also activated in several cancers including gastrointestinal stromal tumors (GIST), the most common sarcoma. In murine gastric muscles, IGF1 promotes Kitl-dependent development of interstitial cells of Cajal (ICC), the non-neoplastic counterpart of GIST, suggesting cooperation between these pathways. Here, we report a novel mechanism linking IGF1-IGF1R and KITLG-KIT signaling in both normal and neoplastic cells. In murine gastric muscles, the microenvironment for ICC and GIST, human hepatic stellate cells (LX-2), a model for cancer niches, and GIST cells, IGF1 stimulated Kitl/KITLG protein and mRNA expression and promoter activity by activating several signaling pathways including AKT-mediated glycogen synthase kinase-3β inhibition (GSK3i). GSK3i alone also stimulated Kitl/KITLG expression without activating mitogenic pathways. Both IGF1 and GSK3i induced chromatin-level changes favoring transcriptional activation at the Kitl promoter including increased histone H3/H4 acetylation and H3 lysine (K) 4 methylation, reduced H3K9 and H3K27 methylation and reduced occupancy by the H3K27 methyltransferase EZH2. By pharmacological or RNA interference-mediated inhibition of chromatin modifiers we demonstrated that these changes have the predicted impact on KITLG expression. KITLG knock-down and immunoneutralization inhibited the proliferation of GIST cells expressing wild-type KIT, signifying oncogenic autocrine/paracrine KITLG-KIT signaling. We conclude that membrane-to-nucleus signaling involving GSK3i establishes a previously unrecognized link between the IGF1-IGF1R and KITLG-KIT pathways, which is active in both physiologic and oncogenic contexts and can be exploited for therapeutic purposes.

Gastrointestinal stromal tumors: molecular markers and genetic subtypes

Mutation-activated signaling from the KIT and PDGFRA kinases has been successfully targeted in gastrointestinal stromal tumors (GISTs), with subtle differences between the mutations serving to refine prognosis and more precisely tailor therapy. There is a growing understanding of the molecular drivers of GISTs lacking mutations in KIT or PDGFRA, so called wild-type GISTs, further aiding in management decisions. This article provides an overview of all the known molecular subtypes of GIST and provides information about clinical correlates, treatment, and prognosis depending on the subtype.

Gastrointestinal stromal tumour

Gastrointestinal stromal tumours (GISTs) are mesenchymal neoplasms that arise in the gastrointestinal tract, usually in the stomach or the small intestine and rarely elsewhere in the abdomen. They can occur at any age, the median age being 60-65 years, and typically cause bleeding, anaemia, and pain. GISTs have variable malignant potential, ranging from small lesions with a benign behaviour to fatal sarcomas. Most tumours stain positively for the mast/stem cell growth factor receptor KIT and anoctamin 1 and harbour a kinase-activating mutation in either KIT or PDGFRA. Tumours without such mutations could have alterations in genes of the succinate dehydrogenase complex or in BRAF, or rarely RAS family genes. About 60% of patients are cured by surgery. Adjuvant treatment with imatinib is recommended for patients with a substantial risk of recurrence, if the tumour has an imatinib-sensitive mutation. Tyrosine kinase inhibitors substantially improve survival in advanced disease, but secondary drug resistance is common.

Update on imatinib for gastrointestinal stromal tumors: duration of treatment

Gastrointestinal stromal tumors (GISTs) are the most common sarcoma of the gastrointestinal tract, with transformation typically driven by activating mutations of c-KIT and less commonly platelet-derived growth factor receptor alpha (PDGFRA). Successful targeting of c-KIT and PDGFRA with imatinib, a tyrosine kinase inhibitor (TKI), has had a major impact in advanced GIST and as an adjuvant and neoadjuvant treatment. If treatment with imatinib fails, further lines of TKI therapy have a role, but disease response is usually only measured in months, so strategies to maximize the benefit from imatinib are paramount. Here, we provide an overview of the structure and signaling of c-KIT coupled with a review of the clinical trials of imatinib in GIST. In doing so, we make recommendations about the duration of imatinib therapy and suggest how best to utilize imatinib in order to improve patient outcomes in the future.

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

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

C-kit-mutated melanomas: the Chinese experience

PURPOSE OF REVIEW

Malignant melanoma is the most frequent cause of mortality in skin cancer. Unlike Caucasians, mucosal and acral melanomas account for approximately 65% of all melanomas in Chinese. Genetic mutations of c-kit are detected in mucosal and acral melanomas, which thus can be regarded as molecular targets for treatments. This review describes the recent proceedings in the c-kit-targeted molecular therapy of melanoma, on the basis of our experiences in Chinese melanoma patients.

RECENT FINDINGS

Somatic mutations within c-kit gene have been detected in 10.8% of Chinese melanoma patients. Imatinib, a selective inhibitor targeting Abl as well as c-kit and the platelet-derived growth factor receptor, has been tested for the efficacy and toxicities in metastatic melanoma patients, suggesting that imatinib may increase the progression-free survival and overall survival in selected melanoma patients harboring mutations in c-kit gene. The current status of c-kit mutation and the standard for selection of imatinib-sensitive patients have been tentatively established.

SUMMARY

C-kit is a proto-oncogene that can serve as a potential target for molecular therapy of metastatic melanoma. Imatinib is effective and well tolerated in the treatment of metastatic melanoma patients. In selected subsets of melanoma patients harboring genetic alterations of c-kit, imatinib may be a promising agent.

Systemic mastocytosis in adults: 2013 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in one or more extracutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of morphologically abnormal MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC expression of CD25 and/or CD2, and presence of KITD816V.

RISK STRATIFICATION

The 2008 World Health Organization (WHO) classification of SM has been shown to be prognostically relevant. Classification of SM patients into indolent (SM), aggressive SM (ASM), SM associated with a clonal non-MC lineage disease (SM-AHNMD) and mast cell leukemia (MCL) subgroups is a useful first step in establishing prognosis.

MANAGEMENT

SM treatment is generally palliative. ISM patients have a normal life expectancy and receive symptom-directed therapy; infrequently, cytoreductive therapy may be indicated for refractory symptoms. ASM patients have disease-related organ dysfunction; interferon-α (±corticosteroids) can control dermatological, hematological, gastrointestinal, skeletal, and mediator-release symptoms, but is hampered by poor tolerability. Similarly, cladribine has broad therapeutic activity, with particular utility when rapid MC debulking is indicated; the main toxicity is myelosuppression. Imatinib has a therapeutic role in the presence of an imatinib-sensitive KIT mutation or in KITD816-unmutated patients. Treatment of SM-AHNMD is governed primarily by the non-MC neoplasm; hydroxyurea has modest utility in this setting.

INVESTIGATIONAL DRUGS

Dasatinib's in vitro anti- KITD816V activity has not translated into significant therapeutic activity in most SM patients. In contrast, recently updated data confirms Midostaurin's significant anti-MC activity in patients with advanced SM.

Gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumor of the gastrointestinal tract. Soon after GIST was recognized as a tumor driven by a KIT or platelet-derived growth factor receptor mutation, it became the first solid tumor target for tyrosine kinase inhibitor therapies. More recently, alternative molecular mechanisms for GIST pathogenesis have been discovered. These are related to deficiencies in the succinate dehydrogenase complex, NF1-gene alterations in connection with neurofibromatosis type 1 tumor syndrome, and mutational activation of the BRAF oncogene in very rare cases.

Extracellular domain c-kit mutation with duplication of Ser501Ala502 found in gastrointestinal stromal tumors is more imatinib- and nilotinib-sensitive than that with duplication of Ala502Tyr503

The great majority of gastrointestinal stromal tumors (GISTs) have gain-of-function mutations of the c-kit gene, which encodes KIT receptor tyrosine kinase. Most of the mutations are located at exon 11, but some are at exon 9 or at other exons. Mutation types at exon 11 vary, while most mutations at exon 9 are a particular duplication of Ala502Tyr503 (KIT-Dup-Ala502Tyr503). Recently a duplication of Ser501Ala502 (KIT-Dup-Ser501Ala502) at exon 9 has been reported in two cases of pediatric mastocytosis and one case of adult mast cell leukemia. Although KIT-Dup-Ser501Ala502 had not been reported in GISTs, we found two GIST cases possessing the mutation in 45 GIST cases with exon 9 c-kit gene mutations, among a total of approximately 500 GIST cases examined. In this report, we briefly summarize clinicopathological findings of the two cases, and characterize the biology of the mutation. When autophosphorylation of KIT-Dup-Ser501Ala502 was examined by transient transfection of c-kit cDNA with Dup-Ser501Ala502 into CHO-K1 cells, KIT-Dup-Ser501Ala502 was ligand-independently activating. The inhibitory effect of selective tyrosine kinase inhibitors, imatinib and nilotinib, on KIT-Dup-Ser501Ala502 was examined and compared with that of KIT-Dup-Ala502Tyr503. Imatinib efficiently inhibited constitutive activation of KIT-Dup-Ser501Ala502 at a concentration of 0.1 μM, whereas it inhibited that of KIT-Dup-Ala502Tyr503 at a concentration of 10 μM. Constitutive activation of KIT-Dup-Ser502Ala503 was not inhibited by nilotinib even at a concentration of 10 μM but that of KIT-Dup-Ala501Tyr502 was almost completely inhibited at a concentration of 1 μM. The results suggest that imatinib and nilotinib could be more effective on GISTs with KIT-Dup-Ser501Ala502 than those with KIT-Dup-Ala502Tyr503. In fact, a patient with KIT-Dup-Ser501Ala502 showed long-term stable disease with administration of the usual dose of 400 mg imatinib. Although mutation sites of KIT-Dup-Ser501Ala502 and KIT-Dup-Ala502Tyr503 are closely located, imatinib- and nilotinib-sensitive KIT-Dup-Ser501Ala502 are distinguishable from KIT-Dup-Ala502Tyr503.

Advances in the systemic treatment of metastatic melanoma

Prior to 2011, the only commercially available agents commonly used to treat metastatic melanoma-including dacarbazine, temozolomide (Temodar), fotemustine, carboplatin, paclitaxel, and interleukin-2-demonstrated limited efficacy, and no study involving these agents had shown an improvement in overall survival. The standard of care for the treatment of metastatic melanoma was radically changed by the subsequent approval of two agents, ipilimumab (Yervoy) and vemurafenib (Zelboraf), both of which improved survival in randomized phase III trials. Within the relatively short time that ipilimumab and vemurafenib have been commercially available, phase II data for the investigational agents nivolumab and MK-3475, for the combination of dabrafenib and trametinib, and for adoptive cell therapy strongly suggest even further improvements in treatment outcomes. Within this rich context of effective agents, the challenge for clinicians and investigators will be to develop predictive biomarkers of response, the optimal sequence of therapy for individual patients, and effective combinations. An additional challenge will be to find the appropriate venue and populations to test promising new agents arising from substantial advances in our understanding of molecular alterations in melanoma cells, of mechanisms of resistance to current agents, and of tumor-host immune interactions.

Contribution of DOG1 expression to the diagnosis of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract, and the majority contain KIT or PDGFRA-activating mutations. However, up to 10% of GISTs are c-kit-negative. Antibodies with increased sensitivity and specificity for the detection of c-kit-negative GIST cases may be of value, especially because some of these cases may also benefit from tyrosine kinase inhibitor therapy. Hematoxylin and Eosin sections of 33 GISTs were re-examined in order to define histopathological criteria used in risk assessment of these tumors. Immunohistochemistry with a panel of antibodies [c-kit, DOG1 (discovered on GIST 1), CD34, smooth muscle actin (SMA), Desmin, S100 and Ki67] was performed on 5μm-thick paraffin sections of all tumors. Statistical analysis of immunohistochemical studies showed that DOG1 and CD117 were the most sensitive and specific antibodies in the diagnosis of GISTs. Other antibodies were unhelpful in confirming a diagnosis of GIST, but were particularly useful in the differential diagnosis. Reactivity for DOG1 may aid in the diagnosis of GISTs, which fail to express c-kit antigen, and lead to appropriate treatment with imatinib mesylate, an inhibitor of the KIT tyrosine kinase.

Imatinib and Dasatinib Inhibit Hemangiosarcoma and Implicate PDGFR-β and Src in Tumor Growth

Hemangiosarcoma, a natural model of human angiosarcoma, is an aggressive vascular tumor diagnosed commonly in dogs. The documented expression of several receptor tyrosine kinases (RTKs) by these tumors makes them attractive targets for therapeutic intervention using tyrosine kinase inhibitors (TKIs). However, we possess limited knowledge of the effects of TKIs on hemangiosarcoma as well as other soft tissue sarcomas. We report here on the use of the TKIs imatinib and dasatinib in canine hemangiosarcoma and their effects on platelet-derived growth factor receptor β (PDGFR-β) and Src inhibition. Both TKIs reduced cell viability, but dasatinib was markedly more potent in this regard, mediating cytotoxic effects orders of magnitude greater than imatinib. Dasatinib also inhibited the phosphorylation of the shared PDGFR-β target at a concentration approximately 1000 times less than that needed by imatinib and effectively blocked Src phosphorylation. Both inhibitors augmented the response to doxorubicin, suggesting that clinical responses likely will be improved using both drugs in combination; however, dasatinib was significantly (P < .05) more effective in this context. Despite the higher concentrations needed in cell-based assays, imatinib significantly inhibited tumor growth (P < .05) in a tumor xenograft model, highlighting that disruption of PDGFR-β/PDGF signaling may be important in targeting the angiogenic nature of these tumors. Treatment of a dog with spontaneously occurring hemangiosarcoma established that clinically achievable doses of dasatinib may be realized in dogs and provides a means to investigate the effect of TKIs on soft tissue sarcomas in a large animal model.

Gastrointestinal Stromal Tumours: Review of 150 Cases from a Single Centre

Gastrointestinal stromal tumours (GIST) are the most common mesenchymal tumours of the gastrointestinal tract. They constitute a significant percentage ranging from 1-2 % of all the gastrointestinal neoplasms [11]. Knowledge on the molecular biology and behavior of these tumours is still not very clear. The clinicopathologial features are variable and surgical resection with chemotherapy is the main modality of treatment. We have retrospectively analyzed the clinicopathological features, treatment and prognosis of 150 patients managed in the Department of Surgery. Retrospective review of the records of 150 patients diagnosed with gastrointestinal stromal tumours and managed during the period January 2006 to December 2011. Clinicopathological features, immunohistochemistry, mitotic index, surgical resection adjuvant chemotherapy and survival analyzed. One hundred and fifty patients diagnosed with GIST and treated were reviewed. Ninety five of them were males (63.3 %). The tumour was most commonly seen during the fourth and fifth decades of life. Abdominal pain (52 %), intestinal bleeding (40 %) and abdominal mass (25 %) were the common clinical symptoms. Sixty percent of the tumours (90/150) were located in the stomach followed by small bowel (20 %) and duodenum (14.6 %). One hundred and thirty-five patients underwent excision of the tumour and five patients had multi organ resection of the adjacent organs like spleen, tail of the pancreas and kidney. Fifteen patients (10 %) received neoadjuvant Imatinib for down staging of the tumour prior to surgery. The tumour size ranged from 1 to 34 cm. One third of the tumours (42/150) belonged to the high-grade category. KIT protein (CD117) was positive in 90 %( 135/150), while CD34 was positive in 50 % (74/150) of tumours. Majority of the patients with high and intermediate-risk category received adjuvant Imatinib (65/77). Seventeen patients (11.3 %) developed recurrence of the tumour on follow-up and rest of the patients had stable disease. Eight of the 15 patients (53 %) who had advanced disease developed recurrence of the disease over 6 months to 1 year. Fifteen patients died on follow-up between 2 and 5 years. Gastrointestinal tumours are the most common non epithelial tumour of the GIT. GISTS are found to show a male preponderance and are common during the fourth and fifth decades. Abdominal pain and intestinal bleeding are the most common clinical presentation. Most of the tumours were located in the stomach. Surgical resection is the best modality of treatment for operable lesions. Tyrosine kinase receptor (KIT) inhibitor like imatinib is used for adjuvant treatment. Regular follow-up with ultra sonogram or computed tomogram helps in diagnosing disease recurrence.

Classification of canine nonangiogenic, nonlymphogenic, gastrointestinal sarcomas based on microscopic, immunohistochemical, and molecular characteristics

Canine nonangiogenic, nonlymphogenic, gastrointestinal sarcomas have been previously diagnosed as gastrointestinal stromal tumors (GIST), leiomyosarcomas, or nonspecified spindle cell sarcomas, but diagnostic criteria for each entity are poorly defined. We propose a classification for canine nonangiogenic, nonlymphogenic, gastrointestinal sarcomas based on microscopic, immunohistochemical, and molecular characteristics. Applying the classification to 40 canine nonangiogenic, nonlymphogenic, gastrointestinal sarcomas documented its diagnostic and prognostic value. Eighteen (45%) sarcomas were classified as GIST based on positive KIT immunoreactivity. All GISTs were positive for vimentin, 14 (78%) were positive for S-100, and 6 (33%) were positive for smooth muscle actin (SMA). In contrast to their human counterparts, canine GISTs occurred mainly in the small intestine (67%) but commonly metastasized (5/18) to liver, lymph nodes, and omentum. Six GISTs had an activated KIT mutation in exon 11 of c-Kit, but no mutations were detected in exons 8, 9, 13, and 17. Twelve (30%) sarcomas were classified as leiomyosarcomas based on positive labeling for SMA and negative labeling for KIT. Four of these neoplasms were well differentiated leiomyosarcomas characterized by weak to no labeling for vimentin, and 8 were poorly differentiated leiomyosarcomas characterized by strong labeling for vimentin. None of the leiomyosarcomas metastasized, but poorly differentiated leiomyosarcomas had a higher risk of local invasion. Ten (25%) sarcomas were classified as non-GIST/nonleiomyosarcomas that were negative for KIT and SMA but positive for vimentin and either S-100 and/or PGP 9.5. These neoplasms most likely represent sarcomas of neurogenic differentiation resembling Schwann cells or perineurial or endoneurial fibroblasts, respectively.

A novel germline SDHB mutation in a gastrointestinal stromal tumor patient without bona fide features of the Carney-Stratakis dyad

Gastrointestinal stromal tumors (GISTs) are the most common mesenchyme neoplasms of the gastrointestinal tract. Gain-of-function somatic mutations of the KIT or PDGFRA genes represent the most prevalent molecular alterations in GISTs. In Carney-Stratakis dyad, patients portray germline mutations of the succinate dehydrogenase subunits B (SDHB), C (SDHC) and D (SDHD) and develop multifocal GISTs and multicentric paragangliomas (PGLs). We herein report a novel germline SDHB mutation (c.T282A--Ile44Asn) occurring in a 26 years-old patient diagnosed with a spindle cell intermediate risk GIST that did not present KIT/PDGFRA/BRAF gene mutations. Further analyses revealed loss of the wild-type SDHB allele and complete loss of SDHB expression in the tumor tissue. After genetic screening of other family members, we detected in the patient's mother a SDHB mutation without any clinical/laboratorial evidence of GIST or PGL. Altogether, our findings (germline SDHB mutation with absence of PGL in the index case and of GIST and/or PGL in his mother) raise the possibility that this familiar setting corresponds to an incomplete phenotype of the Carney-Stratakis dyad.

Expression of stem cell factor in gastrointestinal stromal tumors: Implications for proliferation and imatinib resistance

KIT autophosphorylation caused by mutation of KIT is considered to be a critical mechanism for the oncogenesis of gastrointestinal stromal tumors (GISTs). However, little is known regarding whether stem cell factor (SCF), the KIT ligand, is able to induce the proliferation of GIST cells by activating the wild-type KIT receptor in GISTs. Imatinib, a tyrosine kinase inhibitor, has been demonstrated to be effective as treatment for the majority of GISTs. However, primary resistance to imatinib in GISTs with wild-type KIT and acquired resistance in GISTs with mutant KIT are becoming increasingly significant problems. The aims of this study were to detect the expression and function of SCF in 68 GIST samples, and to explore the relationship between SCF activity and imatinib resistance using immunohistochemical staining and western blot analysis. Results showed abundant expression of SCF in GISTs and demonstrated that SCF is capable of enhancing GIST cell proliferation. Similar to its ineffectiveness in wild-type GISTs, imatinib also failed to inhibit SCF-induced KIT activation in GISTs with mutant KIT. We also found increased SCF expression in GIST cells treated with imatinib. Overall, our results indicated that SCF-induced KIT activation is a novel essential pathway for the proliferation of GISTs. Imatinib was not able to inhibit the activity of SCF, while it promoted the expression of SCF, which may have contributed to acquired imatinib resistance.

KIT gene exon 11 mutations in canine malignant melanoma

The proto-oncogene KIT encodes a receptor tyrosine kinase which has been shown to be upregulated in canine melanomas. KIT mutations lead to constitutive phosphorylation and activation of KIT in the absence of ligand binding. The presence of KIT mutations and KIT protein expression was examined in a cohort of 49 dogs with canine malignant melanoma. An exon 11 synonymous nucleotide 1743C→T mutation was identified in five cases in which one also harbored a L579P mutation. Tumors that harbored the KIT exon 11 mutation(s) correlated significantly with disease recurrence (P = 0.05). All 36 melanomas available for immunohistochemical analysis showed either weak (16 cases, 44.4%) or strong (20 cases, 55.6%) expression of the KIT protein. The five KIT mutation carriers were all strongly positive for KIT by immunohistochemical staining. These findings suggest that a subset of canine malignant melanomas harbors a KIT exon 11 mutation.

Laparoscopic resection of gastrointestinal stromal tumors: safe, efficient, and comparable oncologic outcomes

BACKGROUND

Surgery of gastrointestinal stromal tumors (GISTs) has been modified, and laparoscopic resection of GIST has gained improvement and roles.

PATIENTS AND METHODS

We retrospectively reviewed clinical data and oncological outcomes of our GIST patients who underwent laparoscopic surgery and traditional open surgery. In total, 227 pathologically diagnosed GIST cases were retrospectively reviewed in Chang Gung Memorial Hospital at Linkou, Taipei, Taiwan, between 2005 and 2010. We excluded those with tumor size >5 cm, biopsy-only, combined other operation, endoscopic mucosal resection, tumor located in the duodenum, colon-rectum, esophagocardiac junction, omentum, pelvic area, or retroperitoneum, or metastasis when operated on and those diagnosed as other disease after immunohistologic examination of GIST. Fifty-eight cases were enrolled, including 16 patients in the laparoscopic surgery group (LSG) and 42 patients in the open surgery group (OSG). The patients' demography, perioperative, pathologic result, and oncology result were recorded and analyzed.

RESULTS

Both groups showed no difference in clinical demography, tumor size, and locations. LSG patients showed fewer days to resume diet, shorter postoperative hospital stays, and less use of patient-controlled analgesia. The postoperative morbidity in LSG and OSG was 6.3% and 19%, respectively. The median follow-up time was 32.73 months in LSG and 39.75 months in OSG. Recurrence or metastasis was observed in 3 patients (1 in LSG and 2 in OSG). The recurrence rate between LSG and OSG showed no significant difference.

CONCLUSIONS

Laparoscopic surgery was technically feasible for GIST of no more than 5 cm located at the stomach and small bowel. In the current study, we demonstrated that LSG patients benefited from fewer days to resume diet (5 versus 5.71 days), shorter postoperative stays (8 versus 9.07 days), and less patient-controlled analgesia use (6.7% versus 90.9%) during the perioperative period with the same short-term oncology result compared with OSG patients.

Drug targets and predictive biomarkers in the management of metastatic melanoma

Melanoma is the leading cause of fatal skin cancer, and in the past few decades, there has been an increase in the incidence of and mortality from metastatic melanoma. Until recently, the therapeutic options for treatment of metastatic melanoma were limited. The approval of ipilimumab (an anti-CTLA-4 antibody) and vemurafenib (mutant B-RAF^V600E kinase inhibitor) by the Federal Drug Administration has led to a new era in melanoma treatment, and additional promising drugs and drug combinations are currently being investigated. As the choices of treatment for melanoma have expanded, the need to identify predictive biomarkers to tailor treatment strategies to individual tumor or immune system characteristics has become necessary. Such strategies have the potential of maximizing antitumor effect while minimizing toxicity and improving clinical benefit. In this article, we review the currently approved targeted therapies in melanoma and discuss the future of personalized therapy for this disease.