Phosphodiesterase 3A (PDE3A) is an emerging therapy target in various cancers with high expression, as in the majority of gastrointestinal stromal tumors (GISTs). However, its association with clinicopathological factors and patient survival in GISTs remains unexplored. We investigated PDE3A expression using a novel mouse monoclonal antibody and immunohistochemistry in two GIST patient series consisting of 173 formalin-fixed, paraffin-embedded tissue samples on tissue microarrays. In addition, we analyzed the association between PDE3A staining intensity and clinicopathological variables and patient survival. We also assessed PDE3A mRNA expression using qPCR in a subset of the samples. We found that all GISTs expressed PDE3A. The staining pattern was weak in 6.3%, intermediate in 35.8%, and strong in 57.8% of tumors. Weak PDE3A expression was associated with a lower median mitotic count (1/50 HPF vs. 4/50 HPF vs. 5/50 HPF; p = 0.007) and higher incidence of metastases at diagnosis (28% vs. 8% vs. 3.3%; p = 0.040) than in tumors with intermediate or strong expression, respectively. PDE3A and CD117 staining intensities correlated positively (p < 0.001), but PDE3A expression showed no association with sex, age, tumor size, location, risk stratification, mutation profile, Schlafen 12 expression, or metastasis-free or overall survival. We conclude that PDE3A expression can be reliably assessed in archived tumor material using immunohistochemistry. GISTs, with their consistently high PDE3A expression, are a promising target for PDE3A-targeted therapies. This method may also aid in stratifying patients in cancers where PDE3A expression is less common.

BACKGROUND:Succinate dehydrogenase (SDH) deficient wild-type Gastrointestinal Stromal Tumours (wtGIST) are a rare GIST subtype with limited treatment options. Gallium-68 labelled Gastrin Releasing Peptide Receptor (GRPR) antagonist NeoB has shown promise in PET imaging for multiple primary malignancies. This investigation sought to assess the biodistribution of [68Ga]NeoB via PET/CT imaging in metastatic wtGIST patients and aimed to evaluate GRPR expression in lesions to determine the ligand's potential for patient selection in future therapeutic trials. RESULTS:Twelve patients with histologically confirmed metastatic wtGIST were enrolled. [68Ga]NeoB PET/CT imaging was conducted for lesion segmentation and analysis of uptake characteristics. 8 of 12 (66.7%) patients exhibited intense but heterogeneous [68Ga]NeoB uptake in lesions, with variable tracer uptake both within and between lesions. Physiological uptake was highest in the pancreas, liver, and spleen. Four patients (33.3%) displayed minimal or no uptake in tumour lesions. CONCLUSIONS:The majority of wtGIST patients in this small cohort show lesions with intense [68Ga]NeoB uptake. Heterogeneity of uptake indicates GRPR has highly variable inter- and intralesional expression. NeoB has potential for theranostic application in wtGIST, with limited effective standard of care treatments available. Ongoing trials are investigating the therapeutic use of [177Lu]NeoB in this setting. CLINICAL TRIAL NUMBER:Not applicable.

Esophageal adenocarcinoma is a prominent example of cancer characterized by frequent amplifications in oncogenes. However, the mechanisms leading to amplicons that involve breakage-fusion-bridge cycles and extrachromosomal DNA are poorly understood. Here, we use 710 esophageal adenocarcinoma cases with matched samples and patient-derived organoids to disentangle complex amplicons and their associated mechanisms. Short-read sequencing identifies ERBB2, MYC, MDM2, and HMGA2 as the most frequent oncogenes amplified in extrachromosomal DNAs. We resolve complex extrachromosomal DNA and breakage-fusion-bridge cycles amplicons by integrating of de-novo assemblies and DNA methylation in nine long-read sequenced cases. Complex amplicons shared between precancerous biopsy and late-stage tumor, an enrichment of putative enhancer elements and mobile element insertions are potential drivers of complex amplicons' origin. We find that patient-derived organoids recapitulate extrachromosomal DNA observed in the primary tumors and single-cell DNA sequencing capture extrachromosomal DNA-driven clonal dynamics across passages. Prospectively, long-read and single-cell DNA sequencing technologies can lead to better prediction of clonal evolution in esophageal adenocarcinoma. Esophageal adenocarcinoma is characterised by frequent amplifications in oncogenes. Here, the authors use short- and long-read sequencing approaches to analyze primary tumor samples and tumour-derived organoids and to investigate the mechanisms underlying complex amplifications.

We have developed and validated a highly specific, versatile antibody to the extracellular domain of human LGR5 (α-LGR5). α-LGR5 detects LGR5 overexpression in >90% of colorectal cancer (CRC), hepatocellular carcinoma (HCC) and pre-B-ALL tumour cells and was used to generate an Antibody-Drug Conjugate (α-LGR5-ADC), Bispecific T-cell Engager (α-LGR5-BiTE) and Chimeric Antigen Receptor (α-LGR5-CAR). α-LGR5-ADC was the most effective modality for targeting LGR5+ cancer cells in vitro and demonstrated potent anti-tumour efficacy in a murine model of human NALM6 pre-B-ALL driving tumour attrition to less than 1% of control treatment. α-LGR5-BiTE treatment was less effective in the pre-B-ALL cancer model yet promoted a twofold reduction in tumour burden. α-LGR5-CAR-T cells also showed specific and potent LGR5+ cancer cell killing in vitro and effective tumour targeting with a fourfold decrease in pre-B-ALL tumour burden relative to controls. Taken together, we show that α-LGR5 can not only be used as a research tool and a biomarker but also provides a versatile building block for a highly effective immune therapeutic portfolio targeting a range of LGR5-expressing cancer cells.

AIMS:Wild-type gastrointestinal stromal tumours (wtGIST) are frequently caused by inherited pathogenic variants, or somatic alterations in the succinate dehydrogenase subunit genes (SDHx). Succinate dehydrogenase is a key enzyme in the citric acid cycle. SDH deficiency caused by SDHx inactivation leads to an accumulation of succinate, which inhibits DNA and histone demethylase enzymes, resulting in global hypermethylation. Epigenetic silencing of the DNA repair gene MGMT has proven utility as a positive predictor of the therapeutic efficacy of the alklyating drug temozolomide (TMZ) in tumours such as glioblastoma multiforme. The aim of this study was to examine MGMT promoter methylation status in a large cohort of GIST. METHODS:MGMT methylation analysis was performed on 65 tumour samples including 47 wtGIST (33 SDH-deficient wtGIST and 11 SDH preserved wtGIST) and 21 tyrosine kinase (TK) mutant GIST. RESULTS:MGMT promoter methylation was detected in 8 cases of SDH-deficient (dSDH) GIST but in none of the 14 SDH preserved wild-type GIST or 21 TK mutant GIST samples analysed. Mean MGMT methylation was significantly higher (p 0.0449) and MGMT expression significantly lower (p<0.0001) in dSDH wtGIST compared with TK mutant or SDH preserved GIST. No correlation was identified between SDHx subunit gene mutations or SDHC epimutation status and mean MGMT methylation levels. CONCLUSION:MGMT promoter hypermethylation occurs exclusively in a subset of dSDH wtGIST. Data from this study support testing of tumour MGMT promoter methylation in patients with dSDH wtGIST to identify those patients who may benefit from most from TMZ therapy.

Leucine-rich repeat-containing G-protein receptor 5 (LGR5) has been characterised as a stem cell and cancer stem cell marker. Previous analyses of LGR5 transcript levels indicate high level expression discriminates malignancies such as colorectal cancer (CRC) and pre-B acute lymphoblastic leukaemia (pre-B ALL) from healthy tissues suggesting LGR5 protein expression may provide a molecular handle for prognosis and treatment. We have developed highly specific, high affinity antibodies to the extracellular domain of human LGR5 (α-LGR5) that detect high LGR5 protein levels in colorectal cancer (CRC), hepatocellular carcinoma (HCC), and pre-B ALL. In contrast, there is low to undetectable levels of LGR5 protein in normal colon and rectal epithelia, liver, ovarian tissues, brain and immune cell types. LGR5 is rapidly internalised from the plasma membrane and trafficked to intracellular vesicular compartments including lysosomes. Treatment of high LGR5-expressing CRC and pre-B ALL cancer cell lines with an antibody-drug conjugate version of α-LGR5 (α-LGR5-ADC) lead to effective cell killing at nanomolar concentrations. Interventional treatment of pre-B ALL tumours with α-LGR5-ADC in vivo led to rapid tumour attrition. We further demonstrated the therapeutic utility of humanised α-LGR5 by using the corresponding scFv fragment for the generation of α-LGR5 chimeric antigen receptors (CARs) and a Bispecific T cell Engager (BiTE). α-LGR5-CAR-NK cells were effective at killing LGR5-expressing cells while α-LGR5/α-CD3 BiTEs induce T cell activation and killing of NALM6 cells by cytotoxic CD8 + T cells. Taken together, this study establishes α-LGR5-based therapeutic modalities that effectively discriminate and target CRC, HCC and pre-B ALL tumour cells. One Sentence Summary We generated novel antibodies against the cancer cell marker LGR5, validated diagnostic use in prioritizing specific cancer types for targeting, and developed antibody-based therapeutics.

11534 Background: GISTs are the most common mesenchymal tumours of the gastrointestinal tract with an annual incidence of 10-15 per million. 10% of GISTS have activating mutations in the PDGFRA gene. We report our 13 year experience of all the PDGFRA-mutated GISTs in our regional centre in Cambridge. Methods: PDGFRA-mutant GISTs were identified from the Cambridge GIST database. Demographics, clinical and histopathological features, survival and response to tyrosine kinase inhibitors of all the patients from 2008-2021 were reviewed. Results: n = 50 (male:female 1.5:1) Median age 68 years (range 19-87). 8% of patients were under the age of 40 years. Tumour size ranged from 1-26 cm with a median of 5 cm. Mitotic index ranged from 1-51 with a median of 1 mitosis/5mm2. 52% of GISTs were located in the gastric body. Histological subtypes: 44% epithelioid, 36% mixed and 20% spindle cell. 38% of cases had high KIT expression (immunohistochemistry), whilst 48% had patchy expression and 14% were negative. Most were DOG1-positive (94%). 76% had radical surgery, 60% had laparoscopic resection. 24% were assessed as being high risk GISTs using the modified AFIP model contrasted to 13% being high risk with prognostic contour mapping. 13% developed metastatic disease with liver being the most common metastatic site. The table shows PDGFRA mutational analysis results: 58% had a D842V mutation. None had a KIT mutation. With a median follow up of 55.1 months, 82% were alive. 6 patients died from metastatic GIST and 3 from other causes. Median time to metastatic disease in resected GISTs was 30.1 months and median time from metastatic diagnosis to death was 18.5 months. Patients who presented with metastatic disease had poor survival compared with patients with localised disease ( p=0.001). 8 patients were treated with tyrosine kinase inhibitors including imatinib, sunitinib and regorafenib prior to 2020 with no objective responses. 3 patients were treated with Avapritinib since 2020 within the compassionate use programme. All 3 patients had partial responses and 2 patients are continuing Avapritinib with no grade 3 adverse events. Conclusions: We report the largest single centre PDGFRA-mutant GIST cohort from Europe. Male preponderance and exclusive gastric location were observed. KIT expression was patchy to negative in the majority of patients. 58% had PDGFRA D842V mutations for which Avapritinib has been recently approved. No objective responses were seen with imatinib, sunitinib or regorafenib. Our early experience with Avapritinib is promising.[Table: see text]

Abstract AIMS The DNA mismatch repair (MMR) system is critical for genomic stability correcting errors generated during DNA replication with germline pathogenic variants (PVs) causing Lynch syndrome. Although acquired MMR deficiency is associated with temozolomide resistance, the incidence in treatment naïve tumours is unknown and not routinely screened for. Here we present three MMR deficient gliomas and describe their comprehensive molecular profile. METHOD Thirteen gliomas; 9/34 that had undergone sequencing of 50 cancer-associated genes and found to have frameshift/multiple point PVs, indicative of defective MMR, and four MSI-high tumours, identified following microsatellite analysis for 1p/19q co-deletion as part of routine care, were selected for analysis. MMR expression was then assessed by immunohistochemistry. Seven tumours showed loss of one or more MMR proteins and were molecularly characterised using PCR-based Promega MSI analysis and NGS-based Illumina TruSight500 panel. RESULTS Pathogenic variants in MMR genes and hypermutated phenotypes (TMB > 10mutations/Mb) were identified in three cases. One individual harboured an additional POLE PV resulting in an ultra-hypermutated phenotype (>100mutations/Mb). Two MMR PVs were germline, leading to a new diagnosis of Lynch syndrome. Only one of three tumours was found to be MSI-high using the Promega MSI analysis whilst all three were identified as MSI-high using TruSight500 MSI calling algorithms. CONCLUSION We describe the comprehensive molecular profile of seven treatment naïve gliomas, three being MMR deficient. We show TruSight500 to be more sensitive and reliable for detecting MSI compared to Promega. Given the implications, this additional analysis should be considered as part of the molecular report on all gliomas.

BACKGROUND:For patients with oesophagogastric adenocarcinoma, surgery is the only curative option and despite the use of multimodality therapy, which combines it with chemotherapy and/or radiotherapy, more than 50% of patients will relapse and die. Many UK patients present with advanced disease which is already inoperable or metastatic at diagnosis. For these patients, standard care chemotherapy only offers them survival of less than a year. Nivolumab, a checkpoint blockade inhibitor, has been found to work in some advanced cancers. It is proposed, for those where immunotherapy hasn't worked, that these immunologically evasive tumours need to be sensitized to immunotherapy drugs to allow them to act. METHODS:ELEVATE is a single arm phase II trial testing the overall response to nivolumab following temozolomide treatment in patients with advanced unresectable previously treated adenocarcinoma which is O6-methylguanine-DNA-methyltransferase (MGMT) methylated. 18 patients are being recruited from UK secondary care sites. To be eligible, participants must have been treated with at least 3 months of platinum and fluoropyrimidine chemotherapy. Participants will receive 50 mg/m2 temozolomide continuously for 3 months. If their disease progresses during the 3 months, they will stop temozolomide and start nivolumab at a dose of 240mg every 2 weeks. If there is no progression after 3 months the participant will continue taking temozolomide in combination with nivolumab. All treatment will stop once the participant progresses on nivolumab. The primary endpoint is the best overall response to nivolumab, using both Response Evaluation Criteria in Solid Tumours version 1.1 and immunotherapy modified Response Evaluation Criteria in Solid Tumours. Secondary endpoints include progression-free survival, overall survival, and quality of life. DISCUSSION:ELEVATE will provide evidence for whether giving nivolumab after temozolomide in patients with previously treated advanced oesophagogastric adenocarcinoma is safe and biologically effective prior to future randomised trials. TRIAL REGISTRATIONS:EudraCT Number: 2020-004771-41 (issued 01 October 2020); ISCRTN11398887 (registered 14 July 2021).

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Summary A 38-year-old female was identified as carrying a heterozygous pathogenic MEN1 variant (c.1304delG) through predictive genetic testing, following a diagnosis of familial hyperparathyroidism. Routine screening for parathyroid and pituitary disease was negative. However, cross-sectional imaging by CT revealed a 41 mm pancreatic tail mass. Biopsy via endoscopic ultrasound confirmed the lesion to be a well-differentiated (grade 1) pancreatic neuroendocrine tumour (pNET) with MIB1<1%. Biochemically, hyperinsulinaemic hypoglycaemia was confirmed following an overnight fast, which was subsequently managed by diet alone prior to definitive surgery. Pre-operative work-up with octreotide SPECT CT demonstrated avid tracer uptake in the pancreatic lesion and, unexpectedly, a focal area of uptake in the left breast. Further investigation, and subsequent mastectomy, confirmed ductal carcinoma in situ pT2 (23 mm) grade 1, N0 (ER positive; HER2 negative). Following mastectomy, our patient underwent a successful distal pancreatectomy to resect the pNET. Loss of heterozygosity (LOH) at the MEN1 locus was found in both the breast tumour and pNET, thereby in keeping with a 'two-hit' hypothesis of oncogenesis, a suggestive but non-definitive clue for causation. To obtain further support for a causative relationship between MEN1 and breast cancer, we undertook a detailed review of the published literature which overall supports the notion that breast cancer is a MEN1-related malignancy that presents at a younger age and histologically, is typically of ductal subtype. Currently, clinical guidance regarding breast cancer surveillance in MEN1 does not exist and further research is required to establish a clinical and cost-effective surveillance strategy). Learning points We describe a case of pNET and breast cancer diagnosed at a young age of 38 years in a patient who is heterozygous for a pathogenic MEN1 variant. Loss of the wild-type allele was seen in both breast tissue and pNET specimen. Breast cancer may be an under-recognised MEN1-associated malignancy that presents at a younger age than in the general population with a relative risk of 2–3. Further research is required to determine the cost-effectiveness of breast cancer surveillance approach at a younger age in MEN1 patients relative to the general population .

AbstractBackgroundPDGRFA-mutant gastrointestinal tumours (GISTs) comprise approximately 10% of GISTs and are mostly gastric. Targeted therapies against these tumours have historically been limited by tyrosine kinase inhibitor (TKI)-resistance. We reviewed the characteristics and outcome of all PDGRFA-mutant patients seen at our centre over the last 13 years.MethodsAll PDGRFA-mutant patients seen at the Cambridge University Hospitals NHS Foundation Trust GIST clinic from July 2008-July 2021 were retrospectively reviewed and followed up.Results50 PDGRFA-mutant GIST patients were diagnosed during the 13-year period. 60% were male. Median tumour size was 5 cm and the majority were epithelioid (44%) or mixed (36%) type. Commonest primary location was the gastric body (52%). In non-metastatic patients the low-risk modified AFIP risk group was the most common (65.2%). PDGFRA exon 18 (86%) were the most common PDGFRA mutations, most being imatinib resistant. None harboured a KIT mutation. 38% of cases had high KIT expression (immunohistochemistry), whilst 48% had patchy expression and 14% were negative. Most were positive for DOG1 (94%). CD34 was highly expressed in 48% of cases. 13% developed metastases during the 13-year follow-up period: liver (80%) being the commonest site. 76% of all patients underwent radical resection. 14% received TKI therapy. After a median follow-up of 55.1 months, 82% remained alive: 6 patients died from metastatic GIST; 3 from other causes. Median time to metastatic disease was 30.1 months, and median time from metastatic diagnosis to death was 18.5 months. Patients who presented with metastatic disease had the poorest survival outcome (p=0.001)ConclusionTo date this is the largest single-centre European PDGRFA-mutant GIST cohort. Results highlight the generally indolent nature of PDGRFA-mutant disease (contrasted to the poor outcome of those who present with metastatic disease), male and gastric preponderance (unlike KIT-mutant GISTs), and variable KIT expression.HighlightsLargest single-centre European PDGFRA-mutant GIST series (n=50) to dateResults confirm the relative indolent nature of non-metastatic PDGFRA-mutant GISTsPDGFRA-mutant GISTs had variable levels of KIT protein expression (immunohistochemistry) despite being KIT-wild type.In contrast to KIT-mutant GISTs, PDGFRA-mutant GISTs were more common in males and less frequent in parts of the stomach where KIT-mutant GISTS occur.A minority of patients received TKI therapy. One patient with metastatic imatinib-resistant PDGFRA-mutant GIST had a 6 year response to imatinib.

The aim of the study is to identify the epidemiology of CNS tumours within the West Yorkshire region in comparison to other regions.The study aims to identify if any links can be made between the type or site of CNS tumour and the initial clinical symptoms.It also aims to identify if there is any link between occupation and incidence of CNS tumour.All CNS pathology reports created at Leeds Teaching Hospital between 01/01/2019 and 09/03/2020 were analysed.The histological diagnosis and biopsy site were recorded and the corresponding medical records were used to identify age, gender, occupation and presenting clinical symptoms.Duplicate biopsies and cases where the corresponding medical records could not be identified were excluded.A total of 448 reports were included in the study.The results showed that 13.12% of the samples included in the study represent metastatic disease.The majority being a breast, lung or melanoma as a primary.The most prevalent histological subtypes were meningioma and glioblastoma.The most prevalent group of primary CNS tumours with a total of 26.79% of all the samples was the diffuse astrocytic and oligodendroglial tumours.In this group the top 3 occupations identified were in the healthcare sector, IT and administration, and the retail sector.The most prevalent symptoms in this group were headaches, dysarthria and weakness.Further comparisons and analysis have been drawn across all CNS tumours identified in the study.

Background Malignant oncocytic adrenocortical neoplasms (OANs) are rare tumours with a distinctive biological behaviour compared to conventional adrenocortical carcinoma (ACC). The current prognostic systems overestimate the malignant potential of these tumours, and guidance for surveillance and treatment strategies are lacking. Aim To evaluate the utility of clinical, pathological and molecular markers in predicting the biological behaviour and outcomes of malignant OANs. Methods A retrospective clinicopathological review of 10 histologically confirmed OANs was carried out. Whole exome sequencing (WES) of germline and paired tumour samples was performed for four of the ten OAN cases and compared to WES data from five cases of conventional ACC and data from The Cancer Genome Atlas. We reviewed all the cases of malignant OAN reported in the literature and compared to our case series. Results Eight (80%) tumours were classified as malignant, one borderline and one benign (Lin–Weiss–Bisceglia criteria, LWB). The malignant OAN were larger tumours and had higher MIB index and Helsinki scores. Molecular profiling identified a pathogenic germline variant in MSH6 in an individual in the OAN group. The OAN samples had a lower mutation burden compared to the ACC samples. Somatic driver variants were identified in OAN and ACC samples including a pathogenic missense variant in CTNNB1. Conclusion In this study, the LWB classification demonstrated sensitivity for the differentiation of benign from malignant OAN. Molecular profiling identified dysregulation in DNA repair and Wnt signalling pathways in both OAN and ACC samples, suggesting a molecular overlap between OAN and conventional ACC.

Background [ 68 Ga]Ga-DOTATATE PET/CT is now recognised as the most sensitive functional imaging modality for the diagnosis of well-differentiated neuroendocrine tumours (NET) and can inform treatment with peptide receptor radionuclide therapy with [ 177 Lu]Lu-DOTATATE. However, somatostatin receptor (SSTR) expression is not unique to NET, and therefore, [ 68 Ga]Ga-DOTATATE PET/CT may have oncological application in other tumours. Molecular profiling of gastrointestinal stromal tumours that lack activating somatic mutations in KIT or PDGFRA or so-called ‘wild-type’ GIST (wtGIST) has demonstrated that wtGIST and NET have overlapping molecular features and has encouraged exploration of shared therapeutic targets, due to a lack of effective therapies currently available for metastatic wtGIST. Aims To investigate (i) the diagnostic role of [ 68 Ga]Ga-DOTATATE PET/CT; and, (ii) to investigate the potential of this imaging modality to guide treatment with [ 177 Lu]Lu-DOTATATE in patients with wtGIST. Methods [ 68 Ga]Ga-DOTATATE PET/CT was performed on 11 patients with confirmed or metastatic wtGIST and one patient with a history of wtGIST and a mediastinal mass suspicious for metastatic wtGIST, who was subsequently diagnosed with a metachronous mediastinal paraganglioma. Tumour expression of somatostatin receptor subtype 2 (SSTR2) using immunohistochemistry was performed on 54 tumour samples including samples from 8/12 (66.6%) patients who took part in the imaging study and 46 tumour samples from individuals not included in the imaging study. Results [ 68 Ga]Ga-DOTATATE PET/CT imaging was negative, demonstrating that liver metastases had lower uptake than background liver for nine cases (9/12 cases, 75%) and heterogeneous uptake of somatostatin tracer was noted for two cases (16.6%) of wtGIST. However, [ 68 Ga]Ga-DOTATATE PET/CT demonstrated intense tracer uptake in a synchronous paraganglioma in one case and a metachronous paraganglioma in another case with wtGIST. Conclusions Our data suggest that SSTR2 is not a diagnostic or therapeutic target in wtGIST. [ 68 Ga]Ga-DOTATATE PET/CT may have specific diagnostic utility in differentiating wtGIST from other primary tumours such as paraganglioma in patients with sporadic and hereditary forms of wtGIST.

AIM:There is no known specific biomarker or genetic signal for quadruple wild-type (qWT) gastrointestinal stromal tumours (GISTs). By next-generation sequencing (NGS) of different GIST subgroups, this study aimed to characterise such a biomarker especially as a potential therapeutic target.METHODS AND RESULTS:An NGS panel of 672 kinase genes was applied to DNA extracted from 11 wild-type GISTs (including three qWT GISTs) and 5 KIT/PDGFRA mutated GISTs. Short variants which were present in qWT GISTs but no other GIST subgroup were shortlisted. After removing common population variants, in silico-classified deleterious variants were found in CSNK2A1, MERTK, RHEB, ROCK1, PIKFYVE and TRRAP. None of these variants were demonstrated in a separate cohort of four qWT GISTs.CONCLUSIONS:Short kinase variants which are specific to qWT GISTs are rare and are not universally demonstrated by this whole subgroup. It is therefore possible that the current definition of qWT GIST still covers a heterogenous population.

Gastrointestinal stromal tumour (GIST) is a mesenchymal neoplasm arising in the gastrointestinal tract. A rare subset of GISTs are classified as wild-type GIST (wtGIST) and these are frequently associated with germline variants that affect the function of cancer predisposition genes such as the succinate dehydrogenase subunit genes ( SDHA, SDHB, SDHC, SDHD ) or NF1 . However, despite this high heritability, familial clustering of wtGIST is extremely rare. Here, we report a mother–son diad who developed wtGIST at age 66 and 34 years, respectively. Comprehensive genetic testing revealed germline truncating variants in both SDHA (c.1534C>T (p.Arg512*)) and PALB2 (c.3113G>A (p.Trp1038*)) in both affected individuals. The mother also developed breast ductal carcinoma in-situ at age 70 years. Immunohistochemistry and molecular analysis of the wtGISTs revealed loss of SDHB expression and loss of the wild-type SDHA allele in tumour material. No allele loss was detected at PALB2 suggesting that wtGIST tumourigenesis was principally driven by succinate dehydrogenase deficiency. However, we speculate that the presence of multilocus inherited neoplasia alleles syndrome (MINAS) in this family might have contributed to the highly unusual occurrence of familial wtGIST. Systematic reporting of tumour risks and phenotypes in individuals with MINAS will facilitate the clinical interpretation of the significance of this diagnosis, which is becoming more frequent as strategies for genetic testing for hereditary cancer becomes more comprehensive.