Mutant Gastrointestinal Stromal Tumors Research Articles

Abstract 3142: NN3201, a novel c-Kit targeting ADC, exhibits robust preclinical anti-tumor efficacy in SCLC and GIST models

Abstract c-Kit (CD117) is a type III receptor tyrosine kinase (RTK), which is known to be activated upon binding to its cognate ligand stem cell factor (SCF) to induce critical signaling pathways involved in cell proliferation, survival, and differentiation. Indicative of poor prognosis, overexpression and activating mutations of c-Kit have been implicated in a variety of human cancers including small cell lung cancer (SCLC), gastrointestinal stromal tumors (GIST), and acute myelogenous leukemia (AML). While imatinib, a small molecule c-Kit inhibitor, has been a beneficial treatment for GIST, resistance eventually develops to the drug, moreover, shows limited efficacy in c-Kit overexpressing tumors such as SCLC. Herein, we developed NN3201, a novel c-Kit targeting antibody-drug conjugate (ADC), comprised of fully human 2G4 antibody with a picomolar binding affinity to c-Kit and cytotoxic monomethyl auristatin E (MMAE) as the payload. NN3201 displayed potent in vitro cytotoxicity in various wild-type and mutant c-Kit positive SCLC and GIST cell lines with IC50 in the nanomolar range. In addition, NN3201 was rapidly internalized and inhibited c-Kit-mediated signaling., NN3201 treatment resulted in the increased proportions of the sub G1 and G2/M in the c-Kit positive cancer cell lines, indicating that release of MMAE induced cell cycle arrest. Moreover, bystander effect was confirmed by co-culturing c-Kit high and negative cell lines. Most importantly, in mouse xenograft models, NN3201 showed a remarkable tumor growth inhibition of several wild type, mutant c-Kit positive, and imatinib resistant SCLC and GIST cell lines. Enhanced anti-tumor activity and delayed tumor growth were observed in an SOC-treated (etoposide and carboplatin) SCLC xenograft model, by NN3201 in comparison to second line SOC (topotecan or irinotecan). In the GLP study, repeated intravenous administration of NN3201 was well tolerated at all doses (0.5, 1, 2 mg/kg Q3Wx3) without unscheduled death. Dose-dependent, yet transient, cytotoxicity of NN3201 was observed in the bone marrow. We confirmed HNSTD (Highest Non-Severely Toxic Dose) of NN3201 to be 2 mg/kg through exploratory and GLP repeat dose toxicity studies as no serious irreversible toxicity was observed. Accumulating data suggest that NN3201 is a promising therapeutic alternative for the treatment of SCLC and GIST regardless of wild-type or activating mutations in c-Kit. Citation Format: Chansik Kim, Jin Gu Cho, TaeMin Wi, Jiwoo Moon, Han-Jik Ko, Jina Lee, Jin Woo Park, Yeonjy Lee, Sanghee Kim, Jin-Ock Kim, Jaeyoung Song, Sun-Hwa Lee, Sang Gyu Park. NN3201, a novel c-Kit targeting ADC, exhibits robust preclinical anti-tumor efficacy in SCLC and GIST models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3142.

Reappraisals of biological behaviors of PDGFRA mutant gastrointestinal stromal tumor

Objective: To investigate the biological behavior spectrum of platelet-derived growth factor alpha receptor (PDGFRA)-mutant gastrointestinal stromal tumor (GIST), and to compare the clinical values of the Zhongshan method of benign and malignant evaluation with the modified National Institutes of Health (NIH) risk stratification. Methods: A total of 119 cases of GIST with PDGFRA mutation who underwent surgical resection at Zhongshan Hospital, Fudan University from 2009 to 2020 were collected. The clinicopathological data, follow-up records, and subsequent treatment were reviewed and analyzed statistically. Results: There were 79 males and 40 females. The patients ranged in age from 25 to 80 years, with a median age of 60 years. Among them, 115 patients were followed up for 1-154 months, and 13 patients progressed to disease. The 5-year disease-free survival (DFS) and overall survival (OS) were 90.1% and 94.1%, respectively. According to the modified NIH risk stratification, 8 cases, 32 cases, 38 cases, and 35 cases were very-low risk, low risk, intermediate risk, and high risk, and 5-year DFS were 100.0%, 95.6%, 94.3%, and 80.5%, respectively. There was no significant difference in prognosis among the non-high risk groups, only the difference between high risk and non-high risk groups was significant (P=0.029). However, the 5-year OS was 100.0%, 100.0%, 95.0% and 89.0%, and there was no difference (P=0.221). According to the benign and malignant evaluation Zhongshan method, 43 cases were non-malignant (37.4%), 56 cases were low-grade malignant (48.7%), 9 cases were moderately malignant (7.8%), and 7 cases were highly malignant (6.1%). The 5-year DFS were 100.0%, 91.7%, 77.8%, 38.1%, and the difference was significant (P<0.001). The 5-year OS were 100.0%, 97.5%, 77.8%, 66.7%, the difference was significant (P<0.001). Conclusions: GIST with PDGFRA gene mutation shows a broad range of biological behavior, ranging from benign to highly malignant. According to the Zhongshan method, non-malignant and low-grade malignant tumors are common, the prognosis after surgery is good, while the fewer medium-high malignant tumors showed poor prognosis after surgical resection. The overall biological behavior of this type of GIST is relatively inert, which is due to the low proportion of medium-high malignant GIST. The modified NIH risk stratification may not be effective in risk stratification for PDGFRA mutant GIST.

Hallmarks and novel insights for gastrointestinal stromal tumors: A bibliometric analysis

BackgroundDue to the increasing recognition of gastrointestinal stromal tumor (GIST), novel insights have appeared in both preclinical and clinical research and begun to reshape the field. This study aims to map the research landscape through bibliometric analysis and provide a brief overview for the future of the GIST field. MethodsWe searched the Web of Science Core Collection without publication data restrictions for GISTs and performed a bibliometric analysis with CiteSpace and VOSviewer software. ResultsIn sum, 5,911 of 13,776 records were included, and these studies were published in 948 journals and written by 24,965 authors from 4,633 institutions in 100 countries. Referring to published reviews and bibliometric analysis, we classified the future trends in four groups. In epidemiological study, precise incidence and clinicopathological features in different regions and races might become potential hotspots. Novel therapy, such as drugs, modified strategies, radioligand therapy, was persistent hotspots in GIST fields, and ctDNA-guided diagnosis, monitoring, and treatment might meet future clinical needs. The debate over serosa surgery vs. mucosa surgery will remain active for a long time in GIST surgery, and function reserve surgery, biology-based surgery will play an important role in future. Moreover, rare GIST type, like NF-1-associated GIST, Carney triads and SDH mutant GIST, need more studies in pathogenesis and genetic mutation to provide appropriate treatment for this orphan GIST patients. ConclusionsPotential hotspots in future GIST trends might involve epidemiology, agents, resection therapy and rare type GIST, moreover, researchers could pay more attention in these four fields.

Fluorine-18 fluorodeoxyglucose (18FDG)-uptake assessment of PDGFRA mutant gastrointestinal stromal tumors (GIST): A retrospective multicenter Italian study.

11539 Background: D842V PDGFRA mutation identifies a molecular subtype of GIST, primarly resistant to imatinib and characterized by higher indolent behavior and a prominent immune profile. Although functional imaging with 18FDG-PET plays a proven role in GIST, especially in early assessment tumor response, less is known about 18FDG-uptake according to the GIST molecular subtypes. Taking into account of clinical and molecular features of D842V mutant GIST, we assumed that this subset of GIST could also have a different 18FDG-uptake. Therefore, the aim of the present study has been to investigate the degree of FDG uptake of PDGFRA mutant GIST, focusing on D842V ones, in order to better define the role of functional imaging in this rare and peculiar subset of GIST. Methods: Patients with PDGFRA mutant GIST underwent 18FDG-PET were retrospectively included from seven GIST Italian reference centers. Data on maximum standardized uptake (SUVmax) value of primary tumor or metastatic disease were collected. Results: 71 patients have been included: 37 (55.1%) with D842V PDGFRA mutant GIST (group A) and 34 (47.9%) with PDGFRA non-D842V mutant GIST (group B). Additionally, 30 patients with exon 11 KIT mutant GIST have been included, as control (group C). SUVmax values were obtained from primary tumor and metastatic lesions in 55 (54,4%) and 46 (45,6%) patients, respectively. Considering the whole population of 101 patients, the global median SUVmax was 3,7 (IQR 0-9.1), while the median SUVmax for group A, B, and C was 0, 3.6, and 10.4, respectively. The median SUVmax of PDGFRA mutant GIST was significantly lower than the median value of exon 11 KIT mutant GIST (p &lt; 0.001). Notably, median 18FDG-uptake was significantly lower in D842V PDGFRA mutant GIST compared to PDGFRA non-D842V mutant ones (p = 0.021). Conclusions: PDGFRA D842V-mutant GIST present an overall lower 18FDG uptake compared to other GIST subgroups. This feature could be related to their specific molecular background and is consistent with their higher tendency to an indolent behavior. Therefore, the role of functional imaging with 18FDG-PET in this subset of GIST is limited. Finally, the prognostic value of the 18FDG-uptake degree within all PDGFRA mutant GIST will be investigated in the future.

Sex differences in localized gastrointestinal stromal tumor.

e23511 Background: Sex plays an important role in the incidence and prognosis of several cancer types. Male patients with gastrointestinal stromal tumors (GISTs) have inferior outcomes compared to women, but the reasons behind the sex differences are not well understood. This study aimed to investigate whether sex was a prognostic factor in localized GIST and to explore the relationship between sex and established clinical, molecular and histopathological characteristics. Methods: The study cohort is population-based and consisted of patients who underwent surgical resection of primary, non-metastatic GIST at Oslo University Hospital, Norway between January 2000 and September 2017. Recurrence-free survival (RFS) was the primary endpoint. Mutation analysis was performed by Sanger sequencing or by the AmpliSeq for Illumina Cancer Hotspot Panel version 2. Results: The study cohort comprised 409 patients, 202 women and 207 men. There were 275 gastric tumors (67.2%) and 134 non-gastric tumors (32.8%). Disease recurrence was recorded in 87 patients (21%) after a median follow-up of 64 months. Men with gastric tumors had inferior RFS compared to women (HR 2.18; 95% CI 1.07-4.45; P= 0.029), while there was no difference for non-gastric tumors (HR 0.77; 95% CI 0.44-1.33; P= 0.341). There was a substantial sex variation in the type of primary KIT mutation related to tumor location. Men with gastric tumors had a deletion or insertion-deletion that involved codons 557 and 558 (del557/558) more than twice as frequently as women (34% versus 16%; P= 0.008). Men also had slightly larger tumors (mean 6.6 cm versus 5.5 cm; P= 0.035) and more often tumors located in the upper third of the stomach, but there was no difference in mitotic count (23% versus 22% with &gt; 5 mitoses per 5 mm2). There was no difference in adjuvant imatinib treatment between men and women. No sex differences in primary mutation, tumor size or mitotic count were observed for non-gastric tumors. When KIT del557/558 mutation was included in the Cox regression analysis for gastric tumors, sex was not significantly associated with RFS (HR 1.49; 95% CI 0.70-3.18; P= 0.303), while del557/558 mutation was a strong prognostic factor (HR 6.40; 95% CI 3.17-12.94; P&lt; 0.001). Del557/558 mutation was not associated with RFS in non-gastric tumors (HR 0.67; 95% CI 0.33-1.35; P= 0.262). Conclusions: Women with localized, gastric GISTs had a lower risk of recurrence compared to men. There was no sex difference in outcome or baseline characteristics for non-gastric tumors. Men with gastric tumors more often had KIT del557/558 primary mutations, which may explain their inferior outcome. The observed sex difference in primary mutations in GISTs is unexplained and should be further explored.

Clinical efficacy of avapritinib in gastrointestinal stromal tumors (GIST) with different KIT genotypes: Post hoc analysis of the phase 1 NAVIGATOR and phase 1/2 CS3007-101 trials.

11523 Background: Avapritinib, a novel KIT/platelet-derived growth factor receptor α (PDGFRA) kinase inhibitor, is approved in patients (pts) with GIST harboring PDGFRA activation loop (AL) exon 18 mutations, based on unprecedented clinical antitumor activity. Despite available treatments, there remains a great unmet medical need for pts with KIT-AL-mutant GIST receiving 2nd-line (2L) standard of care (SOC) sunitinib, and pts with primary KIT exon 9 ( KIT 9)-mutant GIST receiving 4th-line (4L) SOC ripretinib. This post hoc analysis assessed the clinical benefit of avapritinib in pts with KIT mutations, especially with AL exons 17 and 18, or primary KIT 9 mutations. Methods: Tumor tissue and liquid biopsy samples were collected and analyzed to determine baseline mutational status. KIT molecular subgroups and outcomes were determined in pts with primary KIT mutations treated with oral avapritinib 300 mg once daily (starting dose) enrolled in the phase 1 NAVIGATOR (NCT02508532) and phase 1/2 (China bridging) trials (NCT04254939, CS3007-101). Pts with PDGFRA mutations and PDGFRA- KIT co-mutations were excluded. Progression-free survival (PFS) and objective response rate (ORR) were compared using Cox and logistic regression, respectively. Results: A total of 160 pts with KIT-mutant GIST were evaluated (NAVIGATOR, n= 131; CS3007-101, n= 29). At data cutoff (NAVIGATOR: March 31, 2021; CS3007-101: June 30, 2021), median follow-up duration was 22.0 months (95% CI 18.3–27.4). KIT-AL mutations were more frequently detected (n = 74, 46.3%) than KIT ATP-binding pocket (ABP) mutations (n = 34, 21.3%). Sixty pts (37.5%) had KIT-AL mutations without KIT-ABP mutations (ALposABPneg group); the remaining 100 pts were designated as KIT OTHERS. Across all lines of therapy, the adjusted (inverse probability weighting of baseline characteristics) median PFS (mPFS) was longer for the ALposABPneg group than for the KIT OTHERS group (9.1 vs 3.4 months; HR 0.47, 95% CI 0.32–0.68; P&lt; 0.0001), and the ORR was higher (31.4% vs 12.1%; odds ratio 3.31, 95% CI 1.44–7.58; P= 0.0047). mPFS and ORR in the KIT ALposABPneg group were 19.3 months and 38.5%, respectively, in the 2L setting (n = 13) and 11.0 months and 36.4%, respectively, in Chinese pts (3–9 lines, n = 11). In pts with KIT 9 mutations in the 4L (n = 14) and &gt; 4L settings (n = 19), mPFS was 5.6 and 3.7 months, respectively. Conclusions: This post hoc analysis demonstrated significantly more robust avapritinib antitumor activity in pts with KIT ALposABPneg GIST versus pts with other KIT mutation profiles. The results suggest that avapritinib could confer meaningful clinical benefit in pts with GIST and specific KIT mutation types, especially KIT-AL or KIT 9 mutations. Avapritinib might be a potential 2L option for pts with KIT ALposABPneg GIST, and in later lines of therapy for pts with ALposABPneg or KIT 9 mutation profiles. Clinical trial information: NCT02508532 , NCT04254939 .

Long-term response to pimitespib in postoperative recurrent gastrointestinal stromal tumors with PDGFRA D842V mutation: a case report

BackgroundExon 18 D842V, which is a point mutation from aspartic acid to valine at codon 842, is the most frequent mutation in Platelet-Derived Growth Factor Receptor alpha (PDGFRA)-mutated gastrointestinal stromal tumor (GIST). In the Japanese GIST guidelines, no standard systematic therapy is available for this type of GIST, which is refractory after recurrence. Recently, pimitespib (PIMI), a novel heat shock protein 90 (HSP90) inhibitor, was approved for the treatment of advanced GIST in a phase III study. This report presents a case of a long-term response to PIMI in GIST with PDGFRA D842V mutation.Case presentationA 55-year-old woman was diagnosed with primary GIST of the stomach and underwent partial gastrectomy. Eight years after the operation, recurrent GISTs were identified as multiple recurrent peritoneal GISTs in the upper right abdomen and pelvic cavity. We administered tyrosine kinase inhibitors, but they achieved poor effects. After failure of the standard treatment, PIMI was administered and achieved a partial response in the patient. The highest reduction rate was 32.7%. After PIMI failed, we performed multiplex gene panel testing, which revealed the PDGFRA D842V mutation.ConclusionsWe report the first case of long-term response to PIMI in PDGFRA D842V mutant GIST. Pimitespib may be effective for treating GIST harboring this mutation by inhibiting HSP90.

Abstract 4033: Pan-exon mutant KIT inhibitor DCC-3009 demonstrates tumor regressions in preclinical gastrointestinal stromal tumor models

Abstract Introduction: Gastrointestinal stromal tumors (GISTs) are typically driven by primary mutations in KIT exons 9 or 11. Heterogeneous drug-resistant secondary mutations arise in patients treated with FDA approved KIT inhibitors, including imatinib and sunitinib. Drug resistant secondary mutations are found at multiple regions in the ATP pocket (encoded by exons 13 and 14) or activation switch (encoded by exons 17 and 18) of KIT kinase. In addition, multiple drug-resistant clones can arise within a tumor or in metastatic tumor sites. An inhibitor that can broadly and potently inhibit the spectrum of KIT mutations is highly sought. Ripretinib has been FDA approved as a 4th line treatment for GIST and has broad activity against KIT mutations, including clinical potency in patients with mutations in KIT exons 11, 17, or 18. DCC-3009 was designed as a next generation KIT inhibitor that broadly and potently inhibits primary KIT mutations in exons 9 and 11 and secondary drug-resistant mutations across exons 13, 14, 17, and 18. DCC-3009 is a potent and selective inhibitor in enzyme and cell-based assays, and has demonstrated efficacy in xenograft models driven by drug resistant KIT mutations. Methods: DCC-3009 was tested for inhibition of KIT mutants using standard enzyme and cell-based assays. Levels of phosphorylated KIT were determined by Western blot or ELISA. Proliferation was measured using the fluorescent dye resazurin. KIT mutant xenograft or patient-derived xenograft models were performed at Crown Biosciences or Labcorp, AAALAC accredited facilities, with the approval of Animal Care and Use Committees. Results: In BaF3 cells transfected with KIT mutants, DCC-3009 was shown to potently inhibit the spectrum of known primary and secondary drug-resistant mutations in GIST. The pan-mutant KIT profile of DCC-3009 was shown in vitro to be superior to 2nd and 3rd line standard of care therapies sunitinib and regorafenib. DCC-3009 was selective for KIT when screened against a large panel of kinases. DCC-3009 has optimized pharmaceutical properties for oral administration. In pharmacokinetic/pharmacodynamic studies DCC-3009 achieved sufficient free drug levels to significantly inhibit drug-resistant KIT mutants for 12 hr post dose. In xenograft studies, treatment with DCC-3009 twice daily led to tumor regression in drug-resistant models with KIT exon 9/13, 11/13 or 11/17 mutations. Conclusions: DCC-3009 is a pan-exon mutant KIT inhibitor exhibiting high potency in KIT mutants in pre-clinical models spanning exons 9, 11, 13, 14, 17 and 18. In vivo, DCC-3009 exhibited efficacy in drug-resistant models with KIT exon 9/13, 11/13 or 11/17 mutations. Based on this profile, DCC-3009 has entered formal preclinical development. Citation Format: Bryan D. Smith, Subha Vogeti, Timothy M. Caldwell, Hanumaiah Telikepalli, Yu Mi Ahn, Gada Al-Ani, Stacie L. Bulfer, Andrew Greenwood, Cale L. Heiniger, Joshua W. Large, Cynthia B. Leary, Wei-Ping Lu, Kylie Luther, William C. Patt, Max D. Petty, Yeni K. Romero, Forrest A. Stanley, Kristen L. Stoltz, Daniel C. Tanner, Sihyung Yang, Yu Zhan, Bertrand Le Bourdonnec, Daniel L. Flynn. Pan-exon mutant KIT inhibitor DCC-3009 demonstrates tumor regressions in preclinical gastrointestinal stromal tumor models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4033.

Abstract 4872: DCC-3116, a first-in-class selective ULK1/2 inhibitor of autophagy, in combination with the KIT inhibitor ripretinib induces complete regressions in GIST preclinical models

Abstract Background: Cancer cells activate autophagy as an adaptive stress response (ASR) mechanism to therapies targeting the RTK/RAS/MAPK/PI3K pathways, limiting antitumor response. Autophagy is initiated through ULK1/2 kinases and is triggered by inhibitors of the MAPK and PI3K pathways. Most gastrointestinal stromal tumors (GIST) are driven by mutations in KIT kinase. KIT signals through MAPK/PI3K pathways, suppressing ULK1/2 kinases and autophagy1,2,3. Inhibition of mutant KIT reverses this suppression, activating autophagy and cancer cell survival. Approved therapies for GIST include imatinib, sunitinib, regorafenib, ripretinib, and avapritinib. Treatment with these inhibitors is initially successful, but drug resistance can develop either through KIT secondary mutations or ASR pathways including autophagy. DCC-3116 is a selective, potent, first-in-class investigational inhibitor of the ULK1/2 in clinical development in combination with targeted therapies that activate the autophagic ASR pathway. Herein we demonstrate that ULK1/2 and autophagy are activated upon treatment with ripretinib in KIT mutant GIST models A combination of ripretinib with DCC-3116 inhibits autophagy in vitro and leads to complete tumor regressions in preclinical models of GIST. Methods: Inhibition of ULK1/2 in cell assays was measured using an ELISA for the ULK substrate phospho-ATG13 (pATG13). Autophagic flux was measured by monitoring mCherry/GFP tagged LC3 protein in GIST cells. Xenograft studies were performed at CROs. Results: Ripretinib treatment led to the activation of ULK1/2 by 2-3-fold in mutant KIT GIST cell lines. DCC-3116 inhibited both ripretinib-induced and basal pATG13 with IC50 values of 12-32 nM. Treatment of GIST-T1 cells with ripretinib increased autophagic flux 3-fold. DCC-3116 potently inhibited flux with an IC50 value of 38 nM. Ripretinib also induced pATG13 and autophagic flux (1.5-2.5-fold) in multiple imatinib-resistant cell lines, which was inhibited by DCC-3116 with IC50 values between 8-189 nM. In a GIST T1 PK/PD model, DCC-3116 inhibited ULK1/2-mediated pATG13. The combination of DCC-3116 with ripretinib resulted in complete tumor regressions in comparison to single agent treatment in GIST preclinical models. Conclusions: These data demonstrate preclinically that, like other receptor tyrosine kinase inhibitors1, ripretinib activates ULK1/2-mediated autophagy as an ASR resistance mechanism which is inhibited by DCC-3116, providing the rationale to study the combination of DCC-3116 with ripretinib in GIST patients. DCC-3116 is currently in a Phase 1 clinical trial in patients with advanced solid tumors (NCT04892017).

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.

Clinicopathological and mutational characteristics of primary double mutant gastrointestinal stromal tumor: a single center study with review of the literature

AimsPrimary double KIT/PDGFRA mutations are very rare in gastrointestinal stromal tumours (GISTs) but have not been comprehensively studied to date. In the present study, we investigated the clinicopathologic and genetic features of eight cases of primary double-mutant GISTs, and we reviewed the literature.Methods and resultsThe tumours occurred in six males and two females (age range 57–83 years) and involved the small intestine (n = 4), stomach (n = 2), rectum (n = 1) and retroperitoneum (n = 1). Clinical manifestations were variable, ranging from indolent (no symptoms) to aggressive disease (tumour rupture and haemorrhage). All patients underwent surgical excision, and six of them were treated with imatinib. No one experienced recurrence or other complications during the follow-up time (10 to 61 months). Histologically, all the tumours exhibited mixed cell types, accompanied by variable interstitial changes. KIT mutations were detected in all cases, and the majority of them were present in different exons (n = 5). No PDGFRA exon 12, 14 or 18 mutations were found. All the mutations were validated by next-generation sequencing, and two additional variants with comparatively low allelic fractions were identified in one case. Two of the cases had available allele distribution data, one with an in cis compound mutation and the other with an in trans compound mutation.ConclusionPrimary double-mutant GISTs have distinctive clinicopathologic and mutational features. Studies of more cases are necessary for a better understanding of these tumours.

TKI Treatment Sequencing in Advanced Gastrointestinal Stromal Tumors.

Prior to the early 2000s, patients with advanced gastrointestinal stromal tumors (GIST) had very poor prognoses owing to a lack of effective therapies. The development of tyrosine kinase inhibitors at the turn of the century significantly improved the overall survival for patients with GIST. The resounding success of imatinib in the first clinical trial of a tyrosine kinase inhibitor to treat GIST led to its approval for first-line therapy for advanced GIST; this study was open to all comers and not restricted to any GIST subtype(s). The trials that led to the approvals of second-, third-, and fourth-line therapy for advanced GIST were also open to all patients with advanced/metastatic GIST. Only in retrospect do we realize the role that the molecular subtypes played in the results observed in these studies. In this review, we discuss the studies that led to the US Food and Drug Administration approval of imatinib (first line), sunitinib (second line), regorafenib (third line), and ripretinib (fourth line) for advanced KIT-mutant GIST. In addition, we review how information about GIST molecular subtypes has been used to accelerate the approval of other targeted therapies for non-KIT mutant GIST, leading to the approval of five additional drugs indicated for the treatment of specific GIST molecular subtypes. We also discuss how our understanding of the molecular subtypes will play a role in the next generation of therapeutic approaches for treating advanced GIST.

GISTs with NTRK Gene Fusions: A Clinicopathological, Immunophenotypic, and Molecular Study.

The most common mutations in gastrointestinal stromal tumors (GISTs) are KIT or PDGFRA mutations. Recently, neurotrophic tyrosine receptor kinase (NTRK) fusions have been reported in WT GISTs, which increased interest in introducing tropomyosin receptor kinase (TRK) inhibitors as treatments for GISTs with NTRK fusions. Hence, we aimed to screen NTRK fusions in WT GISTs; we used fluorescence in situ hybridization (FISH), next-generation sequencing (NGS), and immunohistochemistry (IHC) to screen NTRK fusions in 46 WT GISTs and evaluate each method. We further reviewed NTRK fusion-positive GISTs from the literature and performed clinical and pathological analyses; two GISTs with an ETV6-NTRK3 fusion (5%) were identified, while only one (50%) was positive for Pan-TRK expression. On the other hand, among the six GISTs with Pan-TRK-positive expression, only one (17%) harbored NTRK fusion. The literature review revealed the strong consistency between FISH and NGS and the limited value of Pan-TRK IHC in screening NTRK fusions in GISTs. In addition, the clinical and pathological analysis showed that GISTs with NTRK rearrangement occurred less frequently in the stomach, were more frequently larger in size, and the epithelioid type presented with a higher risk of recurrence. The NTRK3 fusion has been more common than the NTRK1 fusion in GISTs to date; our study identified two ETV6-NTRK3 fusions in 46 WT GISTs. Compared with FISH and IHC, NGS is preferred for screening WT GISTs, including NTRK rearrangements. However, since GISTs with NTRK fusions are rare, further studies including more samples and mechanistic investigations should be conducted in the future.

Current Molecular Profile of Gastrointestinal Stromal Tumors and Systemic Therapeutic Implications.

Gastrointestinal stromal tumors (GISTs) are malignant mesenchymal tumors arising from the intestinal pacemaker cells of Cajal. They compose a heterogenous group of tumors due to a variety of molecular alterations. The most common gain-of-function mutations in GISTs are either in the KIT (60-70%) or platelet-derived growth factor receptor alpha (PDGFRA) genes (10-15%), which are mutually exclusive. However, a smaller subset, lacking KIT and PDGFRA mutations, is considered wild-type GISTs and presents distinct molecular findings with the activation of different proliferative pathways, structural chromosomal and epigenetic changes, such as inactivation of the NF1 gene, mutations in the succinate dehydrogenase (SDH), BRAF, and RAS genes, and also NTRK fusions. Currently, a molecular evaluation of GISTs is imperative in many scenarios, aiding in treatment decisions from the (neo)adjuvant to the metastatic setting. Here, we review the most recent data on the molecular profile of GISTs and highlight therapeutic implications according to distinct GIST molecular subtypes.

MiRNA Expression May Have Implications for Immunotherapy in PDGFRA Mutant GISTs.

Gastrointestinal stromal tumors (GISTs) harboring mutations in the PDGFRA gene occur in only about 5–7% of patients. The most common PDGFRA mutation is exon 18 D842V, which is correlated with specific clinico-pathological features compared to the other PDGFRA mutated GISTs. Herein, we present a miRNA expression profile comparison of PDGFRA D842V mutant GISTs and PDGFRA with mutations other than D842V (non-D842V). miRNA expression profiling was carried out on 10 patients using a TLDA miRNA array. Then, miRNA expression was followed by bioinformatic analysis aimed at evaluating differential expression, pathway enrichment, and miRNA-mRNA networks. We highlighted 24 differentially expressed miRNAs between D842V and non-D842V GIST patients. Pathway enrichment analysis showed that deregulated miRNAs targeted genes that are mainly involved in the immune response pathways. The miRNA-mRNA networks highlighted a signature of miRNAs/mRNA that could explain the indolent behavior of the D842V mutated GIST. The results highlighted a different miRNA fingerprint in PDGFRA D842V GISTs compared to non-D842Vmutated patients, which could explain the different biological behavior of this GIST subset.

P-264 The molecular-metabolic interplay in metastatic gastrointestinal stromal tumors (GISTs): The predictive role of body mass index

KIT exon 11 Pathogenic Variants (PVs) are the most frequent mutations in Gastrointestinal Stromal Tumors (GISTs). These patients represent a heterogeneous subgroup in terms of biological and clinical behavior: despite most GISTs with KIT exon 11 mutations are highly sensitive to front-line imatinib, the Progression Free Survival (PFS) may vary greatly. We investigated the predictive role of Body Mass Index (BMI), Neutrophil–Lymphocyte Ratio (NLR), and type and codon location of KIT exon 11 mutations in metastatic GIST patients treated with first-line imatinib 400 mg/die. Clinico-pathological characteristics, mutational status, BMI and NLR, were analyzed from a GIST System database prospectively collected. The primary outcome investigated was the Time to Treatment Failure (TTF). We classified the patients in 2 groups: i) KIT Exon 11 deletion or insertion/deletion in codons 557 and/or 558 (named “D-557/8”); ii) other than D-557/8 mutations (named “No-D-557/8”). The NLR was recorded from the routinely performed blood cell count as the absolute count of neutrophils divided by the absolute count of lymphocytes from peripheral blood samples collected at baseline. Sixty (60) KIT exon 11 mutated patients were included in the study: 25 (31.3%) showed exon 11 deletion or delins involving 557 and/or 558 codons (D-557/8 group), and 35 patients (43.7%) had a deletion in codons other than 557/558 or other PV types (duplication, insertion or SNV)(No-D-557/8 group). A total of 41 events (progression or death) were observed (68.3%): 18 events in the D-557/8 group of 25 patients (72%); 23 events in the No-D-557/8 group of 35 patients (65.7%). Overall median TTF was 37 months (95% confidence interval [CI]: 26.8-47.1). Median TTF was 24 months (95% CI: 21.3, 26.7) for the D-557/8 Group, and 49 months (95% CI: 39.4, 58.6) for the No-D-557/8 Group (p 25 (median TTF: 57.4 months (range 32-92) vs 24.2 months (range 3-45); p=0.001). In the KIT exon 11 mutated patients, who are the most common molecular-based subgroup of advanced GIST patients, our results reveal the important impact of BMI on TTF. These data support the functional cross-talk between metabolic and molecular features also in GISTs, paradigmatic model of oncogene addiction, and represent the rationale to better investigate whether factors of metabolic interest, such as BMI, could have a further impact on response to treatment.

Tropomyosin-Related Kinase Fusions in Gastrointestinal Stromal Tumors.

Simple SummaryThe canonical mutations in gastrointestinal stromal tumors (GISTs) are typically activating mutations in KIT and platelet-derived growth factor receptor alpha (PDGFRA). Imatinib, the treatment of choice for GISTs, shows a lower response in KIT/PDGFRA wild-type GISTs. Neurotrophic tyrosine receptor kinase (NTRK) fusion, which can be treated with an NTRK target agent, has been reported in KIT/PDGFRA wild-type GISTs, and, therefore, the Yonsei Cancer Center analyzed NTRK fusion incidence in KIT/PDGFRA wild-type GISTs. At the Yonsei Cancer Center, NTRK fusion was confirmed in 16% of cases. Confirmation of NTRK fusion in KIT/PDGFRA wild-type GISTs provides important information for improving therapeutic outcomes. NTRK fusion was confirmed in 16% of KIT/PDGFRA wild-type GIST cases at the Yonsei Cancer Center. Confirmation of NTRK fusion in KIT/PDGFRA wild-type GISTs will improve therapeutic outcomes.The canonical mutations in gastrointestinal stromal tumors (GISTs) are typically activating mutations in KIT and platelet-derived growth factor receptor alpha (PDGFRA). GISTs with non-canonical mutations are a heterogeneous group. Here, we examined tropomyosin-related kinase (TRK) fusion in GIST cases without KIT/PDGFRA mutations (KIT/PDGFRA wild-type (WT) GISTs). We retrospectively analyzed patients who were diagnosed with GISTs at the Yonsei Cancer Center, Severance Hospital, between January 1998 and December 2016. Thirty-one patients with KIT/PDGFRA WT GISTs were included in the analysis. TRK expression in tumor samples was assessed by pan-TRK immunohistochemistry (IHC), and the neurotrophic tyrosine receptor kinase (NTRK: the gene encoding TRK) rearrangement was analyzed by fluorescence in situ hybridization (FISH). IHC analyses revealed that five cases in this cohort exhibited a weak to moderate TRK expression. NTRK1 fusions were detected in three tumor samples, and two samples harbored NTRK3 fusions. The remaining 26 samples did not harbor NTRK fusions. Two types of NTRK fusions were detected, and the overall NTRK fusion frequency in KIT/PDGFRA WT GIST cases was 16% (5/31). Our data provide insights into the molecular alterations underpinning KIT/PDGFRA WT GISTs. More effort should be devoted to improve methods to identify this distinct disease subtype within the KIT/PDGFRA WT GIST group.

Nintedanib overcomes drug resistance from upregulation of FGFR signalling and imatinib-induced KIT mutations in gastrointestinal stromal tumours.

Drug resistance remains a major challenge in the clinical treatment of gastrointestinal stromal tumours (GISTs). While acquired on‐target mutations of mast/stem cell growth factor receptor (KIT) kinase is the major resistance mechanism, activation of alternative signalling pathways may also play a role. Although several second‐ and third‐generation KIT kinase inhibitors have been developed that could overcome some of the KIT mutations conferring resistance, the low clinical responses and narrow safety window have limited their broad application. The present study revealed that nintedanib not only overcame resistance induced by a panel of KIT primary and secondary mutations, but also overcame ERK‐reactivation‐mediated resistance caused by the upregulation of fibroblast growth factor (FGF) activity. In preclinical models of GISTs, nintedanib significantly inhibited the proliferation of imatinib‐resistant cells, including GIST‐5R, GIST‐T1/T670I and GIST patient‐derived primary cells. In addition, it also exhibited dose‐dependent inhibition of ERK phosphorylation upon FGF ligand stimulation. In vivo antitumour activity was also observed in several xenograft GIST models. Considering the well‐documented safety and pharmacokinetic profiles of nintedanib, this finding provides evidence for the repurposing of nintedanib as a new therapy for the treatment of GIST patients with de novo or acquired resistance to imatinib.

Caveolin-1 expression predicts favourable outcome and correlates with PDGFRA mutations in gastrointestinal stromal tumours (GISTs)

AimsNovel prognostic markers are warranted for gastrointestinal stromal tumours. Caveolin-1 is a multifunctional protein that proved to be associated with outcome in multiple tumour types. Aim of this study was...

Protein tyrosine phosphatase receptor type E (PTPRE) regulates the activation of wild-type KIT and KIT mutants differently

Activation of receptor tyrosine kinases needs tight control by tyrosine phosphatases to keep their normal function. In this study, we investigated the regulation of activation of the type III receptor tyrosine kinase KIT by protein tyrosine phosphatase receptor type E (PTPRE). We found that PTPRE can associate with wild-type KIT and inhibit KIT activation in a dose-dependent manner, although the activation of wild-type KIT is dramatically inhibited even when PTPRE is expressed at low level. The D816V mutation of KIT is the most frequently found oncogenic mutation in mastocytosis, and we found that PTPRE can associate and inhibit the activation of KIT/D816V in a dose dependent manner, but the inhibition is much weaker compared with wild-type KIT. Similar to mastocytosis, KIT mutations are the main oncogenic mutations in gastrointestinal stromal tumors (GISTs) although GISTs carry different types of KIT mutations. We further studied the regulation of the activation of GISTs-type KIT mutants and other mastocytosis-type KIT mutants by PTPRE. Indeed, PTPRE can almost block the activation of GISTs-type KIT mutants, while the activation of mastocytosis-type KIT mutants is more resistant to the inhibition of PTPRE. Taken together, our results suggest that PTPRE can associate with KIT, and inhibit the activation of both wild-type KIT and GISTs-type KIT mutants, while the activation of mastocytosis-type KIT mutants is more resistant to PTPRE.