"Pediatric-type" gastrointestinal stromal tumors in adults: distinctive histology predicts genotype and clinical behavior

Succinate dehydrogenase deficiency in pediatric and adult gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) in adults are generally driven by somatic gain-of-function mutations in KIT or PDGFRA, and biological therapies targeted to these receptor tyrosine kinases comprise part of the treatment regimen for metastatic and inoperable GISTs. A minority (10-15%) of GISTs in adults, along with ∼85% of pediatric GISTs, lacks oncogenic mutations in KIT and PDGFRA. Not surprisingly these wild type (WT) GISTs respond poorly to kinase inhibitor therapy. A subset of WT GISTs shares a set of distinguishing clinical and pathological features, and a flurry of recent reports has convincingly demonstrated shared molecular characteristics. These GISTs have a distinct transcriptional profile including over-expression of the insulin-like growth factor-1 receptor, and exhibit deficiency in the succinate dehydrogenase (SDH) enzyme complex. The latter is often but not always linked to bi-allelic inactivation of SDH subunit genes, particularly SDHA. This review will summarize the molecular, pathological, and clinical connections that link this group of SDH-deficient neoplasms, and offer a view toward understanding the underlying biology of the disease and the therapeutic challenges implicit to this biology.

Role of molecular analysis in the adjuvant treatment of gastrointestinal stromal tumours: It is time to define it

Sendur et al pointed out the attention on the importance of mutational analysis for adjuvant treatment of gastrointestinal stromal tumor (GIST) in an article published in World Journal of Gastroenterology. In particular, they suggested that the optimal dose and duration of adjuvant therapy could be defined by the mutational status of the primary disease. This comment would underline the importance of centralised laboratories, given the increasingly important role of molecular analysis in the work-flow of all GIST, and the need of retrospective analyses for subgroups population stratified for the mutational status from the available studies in the adjuvant setting, in order to define the role of mutational analysis in choosing the optimal dose and duration of adjuvant therapy.

Analysis of all subunits, SDHA, SDHB, SDHC, SDHD, of the succinate dehydrogenase complex in KIT/PDGFRA wild-type GIST

Mutations of genes encoding the subunits of the succinate dehydrogenase (SDH) complex were described in KIT/PDGFRA wild-type GIST separately in different reports. In this study, we simultaneously sequenced the genome of all subunits, SDHA, SDHB, SDHC, and SDHD in a larger series of KIT/PDGFRA wild-type GIST in order to evaluate the frequency of the mutations and explore their biological role. SDHA, SDHB, SDHC, and SDHD were sequenced on the available samples obtained from 34 KIT/PDGFRA wild-type GISTs. Of these, in 10 cases, both tumor and peripheral blood (PB) were available, in 19 cases only tumor, and in 5 cases only PB. Overall, 9 of the 34 patients with KIT/PDGFRA wild-type GIST carried mutations in one of the four subunits of the SDH complex (six patients in SDHA, two in SDHB, one in SDHC). WB and immunohistochemistry analysis showed that patients with KIT/PDGFRA wild-type GIST who harbored SDHA mutations exhibited a significant downregulation of both SDHA and SDHB protein expression, with respect to the other GIST lacking SDH mutations and to KIT/PDGFRA-mutated GIST. Clinically, four out of six patients with SDHA mutations presented with metastatic disease at diagnosis with a very slow, indolent course. Patients with KIT/PDGFRA wild-type GIST may harbor germline and/or de novo mutations of SDH complex with prevalence for mutations within SDHA, which is associated with a downregulation of SDHA and SDHB protein expression. The presence of germline mutations may suggest that these patients should be followed up for the risk of development of other cancers.

Loss of SDHA expression identifies SDHA mutations in succinate dehydrogenase-deficient gastrointestinal stromal tumors

Succinate dehydrogenase-deficient gastrointestinal stromal tumors (SDH-deficient GISTs) are a unique class of GIST defined by negative immunohistochemical staining for succinate dehydrogenase B (SDHB). SDH-deficient GISTs show distinctive clinical and pathologic features including absence of KIT and PDGFRA mutations, exclusive gastric location, common lymph node metastasis, a prognosis not predicted by size and mitotic rate, and indolent behavior of metastases. They may be syndromal with some being associated with the Carney Triad or germline SDHA, SDHB, SDHC, or SDHD mutations (Carney-Stratakis syndrome). It is normally recommended that genetic testing for SDHA, SDHB, SDHC, and SDHD be offered whenever an SDH-deficient GIST is encountered. However, testing for all 4 genes is burdensome and beyond the means of most centers. In this study we performed SDHA mutation and immunohistochemical analyses for SDHA on 10 SDH-deficient GISTs. Three showed negative staining for SDHA, and all of these were associated with germline SDHA mutations. In 2 tumors, 3 novel mutations were identified (p.Gln54X, p.Thr267Met, and c.1663+3G>C), none of which have previously been reported in GISTs or other SDH-associated tumors. Seven showed positive staining for SDHA and were not associated with SDHA mutation. In conclusion, 30% of SDH-deficient GISTs in this study were associated with germline SDHA mutation. Negative staining for SDHA can be used to triage formal genetic testing for SDHA when an SDH-deficient GIST is encountered.

Gene expression of the IGF pathway family distinguishes subsets of gastrointestinal stromal tumors wild type for KIT and PDGFRA

Gastrointestinal stromal tumors (GISTs) arise from the interstitial cells of Cajal (ICCs) and are the most common mesenchymal neoplasm of the gastrointestinal tract. While the majority of GISTs harbor activating mutations in either the v-kit Hardy-Zuckerman feline sarcoma viral oncogene homolog (KIT) or platelet-derived growth factor receptor alpha (PDGFRA) tyrosine kinases, approximately 10–15% of adult GISTs and 85% of pediatric GISTs lack such mutations. These “wild-type” GISTs have been reported to express high levels of the insulin-like growth factor 1 receptor (IGF1R), and IGF1R-targeted therapy of wild-type GISTs is being evaluated in clinical trials. However, it is not clear that all wild-type GISTs express IGF1R, because studies to date have predominantly focused on a particular subtype of gastric wild-type GIST that is deficient in the mitochondrial succinate dehydrogenase (SDH) complex. This study of a series of 136 GISTs, including 72 wild-type specimens, was therefore undertaken to further characterize wild-type GIST subtypes based on the relative expression of transcripts encoding IGF1R. Additional transcripts relevant to GIST biology were also evaluated, including members of the IGF-signaling pathway (IGF1, IGF2, and insulin receptor [INSR]), neural markers (CDH2[CDH: Cadherin], neurofilament, light polypeptide, LHX2 [LHX: LIM homeobox], and KIRREL3 [KIRREL: kin of IRRE like]), KIT, PDGFRA, CD34, and HIF1A. Succinate dehydrogenase complex, subunit B protein expression was also assessed as a measure of SDH complex integrity. In addition to the previously described SDH-deficient, IGF1R^high wild-type GISTs, other SDH-intact wild-type subpopulations were defined by high relative expression of IGF1R, neural markers, IGF1 and INSR, or low IGF1R coupled with high IGF2. These results underscore the complexity and heterogeneity of wild-type GISTs that will need to be factored into molecularly-targeted therapeutic strategies.

Loss of expression of SDHA predicts SDHA mutations in gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are usually driven by mutations in KIT or PDGFRA, although 15% of GISTs in adults and >90% in children lack such mutations. The majority of gastric KIT/PDGFRA wild-type GISTs show distinctive morphological and clinical features and loss of expression of succinate dehydrogenase (SDH) B. Only a small subset of SDHB-deficient GISTs carries loss-of-function mutations in SDHB, SDHC, or SDHD. Because of the complexity of its locus (15 exons) and the presence of three pseudogenes, SDHA is rarely analyzed. Recently, mutations in SDHA were shown to lead to loss of expression of SDHA in a small group of paragangliomas. We sought to determine whether immunohistochemistry for SDHA could identify GISTs with SDHA mutations. Tumors (n=33) with pathological features of SDH-deficient GIST were analyzed for expression of SDHA and SDHB by immunohistochemistry, and SDHA exons were sequenced from tumors lacking SDHA expression. Exons harboring somatic mutations were examined in DNA from corresponding normal tissue. All 33 tumors showed loss of SDHB expression. A total of 9 out of 33 (27%) tumors also lacked expression of SDHA. SDHA-deficient GISTs affected five men and four women (median age 38 years). SDHA expression was intact in the 24 remaining tumors, including those with known SDHB (n=3) or SDHC (n=2) mutations. Nonsense (n=8) or missense (n=1) mutations in SDHA were identified in all SDHA-deficient tumors. Heterozygous mutations were also found in DNA from normal tissues from six patients with available material. Somatic loss of the second allele has been found in seven tumors, five by loss of heterozygosity, one by a 13-bp deletion, and one by a missense mutation. Loss of SDHA expression in GIST reliably predicts the presence of SDHA mutations, which represent a relatively common cause of SDH-deficient GIST in adults. Immunohistochemistry for SDHA can be used to select patients for SDHA-specific genetic testing.

Loss of succinate dehydrogenase subunit B (SDHB) expression is limited to a distinctive subset of gastric wild-type gastrointestinal stromal tumours: a comprehensive genotype-phenotype correlation study

AIMS

Gastrointestinal stromal tumours (GISTs) typically harbour KIT or PDGFRA mutations; 15% of adult GISTs and >90% in children lack such mutations ('wild-type' GISTs). Paediatric and occasional adult GISTs show similar, distinctive features: multinodular architecture and epithelioid morphology, indolent behaviour with metastases, and imatinib resistance. Recent studies have suggested that these tumours can be identified by loss of succinate dehydrogenase subunit B (SDHB) expression. The aim of this study was to validate the predictive value of SDHB immunohistochemistry in a large genotyped cohort.

METHODS AND RESULTS

SDHB expression was examined in GISTs with known genotypes: 179 with KIT mutations, 32 with PDGFRA mutations, and 53 wild type. Histological features were recorded without knowledge of genotype or SDHB status. SDHB was deficient in 22 (42%) wild-type GISTs. All other tumours showed intact SDHB expression. All SDHB-deficient GISTs with known primary sites arose in the stomach, and had multinodular architecture and epithelioid or mixed morphology. None of the wild-type GISTs with intact SDHB showed multinodular architecture, and only four (13%) had epithelioid morphology.

CONCLUSIONS

SDHB-deficient GISTs are wild-type gastric tumours with distinctive histology. Immunohistochemistry for SDHB can be used to confirm the diagnosis of this tumour class. SDHB expression is retained in all GISTs with KIT and PDGFRA mutations.

Succinate dehydrogenase (SDH) and mitochondrial driven neoplasia

The genes for the succinate dehydrogenase (SDH) subunits SDHA, SDHB, SDHC and SDHD are encoded in the autosome. The proteins are assembled in the mitochondria to form the mitochondrial complex 2, a key respiratory enzyme which links the Krebs cycle and the electron transport chain. Thirty percent of phaeochromocytoma and paraganglioma (PHEO/PGL) are hereditary and perhaps as many as half of these familial cases are caused by germline mutations of the SDH subunits. Negative immunohistochemical staining for the SDHB subunit identifies PHEO/PGL associated with germline mutation of any of the mitochondrial complex 2 components and can be used to triage formal genetic testing of all PHEO/PGL for SDH mutations. PHEO/PGL associated with SDHA mutation also show negative staining for SDHA as well as SDHB.A unique subgroup of gastrointestinal stromal tumours (GISTs) are driven by mitochondrial complex 2 dysfunction. These SDH deficient GISTs can also be definitively identified by negative staining for SDHB and show distinct clinical and morphological features including frequent onset in childhood and young adulthood, gastric location, a tendency to multifocality, absence of KIT and PDGFRA mutations, a prognosis not predicted by size and mitotic rate and a tendency to indolent behaviour of metastases. Some of these SDH deficient GISTs are driven by classical SDH mutations, but the precise mechanisms of tumourigenesis in many (including those associated with the Carney triad) remain unknown. Germline SDHB mutation is associated with a newly recognised type of renal carcinoma which commonly but not always demonstrates distinctive morphology and can also be recognised by negative staining for SDHB.Immunohistochemistry for SDHB therefore has emerged as a useful tool to recognise these distinct neoplasias driven by mitochondrial complex 2 dysfunction and to triage formal genetic testing for the associated syndromes.

SDHA loss of function mutations in a subset of young adult wild-type gastrointestinal stromal tumors

BACKGROUND

A subset of KIT/PDGFRA wild-type gastrointestinal stromal tumors (WT GIST) have been associated with alteration of the succinate dehydrogenase (SDH) complex II function. A recent report identified four non-syndromic, KIT/PDGFRA WT GIST harboring compound heterozygous or homozygous mutations in SDHA encoding the main subunit of the SDH complex II.

METHODS

Next generation sequencing was applied on five pediatric and one young adult WT GIST, by whole exome capture and SOLiD 3-plus system sequencing. The putative mutations were first confirmed by Sanger sequencing and then screened on a larger panel of 11 pediatric and young adult WT GIST, including 5 in the context of Carney triad.

RESULTS

A germline p.Arg31X nonsense SDHA mutation was identified in one of the six cases tested by SOLiD platform. An additional p.D38V missense mutation in SDHA exon 2 was identified by Sanger sequencing in the extended KIT/PDGFRA WT GIST patients cohort. Western blotting showed loss of SDHA expression in the two cases harboring SDHA mutations, while expression being retained in the other WT GIST tumors. Results were further confirmed by immunohistochemistry for both SDHA and SDHB, which showed a concurrent loss of expression of both proteins in SDHA-mutant lesions, while the remaining WT tumors showed only loss of SDHB expression.

CONCLUSIONS

Germline and/or somatic aberrations of SDHA occur in a small subset of KIT/PDGFRA WT GISTs, outside the Carney's triad and are associated with loss of both SDHA and SDHB protein expression. Mutations of the SDH complex II are more particularly associated with KIT/PDGFRA WT GIST occurring in young adults. Although pediatric GIST consistently display alterations of SDHB protein expression, further molecular studies are needed to identify the crucial genes involved in their tumorigenesis.

Molecular alterations and expression of succinate dehydrogenase complex in wild-type KIT/PDGFRA/BRAF gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract, disclosing somatic KIT, PDGFRA and BRAF mutations. Loss of function of succinate dehydrogenase (SDH) complex is an alternative molecular mechanism in GISTs, namely in carriers of germline mutations of the SDH complex that develop Carney-Stratakis dyad characterized by multifocal GISTs and multicentric paragangliomas (PGLs). We studied a series of 25 apparently sporadic primary wild-type (WT) KIT/PDGFRA/BRAF GISTs occurring in patients without personal or familial history of PGLs, re-evaluated clinicopathological features and analyzed molecular alterations and immunohistochemistry expression of SDH complex. As control, we used a series of well characterized 49 KIT/PDGFRA/BRAF-mutated GISTs. SDHB expression was absent in 20% and SDHB germline mutations were detected in 12% of WT GISTs. Germline SDHB mutations were significantly associated to younger age at diagnosis. A significant reduction in SDHB expression in WT GISTs was found when compared with KIT/PDGFRA/BRAF-mutated GISTs. No significant differences were found when comparing DOG-1 and c-KIT expression in WT, SDHB-mutated and KIT/PDGFRA/BRAF-mutated GISTs. Our results confirm the occurrence of germline SDH genes mutations in isolated, apparently sporadic WT GISTs. WT KIT/PDGFRA/BRAF GISTs without SDHB or SDHA/SDHB expression may correspond to Carney-Stratakis dyad or Carney triad. Most importantly, the possibility of PGLs (Carney-Stratakis dyad) and/or pulmonary chondroma (Carney triad) should be addressed in these patients and their kindred.

Succinate dehydrogenase-deficient GISTs are characterized by IGF1R overexpression

Succinate dehydrogenase-deficient gastrointestinal stromal tumors (GISTs) demonstrate unique pathological and clinical features, including the absence of activating mutations of KIT and PDGFRA, and primary resistance to imatinib. They arise exclusively in the stomach and account for 5-7.5% of all adult stomach GISTs and the great majority of these tumors in childhood. Insulin-like growth factor 1 receptor (IGF1R) overexpression has been associated with wild-type and pediatric GISTs. We propose that IGF1R overexpression is a feature of succinate dehydrogenase-deficient GISTs as a group. We assessed succinate dehydrogenase complex subunit B (SDHB) and IGF1R expression by immunohistochemistry in eight known succinate dehydrogenase-deficient GISTs, three GISTs arising in the setting of neurofibromatosis type 1 syndrome and 40 unselected GISTs. Selected KIT and PDGFRA exons were amplified and sequenced from formalin-fixed paraffin-embedded tumor samples. All eight succinate dehydrogenase-deficient tumors were wild-type for KIT and PDGFRA, succinate dehydrogenase B negative and demonstrated IGF1R overexpression. The three neurofibromatosis-related tumors were succinate dehydrogenase B positive and IGF1R negative. Of the 40 unselected upper GISTs, five were wild-type for KIT and PDGFRA in the selected exons. Two of the wild-type GISTs were succinate dehydrogenase B negative and showed IGF1R overexpression and three were succinate dehydrogenase B positive and IGF1R negative. We conclude that IGF1R overexpression is a feature of succinate dehydrogenase deficient GIST as a group, rather than pediatric or wild-type GIST per se. Therefore, IGF1R inhibition represents a potential rational therapeutic approach in this recently recognized subgroup of GIST.

Primary leiomyosarcomas of the gastrointestinal tract in the post-gastrointestinal stromal tumor era

Most mesenchymal neoplasms of the gastrointestinal tract are currently classified as gastrointestinal stromal tumors (GIST). Gastrointestinal stromal tumors are diagnosed by immunopositivity for CD117, CD34, and DOG1.1, with or without molecular analyses. According to the World Health Organization classification, the diagnosis of primary leiomyosarcomas of the gastrointestinal tract is so rare that there are no significant data on demographic, clinical, or gross features of this tumor. A comprehensive literature search was performed to identify gastrointestinal leiomyosarcomas. Searches were limited to the past 12 years because definitive tools to differentiate leiomyosarcomas from GIST were introduced in the late 1990s. Cases were included only if convincing data were presented. Six cases of esophageal leiomyosarcoma and 5 cases of gastric leiomyosarcoma were confirmed. Furthermore, 26 cases of leiomyosarcoma of the small bowel, 11 cases of the colon, and 8 cases arising in the rectum were identified. Finally, 28 cases of infantile and adolescent leiomyosarcoma were reviewed. Although survival analysis is precluded by small case numbers and limited survival data availability, the trend identifies that increased size and mitotic activity portends to a worse prognosis in small bowel leiomyosarcomas. Colonic leiomyosarcomas appear to be aggressive tumors, regardless of tumor size and mitotic activity. Rectal leiomyosarcomas present as smaller tumors with favorable prognosis. Leiomyosarcomas in post-GIST era are rare tumors of the gastrointestinal tract with distinctive clinicopathologic characteristics. Owing to different treatment options, it is necessary to accurately differentiate these from GIST, using a combination of histologic appearance, presence of smooth muscle antigens, and absence of specific GIST immunomarkers.

Multiplex mutation screening by mass spectrometry in gastrointestinal stromal tumours

AIMS

Clinical decision making and optimal clinical trial design based on cancer genetic information will be increasingly informed by the mutational status of multiple genes.

METHODS

We performed mutation screening on 22 fresh frozen gastrointestinal stromal tumours (GISTs) using a multiplexed oncogene screening panel with a mass spectroscopy readout (MassARRAY). The panel can detect 390 known mutations across 30 genes, including several known to contribute to intracellular signalling in cancers (BRAF, PIK3CA, KRAS HRAS, NRAS, AKT1, CTNNB1, GNAQ, CDK4, MAP2K1 and MAP2K2).

RESULTS

Direct Sanger sequencing confirmed that 16 cases (73%) harboured KIT mutations, affecting exon 11, 13 and 17, and the remaining six were wild-type for both KIT and PDGFRA. The sensitivity of the multiplexed oncogene screening panel was 100% for identifying missense mutations in KIT. Only 17% of the deletion mutations were detected, because the panel was not designed for detecting these. A substitution in FBX4 exon 1 (S8R), representing a germline single-nucleotide polymorphism, was observed in a case with KIT exon 11 missense mutation. No other mutations were identified, including in the six wild-type GISTs.

CONCLUSIONS

Our results indicate that mutations other than KIT or PDGFRA are rare in GISTs. Although multiplex mutation screening by mass spectrometry detected missense mutations accurately, it is not sufficient to screen mutations because deletion mutations are common in GISTs.

Succinate dehydrogenase-deficient tumors: diagnostic advances and clinical implications

Just over 10 years ago, germline mutations in SDHD, a gene that encodes 1 of the 4 proteins of the succinate dehydrogenase (SDH) complex, were reported in a subset of patients with hereditary paraganglioma-pheochromocytoma syndrome. Since that time, rapid discoveries have been made in this area. It is now recognized that all of the SDH genes are involved in the tumorigenesis of not only paragangliomas/pheochromocytomas, but also other tumor types, most notably gastrointestinal stromal tumors. This review will outline the genetics of SDH-deficient tumors, discuss possible mechanisms of tumorigenesis, and describe how these tumors can be identified by immunohistochemistry.

Expression of podoplanin is a rare event in sporadic gastrointestinal stromal tumors and does not influence prognosis

Aims: Podoplanin overexpression is associated with worse prognosis in several human cancers. In gastrointestinal stromal tumors (GISTs) very few data on the expression of podoplanin exist, but it seems to be frequently overexpressed in pediatric/syndromic GISTs. We investigated podoplanin expression and its clinical relevance in a large series of sporadic GISTs. Methods: Podoplanin expression was determined immunohistochemically in 145 sporadic adult GISTs. Aneuploidies of 1p36 and 1q25 were investigated using FISH, and KIT and PDGFRA genes were investigated by sequencing. Results: Overexpression of podoplanin was observed in eight (5.6%) GISTs and no association with amplification of 1p36 or KIT or PDGFRA mutations was seen. The amount of podoplanin expression was not associated with clinical risk factors or patient survival. Conclusion: Overexpression of podoplanin is a rare event in sporadic GISTs and is not associated with amplification of 1p36 or with KIT or PDGFRA mutations, which indicates limited pathobiological or clinical relevance.

Impressive long-term disease stabilization by nilotinib in two pretreated patients with KIT/PDGFRA wild-type metastatic gastrointestinal stromal tumours

KIT/PDGFRA wild-type (WT) gastrointestinal stromal tumours (GISTs) showed a response rate to imatinib ranging from 0 to 25%. Nilotinib is a new-generation tyrosine kinase inhibitor that has demonstrated clinical activity in pretreated GIST patients. At present, no correlation between nilotinib activity and clinical/pathological/molecular features is available. We report on two WT GIST patients resistant to imatinib and sunitinib, and enrolled in the CAMN107A2201 study who achieved an impressive disease control by nilotinib. Both patients have germ-line mutations in the SDHA gene. In April 2004, a 39-year-old woman presented gastric GIST with multiple liver metastases and was treated with imatinib 400 mg/day, followed by imatinib 800 mg/day and then sunitinib. In August 2007, because of disease progression, she was enrolled in the CAMN107A2201 study and assigned to the nilotinib 800 mg/day arm. In March 2005, a 27-year-old woman started imatinib 600 mg/day and then sunitinib for gastric GIST with multiple liver and lung metastases. In October 2007, because of disease progression, she was enrolled in the CAMN107A2201 study and assigned to the nilotinib 800 mg/day arm. One patient still showed stable disease after 46 months of treatment according to the Response Evaluation Criteria In Solid Tumors, and a partial response after 9 months according to Choi's criteria. The other patient still showed stable disease after 42 months according to Response Evaluation Criteria In Solid Tumors. At present, they continue to receive nilotinib. We report very long-term disease stabilization under nilotinib treatment in two pretreated WT GIST patients. In-vitro studies and clinical analyses are warranted to evaluate a potential correlation between nilotinib activity and WT genotype or other clinical/pathological features.

Survival of gastrointestinal stromal tumor patients in the imatinib era: life raft group observational registry

BACKGROUND

Gastrointestinal stromal tumors (GIST), one of the most common mesenchymal tumors of the gastrointestinal tract, prior to routine immunohistochemical staining and the introduction of tyrosine kinase inhibitors, were often mistaken for neoplasms of smooth muscle origin such as leiomyomas, leiomyosarcomas or leiomyoblastomas. Since the advent of imatinib, GIST has been further delineated into adult- (KIT or PDGFRα mutations) and pediatric- (typified by wild-type GIST/succinate dehydrogenase deficiencies) types. Using varying gender ratios at age of diagnosis we sought to elucidate prognostic factors for each sub-type and their impact on overall survival.

METHODS

This is a long-term retrospective analysis of a large observational study of an international open cohort of patients from a GIST research and patient advocacy's lifetime registry. Demographic and disease-specific data were voluntarily supplied by its members from May 2000-October 2010; the primary outcome was overall survival. Associations between survival and prognostic factors were evaluated by univariate Cox proportional hazard analyses, with backward selection at P < 0.05 used to identify independent factors.

RESULTS

Inflections in gender ratios by age at diagnosis in years delineated two distinct groups: above and below age 35 at diagnosis. Closer analysis confirmed the above 35 age group as previously reported for adult-type GIST, typified by mixed primary tumor sites and gender, KIT or PDGFRα mutations, and shorter survival times. The pediatric group (< age 18 at diagnosis) was also as previously reported with predominantly stomach tumors, females, wild-type GIST or SDH mutations, and extended survival. "Young adults" however formed a third group aged 18-35 at diagnosis, and were a clear mix of these two previously reported distinct sub-types.

CONCLUSIONS

Pediatric- and adult-type GIST have been previously characterized in clinical settings and these observations confirm significant prognostic factors for each from a diverse real-world cohort. Additionally, these findings suggest that extra diligence be taken with "young adults" (aged 18-35 at diagnosis) as pediatric-type GIST may present well beyond adolescence, particularly as these distinct sub-types have different causes, and consequently respond differently to treatments.

Pediatric gastrointestinal stromal tumor

Pediatric gastrointestinal stromal tumor (GIST) is a rare entity that can be quite different from its adult counterpart. This report provides a comprehensive review on the diagnosis and management of this tumor in children and adolescents, including its oncogenesis and associated syndromes. Surgery remains a mainstay of treatment, but there are no standard guidelines available at this time regarding the best practice for multimodality therapy as our understanding of the biology of GIST is still in evolution. Therefore, pediatric patients with GIST should be ideally treated in the context of clinical trials at specialized, multidisciplinary centers throughout the course of their disease, especially because these patients may live for years after diagnosis.

Predictors of response to targeted therapies for gastrointestinal stromal tumors

CONTEXT

The inhibition of oncogenic kinase signaling is a successful strategy to treat both hematologic and solid malignancies. Patients with chronic myelogenous leukemia, lung adenocarcinoma, renal cell carcinoma, and gastrointestinal stromal tumors are experiencing tremendous clinical benefits from targeted therapies in the form of kinase inhibitors. These drugs marked a revolution in cancer treatment, not only for their safety and efficacy, but also because they continue to expand our knowledge of the pathophysiology of cancer.

OBJECTIVE

To provide a summary of the biologic predictors of gastrointestinal stromal tumor behavior and response to targeted therapies that currently help guide clinical decision making.

DATA SOURCES

Published articles pertaining to the diagnosis, molecular genetics, prognostication, clinical behavior, and treatment of gastrointestinal stromal tumors, as well as experiences in a multidisciplinary sarcoma clinic.

CONCLUSIONS

In gastrointestinal stromal tumors, the strongest predictor of response to targeted therapies is the mutational status of KIT or PDGFRA. Patients whose tumors harbor a KIT exon 11 mutation benefit the most from imatinib mesylate therapy, in terms of response rate, progression-free survival, and overall survival. Conversely, tumors without detectable mutations in either gene ("wild-type" gastrointestinal stromal tumors) are generally not responsive to imatinib mesylate.

Succinate dehydrogenase-deficient GISTs: a clinicopathologic, immunohistochemical, and molecular genetic study of 66 gastric GISTs with predilection to young age

Most gastrointestinal stromal tumors (GISTs) are driven by KIT or PDGFRA-activating mutations, but a small subset is associated with loss of function of the succinate dehydrogenase (SDH) complex of mitochondrial inner membrane proteins. This occurs by germline mutations of the SDH subunit genes and hitherto unknown mechanisms. SDH-deficient GISTs especially include pediatric GISTs and those associated with Carney triad (CT) or Carney-Stratakis syndromes (CSSs); the latter 2 also include paraganglioma as a component. SDH-deficient GISTs were identified in this study on the basis of immunohistochemical loss of succinate dehydrogenase subunit B (SDHB), which signals functional loss of the SDH complex. We found 66 SDH-deficient GISTs among 756 gastric GISTs, with an estimated frequency of 7.5% of unselected cases. Nearly, all gastric GISTs in patients <20 years, and a substantial percentage of those in patients <40 years, but only rare GISTs in older adults were SDH deficient. There was a female predominance of over 2:1. Two patients each had either pulmonary chondroma or paraganglioma (CT), but none of the examined cases had SDH germline mutations (CSS) or somatic KIT/PDGFRA or BRAF mutations. SDH-deficient GISTs were often multiple and typically showed plexiform muscularis propria involvement and epithelioid hypercellular morphology. They were consistently KIT-positive and DOG1/Ano 1-positive and almost always smooth muscle actin negative. Tumor size and mitotic activity varied, and the tumors were somewhat unpredictable with low mitotic rates developing metastases. Gastric recurrences occurred in 11 patients, and peritoneal and liver metastases occurred in 8 and 10 patients, respectively. Lymph node metastases were detected in 5 patients, but lymphovascular invasion was present in >50% of cases studied; these 2 were not related to adverse outcome. Seven patients died of disease, but many had long survivals, even with peritoneal or liver metastases. All 378 nongastric GISTs and 34 gastric non-GIST mesenchymal tumors were SDHB positive. SDH-deficient GISTs constitute a small subgroup of gastric GISTs; they usually occur in children and young adults, often have a chronic course similar to that of pediatric and CT GISTs, and have potential association with paraganglioma, necessitating long-term follow-up.