Predictors of response to targeted therapies for gastrointestinal stromal tumors

Vascular response patterns to targeted therapies in murine breast cancer models with divergent degrees of malignancy

BACKGROUND

Response assessment of targeted cancer therapies is becoming increasingly challenging, as it is not adequately assessable with conventional morphological and volumetric analyses of tumor lesions. The tumor microenvironment is particularly constituted by tumor vasculature which is altered by various targeted therapies. The aim of this study was to noninvasively assess changes in tumor perfusion and vessel permeability after targeted therapy in murine models of breast cancer with divergent degrees of malignancy.

METHODS

Low malignant 67NR or highly malignant 4T1 tumor-bearing mice were treated with either the multi-kinase inhibitor sorafenib or immune checkpoint inhibitors (ICI, combination of anti-PD1 and anti-CTLA4). Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with i.v. injection of albumin-binding gadofosveset was conducted on a 9.4 T small animal MRI. Ex vivo validation of MRI results was achieved by transmission electron microscopy, immunohistochemistry and laser ablation-inductively coupled plasma-mass spectrometry.

RESULTS

Therapy-induced changes in tumor vasculature differed between low and highly malignant tumors. Sorafenib treatment led to decreased tumor perfusion and endothelial permeability in low malignant 67NR tumors. In contrast, highly malignant 4T1 tumors demonstrated characteristics of a transient window of vascular normalization with an increase in tumor perfusion and permeability early after therapy initiation, followed by decreased perfusion and permeability parameters. In the low malignant 67NR model, ICI treatment also mediated vessel-stabilizing effects with decreased tumor perfusion and permeability, while ICI-treated 4T1 tumors exhibited increasing tumor perfusion with excessive vascular leakage.

CONCLUSION

DCE-MRI enables noninvasive assessment of early changes in tumor vasculature after targeted therapies, revealing different response patterns between tumors with divergent degrees of malignancy. DCE-derived tumor perfusion and permeability parameters may serve as vascular biomarkers that allow for repetitive examination of response to antiangiogenic treatment or immunotherapy.

A rare rectal gastrointestinal stromal tumor with indolent biological behavior: A case study

The overall incidence of rectal gastrointestinal stromal tumor (RGIST) has risen, but it remains a rare disease. Furthermore, tumor rupture is associated with poor prognosis. The present study reported a rare case of RGIST with indolent biological behavior. The biological behavior of this RGIST was analyzed and its malignant potential was evaluated using a guideline-based risk stratification assessment. The patient was diagnosed with a rectal tumor at the Third Affiliated Hospital of Qiqihar Medical University (Qiqihar, China) in April 2020 and a partial resection biopsy was then performed. This resection counts as a rupture. The biopsy confirmed RGIST and the patient refused further examination and treatment due to economic concerns. However, the patient survives with no tumor progression and metastasis until now, May 2022. In conclusion, based on the present case, tumor rupture in indolent RGIST is not necessarily associated with poor outcome.

Mesenchymal tumors of the stomach: radiologic and pathologic correlation

Mesenchymal tumors of the stomach are uncommon, with gastrointestinal stromal tumor (GIST) being the most common among them. Majority of the tumors may arise from cells of Cajal, smooth muscle cells, neural cells, totipotent stem cells, adipocytes or fibroblasts. Imaging plays an important role not only in staging but also in characterizing these tumors. Many of these tumors have characteristic imaging features. GISTs usually present as large cavitating and necrotic tumors with exophytic component. Presence of fat tissue within the tumor suggests a lipoma or a teratoma, early phase hyperenhancement indicates glomus tumor and hemangioma, and delayed contrast enhancement is seen in schwannoma. Their differentiation from epithelial tumors like carcinoma and neuroendocrine tumors is often possible based on the location (mesenchymal tumors are intramural), spread, morphological appearance and enhancement patterns. However, overlapping features exist between these tumors with imaging often being only suggestive. A biopsy is necessary for a definitive diagnosis in many cases.

Current update on molecular cytogenetics, diagnosis and management of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal (GI) tract and are thought to arise from precursors of the interstitial cells of Cajal. GISTs can arise anywhere in the GI tract, but most commonly originate from the stomach and small intestine. The majority of GISTs occur as a result of activating mutations in two receptor protein tyrosine kinases: KIT and/or platelet-derived growth factor receptor-α. Mutational analyses allow for predicting patient prognosis and treatment response. Clinical presentations can vary from no symptoms, typical in the case of small incidentally found tumors, to GI bleeding, abdominal discomfort, and ulcer-related symptoms when the tumor is enlarged. Imaging plays a critical role in the diagnosis and management of these tumors with multiphasic computed tomography serving as the imaging modality of choice. Magnetic resonance imaging and positron emission tomography-computed tomography can serve as imaging adjuncts in lesion characterization, especially with liver metastases, and subsequent staging and assessment for treatment response or recurrence. Surgical resection is the preferred management for small GISTs, while tyrosine kinase inhibitors - imatinib mesylate and sunitinib malate - serve as crucial molecular-targeted therapies for locally advanced and metastatic GISTs. This review article highlights the clinical presentation, pathology and molecular cytogenetics, imaging features, and current management of GISTs.

Abnormal MGMT Promoter Methylation in Gastrointestinal Stromal Tumors: Genetic Susceptibility and Association with Clinical Outcome

Purpose

KIT/PDGFRA wild-type (WT) gastrointestinal stromal tumors (GISTs) represent a heterogeneous subgroup of GISTs that lack KIT or PDGFRA mutations and possess distinct genetic alterations and primary resistance to imatinib. Succinate dehydrogenase (SDH)-deficient GISTs comprise the largest subpopulation of WT GISTs that are characterized by loss-of-function of SDH. O6-methylguanine-DNA methyltransferase (MGMT) is a specific DNA repair enzyme that has been identified as a predictor of positive treatment response to alkylating agents in a variety of cancers. The aim of this study was to evaluate the expression of MGMT and the prevalence of MGMT promoter methylation in GISTs and to determine the association between MGMT promoter methylation and clinicopathological characteristics and clinical outcomes.

Patients and Methods

A heterogeneous cohort of 137 primary GISTs that confirmed by immunohistochemistry and KIT/PDGFRA mutation analysis were retrospectively selected and analyzed for MGMT expression and MGMT promoter methylation using immunohistochemical staining and methylation-specific PCR (MSP). A concordance analysis between MGMT promoter methylation and clinicopathological characteristics and prognosis was also performed.

Results

A total of 44.5% (65/137) of GIST patients displayed loss of MGMT protein expression, and 10.9% (15/137) of these patients exhibited MGMT promoter methylation. However, no significant correlation was observed between the loss of MGMT protein expression and MGMT promoter methylation. WT GISTs possessing an epithelioid or mixed phenotype, particularly those that were SDH-deficient, displayed a markedly higher prevalence of MGMT promoter methylation compared to that in KIT/PDGFRA mutated GISTs. Moreover, MGMT promoter methylation was identified as a potential independent prognostic factor for OS and DFS in patients with GIST.

Conclusion

MGMT promoter methylation is particularly frequent in SDH-deficient GISTs and in WT GISTs possessing an epithelioid/mixed phenotype, and knowledge of this methylation status may offer a novel potential therapeutic option for WT GISTs.

Succinate dehydrogenase-deficient gastrointestinal stromal tumor of stomach diagnosed by endoscopic ultrasound-guided fine-needle biopsy: Report of a distinct subtype in cytology

Succinate dehydrogenase (SDH)-deficient gastrointestinal stromal tumors (GISTs) are characterized by the lack of mutations in KIT receptor tyrosine kinase complex and platelet derived growth factor receptor-alpha (PDGFRA) that are commonly found in the majority of GISTs. SDH-deficient GISTs comprise approximately 5%-10% of all GISTs. This subset may be associated with Carney Triad and Carney-Stratakis syndrome. SDH-deficient GISTs show unique demographic, radiologic, morphologic findings, clinical behavior, and treatment response. To our knowledge, the identification and characterization of this subset of GISTs have not yet been described in the cytopathology literature. By understanding the clinical as well as the other unique features of this tumor, in addition to the rapidly evolving identification of specific molecular alterations and targeted therapies, cytopathologists may play an important role in the diagnosis and work-up of these patients to allow clinicians to better manage and treat them. We present a young female with gastric SDH-deficient GIST diagnosed by fine-needle biopsy with supporting surgical pathology follow-up and molecular confirmation. This report suggests that the diagnosis of SDH-deficient GIST can be made on cytology in the appropriate clinical setting by using cytomorphologic features and demonstrating SDH loss by IHC on the cell block. In addition, molecular testing may be possible on the cytology cell block or supernatant to confirm the diagnosis.

Progress in determining response to treatment in gastrointestinal stromal tumor

Introduction: Gastrointestinal stromal tumor (GIST) is the most common malignant mesenchymal tumor of the gastrointestinal system. Multiple advances in the management of GIST from the discovery of KIT/PDGRA and other genetic alterations have led to the development of multiple tyrosine kinase inhibitors. Response assessment in GIST is determined with iRECIST (Response Evaluation Criteria in Solid Tumors), PERCIST (PET response criteria in solid tumors), or Choi criteria. Molecular genotyping of the tissue samples is the recent standard for diagnosis, treatment, and response to treatment.Areas covered: In this study, we provide a brief overview of the history of the GIST, molecular sequencing, available treatment options and clinical trials, radiologic response assessment, and the role of ctDNA in response evaluation.Expert opinion: Future GIST management is related to the development of sensitive assays to detect genetic alterations for initial diagnosis, treatment selection, monitoring the response to treatment, resistant mutations, and predicting survival.

Gastrointestinal Stromal Tumor (GIST) from esophagus to anorectum - diagnosis, response evaluation and surveillance on computed tomography (CT) scan

Gastrointestinal stromal tumor (GIST) are the most common non epithelial tumor of the gastrointestinal (GI) tract. They arise from interstitial cells of Cajal present in the myenteric plexus. They can also arise outside the GI tract from mesentery, retro peritoneum and omentum. With the advent of new targeted molecular therapy c- tyrosine kinase inhibitor (Imatinib), it has become important to differentiate between response and pseudo-progression of the disease as response evaluation criteria for GIST are different from Response Evaluation Criteria in Solid Tumors (RECIST). Purpose of this pictorial essay is to enumerate the characteristic CT features of GIST, and discuss atypical features and response evaluation criteria.

Clinicopathological and morphological spectrum of gastrointestinal stromal tumours on multi-detector computed tomography

PURPOSE

To describe the clinicopathological and morphological features of gastrointestinal stromal tumours (GISTs) on multi-detector computed tomography (MDCT).

MATERIAL AND METHODS

MDCT (plain and post contrast) images of 25 confirmed cases of GISTs were retrospectively evaluated from our hospital database. The images were analysed for the location, size, growth pattern, attenuation pattern, relation to adjacent structures, presence or absence of ulceration, calcification, metastases, lymphadenopathy, and for any complications such as haemorrhage, intestinal obstruction, etc. Institutional Ethics Committee clearance was obtained prior to the commencement of the study. Statistics used included percentage frequency.

RESULTS

Our study group comprised 14 males and 11 females. The mean age of our study population was 60 years (age range: 40 to 82 years). The mean tumour size was 11.7 cm. The stomach and small bowel accounted for 76% of the primary tumour site. The commonest imaging appearance of GIST observed in our study was that of an exophytic mass (76%) with a heterogenous pattern of enhancement (96%) with intratumoural necrosis (76%). MDCT demonstrated complications in three patients (12%). Six patients presented with metastatic foci (five to the liver and one to the lung), while lymphadenopathy was observed in five patients (20%). Associated complications included intestinal obstruction (8%) and retrogastric haematoma (4%). Incidental findings included uterine fibroid (n = 1), ovarian dermoid (n = 1), and chronic pancreatitis (n = 1).

CONCLUSIONS

GISTs are predominantly large tumours with a well circumscribed and exophytic pattern on MDCT, with or without cystic/necrotic areas, and they mostly show a heterogenous pattern of enhancement on post-contrast administration.

Hallmarks of Cancer in the Reading Room: A Guide for Radiologists

OBJECTIVE

The hallmarks of cancer are mechanisms that cells develop to undergo malignant transformation. The targeting of these hallmarks by newer cancer therapies results in new mechanisms of response, toxicity, and resistance. The purpose of this article is to review these hallmarks, their associated targeted therapies, imaging features of responses, and toxicities.

CONCLUSION

Ten hallmarks, among them proliferative signaling, angiogenesis, immune response, and genome instability, are reviewed. Molecular targeted therapies, including antiangiogenic factors and immune checkpoint inhibitors, target these hallmarks.

Contemporary Sarcoma Diagnosis, Genetics, and Genomics

Sarcomas include diverse mesenchymal neoplasms with widely varied prognosis, clinical behavior, and treatment. Owing to their rarity and histologic overlap, accurate diagnosis of sarcomas can be challenging. Our approach has evolved dramatically in the past few decades, where novel insights into the molecular pathogenetic basis for sarcomas has dramatically (re)shaped contemporary diagnosis, building on a largely morphology- and clinical presentation–based strategy. Examples include the introduction of novel immunohistochemical markers that serve as surrogates for molecular genetic alterations and identification of characteristic molecular alterations. Accordingly, cytogenetic and molecular genetic analyses, such as conventional karyotyping, fluorescence in situ hybridization, reverse transcription–polymerase chain reaction, and targeted sequencing, have increasingly been incorporated into the routine diagnostic work-up of these neoplasms. For those sarcomas with complex cytogenetic changes that lack specific alterations, additional testing is often directed toward identifying lines of differentiation and excluding pathognomonic (cyto-)genetic alterations. Although some gene rearrangements are diagnostic of particular sarcoma types, certain fusion partners, most notably EWSR1, are not tumor specific (and may, in fact, also be found in benign tumors). Correlation with clinical, radiologic, morphologic, and immunohistochemical findings is particularly important in tumors with such rearrangements to establish the correct diagnosis, acknowledging the inherent limitations of diagnostic tests. The recognition of sarcomas occurring in cancer predisposition syndromes is critical, with implications not only for the index patient but also potentially for family members, including the need for genetic counseling and sometimes particular types of surveillance. Together, contemporary sarcoma evaluation involves combining the initial morphologic evaluation with diagnostically relevant cytogenetic, molecular, and immunohistochemical testing methods.

The incidence, mutational status, risk classification and referral pattern of gastro-intestinal stromal tumours in the Netherlands: a nationwide pathology registry (PALGA) study

Symptomatic gastrointestinal stromal tumours (GIST) are infrequent with an incidence of 12.7 per million inhabitants in the western population. We studied whether the incidence of GIST has further increased between 2003 and 2012 and assessed the frequency of mutations, risk groups, histological subtypes and immunohistochemistry results. From PALGA, the nationwide Dutch Pathology Registry, pathology excerpts from all patients with a GIST or GIST-like tumour between 2003 and 2012 were retrieved to calculate incidence rates. Full pathology reports were retrieved of resections in 2011 and 2012 to study the frequency of mutations, risk groups, histological subtypes and immunohistochemistry results. The incidence of GIST increased to 17.7 per million inhabitants in 2012 with a median age of 67 years. Mutational analysis was performed in 33.9% of patients with a resection between 2011 and 2012 (KIT mutation 67.5%, PDGFRA 16.3%, wild-type 11.4%). The percentage of high risk patients in the different risk classifications varied from 19.9% to 38.0% depending on the used classification. Only 35.9% of patients had diagnosis or revision of pathology diagnosis within three months in a designated GIST referral centre. No increase in proportion of central pathology reviews was found. Proportion of patients with mutational analysis increased over the years. The registered incidence of GIST, 17.7 per million inhabitants in 2012 in the Netherlands, is still rising. Despite incorporation in the ESMO GIST guidelines since 2008 for mutational testing and since 2010 for central review of pathology, both are performed in a minority of patients.

What is New in Gastrointestinal Stromal Tumor?

The classification "gastrointestinal stromal tumor" (GIST) became commonplace in the 1990s and since that time various advances have characterized the GIST lineage of origin, tyrosine kinase mutations, and mechanisms of response and resistance to targeted therapies. In addition to tyrosine kinase mutations and their constitutive activation of downstream signaling pathways, GISTs acquire a sequence of chromosomal aberrations. These include deletions of chromosomes 14q, 22q, 1p, and 15q, which harbor putative tumor suppressor genes required for stepwise progression from microscopic, preclinical forms of GIST (microGIST) to clinically relevant tumors with malignant potential. Recent advances extend our understanding of GIST biology beyond that of the oncogenic KIT/PDGFRA tyrosine kinases and beyond mechanisms of KIT/PDGFRA-inhibitor treatment response and resistance. These advances have characterized ETV1 as an essential interstitial cell of Cajal-GIST transcription factor in oncogenic KIT signaling pathways, and have characterized the biologically distinct subgroup of succinate dehydrogenase deficient GIST, which are particularly common in young adults. Also, recent discoveries of MAX and dystrophin genomic inactivation have expanded our understanding of GIST development and progression, showing that MAX inactivation is an early event fostering cell cycle activity, whereas dystrophin inactivation promotes invasion and metastasis.

Gastrointestinal stromal tumor presenting as a right adnexal mass with histopathologic correlation

The authors report and discuss a rare case of a gastrointestinal stromal tumor (GIST) in a 35-year-old female, which was pre-procedurally characterized as a right ovarian mass by magnetic resonance imaging (MRI) features. This manuscript reviews the imaging and clinical features of GISTs with pathologic correlation, and emphasizes how this entity may present a diagnostic challenge in certain anatomic regions owing in large part to its exophytic nature. This case is unique among similarly reported cases in that there was a "claw sign" with the right ovary, which provided convincing evidence of its point of origin.

Update on Gastrointestinal Stromal Tumors for Radiologists

The management of gastrointestinal stromal tumors (GISTs) has evolved significantly in the last two decades due to better understanding of their biologic behavior as well as development of molecular targeted therapies. GISTs with exon 11 mutation respond to imatinib whereas GISTs with exon 9 or succinate dehydrogenase subunit mutations do not. Risk stratification models have enabled stratifying GISTs according to risk of recurrence and choosing patients who may benefit from adjuvant therapy. Assessing response to targeted therapies in GIST using conventional response criteria has several potential pitfalls leading to search for alternate response criteria based on changes in tumor attenuation, volume, metabolic and functional parameters. Surveillance of patients with GIST in the adjuvant setting is important for timely detection of recurrences.

MDCT and clinicopathological features of small bowel gastrointestinal stromal tumours in 102 patients: a single institute experience

OBJECTIVE

Small bowel (SB) is the second most common site of gastrointestinal stromal tumours (GISTs). We evaluated clinical presentation, pathology, imaging features and metastatic pattern of SB GIST.

METHODS

Imaging and clinicopathological data of 102 patients with jejunal/ileal GIST treated at Dana-Farber Cancer Institute and Brigham and Women's Hospital (Boston, MA) between 2002 and 2013 were evaluated. Imaging of treatment-naive primary tumour (41 patients) and follow-up imaging in all patients was reviewed.

RESULTS

90/102 patients were symptomatic at presentation, abdominal pain and lower gastrointestinal blood loss being the most common symptoms. On pathology, 21 GISTs were low risk, 17 were intermediate and 64 were high risk. The mean tumour size was 8.5 cm. On baseline CT (n = 41), tumours were predominantly well circumscribed, exophytic and smooth/mildly lobulated in contour. Of 41 tumours, 16 (39%) were homogeneous, whereas 25 (61%) were heterogeneous. Of the 41 tumours, cystic/necrotic areas (Hounsfield units < 20) were seen in 16 (39%) and calcifications in 9 (22%). CT demonstrated complications in 13/41 (32%) patients in the form of tumour-bowel fistula (TBF) (7/41), bowel obstruction (4/41) and intraperitoneal rupture (2/41). Amongst 102 total patients, metastases developed in 51 (50%) patients (27 at presentation), predominantly involving peritoneum (40/102) and liver (32/102). 7/8 (87%) patients having intraperitoneal rupture at presentation developed metastases. Metastases elsewhere were always associated with hepatic/peritoneal metastases. At last follow-up, 28 patients were deceased (median survival, 65 months).

CONCLUSION

SB GISTs were predominantly large, well-circumscribed, exophytic tumours with or without cystic/necrotic areas. Complications such as TBF, bowel obstruction and intraperitoneal perforation were visualized at presentation, with patients with perforation demonstrating a high risk of metastatic disease. Exophytic eccentric bowel wall involvement and lack of associated adenopathy are useful indicators to help differentiate GISTs from other SB neoplasms.

ADVANCES IN KNOWLEDGE

SB GISTs are predominantly large, well-circumscribed, exophytic tumours, and may present with complications. They often are symptomatic at presentation, are high risk on pathology and metastasize to the peritoneum more commonly than the liver.

An update on the application of newly described immunohistochemical markers in soft tissue pathology

CONTEXT

During the last 5 to 10 years, significant progress has been made in the molecular characterization of soft tissue tumors, predominantly with the identification of recurrent translocations or amplification of certain genes in different tumor types. Alongside this, translational efforts have identified many novel and diagnostically useful immunohistochemical markers for many of these tumor types.

OBJECTIVE

This article reviews a select group of recently described immunohistochemical markers of particular use in the evaluation of mesenchymal neoplasms; the underlying biology of the protein product, practical utility, and limitations of each marker are discussed in detail.

DATA SOURCES

Literature review, authors' research data, and personal practice experience serve as sources.

CONCLUSIONS

There are many diagnostically useful immunohistochemical markers to help confirm the diagnosis of many different soft tissue tumor types, some of which have reduced the need for additional, and more costly, studies, such as fluorescence in situ hybridization. However, no one marker is 100% specific for a given tumor, and knowledge of potential pitfalls and overlap in patterns of staining among other tumor types is crucial to ensure the appropriate application of these markers in clinical practice.

Fluid retention associated with imatinib treatment in patients with gastrointestinal stromal tumor: quantitative radiologic assessment and implications for management

Objective

We aimed to describe radiologic signs and time-course of imatinib-associated fluid retention (FR) in patients with gastrointestinal stromal tumor (GIST), and its implications for management.

Materials and Methods

In this Institutional Review Board-approved, retrospective study of 403 patients with GIST treated with imatinib, 15 patients with imaging findings of FR were identified by screening radiology reports, followed by manual confirmation. Subcutaneous edema, ascites, pleural effusion, and pericardial effusion were graded on a four-point scale on CT scans; total score was the sum of these four scores.

Results

The most common radiologic sign of FR was subcutaneous edema (15/15, 100%), followed by ascites (12/15, 80%), pleural effusion (11/15, 73%), and pericardial effusion (6/15, 40%) at the time of maximum FR. Two distinct types of FR were observed: 1) acute/progressive FR, characterized by acute aggravation of FR and rapid improvement after management, 2) intermittent/steady FR, characterized by occasional or persistent mild FR. Acute/progressive FR always occurred early after drug initiation/dose escalation (median 1.9 month, range 0.3-4.0 months), while intermittent/steady FR occurred at any time. Compared to intermittent/steady FR, acute/progressive FR was severe (median score, 5 vs. 2.5, p = 0.002), and often required drug-cessation/dose-reduction.

Conclusion

Two distinct types (acute/progressive and intermittent/steady FR) of imatinib-associated FR are observed and each type requires different management.

Select biomarkers for tumors of the gastrointestinal tract: present and future

CONTEXT

Advances in molecular biomarkers of the gastrointestinal tract have contributed to a decline in the incidence of and mortality from diseases of the gastrointestinal tract. The discovery and clinical validation of new biomarkers are important to personalized cancer therapy, and numerous clinical trials are currently ongoing to help identify individualized therapy affecting these biomarkers and molecular mechanisms they represent. Distinct molecular pathways leading to cancers of the colorectum, esophagus, stomach, small bowel, and pancreas have been identified. Using biomarkers in these pathways to direct patient care, including selection of proper molecular testing for identification of actionable mutations and reporting the results of these biomarkers to guide clinicians and genetic counselors, is paramount.

OBJECTIVE

To examine and review select clinically actionable biomarkers of the colon, esophagus, stomach, small bowel, and pancreas, including present and future biomarkers with relevant clinical trials.

DATA SOURCES

Extensive literature review and practical and consultation experience of the authors.

CONCLUSIONS

Although numerous biomarkers have been identified and are currently guiding patient therapy, few have shown evidence of clinical utility in the management of patients with gastrointestinal cancers. Inconsistent results and discordant proposed algorithms for testing were identified throughout the literature; however, the potential for biomarkers to improve outcomes for patients with gastrointestinal cancer remains high. Continued advances through high-quality studies are needed.

MDCT features of succinate dehydrogenase (SDH)-deficient gastrointestinal stromal tumours

OBJECTIVE

To describe the multidetector CT (MDCT) features and metastatic pattern of succinate dehydrogenase (SDH)-deficient gastrointestinal stromal tumours (GISTs).

METHODS

In this institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study, we retrospectively identified 34 patients (20 females; mean age, 34 years; range, 12-59 years) with histopathology-confirmed SDH-deficient GIST, who were seen at our institution from 1999 through 2012. MDCT of primary tumour in 8 patients and follow-up imaging in all 34 patients over median follow-up of 106 months [interquartile range (IQR), 52-175 months] were reviewed by two radiologists in consensus. Clinical information was extracted from electronic medical records.

RESULTS

Primary tumour in all 34 patients was located in the stomach. Mean tumour size (n = 8) was 9.6 cm (range, 8-14 cm). Primary tumours were lobulated, variable in growth pattern, hypo- (1/8) to isodense (7/8) and similar in enhancement to the skeletal muscle. Two were multifocal, four of eight had necrosis and one of eight had haemorrhage. Tumour rupture with haemoperitoneum and tumour-bowel fistula was noted in one patient each. During follow-up, 12/34 patients developed tumour in surgical bed, and 28/34 patients developed metastases. Most common sites of metastases were the liver (24/34), peritoneum (20/34) and lymph nodes (18/34). Carney triad and Carney-Stratakis syndrome were noted in 5/34 and 1/34 patients, respectively. At the time of writing, six patients had deceased at a median interval of 109 months (IQR, 54-126 months).

CONCLUSION

SDH-deficient GISTs occur in young patients, commonly arise in stomach, can be multifocal and may be associated with Carney triad or Carney-Stratakis syndrome. They frequently metastasize to lymph nodes in addition to the liver and peritoneum and are associated with indolent course despite metastatic spread.

ADVANCES IN KNOWLEDGE

The presence of features unusual for conventional GIST on imaging should alert the radiologist for the possibility of SDH-deficient GIST, especially, because SDH-deficient GISTs are resistant to imatinib. Young age at diagnosis, prolonged survival, association with Carney triad and Carney-Stratakis syndrome and occurrence of concurrent renal cell carcinoma and thyroid malignancies necessitates long-term follow-up of patients with SDH-deficient GISTs.

Sarcoma classification: an update based on the 2013 World Health Organization Classification of Tumors of Soft Tissue and Bone

The 2013 World Health Organization Classification of Tumors of Soft Tissue and Bone incorporates changes in tumor classification, as well as new genetic insights into the pathogenesis of many different tumor types that have emerged over the 11 years since the publication of the prior volume. This article reviews changes in the classification of soft tissue and bone sarcomas as well as tumors of intermediate biologic potential in the 2013 World Health Organization volume, new molecular insights into these tumors, and associated surgical and clinical implications.

Succinate dehydrogenase deficiency is associated with decreased 5-hydroxymethylcytosine production in gastrointestinal stromal tumors: implications for mechanisms of tumorigenesis

Gastrointestinal stromal tumors (GISTs) usually harbor activating mutations in KIT or PDGFRA, which promote tumorigenesis through activation of growth factor receptor signaling pathways. Around 15% of GISTs in adults and >90% in children lack such mutations ('wild-type' GISTs). Most gastric wild-type GISTs show loss of function of the Krebs cycle enzyme complex succinate dehydrogenase (SDH). However, the mechanism by which SDH deficiency drives tumorigenesis is unclear. Loss of SDH leads to succinate accumulation, which is thought to inhibit α-ketoglutarate-dependent dioxygenase enzymes, such as the TET family of DNA hydroxylases. TET proteins catalyze the conversion of 5-methylcytosine to 5-hydroxymethylcytosine (5-hmC), which is required for subsequent DNA demethylation. Thus, TET-mediated 5-hmC production alters global DNA methylation patterns and may thereby influence gene expression. We investigated 5-hmC levels in a cohort of genotyped GISTs to determine whether loss of SDH was associated with inhibition of TET activity. 5-hmC levels were examined via immunohistochemistry in a cohort of 30 genotyped GISTs, including 10 SDH-deficient tumors (5 SDHA mutant; 1 SDHB mutant; 1 SDHC mutant; 3 unknown), 14 tumors with KIT mutations (10 in exon 11; 3 in exon 9; 1 in exon 17), and 6 tumors with PDGFRA mutations (all in exon 18). Staining for 5-hmC was negative in 9 of 10 (90%) SDH-deficient GISTs, 3 of 14 (21%) KIT-mutant GISTs, and 1 of 6 (17%) PDGFRA-mutant GISTs. The other SDH-deficient GIST showed weak staining for 5-hmC. Thus, 5-hmC was absent in nearly all SDH-deficient GISTs. These findings suggest that SDH deficiency may promote tumorigenesis through accumulation of succinate and inhibition of dioxygenase enzymes. Inhibition of TET activity may, in turn, alter global DNA methylation and gene expression in SDH-deficient tumors.

Behavior of advanced gastrointestinal stromal tumor in a patient with von-Recklinghausen disease: Case report

Gastrointestinal stromal tumors (GISTs) represent a malignant gastrointestinal tumor of neurofibromatosis type 1 (NF1) Von Recklinghausen disease. In the current case, we report a 27-year-old woman with NF1, who presented with a lower abdominal mass, symptomatic anaemia, and significant weight loss. We employed multiple approaches to assess the tumor behavior, including computed tomography (CT) scan, surgical tumor resection, histological and immunohistochemical analysis and gene sequencing. Additionally, the patient was given Imatinib mesylate (Gleevec) as adjuvant therapy. CT scan delineated a large thick wall cavity lesion connecting to the small bowel segment. Resection of the tumor yielded a mass of 17 cm × 13 cm with achievement of safety margins. The diagnosis was GIST, confirmed by immunohistochemical expression of CD117, CD34, and Bcl-2. Sequencing revealed no mutations in either KIT or platelet-derived growth factor receptor-alpha, genes which are mutated in over 85% of sporadic GIST cases. Further, there was no evidence of recurrence, metastasis or metachronous GIST for over three years in our patient. From our analyses, we believe selective genotyping is advisable for high risk patients to predict potential tumor behavior.

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

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

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.