Gastrointestinal stromal tumours: origin and molecular oncology

Gene expression identifies heterogeneity of metastatic behavior among gastrointestinal stromal tumors

BACKGROUND

Adjuvant imatinib is useful in patients with gastrointestinal stromal tumors (GIST) at high risk of recurrence. At present, the risk of recurrence is determined based on tumor size, mitotic rate, tumor site, and tumor rupture. Previous studies using various biochemical pathways identified gene expression patterns that distinguish two subsets of aggressive fibromatosis (AF), serous ovarian carcinoma (OVCA), and clear cell renal cell carcinoma (RCC). These gene sets separated soft tissue sarcomas into two groups with different probabilities of developing metastatic disease. The present study used these gene sets to identify GIST subgroups with different probabilities of developing metastatic disease.

METHODS

We utilized these three gene sets, hierarchical clustering, and Kaplan-Meier analysis, to examine 60 primary resected GIST samples using Agilent chip expression profiling.

RESULTS

Hierarchical clustering using both the combined and individual AF-, OVCA-, and RCC- gene sets identified differences in probabilities of developing metastatic disease between the clusters defined by the first branch point of the clustering dendrograms (p = 0.029 for the combined gene set, p = 0.003 for the AF-gene set, p < 0.001 for the OVCA-gene set, and p = 0.003 for the RCC-gene set).

CONCLUSIONS

Hierarchical clustering using these gene sets identified at least two subsets of GIST with distinct clinical behavior and risk of metastatic disease. The use of gene expression analysis along with other known prognostic factors may better predict the long-term outcome following surgery, and thus restrict the use of adjuvant therapy to high-risk GIST, and reduce heterogeneity among groups in clinical trials of new drugs.

Pancreatic desmoid-type fibromatosis with beta-catenin gene mutation-Report of a case and review of the literature

We experienced a rare case of pancreatic desmoid-type fibromatosis (DTF) in a 75-year-old Japanese woman. She was asymptomatic but routine examination including ultrasonography revealed a mass in the abdomen. For precise examination, she was referred to the regional hospital. Computed tomography showed that the mass was protruding anteriorly from the left-sided pancreas. Because of the enlargement of the mass lesion, distal pancreatectomy with splenectomy was performed after about 3 months. Macroscopically, the mass was encapsulated and approximately 8cm in diameter. Histological examination revealed that spindle or blunt stellate cells were proliferating in parallel or storiform fashion with myxoid and fibrous background. The tumor cells did not show prominent atypia and mitoses were rarely seen, suggesting that the tumor was low grade or borderline. Immunohistochemistry showed obvious nuclear staining of beta-catenin. Furthermore, analysis of beta-catenin gene revealed that the tumor had a typical missense mutation of threonine to alanine at colon 41 (T41A) in exon 3. These findings confirmed the pathological diagnosis of DTF of the pancreas. To the best of our knowledge, 18 cases of pancreatic DTF have been reported in the English literature and beta-catenin gene mutation had been examined in only one case among them. Thus, our case is the 19th pancreatic DTF and the second case with confirmed beta-catenin gene mutation.

The platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) are major players in oncogenesis, drug resistance, and attractive oncologic targets in cancer

The platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) play a key role in signaling pathways in oncogenesis. The overexpression of PDGFs and PDGFRs and the oncogenic alterations of these receptors have been implicated in human cancers and correlated significantly with poor outcomes. This review discusses the biology of the PDGF isoforms and receptors briefly, and their role in oncogenesis. Also, the attractiveness of targeting PDGFs and PDGFRs, based on a wide display of oncologic alterations in cancers, diverse therapeutic strategies, their roles in resistance to cancer treatments with prospects of overcoming drug resistance, and the extent to which validated biomarkers have been developed for effective PDGFs and PDGFRs-based cancer management are discussed.

Detecting Secondary C-KIT Mutations in the Peripheral Blood of Patients with Imatinib-Resistant Gastrointestinal Stromal Tumor

OBJECTIVE

Imatinib is a standard treatment for metastatic gastrointestinal stromal tumor (GIST). Imatinib resistance is mostly caused by secondary mutations in C-KIT. The antitumor effect of second-line agents is correlated with the type of secondary mutation: indeed, sunitinib is effective against tumors with C-KIT exon 13 or 14 mutations. We investigated whether secondary C-KIT mutations can be detected in circulating tumor DNA (ctDNA) from peripheral blood.

METHODS

This study included 4 patients who underwent resection of imatinib-resistant GIST. Tumor-specific mutations in each tumor were determined by Sanger sequencing. ctDNA was extracted from peripheral blood obtained before and after the treatment of imatinib-resistant lesions. Each of the secondary target mutations in ctDNA was investigated, using a next-generation sequencer.

RESULTS

Imatinib-resistant lesions had single-nucleotide substitutions in C-KIT exon 13 in 3 patients and exon 18 in 1 patient. Identical secondary C-KIT mutations could be detected in ctDNA with a mutant fraction range of 0.010-9.385%. One patient had growth of an imatinib-resistant tumor containing a C-KIT exon 13 mutation, and the fraction of ctDNA decreased after initiation of sunitinib.

CONCLUSION

Detection of secondary C-KIT mutations in ctDNA could be useful for the selection of targeted agents and prediction of antitumor effects.

Clinicopathologic Features and Clinical Outcomes of Esophageal Gastrointestinal Stromal Tumor: Evaluation of a Pooled Case Series

Clinicopathologic features and clinical outcomes of gastrointestinal stromal tumors (GISTs) in esophagus are limited, because of the relatively rare incidence of esophageal GISTs. Therefore, the aim of the current study was to investigate the clinicopathologic features and clinical outcomes of esophageal GISTs, and to investigate the potential factors that may predict prognosis.Esophageal GIST cases were obtained from our center and from case reports and clinical studies extracted from MEDLINE. Clinicopathologic features and survivals were analyzed and compared with gastric GISTs from our center.The most common location was lower esophagus (86.84%), followed by middle and upper esophagus (11.40% and 1.76%). The majority of esophageal GISTs were classified as high-risk category (70.83%). Mitotic index was correlated with histologic type, mutational status, and tumor size. The 5-year disease-free survival and disease-specific survival were 65.1% and 65.9%, respectively. Tumor size, mitotic index, and National Institutes of Health risk classification were associated with prognosis of esophageal GISTs. Only tumor size, however, was the independent risk factor for the prognosis of esophageal GISTs. In comparison to gastric GISTs, the distribution of tumor size, histologic type, and National Institutes of Health risk classification were significantly different between esophageal GISTs and gastric GISTs. The disease-free survival and disease-specific survival of esophageal GISTs were significantly lower than that of gastric GISTs.The most common location for esophageal GISTs was lower esophagus, and most of the esophageal GISTs are high-risk category. Tumor size was the independent risk factor for the prognosis of esophageal GISTs. Esophageal GISTs differ significantly from gastric GISTs in respect to clinicopathologic features. The prognosis of esophageal GISTs was worse than that of gastric GISTs.

Gastrointestinal stromal tumors in Japanese patients with neurofibromatosis type I

BACKGROUND

Neurofibromatosis type I (NF1) predisposes patients to various neoplasias, including gastrointestinal stromal tumors (GISTs). Little is known about the risk of developing GISTs for NF1 patients or the clinicopathologic features and prognosis of NF1-GIST.

METHODS

We conducted a multi-detector computed tomography screen for adult NF1 patients between 2003 and 2012. Clinicopathologic data of sporadic GISTs from patients who underwent surgery between 2001 and 2010 were retrospectively collected from 32 hospitals in Japan.

RESULTS

CT screening identified 6 GIST patients from the 95 NF1 patients screened, suggesting that the prevalence rate of GISTs was approximately 6.3/100 in NF1 patients. All 6 NF1 patients exhibited hyperplasia of the interstitial cells of Cajal in the adjoining small intestine. NF1-GISTs may account for 1.1-1.3 % of primary sporadic GISTs and present as multiple tumors in the small intestine, with low mitotic activity and no KIT or PDGFRA mutations. The risk of recurrence and mortality is very similar between NF1 and non-NF1 patients after surgical resection of GISTs.

CONCLUSIONS

NF1 patients may be predisposed to developing small intestinal GISTs, which may appear as multiple GISTs without KIT and PDGFRA mutations. The prognosis of patients with NF1-GISTs is similar to patients with conventional GISTs.

Identifying three-dimensional structures of autophosphorylation complexes in crystals of protein kinases

Protein kinase autophosphorylation is a common regulatory mechanism in cell signaling pathways. Crystal structures of several homomeric protein kinase complexes have a serine, threonine, or tyrosine autophosphorylation site of one kinase monomer located in the active site of another monomer, a structural complex that we call an "autophosphorylation complex." We developed and applied a structural bioinformatics method to identify all such autophosphorylation complexes in x-ray crystallographic structures in the Protein Data Bank (PDB). We identified 15 autophosphorylation complexes in the PDB, of which five complexes had not previously been described in the publications describing the crystal structures. These five complexes consist of tyrosine residues in the N-terminal juxtamembrane regions of colony-stimulating factor 1 receptor (CSF1R, Tyr(561)) and ephrin receptor A2 (EPHA2, Tyr(594)), tyrosine residues in the activation loops of the SRC kinase family member LCK (Tyr(394)) and insulin-like growth factor 1 receptor (IGF1R, Tyr(1166)), and a serine in a nuclear localization signal region of CDC-like kinase 2 (CLK2, Ser(142)). Mutations in the complex interface may alter autophosphorylation activity and contribute to disease; therefore, we mutated residues in the autophosphorylation complex interface of LCK and found that two mutations impaired autophosphorylation (T445V and N446A) and mutation of Pro(447) to Ala, Gly, or Leu increased autophosphorylation. The identified autophosphorylation sites are conserved in many kinases, suggesting that, by homology, these complexes may provide insight into autophosphorylation complex interfaces of kinases that are relevant drug targets.

Adjuvant Imatinib for High-Risk GI Stromal Tumor: Analysis of a Randomized Trial

PURPOSE

Three years of adjuvant imatinib therapy are recommended for patients with GI stromal tumor (GIST) with high-risk features, according to survival findings in the Scandinavian Sarcoma Group XVIII/AIO (Arbeitsgemeinschaft Internistische Onkologie) trial. To investigate whether the survival benefits have persisted, we performed the second planned analysis of the trial.

PATIENTS AND METHODS

Eligible patients had macroscopically completely excised, KIT-positive GIST with a high risk of recurrence, as determined by using the modified National Institutes of Health criteria. After surgery, the patients were randomly assigned to receive imatinib for either 1 or 3 years. The primary objective was recurrence-free survival (RFS), and the secondary objectives included survival.

RESULTS

A total of 400 patients were entered onto this open-label study between February 4, 2004, and September 29, 2008. During a median follow-up of 90 months, 171 recurrences and 69 deaths were detected. Patients assigned to the 3-year group had longer RFS than those assigned to the 1- year group; 5-year RFS was 71.1% versus 52.3%, respectively (hazard ratio [HR], 0.60; 95% CI 0.44 to 0.81; P < .001), and survival was 91.9% versus 85.3% (HR, 0.60; 95% CI, 0.37 to 0.97; P = .036). Patients in the 3-year group survived longer in the subset with centrally confirmed GIST and without macroscopic metastases at study entry (93.4% v 86.8%; HR, 0.53; 95% CI, 0.30 to 0.93; P = .024). Similar numbers of cardiac events and second cancers were recorded in the groups.

CONCLUSION

Three years of adjuvant imatinib therapy results in longer survival than 1 year of imatinib. High 5-year survival rates are achievable in patient populations with high-risk GIST.

Clinical activity of regorafenib in PDGFRA-mutated gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST) is the most frequent mesenchymal tumor of the gastrointestinal tract and one of the most frequent sarcoma. Mutually exclusive KIT and PDGFRA mutations are central events in GIST pathogenesis, and their understanding is crucial because specific treatment targeting oncogenic KIT and PDGFRA activation (especially imatinib) has become available. The most frequent PDGFRA mutation (D842V) is associated with primary resistance to imatinib. Data related to regorafenib efficacy in PDGFRA-mutated GIST are lacking. We report here a case report of a prolonged response with regorafenib in a patient with a PDGFRA-mutated GIST.

This report describes the clinical efficacy of regorafenib in a patient with metastatic gastrointestinal stromal tumor bearing a mutation of the PDGFRA exon 18 gene.

PI3 kinase is indispensable for oncogenic transformation by the V560D mutant of c-Kit in a kinase-independent manner

Oncogenic mutants of c-Kit are often found in mastocytosis, gastrointestinal stromal tumors and acute myeloid leukemia. The activation mechanism of the most commonly occurring mutation, D816V in exon 17 of c-Kit, has been well-studied while other mutations remain fairly uncharacterized in this respect. In this study, we show that the constitutive activity of the exon 11 mutant V560D is weaker than the D816V mutant. Phosphorylation of downstream signaling proteins induced by the ligand for c-Kit, stem cell factor, was stronger in c-Kit/V560D expressing cells than in cells expressing c-kit/D816V. Although cells expressing c-Kit/V560D showed increased ligand-independent proliferation and survival compared to wild-type c-Kit-expressing cells, these biological effects were weaker than in c-Kit/D816V-expressing cells. In contrast to cells expressing wild-type c-Kit, cells expressing c-Kit/V560D were independent of Src family kinases for downstream signaling. However, the independence of Src family kinases was not due to a Src-like kinase activity that c-Kit/D816V displayed. Point mutations that selectively block the association of PI3 kinase with c-Kit/V560D inhibited ligand-independent activation of the receptor, while inhibition of the kinase activity of PI3 kinase with pharmacological inhibitors did not affect the kinase activity of the receptor. This suggests a lipid kinase-independent key role of PI3 kinase in c-Kit/V560D-mediated oncogenic signal transduction. Thus, PI3 kinase is an attractive therapeutic target in malignancies induced by c-Kit mutations independent of its lipid kinase activity.

Lgr5-expressing stem cells are not the cells of origin of pyloric neuroendocrine carcinomas in mice

In intestinal and pyloric epithelia, leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5)-expressing cells represent long-lived adult stem cells that give rise to all epithelial cell types, including endocrine cells. Ablation of the Apc gene in Lgr5-expressing cells leads to intestinal and pyloric adenomas. To assess whether all epithelial tumours of the gastrointestinal tract are derived from LGR5-positive stem cells, we crossed Lgr5-EGFP-IRES-creER(T2) mice, which express EGFP and Cre recombinase driven by the Lgr5 promoter, with CEA424-SV40-TAg mice, which develop pyloric neuroendocrine carcinomas of epithelial origin. In 19 day-old mice, single SV40 T antigen (TAg)-positive cells were identified preferentially at the the bases of pyloric glands, close to the stem cell compartment. However, contrary to previous publications describing subpopulations of LGR5-positive cells in gastrointestinal neoplasia, we could not detect Lgr5-EGFP-positive tumour cells in malignant lesions. The lack of expression of the Wnt target gene Lgr5 is probably not caused by suppression of Wnt signalling by TAg, since β-catenin-mediated Wnt signalling, as measured by the TOPflash assay, was not inhibited. To determine the cellular origin of CEA424-SV40-TAg tumours, we performed tracing experiments using Lgr5-EGFP-IRES-creERT2:CEA424-SV40-TAg:ROSA26-tdRFP mice. Following tamoxifen induction, it was possible to efficiently trace the progeny of Lgr5-expressing cells in gastrointestinal tissue via red fluorescent protein (RFP) expression. No RFP-positive tumour cells were detected, even when RFP gene activation occurred in 7 day-old mice well before the appearance of TAg-positive tumour cells. Hence, we conclude that Lgr5-expressing stem cells probably do not constitute the cells of origin in CEA424-SV40-TAg mice. Consequently, not all epithelial tumours in the pyloric region are initiated by transformation of LGR5-positive stem cells. Thus, additional long-lived LGR5-negative stem cells or progenitor cells with a low turnover rate might exist in the pyloric region, which could give rise to tumours.

Targeted therapy in cancer

PURPOSE

To describe the emergence of targeted therapies that have led to significant breakthroughs in cancer therapy and completed or ongoing clinical trials of novel agents for the treatment of patients with advanced cancer.

METHODS

The literature was systematically reviewed, based on clinical experience and the use of technologies that improved our understanding of carcinogenesis.

RESULTS

Genomics and model systems have enabled the validation of novel therapeutic strategies. Tumor molecular profiling has enabled the reclassification of cancer and elucidated some mechanisms of disease progression or resistance to treatment, the heterogeneity between primary and metastatic tumors, and the dynamic changes of tumor molecular profiling over time. Despite the notable technologic advances, there is a gap between the plethora of preclinical data and the lack of effective therapies, which is attributed to suboptimal drug development for "driver" alterations of human cancer, the high cost of clinical trials and available drugs, and limited access of patients to clinical trials. Bioinformatic analyses of complex data to characterize tumor biology, function, and the dynamic tumor changes in time and space may improve cancer diagnosis. The application of discoveries in cancer biology in clinic holds the promise to improve the clinical outcomes in a large scale of patients with cancer. Increased harmonization between discoveries, policies, and practices will expedite the development of anticancer drugs and will accelerate the implementation of precision medicine.

CONCLUSIONS

Combinations of targeted, immunomodulating, antiangiogenic, or chemotherapeutic agents are in clinical development. Innovative adaptive study design is used to expedite effective drug development.

High APRIL expression correlates with unfavourable survival of gastrointestinal stromal tumour

A proliferation inducing ligand (APRIL) is a member of the tumour necrosis factor superfamily. High APRIL expression has been found to correlate with tumour development, suggesting that APRIL participates in oncogenesis. However, little is known about APRIL expression in gastrointestinal stromal tumours (GISTs) or the relationship between APRIL expression and the clinical characteristics of GIST. Therefore, we assessed the expression of APRIL immunohistochemically using a tissue microarray from 178 patients with GIST and evaluated the relationship between APRIL expression and patient prognosis. Strong APRIL expression was observed in 42.7% of GISTs, with APRIL expression significantly associated with tumour diameter, gross classification and tumour grade (p < 0.05 each). Kaplan-Meier analysis suggested that low APRIL expression and tumour size <5 cm were associated with longer overall survival. These findings indicate that APRIL expression is correlated with malignant GIST phenotypes and it may serve as an unfavourable prognostic marker in patients with GIST.

Clinicopathological significance of c-KIT mutation in gastrointestinal stromal tumors: a systematic review and meta-analysis

Many types of KIT mutations have been observed in gastrointestinal stromal tumors (GISTs), but their prognostic and predictive significance are still unclear. A meta-analysis and literature review were conducted to estimate the contribution of KIT mutations in prognostic parameters and clinic-pathological significance of GISTs. A total of 18 relevant articles from PubMed, EMBASE and Web of Science databases were included in this study. The frequency of KIT mutation was significantly increased in the GIST patients with higher mitosis (≥5/50 high-power fields (HPFs) and larger size (≥5 cm) of tumors than in those with lower MI (≤5/50HPFs) and smaller size (≤5 cm) of GISTs respectively. The rate of KIT mutation was not significantly changed between GISTs in stomachs and in small intestines. KIT mutational status has prognostic significance for patients’ outcome. GIST patients with KIT exon 9 mutations have higher risk of progression than those with exon 11 mutations. 5 year relapse-free survival (RFS) rate was significantly higher in patients with KIT exon 11 deletion than in those with other type of KIT exon 11 mutations. The deletion involving KIT exon 11, particularly codons 557–558, is a valuable predictor of prognosis for patients with GISTs.

Rare Tumors in Children: Progress Through Collaboration

Rare pediatric tumors account for approximately 10% of all childhood cancers, which in themselves are a rare entity. The diverse histologies and clinical behaviors of rare pediatric tumors pose challenges to the investigation of their biologic and clinical features. National and international cooperative groups such as the Rare Tumor Committee of the Children's Oncology Group, Rare Tumors in Pediatric Age Project, and European Cooperative Study Group for Pediatric Rare Tumors have developed several initiatives to advance knowledge about rare pediatric cancers. However, these programs have been only partially effective, necessitating the development of alternative mechanisms to study these challenging diseases. In this article, we review the current national and international collaborative strategies to study rare pediatric cancers and alternative methods under exploration to enhance those efforts, such as independent registries and disease-specific, National Cancer Institute-sponsored clinics.

PDGFRβ and oncogenic mutant PDGFRα D842V promote disassembly of primary cilia through a PLCγ- and AURKA-dependent mechanism

Primary cilia are microtubule-based sensory organelles projecting from most quiescent mammalian cells, which disassemble in cells cultured in serum-deprived conditions upon re-addition of serum or growth factors. Platelet-derived growth factors (PDGF) are implicated in deciliation, but the specific receptor isoforms and mechanisms involved are unclear. We report that PDGFRβ promotes deciliation in cultured cells and provide evidence implicating PLCγ and intracellular Ca(2+) release in this process. Activation of wild-type PDGFRα alone did not elicit deciliation. However, expression of constitutively active PDGFRα D842V mutant receptor, which potently activates PLCγ (also known as PLCG1), caused significant deciliation, and this phenotype was rescued by inhibiting PDGFRα D842V kinase activity or AURKA. We propose that PDGFRβ and PDGFRα D842V promote deciliation through PLCγ-mediated Ca(2+) release from intracellular stores, causing activation of calmodulin and AURKA-triggered deciliation.

Duodenal gastrointestinal stromal tumors: clinicopathological characteristics, surgery, and long-term outcome

Background

Duodenal gastrointestinal stromal tumors (DGIST) are rare, and data on their management is limited. We here report the clinicopathological characteristics, different surgical treatments, and long-term prognosis of DGIST.

Methods

Data of 74 consecutive patients with DGIST in a single institution from June 2000 to June 2014 were retrospectively analyzed. The overall survival (OS) and recurrence/metastasis-free survival rates of 74 cases were calculated using Kaplan–Meier method.

Results

Out of 74 cases, 42 cases were female (56.76 %) and 32 cases (43.24 %) were male. Approximately 22.97, 47.30, 16.22, and 13.51 % of the tumors originated in the first to fourth portion of the duodenum, respectively, with a tumor size of 5.08 ± 2.90 cm. Patients presented with gastrointestinal bleeding (n = 37, 50.00 %), abdominal pain (n = 25, 33.78 %), mass (n = 5, 6.76 %), and others (n = 7, 9.76 %). A total of 18 patients (24.3 %) underwent wedge resection (WR); 39 patients (52.7 %) underwent segmental resection (SR); and 17 cases (23 %) underwent pancreaticoduodenectomy (PD). The median follow-up was 56 months (1–159 months); 19 patients (25.68 %) experienced tumor recurrence or metastasis, and 14 cases (18.92 %) died. The 1-, 3-, and 5-year recurrence/metastasis-free survival rates were 93.9, 73.7, and 69 %, respectively. The 1-, 3- and 5-year OS were 100, 92.5, and 86 %, respectively. The recurrence/metastasis-free survival rate in the PD group within 5 years was lower than that in the WR group (P = 0.047), but was not different from that in the SR group (P = 0.060). No statistically significant difference was found among the three operation types (P = 0.294).

Conclusions

DGIST patients have favorable prognosis after complete tumor removal, and surgical procedures should be determined by the DGIST tumor location and size.

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.

15 YEARS OF PARAGANGLIOMA: Clinical manifestations of paraganglioma syndromes types 1-5

The paraganglioma (PGL) syndromes types 1-5 are autosomal dominant disorders characterized by familial predisposition to PGLs, phaeochromocytomas (PCs), renal cell cancers, gastrointestinal stromal tumours and, rarely, pituitary adenomas. Each syndrome is associated with mutation in a gene encoding a particular subunit (or assembly factor) of succinate dehydrogenase (SDHx). The clinical manifestations of these syndromes are protean: patients may present with features of catecholamine excess (including the classic triad of headache, sweating and palpitations), or with symptoms from local tumour mass, or increasingly as an incidental finding on imaging performed for some other purpose. As genetic testing for these syndromes becomes more widespread, presymptomatic diagnosis is also possible, although penetrance of disease in these syndromes is highly variable and tumour development does not clearly follow a predetermined pattern. PGL1 syndrome (SDHD) and PGL2 syndrome (SDHAF2) are notable for high frequency of multifocal tumour development and for parent-of-origin inheritance: disease is almost only ever manifest in subjects inheriting the defective allele from their father. PGL4 syndrome (SDHB) is notable for an increased risk of malignant PGL or PC. PGL3 syndrome (SDHC) and PGL5 syndrome (SDHA) are less common and appear to be associated with lower penetrance of tumour development. Although these syndromes are all associated with SDH deficiency, few genotype-phenotype relationships have yet been established, and indeed it is remarkable that such divergent phenotypes can arise from disruption of a common molecular pathway. This article reviews the clinical presentations of these syndromes, including their component tumours and underlying genetic basis.

The oncogenic FIP1L1-PDGFRα fusion protein displays skewed signaling properties compared to its wild-type PDGFRα counterpart

Aberrant activation of oncogenic kinases is frequently observed in human cancers, but the underlying mechanism and resulting effects on global signaling are incompletely understood. Here, we demonstrate that the oncogenic FIP1L1-PDGFRα kinase exhibits a significantly different signaling pattern compared to its PDGFRα wild type counterpart. Interestingly, the activation of primarily membrane-based signal transduction processes (such as PI3-kinase- and MAP-kinase- pathways) is remarkably shifted toward a prominent activation of STAT factors. This diverging signaling pattern compared to classical PDGF-receptor signaling is partially coupled to the aberrant cytoplasmic localization of the oncogene, since membrane targeting of FIP1L1-PDGFRα restores activation of MAPK- and PI3K-pathways. In stark contrast to the classical cytokine-induced STAT activation process, STAT activation by FIP1L1-PDGFRα does neither require Janus kinase activity nor Src kinase activity. Furthermore, we investigated the mechanism of STAT5 activation via FIP1L1-PDGFRα in more detail and found that STAT5 activation does not involve an SH2-domain-mediated binding mechanism. We thus demonstrate that STAT5 activation occurs via a non-canonical activation mechanism in which STAT5 may be subject to a direct phosphorylation by FIP1L1-PDGFRα.

Personalized Medicine in Gastrointestinal Stromal Tumor (GIST): Clinical Implications of the Somatic and Germline DNA Analysis

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. They are characterized by gain of function mutations in KIT or PDGFRA tyrosine kinase receptors, with their consequent constitutive activation. The gold standard therapy is imatinib that offers a good and stable response for approximately 18–36 months. However, resistance is very common and it is vital to identify new biomarkers. Up until now, there have been two main approaches with focus to characterize novel targets. On the one hand, the focus is on the tumor genome, as the final clinical outcome depends mainly from the cancer specific mutations/alterations patterns. However, the germline DNA is important as well, and it is inconceivable to think the patients response to the drug is not related to it. Therefore the aim of this review is to outline the state of the art of the personalized medicine in GIST taking into account both the tumor DNA (somatic) and the patient DNA (germline).

PDGFRA-mutant syndrome

Germline PDGFRA mutations cause multiple heterogeneous gastrointestinal mesenchymal tumors. In its familial form this disease, which was formerly termed intestinal neurofibromatosis/neurofibromatosis 3b (INF/NF3b), has been included among familial gastrointestinal stromal tumors (GISTs) because of its genotype, described when GIST was the only known PDGFRA-mutant gastrointestinal tumor. Shortly afterwards, however, inflammatory fibroid polyps also revealed PDGFRA mutations. Subsequently, gastrointestinal CD34+ 'fibrous tumors' of uncertain classification were described in a germline PDGFRA-mutant context. Our aim was to characterize the syndrome produced by germline PDGFRA mutations and establish diagnostic criteria and management strategies for this hitherto puzzling disease. We studied a kindred displaying multiple gastrointestinal mesenchymal tumors, comparing it with published families/individuals with possible analogous conditions. We identified a novel inherited PDGFRA mutation (P653L), constituting the third reported example of familial PDGFRA mutation. In adult mutants we detected inflammatory fibroid polyps, gastric GISTs and gastrointestinal fibrous tumors of uncertain nosology. We demonstrate that the syndrome formerly defined as INF/NF3b (exemplified by the family reported herein) is simplistically considered a form of familial GIST, because inflammatory fibroid polyps often prevail. Fibrous tumors appear variants of inflammatory fibroid polyps. 'INF/NF3b' and 'familial GIST' are misleading terms which we propose changing to 'PDGFRA-mutant syndrome'. In this condition, unlike KIT-dependent familial GIST syndromes, if present, GISTs are stomach-restricted and diffuse Cajal cell hyperplasia is not observed. This restriction of GISTs to the stomach in PDGFRA-mutant syndrome: (i) focuses oncological concern on gastric masses, as inflammatory fibroid polyps are benign; (ii) supports a selective role of gastric environment for PDGFRA mutations to elicit GISTs, justifying the known predilection for stomach of sporadic PDGFRA-mutant GISTs. An awareness that inflammatory fibroid polyps, relatively common among gastrointestinal mesenchymal tumors, may be the prevailing tumor in PDGFRA-mutant syndrome could eventually reveal an unsuspected prevalence of this condition.

Treatment and Prognoses in Patients With Primary Gastrointestinal Stromal Tumors ≥10 cm: A Single-Institution Experience in China

Data on treatments and specific outcomes of primary gastrointestinal stromal tumors (GISTs) ≥10  cm are limited. We here report the treatments and survival outcomes concerning a subgroup of primary giant GISTs. Data of 83 consecutive patients with primary GISTs ≥10  cm in a single institution were retrospectively collected. Fifty-eight patients underwent surgery before imatinib mesylate (IM) treatment (Group A), 10 underwent surgical resection following IM therapy (Group B), whereas 15 patients took IM as drug therapy alone (Group C). The baseline clinical characteristics were similar among the 3 groups. However, a lower proportion in Group A had metastatic disease at the time of diagnosis or surgery compared with Groups B and C (8.6% vs 40.0% vs 40.0%, P < 0.05). The median follow-up duration was 21.5 months. No statistically significant differences were observed on progression-free survival (PFS) among the groups. However, patients in Group B showed significantly better overall survival (OS) compared with those in Group C (P = 0.044). Multivariate analysis showed that patients treated with adjuvant IM were associated with better PFS (hazard ratio [HR] 3.01; 95% confidence interval [CI] 1.13-7.97; P = 0.027) and OS (HR 29.11; 95% CI 3.32-125.36; P = 0.004). The subgroup with mitotic count >10/50 high-power fields (HPF) showed worse PFS (HR 3.50; 95% CI 1.19-10.25; P = 0.022) and OS (HR 20.04; 95% CI 1.67-143.79; P = 0.018) than that of mitotic count ≤5/50 HPF. Clinical treatment patterns for primary giant GISTs are different, and the outcomes of different interventions vary. The optimal treatments for these subgroup of patients still require further long-term investigation. Moreover, mitotic count and adjuvant IM are closely associated with PFS and OS in giant GISTs.

KIT Mutation and Loss of 14q May Be Sufficient for the Development of Clinically Symptomatic Very Low-Risk GIST

The aim of this study was to determine the minimal set of genetic alterations required for the development of a very low risk clinically symptomatic gastro-intestinal stromal tumour within the stomach wall. We studied the genome of a very low-risk gastric gastro-intestinal stromal tumour by whole-genome sequencing, comparative genomic hybridisation and methylation profiling. The studied tumour harboured two typical genomic lesions: loss of the long arm of chromosome 14 and an activating mutation in exon 11 of KIT. Besides these genetic lesions, only two point mutations that may affect tumour progression were identified: A frame-shift deletion in RNF146 and a missense mutation in a zinc finger of ZNF407. Whilst the frameshift deletion in RNF146 seemed to be restricted to this particular tumour, a similar yet germline mutation in ZNF407 was found in a panel of 52 gastro-intestinal stromal tumours from different anatomical sites and different categories. Germline polymorphisms in the mitotic checkpoint proteins Aurora kinase A and BUB1 kinase B may have furthered tumour growth. The epigenetic profile of the tumour matches that of other KIT-mutant tumours. We have identified mutations in three genes and loss of the long arm of chromosome 14 as the so far minimal set of genetic abnormalities sufficient for the development of a very low risk clinically symptomatic gastric stromal tumour.

Prognostic angiogenic markers (endoglin, VEGF, CD31) and tumor cell proliferation (Ki67) for gastrointestinal stromal tumors

AIM: To evaluate the correlation between the immunoexpression of angiogenic markers [CD31, CD105 and vascular endothelial growth factor (VEGF)], proliferative index (Ki67), and prognosis of patients with gastrointestinal stromal tumors (GIST).

METHODS: This is a retrospective study of 54 GIST cases. Medical records were searched to obtain the GIST patients’ demographic and clinical data, and paraffin-embedded blocks of tumor samples were retrieved from the hospital archives to conduct a new immunohistochemical evaluation. The tumor samples of GIST patients were subject to immunohistochemical evaluation for endoglin (CD105), CD31, VEGF, and Ki67 expression. The CD105 and CD31 intratumoral microvascular density (IMVD) was measured using automated analysis. We determined the correlation between the immunoexpression of CD105, CD31, VEGF, Ki67 and prognosis. In addition, we conducted a cutoff analysis using the receiver-operating characteristic curve. VEGF positivity was classified as either null/weak or strong. Ki67 was evaluated using a cutoff of 5% positive cells. The prognosis was classified as good (patient alive without recurrence) or poor (patient with recurrence/death).

RESULTS: The distribution of tumor sites among the 54 analyzed samples was as follows: 27 (50%) in the stomach, 20 (37.1%) in the small intestine, 6 (11.1%) in the colon, and 1 (1.8%) in the esophagus. The size of the tumors ranged from 2 to 33 cm (median: 8 cm); in 12 cases (22.2%), the tumor was below 5 cm at the largest diameter, but in 42 cases (77.7%), the tumor was larger than 5 cm. The means of CD105 and CD31 were significantly higher in the group with poor prognosis (P < 0.001). The cut-off values of CD105 (> 1.2%) and CD31 (> 2.5%) in the receiver-operating characteristic curve were related to a poorer prognosis. Cases with a better prognosis showed significantly null/weak staining for VEGF (P < 0.001). Ki-67 expression of ≥ 5% was strongly correlated with a worse prognosis (P < 0.001). In the multivariate analysis, CD105 was the variable that most strongly correlated with prognosis.

CONCLUSION: The IMVD cutoff values for the angiogenic markers CD105 and CD31, may be prognostic factors for GIST, in addition to VEGF and Ki67.

Imatinib mesylate treatment in a dog with gastrointestinal stromal tumors with a c-kit mutation

A 13-year-old spayed mixed-breed dog was diagnosed with a gastrointestinal stromal tumor (GIST) after histopathological examination of an abdominal mass. Five months after surgical resection of the tumor, we detected the recurrence of GIST with multiple disseminated abdominal lesions. A sequence analysis of cDNA obtained from a biopsy of the recurrent tumors revealed a mutation within exon 9 of the c-kit gene (1523A>T, Asn⁵⁰⁸Ile), which has been shown to cause ligand-independent phosphorylation of the KIT protein in GISTs and canine mast cell tumors (MCTs). Upon detection of the recurrent tumors, we initiated treatment with imatinib mesylate (10 mg/kg, q 24 hr). After 2 months, the dog achieved complete remission. Our findings indicate that canine GIST, and possibly MCT, may be responsive to molecular-targeted therapy.

Chronic myeloid leukemia: advances in understanding disease biology and mechanisms of resistance to tyrosine kinase inhibitors

The successful implementation of tyrosine kinase inhibitors (TKIs) for the treatment of chronic myeloid leukemia (CML) remains a flagship for molecularly targeted therapy in cancer. This focused review highlights critical elements of the underlying biology of CML and provides a summary of the molecular mechanisms that lead to TKI resistance: BCR-ABL1 mutation-based resistance and therapy escape through alternative pathway activation despite inhibition of BCR-ABL1 tyrosine kinase activity. We direct attention to the most current manifestations of these issues, including emergence of pan-TKI-resistant BCR-ABL1 compound mutants, new strategies for identification and therapeutic targeting of alternative pathways, and the exciting, controversial topic of cessation of TKI therapy leading to durable treatment-free remissions for a subset of patients. Further gains in our understanding of the biology of Philadelphia chromosome-positive (Ph-positive) leukemia and mechanisms of resistance to BCR-ABL1 TKIs will benefit patients and also provide a blueprint for similar discovery in other cancers.

Adherence to Guidelines for Adjuvant Imatinib Therapy for GIST: A Multi-institutional Analysis

BACKGROUND

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. Adjuvant imatinib therapy improves recurrence-free and overall survival following surgery for patients with high-risk GIST; however, the factors associated with use of adjuvant imatinib therapy are unclear, and adherence to adjuvant imatinib has not been investigated. We sought to determine the clinicopathologic predictors of therapy with adjuvant imatinib following surgical resection for GIST and to determine the utilization of adjuvant imatinib in patients who underwent surgical resection of primary GIST in 2009 or later as recommended by National Comprehensive Cancer network (NCCN) guidelines.

METHODS

A multi-institutional cohort including 171 patients who underwent surgery for primary GIST at seven high-volume cancer centers in the USA and Canada between January 2009-December 2012 was used in this study. Receipt of adjuvant imatinib therapy was ascertained, and factors associated with imatinib therapy were analyzed.

RESULTS

Following surgery for primary GIST, tumor size (<5.0 cm: ref; 5.0-9.9 cm: odds ratio (OR) 2.36, 95 % confidence interval (CI) 0.74-7.55; >10.0 cm: OR 9.15, 95 % CI 2.28-36.75; p = 0.007), mitotic rate (≤5/50 mitoses per 50 high powered field [HPF]: ref; 6-10/50 HPF: OR 24.91, 95 % CI 3.64-170.35; >10/50 HPF: OR 5.80, 95 % CI 3.64-170.35; p < 0.001), and neoadjuvant therapy (OR 9.52; 95 % CI 2.51-36.14; p = 0.001) were associated with receipt of adjuvant imatinib therapy. Overall, 75 % of patients received appropriate treatment, 23 % of patients were undertreated, and 2 % of patients were overtreated as compared to NCCN guidelines. Adjuvant imatinib therapy was administered in only 53 % of patients for which the NCCN guidelines recommended adjuvant therapy.

CONCLUSION

The clinicopathologic factors associated with use of adjuvant imatinib therapy in patients following resection of primary GIST are consistent with established risk factors for recurrence. Adjuvant imatinib therapy remains underutilized in patients with intermediate and high-risk GIST and in patients who receive neoadjuvant therapy. Barriers to adjuvant imatinib therapy in this group of patients needs to be further explored.

Follow-up strategies for patients with gastrointestinal stromal tumour treated with or without adjuvant imatinib after surgery

BACKGROUND

Patients with gastrointestinal stromal tumour (GIST) are often followed up after surgery with longitudinally repeated imaging examinations to detect recurrence early. Studies on follow-up of GIST patients are few, the optimal follow-up methods are unknown and the recommendations for follow-up vary in guidelines.

METHODS

We reviewed the current evidence for follow-up of patients treated with surgery alone and of patients who were treated with adjuvant or neoadjuvant imatinib.

RESULTS

Imaging of the abdomen and the pelvis with computerised tomography (CT) or magnetic resonance imaging (MRI) usually suffices, since metastases are uncommon at other sites. The frequency of imaging may be adjusted with the risk of recurrence with time. Very low risk GISTs are very frequently cured with surgery and usually require no regular follow-up after complete surgery, and annual CT of the abdomen and the pelvis for 5 years suffices for most patients with a low to intermediate risk for recurrence. Most high-risk patients are treated with imatinib for at least 3 years after surgery. CT or MRI may be carried out 6-monthly during adjuvant imatinib, 3 to 4-monthly during the 2 years that follow discontinuation of imatinib when the risk of recurrence is high, and then at 6-12 month intervals to complete 10 years of follow-up. Recurrence after the first 10 years of follow-up is infrequent.

CONCLUSIONS

The follow-up schedules are best tailored with the risk of recurrence. The risk of recurrence should be estimated with the prognostic tools that consider the most relevant prognostic factors.

GIST treatment options after tyrosine kinase inhibitors

OPINION STATEMENT

The management of advanced gastrointestinal stromal tumor (GIST) has been dramatically altered by the development of tyrosine kinase inhibitors. The disease, which had a median overall survival of 12 months for patients with unresectable disease, now has a median survival approaching 5 or more years. The challenge faced clinically is how to care for patients when they have progressed on all approved therapies. Clinical trials evaluating the role of novel combination therapies with investigational agents that target AKT/PI3K pathways are of interest especially given the preclinical rationale available. The addition of an mTOR inhibitor can be tried as these are available, but requires care and monitoring for additional toxicities. With improved understanding of this disease, which we thought of as one biology, personalized therapies are being studied and tested and is particularly relevant for GIST that are less responsive to the standard kinase inhibitors, such as platelet-derived growth factor alpha (PDGFRA) D842V and wild-type/succinate dehydrogenase (SDH)-deficient GIST. IGF1R inhibitors as a class are not being developed because of the lack of significant efficacy in many clinical trials and the efficacy in WT GIST has been limited; to date drugs targeting VEGFR, such as sunitinib and regorafenib, appear to be the best agents available for this group of patients. The exciting findings seen with CTLA4 and PD-1/PD-L1 antibodies in melanoma and other solid tumors is exciting, especially because there is a growing body of evidence that such approaches have biologic rationale; clinical trials evaluating these agents are awaited with interest. Last, recent work has shed light on older agents that may have a role in GIST. Moving forward to test these agents alone or in combination with TKIs offers potentially new strategies for treating advanced disease.

Targeting Disease Persistence in Gastrointestinal Stromal Tumors

SummaryGastrointestinal stromal tumors (GISTs) represent 20%-40% of human sarcomas. Although approximately half of GISTs are cured by surgery, prognosis of advanced disease used to be poor due to the high resistance of these tumors to conventional chemo- and radiotherapy. The introduction of molecularly targeted therapy (e.g., with imatinib mesylate) following the discovery of the role of oncogenic mutations in the receptor tyrosine kinases KIT and platelet-derived growth factor α (PDGFRA) significantly increased patient survival. However, GIST cells persist in 95%-97% of imatinib-treated patients who eventually progress and die of the disease because of the emergence of clones with drug-resistant mutations. Because these secondary mutations are highly heterogeneous, even second- and third-line drugs that are effective against certain genotypes have only moderately increased progression-free survival. Consequently, alternative strategies such as targeting molecular mechanisms underlying disease persistence should be considered. We reviewed recently discovered cell-autonomous and microenvironmental mechanisms that could promote the survival of GIST cells in the presence of tyrosine kinase inhibitor therapy. We particularly focused on the potential role of adult precursors for interstitial cells of Cajal (ICCs), the normal counterpart of GISTs. ICC precursors share phenotypic characteristics with cells that emerge in a subset of patients treated with imatinib and in young patients with GIST characterized by loss of succinate dehydrogenase complex proteins and lack of KIT or PDGFRA mutations. Eradication of residual GIST cells and cure of GIST will likely require individualized combinations of several approaches tailored to tumor genotype and phenotype.

SIGNIFICANCE

Gastrointestinal stromal tumors (GISTs) are one of the most common connective tissue cancers. Most GISTs that cannot be cured by surgery respond to molecularly targeted therapy (e.g., with imatinib); however, tumor cells persist in almost all patients and eventually acquire drug-resistant mutations. Several mechanisms contribute to the survival of GIST cells in the presence of imatinib, including the activation of "escape" mechanisms and the selection of stem-like cells that are not dependent on the expression of the drug targets for survival. Eradication of residual GIST cells and cure of GIST will likely require individualized combinations of several approaches tailored to the genetic makeup and other characteristics of the tumors.

Therapeutic Efficacy Assessment of CK6, a Monoclonal KIT Antibody, in a Panel of Gastrointestinal Stromal Tumor Xenograft Models

We evaluated the efficacy of CK6, a KIT monoclonal antibody, in a panel of human gastrointestinal stromal tumor (GIST) xenograft models. Nude mice were bilaterally transplanted with human GIST xenografts (four patient derived and two cell line derived), treated for 3 weeks, and grouped as follows: control (untreated); CK6 (40 mg/kg, 3 × weekly); imatinib (50 mg/kg, twice daily); sunitinib (40 mg/kg, once daily); imatinib + CK6; sunitinib + CK6 (same doses and schedules as in the single-agent treatments). Tumor volume assessment, Western blot analysis, and histopathology were used for evaluation of efficacy. Statistical analysis was performed using Mann-Whitney U (MWU) and Wilcoxon matched-pairs tests. CK6 as a single agent only reduced tumor growth rate in the UZLX-GIST3 model (P = .053, MWU compared to control), while in none of the other GIST models an effect on tumor growth rate was observed. CK6 did not result in significant anti-proliferative or pro-apoptotic effects in any of the GIST models, and moreover, CK6 did not induce a remarkable inhibition of KIT activation. Furthermore, no synergistic effect of combining CK6 with tyrosine kinase inhibitors (TKIs) was observed. Conversely, in certain GIST xenografts, anti-tumor effects seemed to be inferior under combination treatment compared to single-agent TKI treatment. In the GIST xenografts tested, the anti-tumor efficacy of CK6 was limited. No synergy was observed on combination of CK6 with TKIs in these GIST models. Our findings highlight the importance of using relevant in vivo human tumor xenograft models in the preclinical assessment of drug combination strategies.

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.

Resection of a large carotid paraganglioma in Carney-Stratakis syndrome: a multidisciplinary feat

A 39-year-old man was referred to the vascular surgeons with a right-sided cervical mass, palpitations, headaches and sweating. He had presented with abdominal discomfort 12 months earlier. Investigations had revealed a gastrointestinal stromal tumour (GIST) and left adrenalectomy. CT of the neck with contrast demonstrated a large right carotid paraganglioma, extending superiorly from below the carotid bifurcation to encase the internal carotid artery. Genetic screening confirmed the diagnosis of Carney-Stratakis syndrome, an SDH-D germline mutation leading to GIST and multifocal paragangliomas. Successful surgical excision required considerable multidisciplinary teamwork between neuroendocrinologists, anaesthetists and surgeons. The tumour was highly vascular and involved the right carotid body, hypoglossal and vagus nerves. Access was challenging and maxillofacial surgical expertise were required for division of the mandible. The patient made a good recovery following speech and swallowing rehabilitation.

Expression of L1 protein correlates with cluster of differentiation 24 and integrin β1 expression in gastrointestinal stromal tumors

The present study examined 66 cases of gastrointestinal stromal tumors (GISTs), 20 cases of smooth muscle tumors, 20 cases of schwannomas and 20 cases of normal gastric tissues in order to analyze the expression of L1, cluster of differentiation (CD)24 and integrin β1 by immunohistochemical staining. Patients were subjected to follow-up, and survival data were evaluated. L1 expression was detected in 57.6% of GIST cases; this was a significantly higher percentage compared with that found in the smooth muscle tumor cases or the normal control group. CD24 and integrin β1 were also expressed at significantly higher levels in the GIST cases than in the normal control group, although no significant difference was found in the expression levels of these proteins in smooth muscle tumor or schwannoma cases. These higher levels of L1 and integrin β1 expression were associated with an increased risk of invasive GIST, and were significantly positively correlated with Ki-67 expression. CD24 expression was not associated with the risk of GIST invasion or Ki-67 expression. There were positive correlations between L1, CD24 and integrin β1 expression; however, these had no significant association with patient survival. Therefore, L1 alone or in conjunction with CD24 (L1 + CD24), or integrin β1 (L1 + integrin β1) can be considered a valuable indicator for the differential diagnosis of GIST. Furthermore, L1 and integrin β1 can be used alone or in combination to evaluate the biological behavior of GISTs. Future studies are required to evaluate the prognostic value of these markers.

Immunostaining of phospho-histone H3 and Ki-67 improves reproducibility of recurrence risk assessment of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common non-epithelial tumors in the digestive tract. Beyond surgery, therapeutic management depends on risk of recurrence. Risk evaluation of GIST takes into account location and size of the tumor, whether or not the tumor was intact or ruptured and mitotic index. The mitotic index lacks in intra- and interobserver reproducibility. In this study, we evaluated on 61 GISTs, the reproducibility of mitotic counting using classical hematoxylin-eosin-saffron (HES) staining, and its correlation with the mitotic count obtained through immunohistochemical staining for phospho-histone H3 (PHH3) and the proliferation index based upon Ki-67 immunostaining. Mitotic counts by HES and PHH3 staining and Ki-67 proliferation index were evaluated twice by three independent observers taking into account interpretation times per tumor for each technique. HES-based and PHH3-based mitotic counts and Ki-67 proliferation index correlated well and presented good intra- and interobserver reproducibility. PHH3 staining resulted in a slight but statistically significant difference of about two more mitotic figures per 5 mm(2) than the HES-based count, which might have put some borderline tumors in a different risk category. Immunohistochemical staining for PHH3 and Ki-67 allowed more rapid interpretation than mitotic counts based upon HES staining, but only PHH3 staining allows counting of mitoses. Immunostaining using anti-PHH3 and anti-Ki-67 antibodies will eventually provide improved recurrence risk stratification of GIST and may become effective ancillary tools in deciding on optimal therapeutic management.

Somatic DNA mutation analysis in targeted therapy of solid tumours

Cancer is a disease of the genome with diverse aetiologies including the accumulation of acquired mutations throughout the genome. There has been a flood of knowledge improving our understanding of the biology and molecular genetics of melanoma, lung and colorectal cancer since the genomics era started. Translation of this knowledge into a better understanding of cell proliferation, survival and apoptosis has produced a paradigm shift in medical oncology enabling gene-based cancer treatment (called personalised or precision medicine). Somatic mutation analysis is crucial for a genomics approach since it can identify driver mutations-the "Achilles' heel" of cancer, and support clinical decision-making through targeted therapy. Nevertheless, the applications of somatic DNA testing in cancer face many challenges such as obtaining comprehensive coverage of the cancer genome with limited DNA being available, and delivering an accurate report in a timely fashion without false-negative and false-positive results. Further advances in DNA technologies and bioinformatics will overcome these issues and maximise opportunities for targeted therapy. Somatic mutation analysis will then become an integral part of cancer management for all malignancies.

Endoscopic ultrasound-guided fine needle tissue acquisition biopsy samples do not allow a reliable proliferation assessment of gastrointestinal stromal tumours

BACKGROUND

Current prognostication of gastrointestinal stromal tumours is validated on/applies to resected tumours, mainly because surgery is recommended whenever possible. However, pre-treatment prognostication is increasingly warranted, considering the follow-up strategy recently admitted for expectedly low-risk tumours and the possible distinctive molecular features/spontaneous regression of some small cases.

AIMS

To investigate whether endoscopic ultrasound-guided fine-needle tissue acquisition-biopsies reflect prognosticators of resected gastrointestinal stromal tumours, for possibly developing reliable pre-treatment prognostic criteria.

METHODS

The applicability/reliability of mitotic index/5mm(2) and MIB1 proliferative index/1000 cells were tested in 35 endoscopic ultrasound-guided fine-needle tissue acquisition-biopsies diagnosed as gastrointestinal stromal tumour, subsequently resected without intervening therapy, consecutively collected in thirty months. Size and mitotic/proliferative indexes were compared with resection specimens. The feasibility of bioptic genotyping was also tested.

RESULTS

35 patients were studied (45.7% males; mean age 61.6 years, range 26-83 years). Mitotic/proliferative indexes were determinable in 68.6%/88.6% of biopsies, respectively; they were nevertheless underestimated, as happened with endoscopic ultrasound-determined tumour size. Bioptic genotyping revealed reliable.

CONCLUSIONS

Endoscopic ultrasound-guided fine-needle tissue acquisition does not reliably reflect gastrointestinal stromal tumours' proliferation and size. Alternative parameters should be validated for a pre-surgical prognostic classification. Considering the emerging potentially prognostic genetic markers in gastrointestinal stromal tumours, the reliability of bioptic genotyping is a promising result.

Constitutive activation of oncogenic PDGFRα-mutant proteins occurring in GIST patients induces receptor mislocalisation and alters PDGFRα signalling characteristics

Background

Gastrointestinal stromal tumours (GIST) are mainly characterised by the presence of activating mutations in either of the two receptor tyrosine kinases c-KIT or platelet-derived growth factor receptor-α (PDGFRα). Most mechanistic studies dealing with GIST mutations have focused on c-KIT and far less is known about the signalling characteristics of the mutated PDGFRα proteins. Here, we study the signalling capacities and corresponding transcriptional responses of the different PDGFRα proteins under comparable genomic conditions.

Results

We demonstrate that the constitutive signalling via the oncogenic PDGFRα mutants favours a mislocalisation of the receptors and that this modifies the signalling characteristics of the mutated receptors. We show that signalling via the oncogenic PDGFRα mutants is not solely characterised by a constitutive activation of the conventional PDGFRα signalling pathways. In contrast to wild-type PDGFRα signal transduction, the activation of STAT factors (STAT1, STAT3 and STAT5) is an integral part of signalling mediated via mutated PDGF-receptors. Furthermore, this unconventional STAT activation by mutated PDGFRα is already initiated in the endoplasmic reticulum whereas the conventional signalling pathways rather require cell surface expression of the receptor. Finally, we demonstrate that the activation of STAT factors also translates into a biologic response as highlighted by the induction of STAT target genes.

Conclusion

We show that the overall oncogenic response is the result of different signatures emanating from different cellular compartments. Furthermore, STAT mediated responses are an integral part of mutated PDGFRα signalling.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-015-0096-8) contains supplementary material, which is available to authorized users.

Targeted therapies for advanced Ewing sarcoma family of tumors

The prognosis of adolescent and young adult patients battling metastatic Ewing sarcoma family of tumors (ESFT) remains less than 30% despite the development of systemic therapies. In the era of personalized medicine, novel molecular targets have been tested in preclinical or clinical settings in ESFT. In this review, we focus on early clinical and translational research that identified multiple molecular targets, including IGF-1R; mTOR; tyrosine kinase inhibitors; EWS-FLI1-related targets, and others. Overall, novel targeted therapies demonstrated modest efficacy; however pronounced and durable antineoplastic responses have been observed in small subsets of treated patients, for example with IGF-1R antibodies. Identifying outcome-predicting biomarkers and overcoming treatment resistance remain major challenges. Due to the rarity of ESFT, multi-institutional collaboration efforts of clinicians, basic and translational scientists are needed in order to understand biology of therapeutic response or resistance, which can lead to development of novel therapeutic methods and improved patient outcomes.

FAM96A is a novel pro-apoptotic tumor suppressor in gastrointestinal stromal tumors

The ability to escape apoptosis is a hallmark of cancer-initiating cells and a key factor of resistance to oncolytic therapy. Here, we identify FAM96A as a ubiquitous, evolutionarily conserved apoptosome-activating protein and investigate its potential pro-apoptotic tumor suppressor function in gastrointestinal stromal tumors (GISTs). Interaction between FAM96A and apoptotic peptidase activating factor 1 (APAF1) was identified in yeast two-hybrid screen and further studied by deletion mutants, glutathione-S-transferase pull-down, co-immunoprecipitation and immunofluorescence. Effects of FAM96A overexpression and knock-down on apoptosis sensitivity were examined in cancer cells and zebrafish embryos. Expression of FAM96A in GISTs and histogenetically related cells including interstitial cells of Cajal (ICCs), "fibroblast-like cells" (FLCs) and ICC stem cells (ICC-SCs) was investigated by Northern blotting, reverse transcription-polymerase chain reaction, immunohistochemistry and Western immunoblotting. Tumorigenicity of GIST cells and transformed murine ICC-SCs stably transduced to re-express FAM96A was studied by xeno- and allografting into immunocompromised mice. FAM96A was found to bind APAF1 and to enhance the induction of mitochondrial apoptosis. FAM96A protein or mRNA was dramatically reduced or lost in 106 of 108 GIST samples representing three independent patient cohorts. Whereas ICCs, ICC-SCs and FLCs, the presumed normal counterparts of GIST, were found to robustly express FAM96A protein and mRNA, FAM96A expression was much reduced in tumorigenic ICC-SCs. Re-expression of FAM96A in GIST cells and transformed ICC-SCs increased apoptosis sensitivity and diminished tumorigenicity. Our data suggest FAM96A is a novel pro-apoptotic tumor suppressor that is lost during GIST tumorigenesis.