Syndromic gastrointestinal stromal tumors

Identifying and managing rare subtypes of gastrointestinal stromal tumors

INTRODUCTION

A subset of gastrointestinal stromal tumors (GISTs) lacks the common mutations in KIT/PDGFRa genes. This is a rare and heterogeneous group of challenging GISTs due to their diversity and absence of sensitivity to the tyrosine kinase inhibitor (TKI) imatinib.

AREAS COVERED

In this manscript, we review the pathogenesis, natural history, diagnostic features and management of KIT/PDGFRa wild-type (WT) GISTs, including SDH-deficient GISTs, GISTs with mutations in the RAS/RAF pathway, and quadruple WT GISTs which lack mutations in either KIT/PDGFRa and SDH genes or components of the RAS/RAF pathway, and syndromic GISTs as well as GISTs with rare KIT/PDGFRa mutations.

EXPERT OPINION

Patients should be managed in reference centers. There has been progress in the understanding of the biology of these GISTs, and promising therapeutic targets have been identified. In SDH-deficient GISTs, the TKI olverembatinib has shown encouraging clinical activity but requires further clinical validation, while the HIF2a inhibitor bezultifan and temozolomide alone or in combination with the death receptor agonist 5 are under clinical investigation. Targeting the RAS/RAF pathway in RAS/RAF-mutated GISTs warrants evaluation in clinical trials. Rare molecular alterations in quadruple WT GISTs require investigation for their oncogenic potential. Collaborative research and patient advocacy is critical for these extremely rare tumors.

Clinical description and development of a prognostic score for neurofibromatosis type 1 (NF1)-associated GISTs: a retrospective study from the NETSARC

BACKGROUND

Gastrointestinal stromal tumors (GISTs) occur in ∼7% of neurofibromatosis type 1 (NF1) patients. Data about their natural history remain scarce and neither risk classifications, prognosis model nor adjuvant treatment have been validated in this population.

METHODS

This national retrospective study included consecutive operated NF1-GIST cases from 31 reference centers in France, mostly from the NETSARC+ network. Factors associated with relapse were used to build a new prognostic score (RECKGIST). To address potential bias between adjuvant group and follow-up group, a propensity score was used.

RESULTS

A total of 119 patients were included between 2008 and 2023, of whom 61% were women. Median age was 53 years (range 20-78 years). The main primary location was the small bowel (86%) and the stomach (11%). Median size and mitotic count (mit) were 45 mm [95% confidence interval (CI) 45-58 mm] and 2 mit/5 mm2 (95% CI 3-9 mit/5 mm2), respectively. The vast majority were KIT/PDGFRA wild type (mutation KIT 2%, PDGFRA 3%). The median follow-up was 6 years. For GISTs <30 mm (n = 35), none relapsed. For GISTS >30 mm (n = 84), 18 developed metastases (21%). There was no difference in relapse according to tumor location (P = 0.45) or tumor rupture (P = 0.11), whereas KIT/PDGFRA-mutated GISTs were at higher risk of relapse [recurrence-free survival (RFS) at 10 years of 30% versus 82.5% for wild type, P = 0.03]. Miettinen and Joensuu classification did not predict relapse accurately. For the RECKGIST score A (size ≤30 mm, n = 34) group, 10-year RFS was 100%; it was 78.5% in the RECKGIST B group (size >30 mm and 0 < mit ≤ 5, n = 60), and 45.5% in the RECKGIST C group (size >30 mm and mit >5, n = 20) (P < 0.0001). After matching, 10-year RFS was similar between adjuvant and surveillance groups (P = 0.34).

CONCLUSIONS

For NF1-GISTs <30 mm, prognosis without relapse is excellent. RECKGIST score accurately predicts recurrence and needs to be validated in an external cohort, but it may help treatment decision making. No efficacy of adjuvant treatment was observed.

Pediatric cancer predisposition syndromes involving non-central nervous system solid pediatric tumors: a review on their manifestations with a focus on histopathology

Germline genetic alterations and their associated cancer predisposition syndromes (CPS) are an important cause of pediatric cancer. Early recognition is of great importance for targeted surveillance, early detection, and prompt (personalized) therapeutic interventions. This review provides an overview of non-central nervous system solid pediatric tumor types, in relation to their associated CPS, with an emphasis on their histology. It serves as a guide for (pediatric) pathologists to increase their awareness of histological clues that suggest a CPS and warrant referral to the clinical geneticist.

Molecular Profiling of KIT/PDGFRA-Mutant and Wild-Type Gastrointestinal Stromal Tumors (GISTs) with Clinicopathological Correlation: An 18-Year Experience at a Tertiary Center in Kuwait

In gastrointestinal stromal tumors (GISTs), identifying prototypical mutations in the KIT/PDGFRA oncogenes, or in rare alternate genes, is essential for prognostication and predicting response to tyrosine kinase inhibitors. Conversely, wild-type GISTs (WT-GIST), which lack known mutations, have limited treatment options. Data on the mutational landscape of GISTs and their impact on disease progression are very limited in Kuwait. Using a targeted next-generation sequencing panel, we investigated the spectrum and frequency of KIT, PDGFRA, and RAS-pathway-related mutations in 95 out of 200 GISTs diagnosed at Kuwait Cancer Center from 2005 to 2023 and assessed their correlation with clinicopathological parameters. Among the 200 tumors (median age 55 years; 15-91), 54% originated in the stomach, 33% in the small bowel, 7% in the colorectum, 1.5% in the peritoneum, and 4.5% had an unknown primary site. Of the 95 molecularly profiled cases, 88% had a mutation: KIT (61%), PDGFRA (25%), NF1 (2%), and one NTRK1 rearrangement. Ten WT-GISTs were identified (stomach = 6, small bowel = 2, and colorectum = 2). WT-GISTs tended to be smaller (median 4.0 cm; 0.5-8.0) (p = 0.018), with mitosis ≤5/5 mm2, and were of lower risk (p = 0.019). KIT mutations were an adverse indicator of disease progression (p = 0.049), while wild-type status did not significantly impact progression (p = 0.934). The genetic landscape in this cohort mirrors that of global studies, but regional collaborations are needed to correlate outcomes with genetic variants.

English version of Japanese Clinical Practice Guidelines 2022 for gastrointestinal stromal tumor (GIST) issued by the Japan Society of Clinical Oncology

The Japan Society of Clinical Oncology Clinical Practice Guidelines 2022 for gastrointestinal stromal tumor (GIST) have been published in accordance with the Minds Manual for Guideline Development 2014 and 2017. A specialized team independent of the working group for the revision performed a systematic review. Since GIST is a rare type of tumor, clinical evidence is not sufficient to answer several clinical and background questions. Thus, in these guidelines, we considered that consensus among the experts who manage GIST, the balance between benefits and harms, patients' wishes, medical economic perspective, etc. are important considerations in addition to the evidence. Although guidelines for the treatment of GIST have also been published by the National Comprehensive Cancer Network (NCCN) and the European Society for Medical Oncology (ESMO), there are some differences between the treatments proposed in those guidelines and the treatments in the present guidelines because of the differences in health insurance systems among countries.

[Gastrointestinal stromal tumors : Where do we stand?]

For more than 20 years gastrointestinal stromal tumors (GIST) have been a paradigm for a targeted treatment with tyrosine kinase inhibitors. A fundamental prerequisite for a neoadjuvant or adjuvant treatment of localized GIST or an additive treatment of metastatic GIST is the molecular typing of tumors, ideally at the initial diagnosis. In addition, the possibility of a hereditary or syndromic predisposition must be considered because this results in consequences for the treatment and a different follow-up strategy.

Sarco/endoplasmic reticulum calcium ATPase 3 (SERCA3) expression in gastrointestinal stromal tumours

Accurate characterisation of gastrointestinal stromal tumours (GIST) is important for prognosis and the choice of targeted therapies. Histologically the diagnosis relies on positive immunostaining of tumours for KIT (CD117) and DOG1. Here we report that GISTs also abundantly express the type 3 Sarco/Endoplasmic Reticulum Calcium ATPase (SERCA3). SERCA enzymes transport calcium ions from the cytosol into the endoplasmic reticulum and play an important role in regulating the intensity and the periodicity of calcium-induced cell activation. GISTs from various localisations, histological and molecular subtypes or risk categories were intensely immunopositive for SERCA3 with the exception of PDGFRA-mutated cases where expression was high or moderate. Strong SERCA3 expression was observed also in normal and hyperplastic interstitial cells of Cajal. Decreased SERCA3 expression in GIST was exceptionally observed in a zonal pattern, where CD117 staining was similarly decreased, reflecting clonal heterogeneity. In contrast to GIST, SERCA3 immunostaining of spindle cell tumours and other gastrointestinal tumours resembling GIST was negative or weak. In conclusion, SERCA3 immunohistochemistry may be useful for the diagnosis of GIST with high confidence, when used as a third marker in parallel with KIT and DOG1. Moreover, SERCA3 immunopositivity may be particularly helpful in cases with negative or weak KIT or DOG1 staining, a situation that may be encountered de novo, or during the spontaneous or therapy-induced clonal evolution of GIST.

Precision Oncology in Soft Tissue Sarcomas and Gastrointestinal Stromal Tumors

Soft tissue sarcomas (STSs), including gastrointestinal stromal tumors (GISTs), are mesenchymal neoplasms with heterogeneous clinical behavior and represent broad categories comprising multiple distinct biologic entities. Multidisciplinary management of these rare tumors is critical. To date, multiple studies have outlined the importance of biological characterization of mesenchymal tumors and have identified key molecular alterations which drive tumor biology. GIST has represented a flagship for targeted therapy in solid tumors with the advent of imatinib which has revolutionized the way we treat this malignancy. Herein, the authors discuss the importance of biological and molecular diagnostics in managing STS and GIST patients.

Exploring Perforated Jejunal GIST: A Rare Case Report and Review of Molecular and Clinical Literature

This case report details a rare instance of a perforated jejunal gastrointestinal stromal tumor (GIST) in a 76-year-old female patient. The patient presented with acute abdominal pain and distension without any changes in bowel habits or episodes of nausea and vomiting. Initial diagnostics, including abdominal plain radiography and ultrasonography, were inconclusive; however, a computed tomography (CT) scan revealed pneumoperitoneum and an irregular fluid collection suggestive of small intestine perforations. Surgical intervention uncovered a 35 mm jejunal GIST with a 10 mm perforation. Histopathological examination confirmed a mixed cell type GIST with high malignancy potential, further substantiated by immunohistochemistry markers CD117, DOG1, and vimentin. Molecular analysis illuminated the role of key oncogenes, primarily KIT and PDGFRA mutations, emphasizing the importance of molecular diagnostics in GIST management. Despite the severity of the presentation, the patient's postoperative recovery was favorable, highlighting the effectiveness of prompt surgical and multidisciplinary approaches in managing complex GIST cases.

Diagnosis, Treatment, and Prognosis of Patients with Primary Familial Gastrointestinal Stromal Tumor: A Case Report and Literature Review

Gastrointestinal stromal tumors are the most common mesenchymal tumors of the digestive tract, most of which are sporadic, and familial GISTs with germline mutations are rarely seen. Here, we report a 26-year-old female with a germline p. W557R mutation in exon 11 of the KIT gene. The proband and her father and sister presented with multifocal GIST and pigmented nevi. All 3 patients underwent surgery and imatinib therapy. To date, only 49 kindreds with germline KIT mutations and 6 kindreds with germline PDGFRA mutations have been reported. Summarizing the reported kindreds, the majority of familial GISTs manifest as multiple primary GISTs complicated with special clinical manifestations, including cutaneous hyperpigmentation, dysphagia, mastocytosis, inflammatory fibrous polyps, and large hands. Familial GISTs are generally thought to exhibit TKI sensitivity similar to that of sporadic GISTs with the same mutation.

Neurofibromatosis- and schwannomatosis-associated tumors: Approaches to genetic testing and counseling considerations

Neurofibromatosis (NF) and schwannomatosis (SWN) are genetic conditions characterized by the risk of developing nervous system tumors. Recently revised diagnostic criteria include the addition of genetic testing to confirm a pathogenic variant, as well as to detect the presence of mosaicism. Therefore, the use and interpretation of both germline and tumor-based testing have increasing importance in the diagnostic approach, treatment decisions, and risk stratification of these conditions. This focused review discusses approaches to genetic testing of NF- and SWN-related tumor types, which are somewhat rare and perhaps lesser known to non-specialized clinicians. These include gastrointestinal stromal tumors, breast cancer, plexiform neurofibromas with or without transformation to malignant peripheral nerve sheath tumors, gliomas, and schwannomas, and emphasizes the need for inclusion of genetic providers in patient care and appropriate pre- and post-test education, genetic counseling, and focused evaluation by a medical geneticist or other healthcare provider familiar with clinical manifestations of these disorders.

Surgical Management of Germline Gastrointestinal Stromal Tumor

Gastrointestinal stromal tumor (GIST) is the most common human sarcoma and usually results from a sporadic mutation in KIT or, less frequently, platelet-derived growth factor alpha (PDGFRA). Rarely, a germline mutation in the KIT, PDGFRA, succinate dehydrogenase (SDH), or neurofibromatosis 1 (NF1) gene is responsible for GIST. These tumors are found in the stomach (PDGFRA and SDH), small bowel (NF1), or a combination of both (KIT). There is a need to improve care for these patients regarding genetic testing, screening, and surveillance. Since most GISTs due to a germline mutation do not respond to tyrosine kinase inhibitors, the role of surgery is critical, especially when considering germline gastric GIST. However, in contrast to the established recommendation for prophylactic total gastrectomy in cadherin 1 (CDH1) mutation carriers once they reach adulthood, there are no formal guidelines as to the timing or extent of surgical resection for patients who are either carriers of a germline GIST mutation causing gastric GIST or have already developed gastric GIST(s). Surgeons must balance treating what is often multicentric, yet initially indolent disease with the chance of cure and the complications associated with total gastrectomy. Here, we consider the major issues in performing surgery in patients with germline GIST and illustrate the principles with a previously unreported patient harboring a germline KIT 579 deletion.

Characterization of cell line with dedifferentiated GIST-like features established from cecal GIST of familial GIST model mice

Approximately 40 families with multiple gastrointestinal stromal tumors (GISTs) and germline c-kit gene mutations have been reported. Three knock-in mouse models have been generated, and all the models showed a cecal GIST. In the present study, we established a cell line derived from cecal GIST in a familial GIST model mouse with KIT-Asp818Tyr. Since the established cells showed spindle-shaped morphology with atypical nuclei, and since immunohistochemistry revealed that they were positive for α-SMA but negative for KIT, CD34 and desmin, the phenotypes of the cells were reminiscent of dedifferentiated GIST-like ones but not the usual GIST-like ones. Gene expression analysis showed that the cell line, designated as DeGISTL1 cell, did not express c-kit gene apparently, but highly expressed HSP90 families and glutaminase 1. Pathway analysis of the cells revealed that metabolic pathway might promote their survival and growth. Pimitespib, a heat shock protein 90α/β inhibitor, and Telaglenastat, a selective glutaminase 1 inhibitor, inhibited proliferation of DeGISTL1 cells and the combination of these showed an additive effect. DeGISTL1 cells might be a good model of dedifferentiated GISTs, and combination of Pimitespib and Telaglenastat could be a possible candidate for treatment strategy for them.

Emerging Targeted Therapeutic Strategies to Overcome Imatinib Resistance of Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are the most common malignant mesenchymal neoplasms of the gastrointestinal tract. The gold standard for the diagnosis of GISTs is morphologic analysis with an immunohistochemical evaluation plus genomic profiling to assess the mutational status of lesions. The majority of GISTs are driven by gain-of-function mutations in the proto-oncogene c-KIT encoding the tyrosine kinase receptor (TKR) known as KIT and in the platelet-derived growth factor-alpha receptor (PDGFRA) genes. Approved therapeutics are orally available as tyrosine kinase inhibitors (TKIs) targeting KIT and/or PDGFRA oncogenic activation. Among these, imatinib has changed the management of patients with unresectable or metastatic GISTs, improving their survival time and delaying disease progression. Nevertheless, the majority of patients with GISTs experience disease progression after 2-3 years of imatinib therapy due to the development of secondary KIT mutations. Today, based on the identification of new driving oncogenic mutations, targeted therapy and precision medicine are regarded as the new frontiers for GISTs. This article reviews the most important mutations in GISTs and highlights their importance in the current understanding and treatment options of GISTs, with an emphasis on the most recent clinical trials.

Molecular Mechanisms of Gastrointestinal Stromal Tumors and Their Impact on Systemic Therapy Decision

Gastrointestinal stromal tumors (GISTs) are soft tissue sarcomas that mostly derive from Cajal cell precursors. They are by far the most common soft tissue sarcomas. Clinically, they present as gastrointestinal malignancies, most often with bleeding, pain, or intestinal obstruction. They are identified using characteristic immunohistochemical staining for CD117 and DOG1. Improved understanding of the molecular biology of these tumors and identification of oncogenic drivers have altered the systemic treatment of primarily disseminated disease, which is becoming increasingly complex. Gain-of-function mutations in KIT or PDGFRA genes represent the driving mutations in more than 90% of all GISTs. These patients exhibit good responses to targeted therapy with tyrosine kinase inhibitors (TKIs). Gastrointestinal stromal tumors lacking the KIT/PDGFRA mutations, however, represent distinct clinico-pathological entities with diverse molecular mechanisms of oncogenesis. In these patients, therapy with TKIs is hardly ever as effective as for KIT/PDGFRA-mutated GISTs. This review provides an outline of current diagnostics aimed at identifying clinically relevant driver alterations and a comprehensive summary of current treatments with targeted therapies for patients with GISTs in both adjuvant and metastatic settings. The role of molecular testing and the selection of the optimal targeted therapy according to the identified oncogenic driver are reviewed and some future directions are proposed.

Expanded genetic testing of GIST patients identifies high proportion of non-syndromic patients with germline alterations

Traditional genetic testing for patients with gastrointestinal stromal tumors (GISTs) focus on those with syndromic features. To assess whether expanded genetic testing of GIST patients could identify hereditary cancer predisposition, we analyzed matched tumor-germline sequencing results from 103 patients with GISTs over a 6-year period. Germline pathogenic/likely pathogenic (P/LP) variants in GIST-associated genes (SDHA, SDHB, SDHC, NF1, KIT) were identified in 69% of patients with KIT/PDGFRA-wildtype GISTs, 63% of whom did not have any personal or family history of syndromic features. To evaluate the frequency of somatic versus germline variants identified in tumor-only sequencing of GISTs, we analyzed 499 de-identified tumor-normal pairs. P/LP variants in certain genes (e.g., BRCA1/2, SDHB) identified in tumor-only sequencing of GISTs were almost exclusively germline in origin. Our results provide guidance for genetic testing of GIST patients and indicate that germline testing should be offered to all patients with KIT/PDGFRA-wildtype GISTs regardless of their history of syndromic features.

KIT-Associated Familial GIST Syndrome: Response to Tyrosine Kinase Inhibitors and Implications for Risk Management

Sporadic gastrointestinal stromal tumors (GIST) are rare tumors, with a median age at diagnosis of 60 years. Familial GISTs are very rare and typically associated with earlier onset, with an average age at diagnosis of 48 years. To date, just over 50 familial cases associated with a germline variant KIT or PDGFRa genes have been published. Therefore, there are many challenges in managing these patients, including the timing of starting systemic treatment, considering that most patients have been asymptomatic for a long period before being diagnosed, as well as the choice of tyrosine kinase inhibitor and the plan for surveillance.

It is uncertain if early diagnosis through screening of asymptomatic individuals improves overall survival. Screening could start from the age of 18 years but may be considered at earlier ages depending on the underlying genotype and family history. The long-term benefit of early diagnosis or palliative/prophylactic treatment with tyrosine kinase inhibitors is unknown as there are no data available. Long-term side effects of treatment with imatinib are rare but well documented and could be damaging in patients who have no or minimal disease.

We present the case of a 53-year-old Caucasian patient who was diagnosed with multifocal GIST and subsequently found to be a carrier of a pathogenic germline KIT variant in exon 11. We discuss the implication of treatment and genetic testing in this case and in familial KIT associated GISTs.

Noncoding RNAs in Drug Resistance of Gastrointestinal Stromal Tumor

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor in the gastrointestinal tracts and a model for the targeted therapy of solid tumors because of the oncogenic driver mutations in KIT and PDGDRA genes, which could be effectively inhibited by the very first targeted agent, imatinib mesylate. Most of the GIST patients could benefit a lot from the targeted treatment of this receptor tyrosine kinase inhibitor. However, more than 50% of the patients developed resistance within 2 years after imatinib administration, limiting the long-term effect of imatinib. Noncoding RNAs (ncRNAs), the non-protein coding transcripts of human, were demonstrated to play pivotal roles in the resistance of various chemotherapy drugs. In this review, we summarized the mechanisms of how ncRNAs functioning on the drug resistance in GIST. During the drug resistance of GIST, there were five regulating mechanisms where the functions of ncRNAs concentrated: oxidative phosphorylation, autophagy, apoptosis, drug target changes, and some signaling pathways. Also, these effects of ncRNAs in drug resistance were divided into two aspects. How ncRNAs regulate drug resistance in GIST was further summarized according to ncRNA types, different drugs and categories of resistance. Moreover, clinical applications of these ncRNAs in GIST chemotherapies concentrated on the prognostic biomarkers and novel therapeutic targets.

[Abdominal soft tissue tumors]

Gastrointestinal stromal tumors are the most common mesenchymal tumors in the abdomen and occur in Germany with an incidence of 10 to 15 cases per million inhabitants. Clear identification and characterization are of major importance for the prognosis and therapy of patients. Similarly, they have to be differentiated from other mesenchymal neoplasias such as leiomyomatous, neurogenic, adipocytic, and fibroblastic tumors. Additionally, the number of translocation positive neoplasias is increasing, requiring the use of adequate molecular assays. The aim of this paper is to give practical advice for their identification. Reference pathology is one possibility to support the correct diagnosis.

Unusual Presentation of a Gastrointestinal Stromal Tumor in a Small Intestine Diverticulum

A 50-year-old female with no significant medical history initially presented to an urgent care center with symptoms of acute onset abdominal pain, nausea, and emesis. Chest and abdominal X-ray revealed free air under the diaphragm, prompting immediate transfer to the emergency department. Continued abdominal tenderness and pain were concerning for perforated viscus. The patient was transferred to the operating room, and diagnostic laparoscopy was performed. Inflammation and contamination were discovered in the right side of the abdomen and pelvis secondary to a small bowel (SB) perforation. Segmental SB resection revealed a perforated diverticulum. Pathological examination confirmed a diagnosis of gastrointestinal stromal tumor (GIST) at the perforated segment. On postoperative day 5, the patient was discharged home, and at 30-month follow-up, the patient continued to do well. Although rare, SB diverticula are commonly false (i.e., pseudodiverticula). The concomitant presence of a GIST in a true SB diverticulum presenting with perforation has not yet been reported.

Pimitespib is effective on cecal GIST in a mouse model of familial GISTs with KIT-Asp820Tyr mutation through KIT signaling inhibition

Three families with multiple gastrointestinal stromal tumors (GISTs) caused by a germline Asp820Tyr mutation at exon 17 of the c-kit gene (KIT-Asp820Tyr) have been reported. We previously generated a knock-in mouse model of the family, and the mice with KIT-Asp818Tyr corresponding to human KIT-Asp820Tyr showed a cecal tumor equivalent to human GIST. In the model mice, we reported that tyrosine kinase inhibitor, imatinib, could stabilize but not decrease the cecal tumor volume. In this report, we examined whether a heat shock protein 90 inhibitor, pimitespib (TAS-116), has an inhibitory effect on phosphorylation of KIT-Asp818Tyr and can decrease the cecal tumor volume in the model mice. First, we showed that pimitespib inhibited KIT phosphorylation both dose- and time-dependently in KIT-Asp818Tyr transfected murine Ba/F3 cells. Then, four 1-week courses of pimitespib were orally administered to heterozygous (KIT-Asp818Tyr/+) model mice. Each course consisted of once-daily administration for consecutive 5 days followed by 2 days-off. Cecal tumors were dissected, and tumor volume was histologically analyzed, Ki-67 labeling index was immunohistochemically examined, and apoptotic figures were counted. Compared to the vehicle treated mice, pimitespib administered mice showed statistically significantly smaller cecal tumor volume, lower Ki-67 labeling index, and higher number of apoptotic figures in 10 high power fields (P = 0.0344, P = 0.0019 and P = 0.0269, respectively). Western blotting revealed that activation of KIT signaling molecules was strongly inhibited in the tumor tissues of pimitespib-administered mice compared to control mice. Thus, pimitespib seemed to inhibit in vivo tumor progression effectively in the model mice. These results suggest that the progression of multiple GISTs in patients with germline KIT-Asp820Tyr might be controllable by pimitespib.

The Mechanisms for the Association of Cancer and Esophageal Dysmotility Disorders

BACKGROUND

Achalasia and other esophageal dysmotility disorders mimicking achalasia can be associated with cancer. This study aimed to review the main mechanisms for which cancer may develop in esophageal dysmotility disorder patients.

METHODS

A narrative review was performed.

RESULTS

The mechanism for developing squamous cell carcinoma and adenocarcinoma are discussed. Besides, achalasia-like syndromes related to familial KIT-gene mutation and pseudoachalasia are discussed.

CONCLUSIONS

Knowing the main mechanism for which achalasia can be related to cancer is essential for clinicians to conduct the proper investigation, surveillance, and treatment.

Gastrointestinal Stromal Tumor in Monozygotic Twins Shows Distinct Mutational Status: A Case Report

Case series

Patients: Female, 62-year-old • Female, 62-year-old

Final Diagnosis: Gastrointestinal stromal tumor (GIST)

Symptoms: Abdominal pain • fatigue

Medication: —

Clinical Procedure: Genetic analysis

Specialty: Oncology

Diagnosis of digestive system tumours

The WHO Classification of Tumours provides the international standards for the classification and diagnosis of tumours. It enables direct comparisons to be made between different countries. In the new fifth edition, the series has gone digital with the launch of a website as well as a series of books, known widely as the WHO Blue Books. The first volume to be produced is on the classification of Digestive System tumours, replacing the successful 2010 version. It has been rewritten and updated accordingly. This article summarises the major diagnostic innovations that have occurred over the last decade and that have now been incorporated in the classification. As an example, it incorporates the recently proposed classification of neuroendocrine tumours, based on the recognition that neuroendocrine tumours and carcinomas differ substantially in the genetic abnormalities that drive their growth, findings relevant to treatment selection and outcome prediction. Several themes have emerged during the production process. One is the importance of the progression from hyperplasia to dysplasia to carcinoma in the evolution of the malignant process. Advances in imaging techniques and endoscopy have resulted in enhanced access to precancerous lesions in the gastrointestinal and biliary tract, necessitating both changes in classification schema and clinical practice. Diagnosis of tumours is no longer the sole purview of pathologists, and some patients now receive treatment before tissue is obtained, based on clinical, radiological and liquid biopsy results. This makes the classification relevant to many disciplines involved in the care of patients with tumours of the digestive system.

Significance of Primary Malignant Tumors on the Outcome of Patients With Resected Gastrointestinal Stromal Tumors

AIM

This study aimed to clarify the significance of primary malignant tumors for the outcome of resected gastrointestinal stromal tumors (GISTs).

PATIENTS AND METHODS

The medical history, pathological findings and prognosis of 66 patients with GISTs resected at our institute between January 2003 and December 2018 were investigated retrospectively and compared statistically.

RESULTS

Among 66 patients with GISTs, 24 (36%) had concomitant malignant tumors. In an average study period of 57 months, one patient died from GIST, seven from other malignant tumors, and one from another disease. Only coexistence of GIST and other malignant tumors was recognized as a prognostic factor. Increasing age was significantly correlated with other malignant tumor in combination with GIST. When comparing patients with GIST alone and GIST with other malignant tumors, the latter showed significantly poorer prognosis.

CONCLUSION

Coexistence of other malignant tumors was commonly observed in patients with GIST, and was associated with poorer prognosis. This association should be carefully considered and monitored in patients with GISTs.

Gastrointestinal Stromal Tumors (GISTs): Novel Therapeutic Strategies with Immunotherapy and Small Molecules

Gastrointestinal stromal tumors (GISTs) are the most common types of malignant mesenchymal tumors in the gastrointestinal tract, with an estimated incidence of 1.5/100.000 per year and 1-2% of gastrointestinal neoplasms. About 75-80% of patients have mutations in the KIT gene in exons 9, 11, 13, 14, 17, and 5-10% of patients have mutations in the platelet-derived growth factor receptor a (PDGFRA) gene in exons 12, 14, 18. Moreover, 10-15% of patients have no mutations and are classified as wild type GIST. The treatment for metastatic or unresectable GISTs includes imatinib, sunitinib, and regorafenib. So far, GIST therapies have raised great expectations and offered patients a better quality of life, but increased pharmacological resistance to tyrosine kinase inhibitors is often observed. New treatment options have emerged, with ripretinib, avapritinib, and cabozantinib getting approvals for these tumors. Nowadays, immune checkpoint inhibitors form a new landscape in cancer therapeutics and have already shown remarkable responses in various tumors. Studies in melanoma, non-small-cell lung cancer, and renal cell carcinoma are very encouraging as these inhibitors have increased survival rates. The purpose of this review is to present alternative approaches for the treatment of the GIST patients, such as combinations of immunotherapy and novel inhibitors with traditional therapies (tyrosine kinase inhibitors).

The Outcome of Neoadjuvant Imatinib Therapy Combined With Surgery for Rectal Gastrointestinal Stromal Tumors: A Report of Three Cases and a Review of the Literature

Gastrointestinal stromal tumors (GISTs) represent the most frequent mesenchymal tumors of the gastrointestinal tract. They occur most frequently in the stomach. Rectal localization remains rare and represents only 5% of all GIST cases and 0.1% of all rectal tumors. Immunohistochemical staining (CD117, DOG1) and molecular analysis remain the gold standard for diagnosis; DOG1 represents a very sensitive marker regardless of CD117 expression. Complete en-bloc resection constitutes the only curative treatment; however, surgical management of rectal GIST remains challenging and can involve extensive surgery such as abdominoperineal resection with significant morbidity. The role of neoadjuvant Imatinib therapy in rectal GISTs is controversial and mainly indicated in a locally advanced tumor or sphincter invasion to increase the chance of complete resection and sphincter preservation. Herein, we report three cases of a rectal GIST treated with neoadjuvant Imatinib therapy and who underwent extensive surgery with complete resection (R0), as well as a recent review of the literature, to study clinicopathological features, surgical challenges, and perioperative Imatinib therapy outcome of rectal GISTs.

New insights into the clinical management of advanced gastrointestinal stromal tumors

INTRODUCTION

90% of gastrointestinal stromal tumors (GISTs) harbor an activating mutation in the KIT or PDGFRα oncogene, and these are known to confer imatinib sensitivity.

AREAS COVERED

The author reviews the data regarding the current management of GIST, mechanisms of resistance to imatinib, and new drugs currently in clinical development and provides his unique perspectives on the subject matter.

EXPERT OPINION

Several studies have shown that the response to imatinib in GIST patients mainly depends on the mutational status of KIT or PDGFRα. Moreover, most, if not all, patients treated with imatinib for advanced GIST will develop a secondary progressive disease under the treatment. In most cases, such progressions are the result of acquired resistance due to the occurrence of secondary c-KIT mutations, especially in GISTs with primary exon 11 mutations. Sunitinib and regorafenib are inhibitors of multiple tyrosine kinases, including KIT, PDGFRα, PDGFRβ, and VEGFRs, and are approved for the management of imatinib- and imatinib/sunitinib-refractory GIST patients, respectively. Clearly, better knowledge of the molecular mechanisms underlying the resistance to imatinib as well as the development of a new class of broad-spectrum tyrosine kinase inhibitors such as avapritinib and ripretinib will provide new individualized therapeutic strategies for GIST patients.

A Novel Kindred with Familial Gastrointestinal Stromal Tumors Caused by a Rare KIT Germline Mutation (N655K): Clinico-Pathological Presentation and TKI Sensitivity

Gastrointestinal stromal tumors (GISTs), the most common mesenchymal tumors of the gastrointestinal tract, are characterized by activating mutations in KIT or PDGFRA genes. The vast majority of GISTs are sporadic, but rare hereditary forms have been reported, often featuring multifocality and younger age of onset. We here report the identification of a novel kindred affected by familial GIST caused by a KIT germline mutation in exon 13 (N655K). No family affected by hereditary GIST due to this KIT variant has been reported in literature so far. We were able to track the mutation in three members of the family (proband, mother, and second-degree cousin), all affected by multiple GISTs. Due to its rarity, the N655K variant is poorly characterized. We conducted in vitro drug sensitivity assays that indicated that most tyrosine kinase inhibitors (TKIs) currently included in the therapeutic armamentarium for GISTs have a limited inhibitory activity toward this mutation. However, when compared to a classical imatinib-resistant KIT mutation (T670I), N655K was slightly more sensitive to imatinib, and encouraging responses were observed with last-generation TKIs.

Comparison of endoscopic versus laparoscopic resection for gastric gastrointestinal stromal tumors: A preliminary meta-analysis

BACKGROUND AND AIM

For localized disease, complete surgical resection is regarded as the "gold standard" therapeutic modality. With the rapid development of endoscopic techniques, endoscopic resection (ESR) has been confirmed as an efficient and safe alternative for the treatment of gastrointestinal stromal tumors (GISTs) in the stomach. Nevertheless, the management of gastric GISTs remains poorly defined. The purpose of this study is to evaluate the security and effectiveness of ESR with laparoscopic resection (LAR) for gastric GISTs.

METHODS

A literature search of online databases was conducted to identify relevant comparative studies of ESR and LAR procedures for gastric GISTs published before April 10, 2020. The cumulative data analysis was also performed utilizing the software STATA.

RESULTS

In total, 10 studies involving 1165 patients met the inclusion criteria for analysis (651 for ESR and 514 for LAR). From the results of meta-analysis, patients who underwent ESR experienced decreased operative time (P = 0.000), less intraoperative blood loss (P = 0.002), earlier time to diet (P = 0.000), shorter hospital stay (P = 0.000), and lower total charges (P = 0.000) compared with LAR. Moreover, there were no significant differences between these two approaches concerning tumor rupture, conversion rate to other procedure, complete resection rate, postoperative complication rate, recurrence rate, and disease-free survival.

CONCLUSIONS

Endoscopic resection, as an effective alternative treatment strategy with satisfactory outcomes, is acceptable for selective patients with gastric GISTs compared with LAR. Further well-designed randomized controlled trials with large samples are warranted to corroborate our observations.

[Rare tumors as leading symptom of hereditary tumor syndromes]

BACKGROUND

Monogenic hereditary tumor syndromes or tumor disposition syndromes (TDS) are based on germline/constitutional mutations in key genes of carcinogenesis. Early onset and a clustering of tumors belonging to a typical spectrum in the personal or family history are indicators for a hereditary form. In particular, rare specific tumors occur relatively frequently in the context of TDS.

METHODS

Based on a literature search the current article presents information on which TDS should be considered for differential diagnosis (DD) in the presence of a rare tumor.

RESULTS

The identification of a causal germline mutation in the index patient is important for the DD, the evaluation of recurrence risks, and predictive testing of asymptomatic at-risk family members. In TDS with autosomal dominant inheritance, it is often possible to identify several high-risk individuals in the affected families.

CONCLUSION

Early detection and correct classification are of high clinical relevance as the patients and persons at risk can often be offered effective preventive procedures (surveillance, prophylactic operations), and in some cases, special therapeutic options exist. TDS are paradigmatic for an extremely successful concept of preventive oncology and personalized medicine. The introduction of new methods of high-throughput sequencing (next generation sequencing) enables a more effective genetic diagnosis, but also poses a challenge for the interpretation of findings and counseling. Referral to multidisciplinary expert centers is useful for care of the families.

Retrospective Analysis of Chilean and Mexican GI Stromal Tumor Registries: A Tale of Two Latin American Realities

PURPOSE

Like other malignancies, GI stromal tumors (GIST) are highly heterogeneous. This not only applies to histologic features and malignant potential, but also to geographic incidence rates. Several studies have reported GIST incidence and prevalence in Europe and North America. In contrast, GIST incidence rates in South America are largely unknown, and only a few studies have reported GIST prevalence in Latin America.

PATIENTS AND METHODS

Our study was part of a collaborative effort between Chile and Mexico, called Salud con Datos. We sought to determine GIST prevalence and patients' clinical characteristics, including survival rates, through retrospective analysis.

RESULTS

Overall, 624 patients were included in our study. Our results found significant differences between Mexican and Chilean registries, such as stage at diagnosis, primary tumor location, CD117-positive immunohistochemistry status, mitotic index, and tumor size. Overall survival (OS) times for Chilean and Mexican patients with GIST were 134 and 156 months, respectively. No statistically significant differences in OS were detected by sex, age, stage at diagnosis, or recurrence status in both cohorts. As expected, patients categorized as being at high risk of recurrence displayed a trend toward poorer progression-free survival in both registries.

CONCLUSION

To the best of our knowledge, this is the largest report from Latin America assessing the prevalence, clinical characteristics, postsurgery risk of recurrence, and outcomes of patients with GIST. Our data confirm surgery as the standard treatment of localized disease and confirm a poorer prognosis in patients with regional or distant disease. Finally, observed differences between registries could be a result of registration bias.

[Wild-type gastroinestinal stromal tumors]

Gastrointestinal stromal tumors (GIST) are the most common non-epithelial tumors of the gastrointestinal tract. Wild-type GISTs (WT-GIST) consist of a rare heterogeneous group characterized by the lack of activating mutations in the tyrosine kinase receptor (Kit) and/or platelet derived growth factor receptor A (PDGFRA). However, WT-GIST is characterized by other genomic alterations, including dehydrogenase succinate (SDH) deficiency or mutations in the Ras pathway. Recent studies have reported many mutations in others genes that may be incriminated in the development of WT-GISTs. Moreover, WT-GIST is frequently associated with hereditary cancer syndromes such as the Carney Triad and Type 1 Neurofibromatosis (NF1). WT-GIST affects usually young and pediatric patients. Most WT-GIST subtypes are insensitive to imatinib; therefore, their therapeutic management is somewhat different from usual GISTs. This review resumes the molecular and therapeutic features of this rare entity.

A Huge Pelvic-Abdominal Malignant GIST Tumour in a Patient with Neurofibromatosis Type 1: Case Report and Literature Review

Gastrointestinal stromal tumours are rare tumours of the gastrointestinal tract (GIT) accounting for 0.1%–3% of all gastrointestinal tumours. The most common location is the stomach (55%) followed by the small bowel (31.8%), colon (6%), other various locations (5.5%), and the oesophagus (0.7%). They may also occur in extraintestinal locations. The signs and symptoms of GIST depend on the tumour's location and size. Gastrointestinal bleeding is one of the most common symptoms. Other signs and symptoms include abdominal discomfort, pain or distention; intestinal obstruction, and weight loss. The association between the development of GISTs and neurofibromatosis 1 (NF1) has been established. NF1-associated GISTs tend to have a distinct phenotype, and the absence of KIT/PDGRFα mutations in turn has implications on further management when they do not respond well to imatinib treatment. Here, we present one of the largest GISTs reported in the literature with a total volume of 25.3 × 20 × 14 cm + 27.9 × 23 × 8 cm and an overall weight of 7.3 kg, which developed in a 43-year-old female patient with NF1 and was resected on an emergency basis due to the rapid deterioration and development of abdominal compartment syndrome. Pathology assessment showed a malignant GIST composed of spindle cells with elongated nuclei with necrosis, marked pleomorphism and numerous giant cell. The mitotic count was >15/50 HPF, Ki 67 was 80%, and the lymphovascular invasion was clear. Immunohistochemistry investigations showed that Vimentin, CD117, and DOG1 were positive, while BCL-2 and CD99 were focal positives. Pan-CK, S-100, CD34, Desmin, SMA, and HMB-45 were negatives.

Pediatric gastrointestinal stromal tumor: Report of two novel patients harboring germline variants in SDHB and SDHC genes

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract and rarely occur in pediatric patients. 85% of pediatric GISTs and 15% of adult GISTs lack of KIT or PDGFRA mutations. 40% of these "wild-type" GISTs present loss of function mutations in genes encoding for the subunits of the succinate dehydrogenase (SDH) complex. Germline mutations in SDH complex genes have been described in patients with the Carney-Stratakis syndrome (CSS), a rare inherited condition that predisposes to GIST and paraganglioma. We report two pediatric patients with multifocal GIST, harboring respectively a novel and a previously reported loss-of-function germline variant, in SDHC and SDHB genes.

Translational insights into gastrointestinal stromal tumor and current clinical advances

Gastrointestinal stromal tumor (GIST) is the most common soft tissue sarcoma of the gastrointestinal tract and, in the vast majority of cases, is characterized by activating mutations in KIT or, less commonly, PDGFRA. Mutations in these type III receptor tyrosine kinases (RTKs) account for over 85% of GIST cases, and the majority of KIT primary mutations respond to treatment with the tyrosine kinase inhibitor (TKI) imatinib. However, drug resistance develops over time, most commonly due to secondary kinase mutations. Sunitinib and regorafenib are approved for the treatment of imatinib-resistant GIST in the second and third lines, respectively. However, resistance to these agents also develops and new therapeutic options are needed. In addition, a small number of GISTs harbor primary activating mutations that are resistant to currently available TKIs, highlighting an additional unmet medical need. Several novel and selective TKIs that overcome known mechanisms of resistance in GIST have been developed and show promise in early clinical trials. Additional emerging targeted therapies in GIST include modulation of cellular signaling pathways downstream of KIT, antibodies targeting KIT and PDGFRA and immune checkpoint inhibitors. These advancements highlight the rapid evolution in the understanding of this malignancy and provide perspective on the encouraging horizon of current and forthcoming therapeutic strategies for GIST.

Gastrointestinal stromal tumours (GISTs): French Intergroup Clinical Practice Guidelines for diagnosis, treatments and follow-up (SNFGE, FFCD, GERCOR, UNICANCER, SFCD, SFED, SFRO)

BACKGROUND

This document is a summary of the French Intergroup guidelines regarding the management of gastrointestinal stromal tumours (GISTs) updated in December 2018.

DESIGN

This collaborative work summarizes clinical practice recommendations (guidelines) on the management of GISTs. It is based on recent literature review, ESMO recommendations and expert opinions.

RESULTS

The diagnosis of GIST is based on histological examination and immunohistochemistry with markers KIT and DOG-1. Each case must be discussed within a multidisciplinary team. Complete surgical resection tumour, avoiding peroperative perforation, is the potentially curative treatment of localized GISTs. The estimation of the recurrence risk is essential, or adjuvant treatment,and follow-up adaptation. Genotyping (KIT and PDGFRA) of all but very low-risk GISTs is recommended. The nature of mutation has a prognostic value and predictive influence on drug efficacy. Imatinib, a tyrosine-kinase inhibitor, is the standard adjuvant treatment after R0 resection of a GIST with a high risk of recurrence, and the first line therapy for advanced GISTs. Suninitib and regorafenib are respectively the second- and third-line standard treatments for advanced GISTs.

CONCLUSION

Guidelines for management of GISTs are continuously evolving and need to be regularly updated. This constant progress is made possible through clinical and translational research.

Screening populations at high risk for soft tissue sarcoma and surveillance following soft tissue sarcoma resection

Soft tissue sarcomas (STS) are a rare and diverse group of tumors that affect both adult and pediatric populations. This review discusses current screening recommendations for populations at increased risk for STS, including those with genetic predispositions. We also review surveillance guidelines for those at risk for recurrence following curative-intent surgery.

Germline c.1A>C heterozygous pathogenic variant in SDHA reported for the first time in a young adult with a gastric gastrointestinal stromal tumour (GIST): a case report

Background

Gastrointestinal stromal tumors (GISTs) represent the most frequent mesenchymal tumor of the gastrointestinal tract. Less than 5% of them seem to be hereditary, being succinate dehydrogenase complex (SDHx) deficient disorders and neurofibromatosis type 1 the more related inherited conditions. Wild type (WT) KIT and PDGFRα GISTs constitute a clue for a hypothetical underlying germline condition.

Case presentation

We present a case of a 20 years old female diagnosed of a gastric WT GIST who developed hepatic metastases during her clinical course. No significant or typical phenotypic features suggestive of a specific syndrome were detected by physical examination. Also, her family history seemed to be irrelevant, since no other cases of GISTs, paragangliomas or pheochromocytomas were reported. Her paternal grandfather died as a consequence of a pituitary adenoma. In light of the age of tumor presentation and somatic features of gastric GIST, we performed genetic testing of SDHx genes. Analysis obtained from peripheral blood sample revealed the presence, in heterozygous state, of the c.1A > C; p.(Met1?) pathogenic variant in the SDHA.

Conclusions

To the best of our knowledge, this is the first published report in which the c.1A > C; p.(Met1?) pathogenic variant in the SDHA is associated with a GIST. SDHA pathogenic variants increase the risk of paraganglioma, pheochromocytoma, GIST, pituitary adenoma and renal cancer in an autosomal dominant inherited condition named paraganglioma syndrome type 5. The absence of family history of tumors in SDHA pathogenic variants carriers could be related to its low penetrance. All patients diagnosed with WT GISTs should be referred to a hereditary cancer genetic counseling unit regardless of the age at presentation or the absence of a suspicious family history.

Succinate Dehydrogenase-Deficient Gastrointestinal Stromal Tumors: Small Steps Toward Personalized Medicine?

Various molecular triggers define heterogeneous subsets of gastrointestinal stromal tumors (GISTs), differing in clinical behavior and drug sensitivity. KIT/PDGFRA-wild-type GISTs, including those succinate dehydrogenase (SDH)-deficient, are overall unresponsive to the tyrosine kinase inhibitors commonly used, fostering the development of specific alternative therapeutic strategies. Epigenetic inactivation of O⁶-methylguanine-DNA methyltransferase (MGMT) through promoter methylation leads to effectiveness of alkylating agents in several human cancers. SDH-deficient GISTs typically feature widespread DNA methylation. However, the actual occurrence of MGMT methylation in these tumors, potentially predisposing them to respond to alkylating drugs, has not been investigated so far. Here we discuss the recent findings concerning the occurrence of MGMT methylation in different GIST subgroups, including SDH-deficient ones, as a premise for a possible reappraisal of alkylating agents specifically targeting these small, otherwise overall chemorefractory, GIST subgroups.

Enhancer Domains in Gastrointestinal Stromal Tumor Regulate KIT Expression and Are Targetable by BET Bromodomain Inhibition

Gastrointestinal stromal tumor (GIST) is a mesenchymal neoplasm characterized by activating mutations in the related receptor tyrosine kinases KIT and PDGFRA. GIST relies on expression of these unamplified receptor tyrosine kinase (RTK) genes through a large enhancer domain, resulting in high expression levels of the oncogene required for tumor growth. Although kinase inhibition is an effective therapy for many patients with GIST, disease progression from kinase-resistant mutations is common and no other effective classes of systemic therapy exist. In this study, we identify regulatory regions of the KIT enhancer essential for KIT gene expression and GIST cell viability. Given the dependence of GIST upon enhancer-driven expression of RTKs, we hypothesized that the enhancer domains could be therapeutically targeted by a BET bromodomain inhibitor (BBI). Treatment of GIST cells with BBIs led to cell-cycle arrest, apoptosis, and cell death, with unique sensitivity in GIST cells arising from attenuation of the KIT enhancer domain and reduced KIT gene expression. BBI treatment in KIT-dependent GIST cells produced genome-wide changes in the H3K27ac enhancer landscape and gene expression program, which was also seen with direct KIT inhibition using a tyrosine kinase inhibitor (TKI). Combination treatment with BBI and TKI led to superior cytotoxic effects in vitro and in vivo, with BBI preventing tumor growth in TKI-resistant xenografts. Resistance to select BBI in GIST was attributable to drug efflux pumps. These results define a therapeutic vulnerability and clinical strategy for targeting oncogenic kinase dependency in GIST. SIGNIFICANCE: Expression and activity of mutant KIT is essential for driving the majority of GIST neoplasms, which can be therapeutically targeted using BET bromodomain inhibitors.

Remarkable effects of imatinib in a family with young onset gastrointestinal stromal tumors and cutaneous hyperpigmentation associated with a germline KIT-Trp557Arg mutation: case report and literature overview

Gastrointestinal stromal tumors (GISTs) occur mostly sporadically. GISTs associated with a familial syndrome are very rare and are mostly wild type for KIT and platelet-derived growth factor alpha (PDGFRA). To date 35 kindreds and 8 individuals have been described with GISTs associated with germline KIT mutations. This is the third family described with a germline p.Trp557Arg mutation in exon 11 of the KIT gene. The effect of imatinib in patients harboring a germline KIT mutation has been rarely described. Moreover, in some studies imatinib treatment was withheld considering the lack of evidence for efficacy of this treatment in GIST patients harboring a germline KIT mutation. This paper describes a 52-year old patient with a de novo germline p.Trp557Arg mutation with multiple GISTs throughout the gastrointestinal tract and cutaneous hyperpigmentation. Imatinib treatment showed long-term regression of the GISTs and evident pathological response was seen after resection. Remarkably, the hyperpigmentation of the skin also diminished during imatinib treatment. Genetic screening of the family revealed the same mutation in two daughters, both with similar cutaneous hyperpigmentation. One daughter, aged 23, was diagnosed with multiple small intestine GISTs, which were resected. She was treated with adjuvant imatinib which prompted rapid regression of the cutaneous hyperpigmentation. Imatinib treatment in GIST patients harboring a germline KIT mutation shows favorable and long-term responses in both the tumor and the phenotypical hyperpigmentation.

Enhancer Domains in Gastrointestinal Stromal Tumor Regulate KIT Expression and Are Targetable by BET Bromodomain Inhibition

Gastrointestinal stromal tumor (GIST) is a mesenchymal neoplasm characterized by activating mutations in the related receptor tyrosine kinases KIT and PDGFRA. GIST relies on expression of these unamplified receptor tyrosine kinase (RTK) genes through a large enhancer domain, resulting in high expression levels of the oncogene required for tumor growth. Although kinase inhibition is an effective therapy for many patients with GIST, disease progression from kinase-resistant mutations is common and no other effective classes of systemic therapy exist. In this study, we identify regulatory regions of the KIT enhancer essential for KIT gene expression and GIST cell viability. Given the dependence of GIST upon enhancer-driven expression of RTKs, we hypothesized that the enhancer domains could be therapeutically targeted by a BET bromodomain inhibitor (BBI). Treatment of GIST cells with BBIs led to cell-cycle arrest, apoptosis, and cell death, with unique sensitivity in GIST cells arising from attenuation of the KIT enhancer domain and reduced KIT gene expression. BBI treatment in KIT-dependent GIST cells produced genome-wide changes in the H3K27ac enhancer landscape and gene expression program, which was also seen with direct KIT inhibition using a tyrosine kinase inhibitor (TKI). Combination treatment with BBI and TKI led to superior cytotoxic effects in vitro and in vivo, with BBI preventing tumor growth in TKI-resistant xenografts. Resistance to select BBI in GIST was attributable to drug efflux pumps. These results define a therapeutic vulnerability and clinical strategy for targeting oncogenic kinase dependency in GIST. SIGNIFICANCE: Expression and activity of mutant KIT is essential for driving the majority of GIST neoplasms, which can be therapeutically targeted using BET bromodomain inhibitors.

Preferential MGMT methylation could predispose a subset of KIT/PDGFRA-WT GISTs, including SDH-deficient ones, to respond to alkylating agents

BACKGROUND

Succinate dehydrogenase (SDH)-deficient gastrointestinal stromal tumors (GISTs) constitute a small KIT/PDGFRA-WT GIST subgroup featuring DNA methylation which, although pervasive, appears nevertheless not randomly distributed. Although often indolent, these tumors are mostly chemorefractory in aggressive cases. Promoter methylation-induced O⁶-methylguanine DNA methyltransferase (MGMT) inactivation improves the efficacy of alkylating agents in gliomas, colorectal cancer and diffuse large B cell lymphoma. MGMT methylation has been found in some GISTs, without determining SDH status. Thirty-six GISTs were enrolled in past sarcoma trials testing alkylating agents, with negative results. Nevertheless, a possible effect on MGMT-methylated GISTs could have escaped detection, since tested GISTs were neither selected by genotype nor investigated for SDH; MGMT was studied in two cases only, revealing baseline activity; these trials were performed prior to the adoption of Choi criteria, the most sensitive for detecting GIST responses to therapy. Under these circumstances, we investigated whether MGMT methylation is preferentially found in SDH-deficient cases (identified by SDHB immunohistochemistry) by analyzing 48 pathogenetically heterogeneous GISTs by methylation-specific PCR, as a premise for possible investigations on the use of alkylating drugs in these tumors.

RESULTS

Nine GISTs of our series were SDH-deficient, revealing significantly enriched in MGMT-methylated cases (6/9-67%-, vs. 6/39-15%- of SDH-proficient GISTs; p = 0.004). The pathogenetically heterogeneous KIT/PDGFRA-WT GISTs were also significantly MGMT-methylated (11/24-46%-, vs. 1/24-4%- of KIT/PDGFRA-mutant cases, p = 0.002).

CONCLUSIONS

A subset of KIT/PDGFRA-WT GISTs, including their largest pathogenetically characterized subgroup (i.e., SDH-deficient ones), is preferentially MGMT-methylated. This finding could foster a reappraisal of alkylating agents for treating malignant cases occurring among these overall chemorefractory tumors.

Approach to wild-type gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) arise from the intestinal pacemaker cells of Cajal. Wild-type gastrointestinal stromal tumors (WT-GIST) are a unique and uncommon subtype of GISTs that lack activating mutations in the tyrosine kinase c-KIT or platelet derived growth factor receptor alpha (PDGFRA) receptors. The lack of these growth-stimulating mutations renders tyrosine kinase receptor inhibitors, such as imatinib mesylate, relatively ineffective against these tumors. WT-GIST arises most commonly due to underlying alternate proliferative signals associated with germ-line, genetic mutations. WT-GIST frequently arises in patients with BRAF mutations, Carney's Triad or neurofibromatosis type-1 (NF-1). All patients with WT-GIST require a careful examination for germ-line mutations and very close observation for recurrent tumors. Surgery remains a mainstay therapy for these patients. This review aims to discuss the most recent data available on the diagnosis and treatment of WT-GIST.

A unique model for SDH-deficient GIST: an endocrine-related cancer

We describe a unique patient-derived xenograft (PDX) and cell culture model of succinate dehydrogenase-deficient gastrointestinal stromal tumor (SDH-deficient GIST), a rare mesenchymal tumor that can occur in association with paragangliomas in hereditary and non-hereditary syndromes. This model is potentially important for what it might reveal specifically pertinent to this rare tumor type and, more broadly, to other types of SDH-deficient tumors. The primary tumor and xenografts show a very high proliferative fraction, and distinctive morphology characterized by tiny cells with marked autophagic activity. It is likely that these characteristics resulted from the combination of the germline SDHB mutation and a somatic KRAS G12D mutation. The most broadly relevant findings to date concern oxygen and oxidative stress. In paragangliomas harboring SDHx mutations, both hypoxic signaling and oxidative stress are putative drivers of tumor growth. However, there are no models for SDH-deficient paragangliomas. This related model is the first from a SDHB-mutated human tumor that can be experimentally manipulated to study mechanisms of oxygen effects and novel treatment strategies. Our data suggest that tumor growth and survival require a balance between protective effects of hypoxic signaling vs deleterious effects of oxidative stress. While reduced oxygen concentration promotes tumor cell survival, a further survival benefit is achieved with antioxidants. This suggests potential use of drugs that increase oxidative stress as novel therapies. In addition, autophagy, which has not been reported as a major finding in any type of SDH-deficient tumor, is a potential target of agents that might trigger autophagic cell death.

Gastrointestinal juvenile-like (inflammatory/hyperplastic) mucosal polyps in neurofibromatosis type 1 with no concurrent genetic or clinical evidence of other syndromes

Gastrointestinal "juvenile-like (inflammatory/hyperplastic) mucosal polyps" (JLIHMPs) have been proposed as a neurofibromatosis type 1 (NF1)-specific gastrointestinal manifestation. Juvenile polyposis syndrome (JPS) has also been reported in a NF1 patient, harboring concurrent NF1 and SMAD4 germline mutations. Additionally, NF1-like cafe-au-lait spots have been described in biallelic mismatch repair deficiency, another condition featuring gastrointestinal polyps. The SMAD4 and BMPR1A genes that are involved in 50-60% of JPS cases have not been investigated in the ~ 20 published cases of NF1-associated JLIHMPs with the exception of the abovementioned patient with concomitant JPS and NF1. NF1 defects have been found in the only two cases exhaustively tested. Therefore, JLIHMP has been questioned as an independent, NF1-specific entity. Incidental associations between NF1 and gastrointestinal polyposes at risk for gastrointestinal carcinoma should not be overlooked, given their implications in terms of clinical surveillance. We describe two patients featuring JLIHMPs in clinically/genetically proven NF1, in the absence of SMAD4 and BMPR1A mutations. In one case, the intervening mucosa was markedly inflamed, unlike JPS. We suggest that JLIHMP probably represents a gastrointestinal lesion specific to NF1.

Identification of key genes and associated pathways in KIT/PDGFRA wild‑type gastrointestinal stromal tumors through bioinformatics analysis

Gastrointestinal stromal tumors (GISTs) are the most common type of mesenchymal tumor in the gastrointestinal tract. The present study aimed to identify the potential candidate biomarkers that may be involved in the pathogenesis and progression of v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT)/platelet-derived growth factor receptor α (PDGFRA) wild-type GISTs. A joint bioinformatics analysis was performed to identify the differentially expressed genes (DEGs) in wild-type GIST samples compared with KIT/PDGFRA mutant GIST samples. Gene Ontology function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of DEGs was conducted using Database for Annotation, Visualization and Integrated Discovery and KEGG Orthology-Based Annotation System (KOBAS) online tools, respectively. Protein-protein interaction (PPI) networks of the DEGs were constructed using Search Tool for the Retrieval of Interacting Genes online tool and Cytoscape, and divided into sub-networks using the Molecular Complex Detection (MCODE) plug-in. Furthermore, enrichment analysis of DEGs in the modules was analyzed with KOBAS. In total, 546 DEGs were identified, including 238 upregulated genes primarily enriched in ‘cell adhesion’, ‘biological adhesion’, ‘cell-cell signaling’, ‘PI3K-Akt signaling pathway’ and ‘ECM-receptor interaction’, while the 308 downregulated genes were predominantly involved in ‘inflammatory response’, ‘sterol metabolic process’ and ‘fatty acid metabolic process’, ‘small GTPase mediated signal transduction’, ‘cAMP signaling pathway’ and ‘proteoglycans in cancer’. A total of 25 hub genes were obtained and four modules were mined from the PPI network, and sub-networks also revealed these genes were primarily involved in significant pathways, including ‘PI3K-Akt signaling pathway’, ‘proteoglycans in cancer’, ‘pathways in cancer’, ‘Rap1 signaling pathway’, ‘ECM-receptor interaction’, ‘phospholipase D signaling pathway’, ‘ras signaling pathway’ and ‘cGMP-PKG signaling pathway’. These results suggested that several key hub DEGs may serve as potential candidate biomarkers for wild-type GISTs, including phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit γ, insulin like growth factor 1 receptor, hepatocyte growth factor, thrombospondin 1, Erb-B2 receptor tyrosine kinase 2 and matrix metallopeptidase 2. However, further experiments are required to confirm these results.