KIT/PDGFRA Variant Allele Frequency as Prognostic Factor in Gastrointestinal Stromal Tumors (GISTs): Results From a Multi-Institutional Cohort Study.

BACKGROUND: The patient selection for optimal adjuvant therapy in gastrointestinal stromal tumors (GISTs) is provided by nomogram based on tumor size, mitotic index, tumor location, and tumor rupture. Although mutational status is not currently used to risk assessment, tumor genotype showed a prognostic influence on natural history and tumor relapse. Innovative measures, such as KIT/PDGFRA-mutant-specific variant allele frequency (VAF) levels detection from next-generation sequencing (NGS), may act as a surrogate of tumor burden and correlate with prognosis and overall survival of patients with GIST, helping the choice for adjuvant treatment. PATIENTS AND METHODS: This was a multicenter, hospital-based, retrospective/prospective cohort study to investigate the prognostic role of KIT or PDGFRA-VAF of GIST in patients with radically resected localized disease. In the current manuscript, we present the results from the retrospective phase of the study. RESULTS: Two-hundred (200) patients with GIST between 2015 and 2022 afferent to 6 Italian Oncologic Centers in the EURACAN Network were included in the study. The receiver operating characteristic (ROC) curves analysis was used to classify "low" vs. "high" VAF values, further normalized on neoplastic cellularity (nVAF). When RFS between the low and high nVAF groups were compared, patients with GIST with KIT/PDGFRA nVAF > 50% showed less favorable RFS than patients in the group of nVAF ≤ 50% (2-year RFS, 72.6% vs. 93%, respectively; P = .003). The multivariable Cox regression model confirmed these results. In the homogeneous sub-population of intermediate-risk, patients with KIT-mutated GIST, the presence of nVAF >50% was statistically associated with higher disease recurrence. CONCLUSION: In our study, we demonstrated that higher nVAF levels were independent predictors of GIST prognosis and survival in localized GIST patients with tumors harboring KIT or PDGFRA mutations. In the cohort of intermediate-risk patients, nVAF could be helpful to improve prognostication and the use of adjuvant imatinib.

Expanding the Spectrum of BRAF Non-V600E Mutations in Thyroid Nodules: Evidence-Based Data from a Tertiary Referral Centre.

The BRAF p.V600E mutation represents the most specific marker for papillary thyroid carcinoma and is potentially related to aggressive behavior and persistent disease. BRAF alterations other than the p.V600E are less common in thyroid carcinoma and represent an alternative mechanism of BRAF activation with unclear clinical significance. The study aims to describe the frequency and clinicopathologic characteristics of BRAF non-V600E mutations in a large cohort (1654 samples) of thyroid lesions characterized by next-generation sequencing. BRAF mutations have been found in 20.3% (337/1654) of thyroid nodules, including classic (p.V600E) mutation in 19.2% (317/1654) of samples and non-V600E variants in 1.1% of cases (19/1654). BRAF non-V600E alterations include 5 cases harboring p.K601E, 2 harboring p.V600K substitutions, 2 with a p.K601G variant, and 10 cases with other BRAF non-V600E alterations. BRAF non-V600E mutations have been reported in one case of follicular adenoma, three cases of conventional papillary thyroid carcinoma, eight cases of follicular variant of papillary carcinomas, one case of columnar cell variant papillary thyroid carcinoma, one case of oncocytic follicular carcinoma, and two bone metastasis of follicular thyroid carcinoma. We confirm that BRAF non-V600E mutations are uncommon and typically found in indolent follicular-patterned tumors. Indeed, we show that BRAF non-V600E mutations can be found in tumors with metastatic potential. However, in both aggressive cases, the BRAF mutations were concomitant with other molecular alterations, such as TERT promoter mutation.

Analysis of microbiome in gastrointestinal stromal tumors: Looking for different players in tumorigenesis and novel therapeutic options.

Preclinical forms of gastrointestinal stromal tumor (GIST), small asymptomatic lesions, called microGIST, are detected in approximately 30% of the general population. Gastrointestinal stromal tumor driver mutation can be already detected in microGISTs, even if they do not progress into malignant cancer; these mutations are necessary, but insufficient events to foster tumor progression. Here we profiled the tissue microbiota of 60 gastrointestinal specimens in three different patient cohorts-micro, low-risk, and high-risk or metastatic GIST-exploring the compositional structure, predicted function, and microbial networks, with the aim of providing a complete overview of microbial ecology in GIST and its preclinical form. Comparing microGISTs and GISTs, both weighted and unweighted UniFrac and Bray-Curtis dissimilarities showed significant community-level separation between them and a pronounced difference in Proteobacteria, Firmicutes, and Bacteroidota was observed. Through the LEfSe tool, potential microbial biomarkers associated with a specific type of lesion were identified. In particular, GIST samples were significantly enriched in the phylum Proteobacteria compared to microGISTs. Several pathways involved in sugar metabolism were also highlighted in GISTs; this was expected as cancer usually displays high aerobic glycolysis in place of oxidative phosphorylation and rise of glucose flux to promote anabolic request. Our results highlight that specific differences do exist in the tissue microbiome community between GIST and benign lesions and that microbiome restructuration can drive the carcinogenesis process.

Validation of a novel risk score to predict early and late recurrence in solitary fibrous tumour.

BACKGROUND: Current risk models in solitary fibrous tumour (SFT) were developed using cohorts with short follow-up and cannot reliably identify low-risk patients. We recently developed a novel risk model (G-score) to account for both early and late recurrences. Here, we aimed to validate the G-score in a large international cohort with long-term follow-up. METHODS: Data were collected from nine sarcoma referral centres worldwide. Recurrence-free interval (RFi) was the primary endpoint. RESULTS: The cohort comprised 318 patients with localised extrameningeal SFTs. Disease recurrence occurred in 96 patients (33%). The estimated 5-year RFi rate was 72%, and the 10-year RFi rate was 52%. G-score precisely predicted recurrence risk with estimated 10-year RFi rate of 84% in low risk, 54% in intermediate risk and 36% in high risk (p < 0.001; C-index 0.691). The mDemicco (p < 0.001; C-index 0.749) and SalasOS (p < 0.001; C-index 0.674) models also predicted RFi but identified low-risk patients less accurate with 10-year RFi rates of 72% and 70%, respectively. CONCLUSIONS: G-score is a highly significant predictor of early and late recurrence in SFT and is superior to other models to predict patients at low risk of relapse. A less intensive follow-up schedule could be considered for patients at low recurrence risk according to G-score.

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.

Primary malignant pericardial tumour in Lynch syndrome.

BACKGROUND: This case represents the first report of malignant primary cardiac tumour in a patient with Lynch Syndrome associated with MSH2 pathogenic variant. CASE PRESENTATION: A 57-year-old woman with previous ovarian cystadenocarcinoma was admitted to the emergency room for hematic pericardial effusion. Multimodal diagnostic imaging revealed two solid pericardial vascularized masses. After pericardiectomy, the final histological diagnosis was poorly differentiated pleomorphic sarcomatoid carcinoma. During follow-up she developed an ampulla of Vater adenocarcinoma. Genetic analysis identified an MSH2 pathogenic variant. CONCLUSION: This case contributes to expand the tumour spectrum of Lynch syndrome, suggesting that MSH2 pathogenic variants cause a more complex multi-tumour cancer syndrome than the classic Lynch Syndrome. In MSH2 variant carriers, symptoms such as dyspnoea and chest discomfort might alert for rare tumours and a focused cardiac evaluation should be considered.

The Emerging Role of the FGF/FGFR Pathway in Gastrointestinal Stromal Tumor.

Gastrointestinal stromal tumors (GIST) are rare neoplasms of mesenchymal origin arising in the gastrointestinal tract. The vast majority are characterized by mutually exclusive activating mutations in KIT or Platelet-derived growth factor alpha (PDGFRA) receptors, or less frequently by succinate dehydrogenase complex (SDH) or NF1 inactivation, with very rare cases harboring mutant BRAF or RAS alleles. Approximately 5% of GISTs lack any of such mutations and are called quadruple wild-type (WT) GISTs. Recently, deregulated Fibroblast Growth Factor (FGF)/FGF-receptor (FGFR) signaling emerged as a relevant pathway driving oncogenic activity in different molecular subgroups of GISTs. This review summarizes all the current evidences supporting the key role of the FGF/FGFR pathway activation in GISTs, whereby either activating mutations, oncogenic gene fusions, or autocrine/paracrine signaling have been detected in quadruple WT, SDH-deficient, or KIT-mutant GISTs.

Gain of FGF4 is a frequent event in KIT/PDGFRA/SDH/RAS-P WT GIST.

Gastrointestinal stromal tumors (GIST) lacking mutations in KIT/PDGFRA or RAS pathways and retaining an intact SDH complex are usually referred to as KIT/PDGFRA/SDH/RAS-P WT GIST or more simply quadruple WT GIST (~5% of all GIST). Despite efforts made, no recurrent genetic event in quadruple WT GIST has been identified so far. To further investigate this disease, we performed high throughput copy number analysis on quadruple WT GIST specimens identifying a recurrent focal gain in band 11q13.3 (involving FGF3/FGF4) in 6/8 cases. This event was not found in the other molecular GIST subgroups. FGF3/FGF4 duplication was associated with high expression of FGF4, both at mRNA and protein level, a growth factor normally not expressed in adult tissues or in KIT/PDGFRA-mutated GIST. FGFR1 was found to be the predominant FGF receptor expressed and phosphorylation of AKT was detected, suggesting that a FGF4-FGFR1 autocrine loop could stimulate downstream signaling in quadruple WT GIST. Together with the recent reports of quadruple WT cases carrying FGFR1 activating alterations, these findings strengthen the hypothesis of a potential involvement of FGFR pathway deregulation in quadruple WT GIST, which may represent a rationale for novel therapeutic approaches.

An exploratory study by DMET array identifies a germline signature associated with imatinib response in gastrointestinal stromal tumor.

Imatinib represents the standard therapy for gastrointestinal stromal tumor (GIST) patients with metastatic/unresectable disease. Despite  the excellent results achieved with its introduction, the majority of patients quite invariably experience disease progression. The aim of this study was to understand the contribution of germline DNA polymorphisms in discriminating between imatinib clinical response [evaluated as progression free survival (PFS)] and toxicity. In particular, a discovery cohort (34 GIST with a KIT exon 11 primary mutation, and no toxicity) was analyzed through DMET array that interrogates 1936 variants in 231 genes of the ADME process. We further confirmed the genotype of selected variants in an extended cohort of 49 patients (the original cohort and 15 new cases, all with exon 11 primary mutation), identifying 6 SNPs- ABCB4 rs1202283, ABCC2 rs2273697, ABCG1 rs1541290, CYP11B1 rs7003319, CYP7B1 rs6987861, and NQO1 rs10517-significantly associated with response to imatinib. Three SNPs, ABCB4 rs1202283, ABCC2 rs2273697, and NQO1 rs10517, which had a significant association after adjusted multivariate analysis, were included in a genetic prediction model. We confirmed that these SNPs could stratify the cohort of 49 patients according to the risk of developing progression under imatinib treatment. In conclusion, we identified a genetic signature of response to imatinib therapy in GIST patients able to stratify patients at low and high risk to progress, according to their genotype.

Unusual bilateral ovarian metastases from ileal gastrointestinal stromal tumor (GIST): a case report.

BACKGROUND: Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract and liver and peritoneum are the main sites of recurrence. Ovarian metastases from GIST are very rare. CASE PRESENTATION: A 50 years-old woman was found to have a pelvic mass on transvaginal ultrasound (TV-US) and computed tomography (CT)-scan, considered as a right ovarian mass. The patient underwent surgical abdominal exploration that showed an ileal mass, a normal right ovary and an irregular and vascularized surface of the left ovary. A segmental ileal resection and an ileal anastomosis were performed. Frozen section showed a GIST and surgery was completed with hysterectomy, bilateral salpingo-oophorectomy, pelvic peritonectomy, peritoneal washing and Burch procedure. The histological examination confirmed an ileal GIST with ovarian metastases, harboring in both sites of disease a KIT exon 11 deletion. CONCLUSIONS: Ovarian localizations, as far as rare, can be a clinical finding in case of ileal GIST patients, and both gynecologists, pathologists and medical oncologists should be able to recognize them.

Integrated Molecular Characterization of Gastrointestinal Stromal Tumors (GIST) Harboring the Rare D842V Mutation in PDGFRA Gene.

Gastrointestinal stromal tumors (GIST) carrying the D842V activating mutation in the platelet-derived growth factor receptor alpha (PDGFRA) gene are a very rare subgroup of GIST (about 10%) known to be resistant to conventional tyrosine kinase inhibitors (TKIs) and to show an indolent behavior. In this study, we performed an integrated molecular characterization of D842V mutant GIST by whole-transcriptome and whole-exome sequencing coupled with protein-ligand interaction modelling to identify the molecular signature and any additional recurrent genomic event related to their clinical course. We found a very specific gene expression profile of D842V mutant tumors showing the activation of G-protein-coupled receptor (GPCR) signaling and a relative downregulation of cell cycle processes. Beyond D842V, no recurrently mutated genes were found in our cohort. Nevertheless, many private, clinically relevant alterations were found in each tumor (TP53, IDH1, FBXW7, SDH-complex). Molecular modeling of PDGFRA D842V suggests that the mutant protein binds imatinib with lower affinity with respect to wild-type structure, showing higher stability during the interaction with other type I TKIs (like crenolanib). D842V mutant GIST do not show any actionable recurrent molecular events of therapeutic significance, therefore this study supports the rationale of novel TKIs development that are currently being evaluated in clinical studies for the treatment of D842V mutant GIST.

Identification of an Actionable Mutation of KIT in a Case of Extraskeletal Myxoid Chondrosarcoma.

Extraskeletal myxoid chondrosarcoma (EMC) is an extremely rare soft tissue sarcoma, marked by a translocation involving the NR4A3 gene. EMC is usually indolent and moderately sensitive to anthracycline-based chemotherapy. Recently, we reported on the therapeutic activity of sunitinib in a series of EMC cases, however the molecular target of sunitinib in EMC is unknown. Moreover, there is still the need to identify alternative therapeutic strategies. To better characterize this disease, we performed whole transcriptome sequencing in five EMC cases. Peculiarly, in one sample, an in-frame deletion (c.1735_1737delGAT p.D579del) was identified in exon 11 of KIT. The deletion was somatic and heterozygous and was validated both at DNA and mRNA level. This sample showed a marked high expression of KIT at the mRNA level and a mild phosphorylation of the receptor. Sanger sequencing of KIT in additional 15 Formalin Fixed Paraffin Embedded (FFPE) EMC did not show any other mutated cases. In conclusion, exon 11 KIT mutation was detected only in one out of 20 EMC cases analyzed, indicating that KIT alteration is not a recurrent event in these tumors and cannot explain the EMC sensitivity to sunitinib, although it is an actionable mutation in the individual case in which it has been identified.

An exploratory association of polymorphisms in angiogenesis-related genes with susceptibility, clinical response and toxicity in gastrointestinal stromal tumors receiving sunitinib after imatinib failure.

The angiogenic pathway plays a pivotal role in tumor growth, invasiveness and metastasis. The most important actors in the angiogenic pathway are VEGFA and its receptors VEGFR1, 2 and 3. These genes are polymorphic, and the presence of single nucleotide polymorphisms may result in angiogenic deregulation. Herein, we hypothesized that germline variants may affect sunitinib efficacy (TTP and OS) and/or toxicity. Therefore, we investigated 19 polymorphisms, in four genes, in 54 GIST patients, treated with second-line sunitinib and 147 healthy controls. Through a multiple candidate gene approach, we also investigated, for the first time, any possible significant associations with GIST susceptibility and clinical pathological features. The most important result shows two associations between polymorphisms in VEGFR3 rs6877011 (CC vs. CG, OR 9.7, 95% CI 3.31-28.4; P < 0.001) and rs7709359 (AA+AG vs. GG, OR 5.01, 95% CI 1.33-18.8; P = 0.017) and TTP. Interestingly, the association between VEGFR3 rs6877011 and TTP maintained the significance after applying the Bonferroni correction for multiple testing (P = 0.017). We also highlighted the association with sunitinib-related toxicity; in particular, VEGFA polymorphism rs3025039 (CT+TT vs. CC, OR 15.3, 95% CI 2.2-102.1; P = 0.005) is associated with severe toxicity, with the presence of the variant T allele associated with a grade ≥3 AE. Because of the small sample size and large number of tests performed, we cannot ignore the possibility that some associations have been retrieved by chance. However, the influence of VEGF polymorphisms in angiogenesis is a hypothesis worthy of exploration in cellular models and confirmation in a sizeable cohort of patients.

The progressive fragmentation of the KIT/PDGFRA wild-type (WT) gastrointestinal stromal tumors (GIST).

Recent advances in molecular biology have revolutionized the concept of KIT/PDGFRA wild type (WT) gastrointestinal stromal tumors (GIST) than the past. Indeed, from being defined as GIST without KIT or PDGFRA mutations, we are now faced with the opposite scenario, where KIT/PDGFRA WT GIST are "positively" defined according to their specific molecular alterations. In particular, if until recently KIT/PDGFRA GIST without abnormalities of KIT, PDGFRA, SDH, and the RAS signaling pathway were referred as quadruple WT GIST, today also this small subset of GIST is emerging out as a group of heterogeneous distinct entities with multiple different molecular alterations. Therefore, given this still growing and rapidly evolving scenario, the progressive molecular fragmentation may inevitably lead over the time to the disappearance of KIT/PDGFRA WT GIST, destined to be singularly defined by their molecular fingerprint.

Polymorphisms in DNA repair genes in gastrointestinal stromal tumours: susceptibility and correlation with tumour characteristics and clinical outcome.

DNA repair pathways play an essential role in cancer susceptibility by maintaining genomic integrity. This led us to investigate the influence of polymorphisms in the genes coding repair pathway enzymes on gastrointestinal stromal tumours (GIST) susceptibility, tumour characteristics and clinical outcome. We investigated a panel of 20 polymorphisms in 11 genes in 81 cases and 147 controls. The XPD rs13181 wild-type allele and hOGG1 rs1052133 and XPF rs1800067 minor alleles were significantly associated with disease susceptibility. XPA rs1800975 and rs2808668 were associated with tumour size (P = 0.018), metastatic status at onset (P = 0.035) and mitotic index (P = 0.002). With regards to outcome treatment, the XPD rs50872 minor allele had a significant favourable impact on time to progression (TTP). Similarly, the XPC rs2228000 minor allele was correlated with a longer TTP (P = 0.03). On the contrary, the XPC rs2228001 and hOGG1 rs1052133 minor alleles were associated with a diminished TTP (P = 0.005 and P = 0.01, respectively). Regarding OS, we found the presence of at least one hOGG1 (rs1052133) minor allele that had a 60 % lower risk to die compared to the wild-type carriers (P = 0.04). Furthermore, the XRCC3 rs861539 variant allele is associated with a hazard of early death compared with the wild-type genotype (P = 0.04). To the best of our knowledge, this is the first study on polymorphisms in DNA repair genes, belonging to the different pathways, extensively evaluated in GIST patients. Through this multiple candidate gene approach, we report for the first time the significant associations between polymorphisms in DNA repair genes, susceptibility, clinical pathological features and clinical outcome in GIST.

Successful treatment with personalized dosage of imatinib in elderly patients with gastrointestinal stromal tumors.

Imatinib is the standard first-line therapy for metastatic gastrointestinal stromal tumors. It has markedly improved the prognosis and outcome of patients affected by gastrointestinal stromal tumors, especially in the case of exon 11 KIT mutations. Imatinib-associated adverse events are generally mild to moderate; however, in clinical practice, intolerance caused by chronic toxicities frequently leads to breaks in treatment. This is particularly true in elderly patients in whom age, decline in drug metabolism, and polypharmacy, with a possible drug-drug interaction, may influence the tolerability of imatinib. In the present article, we report our extensive experience with the management of imatinib therapy in a 'real' population, in particular in very elderly patients, discussing whether the use of personalized imatinib dosage could be a safe and advantageous option, enabling continuous administration, thus ensuring effective treatment. Only a few case reports in the literature provide data on outcome with low tailored dosage of imatinib and none of them has been carried out on a Western population. Here, we report four cases treated with low imatinib dosage as a safe and useful option enabling continued treatment with imatinib, improving tolerance, and maintaining good and lasting disease control.

Whole exome sequencing (WES) on formalin-fixed, paraffin-embedded (FFPE) tumor tissue in gastrointestinal stromal tumors (GIST).

BACKGROUND: Next generation sequencing (NGS) technology has been rapidly introduced into basic and translational research in oncology, but the reduced availability of fresh frozen (FF) tumor tissues and the poor quality of DNA extracted from formalin-fixed, paraffin-embedded (FFPE) has significantly impaired this process in the field of solid tumors. To evaluate if data generated from FFPE material can be reliably produced and potentially used in routine clinical settings, we performed whole exome sequencing (WES) from tumor samples of Gastrointestinal stromal tumors (GIST), either extracted FF or FFPE, and from matched normal DNA. METHODS: We performed whole exome enrichment and sequencing at 100bp in paired end on four GIST samples, either from FFPE or fresh-frozen tissue, and from matched normal DNA. RESULTS: The integrity of DNA extracted from FFPE was evaluated by a modified RAPD PCR method, thus identifying high quality (HQ) and low quality (LQ) FFPE. DNA library production and exome capture was feasible for both classes of FFPE, despite the smaller yield and insert size of LQ-FFPE. WES produced data of equal quality from FF and FFPE, while only HQ-FFPE yielded an amount of data comparable to FF samples. Bioinformatic analysis showed that the percentage of variants called both in FF and FFPE samples was very high in HQ-FFPE, reaching 94-96 % of the total number of called variants. Classification of somatic variants by nucleotide substitution type showed that HQ-FFPE and FF had similar mutational profiles, while LQ-FFPE samples carried a much higher number of mutations than the FF counterpart, with a significant enrichment of C > T/G > A substitutions. Focusing on potential disease-related variants allowed the discovery of additional somatic variants in GIST samples, apart from the known oncogenic driver mutation, both from sequencing of FF and FFPE material. False positive and false negative calls were present almost exclusively in the analysis of FFPE of low quality. On the whole this study showed that WES is feasible also on FFPE specimens and that it is possible to easily select FFPE samples of high quality that yield sequencing results comparable to the FF counterpart. CONCLUSIONS: WES on FFPE material may represent an important and innovative source for GIST research and for other solid tumors, amenable of possible application in clinical practice.

Good survival outcome of metastatic SDH-deficient gastrointestinal stromal tumors harboring SDHA mutations.

PURPOSE: A subset of patients with KIT/PDGFRA wild-type gastrointestinal stromal tumors show loss of function of succinate dehydrogenase, mostly due to germ-line mutations of succinate dehydrogenase subunits, with a predominance of succinate dehydrogenase subunit A. The clinical outcome of these patients seems favorable, as reported in small series in which patients were individually described. This work evaluates a retrospective survival analysis of a series of patients with metastatic KIT/PDGFRA wild-type succinate dehydrogenase-deficient gastrointestinal stromal tumors. METHODS: Sixty-nine patients with metastatic gastrointestinal stromal tumors were included in the study (11 KIT/PDGFRA wild-type, of whom 6 were succinate dehydrogenase deficient, 5 were non-succinate dehydrogenase deficient, and 58 were KIT/PDGFRA mutant). All six succinate dehydrogenase-deficient patients harbored SDHA mutations. Kaplan-Meier curves and log-rank tests were used to compare the survival of patients with succinate dehydrogenase subunit A-mutant gastrointestinal stromal tumors with that of KIT/PDGFRA wild-type patients without succinate dehydrogenase deficiency and patients with KIT/PDGFRA-mutant gastrointestinal stromal tumors. RESULTS: Follow-up ranged from 8.5 to 200.7 months. The difference between succinate dehydrogenase subunit A-mutant gastrointestinal stromal tumors and KIT/PDGFRA-mutant or KIT/PDGFRA wild-type non-succinate dehydrogenase deficient gastrointestinal stromal tumors was significant considering different analyses (P = 0.007 and P = 0.033, respectively, from diagnosis of gastrointestinal stromal tumor for the whole study population; P = 0.005 and P = 0.018, respectively, from diagnosis of metastatic disease for the whole study population; P = 0.007 for only patients who were metastatic at diagnosis). CONCLUSION: Patients with metastatic KIT/PDGFRA wild-type succinate dehydrogenase-deficient gastrointestinal stromal tumors harboring succinate dehydrogenase subunit A mutations present an impressively long survival. These patients should be identified in clinical practice to better tailor treatments and follow-up over time.