PDGFRB mutants found in patients with familial infantile myofibromatosis or overgrowth syndrome are oncogenic and sensitive to imatinib

Somatic PDGFRB activating variants promote smooth muscle cell phenotype modulation in intracranial fusiform aneurysm

BACKGROUND

The fusiform aneurysm is a nonsaccular dilatation affecting the entire vessel wall over a short distance. Although PDGFRB somatic variants have been identified in fusiform intracranial aneurysms, the molecular and cellular mechanisms driving fusiform intracranial aneurysms due to PDGFRB somatic variants remain poorly understood.

METHODS

In this study, single-cell sequencing and immunofluorescence were employed to investigate the phenotypic changes in smooth muscle cells within fusiform intracranial aneurysms. Whole-exome sequencing revealed the presence of PDGFRB gene mutations in fusiform intracranial aneurysms. Subsequent immunoprecipitation experiments further explored the functional alterations of these mutated PDGFRB proteins. For the common c.1684 mutation site of PDGFRβ, we established mutant smooth muscle cell lines and zebrafish models. These models allowed us to simulate the effects of PDGFRB mutations. We explored the major downstream cellular pathways affected by PDGFRBY562D mutations and evaluated the potential therapeutic effects of Ruxolitinib.

RESULTS

Single-cell sequencing of two fusiform intracranial aneurysms sample revealed downregulated smooth muscle cell markers and overexpression of inflammation-related markers in vascular smooth muscle cells, which was validated by immunofluorescence staining, indicating smooth muscle cell phenotype modulation is involved in fusiform aneurysm. Whole-exome sequencing was performed on seven intracranial aneurysms (six fusiform and one saccular) and PDGFRB somatic mutations were detected in four fusiform aneurysms. Laser microdissection and Sanger sequencing results indicated that the PDGFRB mutations were present in smooth muscle layer. For the c.1684 (chr5: 149505131) site mutation reported many times, further cell experiments showed that PDGFRBY562D mutations promoted inflammatory-related vascular smooth muscle cell phenotype and JAK-STAT pathway played a crucial role in the process. Notably, transfection of PDGFRBY562D in zebrafish embryos resulted in cerebral vascular anomalies. Ruxolitinib, the JAK inhibitor, could reversed the smooth muscle cells phenotype modulation in vitro and inhibit the vascular anomalies in zebrafish induced by PDGFRB mutation.

CONCLUSION

Our findings suggested that PDGFRB somatic variants played a role in regulating smooth muscle cells phenotype modulation in fusiform aneurysms and offered a potential therapeutic option for fusiform aneurysms.

Corneal Infantile Myofibromatosis Caused by Novel Activating Imatinib-Responsive Variants in PDGFRB

Purpose

To investigate the genetic cause, clinical characteristics, and potential therapeutic targets of infantile corneal myofibromatosis.

Design

Case series with genetic and functional in vitro analyses.

Participants

Four individuals from 2 unrelated families with clinical signs of corneal myofibromatosis were investigated.

Methods

Exome-based panel sequencing for platelet-derived growth factor receptor beta gene (PDGFRB) and notch homolog protein 3 gene (NOTCH3) was performed in the respective index patients. One clinically affected member of each family was tested for the pathogenic variant detected in the respective index by Sanger sequencing. Immunohistochemical staining on excised corneal tissue was conducted. Functional analysis of the individual PDGFRB variants was performed in vitro by luciferase reporter assays on transfected porcine aortic endothelial cells using tyrosine kinase inhibitors. Protein expression analysis of mutated PDGFRB was analyzed by Western blot.

Main Outcome Measures

Sequencing data, immunohistochemical stainings, functional analysis of PDGFRB variants, and protein expression analysis.

Results

We identified 2 novel, heterozygous gain-of-function variants in PDGFRB in 4 individuals from 2 unrelated families with corneal myofibromatosis. Immunohistochemistry demonstrated positivity for alpha-smooth muscle actin and β-catenin, a low proliferation rate in Ki-67 (< 5%), marginal positivity for Desmin, and negative staining for Caldesmon and CD34. In all patients, recurrence of disease occurred after corneal surgery. When transfected in cultured cells, the PDGFRB variants conferred a constitutive activity to the receptor in the absence of its ligand and were sensitive to the tyrosine kinase inhibitor imatinib. The variants can both be classified as likely pathogenic regarding the American College of Medical Genetics and Genomics classification criteria.

Conclusions

We describe 4 cases of corneal myofibromatosis caused by novel PDGFRB variants with autosomal dominant transmission. Imatinib sensitivity in vitro suggests perspectives for targeted therapy preventing recurrences in the future.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Case report: Navigating treatment pathways for cardiac intimal sarcoma with PDGFRβ N666K mutation

In the realm of rare cardiac tumors, intimal sarcoma presents a formidable challenge, often requiring innovative treatment approaches. This case report presents a unique instance of primary intimal sarcoma in the left atrium, underscoring the critical role of genomic profiling in guiding treatment. Initial genomic testing unveiled a somatic, active mutation in PDGFRβ (PDGFRβ N666K), accompanied by MDM2 and CDK4 amplifications. This discovery directed the treatment course toward pazopanib, a PDGFRβ inhibitor, following irradiation. The patient's response was remarkable, with the therapeutic efficacy of pazopanib lasting for 16.3 months. However, the patient experienced a recurrence in the left atrium, where subsequent genomic analysis revealed the absence of the PDGFRβ N666K mutation and a significant reduction in PDGFRβ expression. This case report illustrates the complexities and evolving nature of cardiac intimal sarcoma treatment, emphasizing the potential of PDGFRβ signaling as a strategic target and highlighting the importance of adapting treatment pathways in response to genetic shifts.

PDGFRA K385 mutants in myxoid glioneuronal tumors promote receptor dimerization and oncogenic signaling

Myxoid glioneuronal tumors (MGNT) are low-grade glioneuronal neoplasms composed of oligodendrocyte-like cells in a mucin-rich stroma. These tumors feature a unique dinucleotide change at codon 385 in the platelet-derived growth factor receptor α (encoded by the PDGFRA gene), resulting in the substitution of lysine 385 into leucine or isoleucine. The functional consequences of these mutations remain largely unexplored. Here, we demonstrated their oncogenic potential in fibroblast and Ba/F3 transformation assays. We showed that the K385I and K385L mutants activate STAT and AKT signaling in the absence of ligand. Co-immunoprecipitations and BRET experiments suggested that the mutations stabilized the active dimeric conformation of the receptor, pointing to a new mechanism of oncogenic PDGF receptor activation. Furthermore, we evaluated the sensitivity of these mutants to three FDA-approved tyrosine kinase inhibitors: imatinib, dasatinib, and avapritinib, which effectively suppressed the constitutive activity of the mutant receptors. Finally, K385 substitution into another hydrophobic amino acid also activated the receptor. Interestingly, K385M was reported in a few cases of brain tumors but not in MGNT. Our results provide valuable insights into the molecular mechanism underlying the activation of PDGFRα by the K385I/L mutations, highlighting their potential as actionable targets in the treatment of myxoid glioneuronal tumors.

Corneal Vascularization Associated With a Novel PDGFRB Variant

Purpose

The purpose of this study was to identify the genetic cause of aggressive corneal vascularization in otherwise healthy children in one family. Further, to study molecular consequences associated with the identified variant and implications for possible treatment.

Methods

Exome sequencing was performed in affected individuals. HeLa cells were transduced with the identified c.1643C>A, p.(Ser548Tyr) variant in the platelet-derived growth factor receptor beta gene (PDGFRB) or wild-type PDGFRB. ELISA and immunoblot analysis were used to detect the phosphorylation levels of PDGFRβ and downstream signaling proteins in untreated and ligand-stimulated cells. Sensitivity to various receptor tyrosine kinase inhibitors (TKIs) was determined.

Results

A novel c.1643C>A, p.(Ser548Tyr) PDGFRB variant was found in affected family members. HeLa cells transduced with this variant did not have increased baseline levels of phosphorylated PDGFRβ. However, upon stimulation with ligand, excessive activation of PDGFRβ was observed compared to cells transduced with the wild-type variant. PDGFRβ with the p.(Ser548Tyr) amino acid substitution was successfully inhibited with tyrosine kinase inhibitors (axitinib, dasatinib, imatinib, and sunitinib) in vitro.

Conclusions

A novel c.1643C>A, p.(Ser548Tyr) PDGFRB variant was found in family members with isolated corneal vascularization. Cells transduced with the newly identified variant showed increased phosphorylation of PDGFRβ upon ligand stimulation. This suggests that PDGF-PDGFRβ signaling in these patients leads to overactivation of PDGFRβ, which could lead to abnormal wound healing of the cornea. The examined TKIs prevented such overactivation, introducing the possibility for targeted treatment in these patients.

Understanding cancer drug resistance with Sleeping Beauty functional genomic screens: Application to MAPK inhibition in cutaneous melanoma

Combined BRAF and MEK inhibition is an effective treatment for BRAF-mutant cutaneous melanoma. However, most patients progress on this treatment due to drug resistance. Here, we applied the Sleeping Beauty transposon system to understand how melanoma evades MAPK inhibition. We found that the specific drug resistance mechanisms differed across melanomas in our genetic screens of five cutaneous melanoma cell lines. While drivers that reactivated MAPK were highly conserved, many others were cell-line specific. One such driver, VAV1, activated a de-differentiated transcriptional program like that of hyperactive RAC1, RAC1P29S. To target this mechanism, we showed that an inhibitor of SRC, saracatinib, blunts the VAV1-induced transcriptional reprogramming. Overall, we highlighted the importance of accounting for melanoma heterogeneity in treating cutaneous melanoma with MAPK inhibitors. Moreover, we demonstrated the utility of the Sleeping Beauty transposon system in understanding cancer drug resistance.

Pathogenic mutation hotspots in protein kinase domain structure

Control of eukaryotic cellular function is heavily reliant on the phosphorylation of proteins at specific amino acid residues, such as serine, threonine, tyrosine, and histidine. Protein kinases that are responsible for this process comprise one of the largest families of evolutionarily related proteins. Dysregulation of protein kinase signaling pathways is a frequent cause of a large variety of human diseases including cancer, autoimmune, neurodegenerative, and cardiovascular disorders. In this study, we mapped all pathogenic mutations in 497 human protein kinase domains from the ClinVar database to the reference structure of Aurora kinase A (AURKA) and grouped them by the relevance to the disease type. Our study revealed that the majority of mutation hotspots associated with cancer are situated within the catalytic and activation loops of the kinase domain, whereas non-cancer-related hotspots tend to be located outside of these regions. Additionally, we identified a hotspot at residue R371 of the AURKA structure that has the highest number of exclusively non-cancer-related pathogenic mutations (21) and has not been previously discussed.

Prenatal genetic diagnosis of disseminated infantile myofibromatosis: a case report and literature review

BACKGROUND

Infantile myofibromatosis (IM) is a rare disorder characterized by the formation of nodules in the skin, muscle, bone, and, more rarely, visceral organs. Very few cases are detected prenatally, and the final diagnosis cannot be made until pathology is completed after birth. Here, we present a case of disseminated form IM (DFIM) with a diagnosis established on prenatal genetic grounds.

CASE PRESENTATION

A woman at 23 weeks of gestation was referred for ultrasound evaluation of fetal kidney abnormality. Generalized masses in the skin and muscle of the fetus developed at 28 weeks. Prenatal genetic testing identified the pathogenic heterozygous variant c.1681C > T (p.R561C) of the PDGFRB gene inherited from the asymptomatic father. Intrauterine demise occurred at 31 weeks. Autopsy confirmed DFIM with involvement of the heart and kidney. All cases of prenatally detected IM were reviewed, revealing an association of high mortality with DFIM.

CONCLUSIONS

Prenatal IM diagnosis is difficult. Initial detection is always based on ultrasound. DFIM has high mortality. The germline p.R561C mutation in PDGFRB may cause fetal demise due to severe visceral involvement of IM. Prenatal genetic testing provides a diagnosis before pathological results are available, leading to better counseling and management of pregnancy with a fetus with IM.

High-Grade Sarcomas with Myogenic Differentiation Harboring Hotspot PDGFRB Mutations

PDGFRB-activating mutations have been reported in pediatric myofibroma and myofibromatosis. However, recurrent gain-of-function PDGFRB mutations have not been documented in sarcomas with myogenic differentiation. Driven by occasional sarcomas harboring PDGFRB mutations, we investigated their prevalence and clinicopathologic and genomic features in a large cohort of sarcomas. An institutional targeted DNA next-generation sequencing database was searched for sarcomas with myogenic differentiation harboring hotspot PDGFRB gene alterations. Among 3300 patients with sarcomas, 21 (0.6%) patients were identified (17 women, 4 men) with an age range of 35 to 88 years. The site distribution included 13 gynecologic tract (12 uteri, 1 vagina), 4 bone and soft tissue, and 4 viscera. All except 1 were high grade. Most patients were diagnosed as sarcomas with myogenic differentiation based on partial staining for 1 or more muscle markers, whereas 6 were labeled as leiomyosarcoma (LMS). Most tumors showed monomorphic spindle morphology, with either heterogeneous features of myofibroblastic and smooth muscle differentiation or an undifferentiated phenotype. Hormone receptors were negative in all uterine cases. PDGFRB immunostaining in all cases tested was strong and diffuse, whereas PDGFRA was negative/focal. The most frequent PDGFRB mutations were exon 12 (43%), exon 14 (N666K/S/T) (38%), and exon 18 (D850Y/H/V or insertion/deletion) (19%). The most frequent co-existing genetic alterations (26% to 37%) occurred in CDKN2A/B, TP53, TERT, and MED12. Moreover, PDGFRB-mutant sarcomas had an overall distinct genomic landscape compared with both uterine and soft tissue LMS control groups. These tumors were associated with a highly aggressive clinical course, with frequent distant metastases (81%) and death (76%), regardless of anatomic location, and worse overall survival compared with the 2 LMS control groups. This is the first study documenting recurrent hotspot PDGFRB alterations in high-grade sarcomas, which show a predilection for uterine location and myogenic differentiation that fall short of the diagnostic criteria for LMS. Further studies are needed to investigate the therapeutic potential of kinase inhibitors in this group of tumors.

Generalized Infantile Myofibromatosis with Extensive Small Bowel Involvement in a Neonate

Infantile myofibromatosis is a rare benign congenital tumour that often regresses spontaneously but may pose therapeutic challenges in its widespread visceral form. We present the case of a full-term neonate with generalized infantile myofibromatosis including ubiquitous subcutaneous and muscular nodules, a tumour in the mastoid and disseminated intestinal involvement. The intestinal tumours led to a mechanical ileus with intestinal perforation within the first days of life. After partial small bowel resection and necessary proximal jejunostomy the boy was dependent on total parenteral nutrition. Chemotherapy with vinblastine and methotrexate was started and was temporarily supplemented with imatinib. Feeding stayed impossible despite tumour shrinkage. At the age of 4.5 months, restoration of intestinal continuity with further stricturoplasties was performed which - for the first time - allowed complete oral feeding. Chemotherapy was continued for further two months. Currently, the child is in good general condition with growth and further disease regression. This report suggests that massive visceral involvement of infantile myofibromatosis may require extensive intestinal surgery, as conservative therapy cannot resolve the disease and its sequelae.

An integrative approach for exploring the nature of fibroepithelial neoplasms

BACKGROUND

Malignant phyllodes tumour (MPT) is a rare breast malignancy with epithelial and mesenchymal features. Currently, there are no appropriate research models or effective targeted therapeutic approaches for MPT.

METHODS

We collected fresh frozen tissues from nine patients with MPT and performed whole-exome and RNA sequencing. Additionally, we established patient-derived xenograft (PDX) models from patients with MPT and tested the efficacy of targeting dysregulated pathways in MPT using the PDX model from one MPT.

RESULTS

MPT has unique molecular characteristics when compared to breast cancers of epithelial origin and can be classified into two groups. The PDX model derived from one patient with MPT showed that the mouse epithelial component increased during tumour growth. Moreover, targeted inhibition of platelet-derived growth factor receptor (PDGFR) and phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) by imatinib mesylate and PKI-587 showed in vivo tumour suppression effects.

CONCLUSIONS

This study revealed the molecular profiles of MPT that can lead to molecular classification and potential targeted therapy, and suggested that the MPT PDX model can be a useful tool for studying the pathogenesis of fibroepithelial neoplasms and for preclinical drug screening to find new therapeutic strategies for MPT.

Penttinen syndrome-associated PDGFRB Val665Ala variant causes aberrant constitutive STAT1 signalling

Penttinen syndrome is a rare progeroid disorder caused by mutations in platelet‐derived growth factor (PDGF) receptor beta (encoded by the PDGFRB proto‐oncogene) and characterized by a prematurely aged appearance with lipoatrophy, skin lesions, thin hair and acro‐osteolysis. Activating mutations in PDGFRB have been associated with other human diseases, including Kosaki overgrowth syndrome, infantile myofibromatosis, fusiform aneurysms, acute lymphoblastic leukaemia and myeloproliferative neoplasms associated with eosinophilia. The goal of the present study was to characterize the PDGFRB p.Val665Ala variant associated with Penttinen syndrome at the molecular level. This substitution is located in a conserved loop of the receptor tyrosine kinase domain. We observed that the mutant receptor was expressed at a lower level but showed constitutive activity. In the absence of ligand, the mutant activated STAT1 and elicited an interferon‐like transcriptional response. Phosphorylation of STAT3, STAT5, AKT and phospholipase Cγ was weak or undetectable. It was devoid of oncogenic activity in two cell proliferation assays, contrasting with classical PDGF receptor oncogenic mutants. STAT1 activation was not sensitive to ruxolitinib and did not rely on interferon‐JAK2 signalling. Another tyrosine kinase inhibitor, imatinib, blocked signalling by the p.Val665Ala variant at a higher concentration compared with the wild‐type receptor. Importantly, this concentration remained in the therapeutic range. Dasatinib, nilotinib and ponatinib also inhibited the mutant receptor. In conclusion, the p.Val665Ala variant confers unique features to PDGF receptor β compared with other characterized gain‐of‐function mutants, which may in part explain the particular set of symptoms associated with Penttinen syndrome.

Identification of a novel PHIP::BRAF gene fusion in infantile fibrosarcoma

INTRODUCTION

The ETV6::NTRK3 fusion is the most common gene alteration in infantile fibrosarcoma, a soft tissue tumor affecting patients under two years of age. Less frequently, these tumors harbor fusions of genes encoding other kinases, such as BRAF, which activates MEK in the mitogen-activated protein kinase pathway. The identification and characterization of these oncogenes is crucial to facilitate diagnosis, validate new treatments and better understand the pathophysiology of these neoplasms.

METHODS

Herein, we analyzed an ETV6::NTRK3-negative infantile fibrosarcoma from a 5-day-old patient by RNA-sequencing to identify new fusion transcripts. Functional exploration of the fusion of interest was performed by in vitro assays to study its activity, oncogenicity and sensitivity to the MEK inhibitor trametinib.

RESULTS

We identified a novel fusion involving the PHIP and BRAF genes. The corresponding fusion protein constitutively activated the mitogen-activated protein kinase pathway, resulting in fibroblast transformation. Treatment of transfected cells with trametinib effectively inhibited signaling by PHIP::BRAF.

CONCLUSION

PHIP::BRAF is a novel fusion oncogene that can be targeted by trametinib in infantile fibrosarcoma. This article is protected by copyright. All rights reserved.

Giant intracranial infantile myofibromatosis of the skull base: report of two cases

Infantile myofibromatosis is a rare and nonmalignant pediatric tumor of myofibroblastic origin that may occur in solitary or multifocal forms. Soft tissue of the head and neck, trunk, and extremities, skeleton, and viscera are usually involved. Intracranial involvement is reported to be extremely rare, and its clinical picture has been poorly characterized. We present two cases of giant infantile myofibromatosis of the skull base with intracranial involvement. The first case with prenatal diagnosis involved extensively the extradural space of the occipital region and was previously treated by chemotherapy for a previous diagnosis of hemangioperycitoma. Tumor was removed at the age of 5 months and no recurrence was observed during the 3-year follow-up. The second case in a 2-year-old baby involved the anterior cranial base, the nasal cavity, the right orbit, and presented massive involvement of the anterior cranial fossa. Surgery allowed complete removal and a recurrence-free period of 7 years after surgery. Treatment options for these unusual cases are presented and details of histological diagnosis are discussed.

Avoidance of surgery for head and neck infantile myofibromatosis using imatinib monotherapy

Describe a novel use for a kinase inhibitor, imatinib, in young children with a known activated somatic mutation in PDGFR-beta. Two patients with infantile myofibromatosis treated with imatinib. Case description of evaluation, diagnosis and treatment decisions for infantile myfibromatosis of the head and neck. Description of medical therapy for infantile myofibromatosis in these patients. For function threatening myofibromas of a known genotype, in infants, targeted medical therapy is a treatment option.

Clinical and molecular response to dasatinib in an adult patient with Penttinen syndrome

Penttinen type of premature aging syndrome is an autosomal-dominant disorder that can be caused by the c.1994T>A pVal665Ala pathogenic variant in platelet-derived growth factor receptor-B (PDGFRB). Imatinib, a receptor tyrosine kinase (RTK) inhibitor, has been used in Penttinen syndrome (PS) patients with good results. A 21-year-old male presented shortly after birth with a prematurely aged appearance with distinctive facial features and cutaneous atrophy with hypertrophic scar-like lesions. Generalized brachydactyly with acro-osteolysis was observed. Flexion contractures limited his daily activities. Cognitive impairment was not present. Genetic testing found a heterozygous variant c.1994T>A pVal665Ala in exon 14 of PDGFRB. A diagnosis of PS was made and imatinib treatment was started with partial response. After lack of further improvement, in vitro molecular studies with imatinib and dasatinib showed that the Val665Ala variant had greater sensitivity to dasatinib than imatinib. This was seen examining levels of P-PDGFRB directly and on downstream ligands P-AKT and P-STAT. Improved clinical response was observed after treatment with dasatinib. We report a new case of PS with clinical and molecular response to dasatinib after incomplete response to imatinib. Our work provides further molecular and clinical evidence of RTK inhibitors' efficacy in this rare disorder.

Identification of Early Diagnostic and Prognostic Biomarkers via WGCNA in Stomach Adenocarcinoma

Stomach adenocarcinoma (STAD) is a leading cause of cancer deaths, and the outcome of the patients remains dismal for the lack of effective biomarkers of early detection. Recent studies have elucidated the landscape of genomic alterations of gastric cancer and reveal some biomarkers of advanced-stage gastric cancer, however, information about early-stage biomarkers is limited. Here, we adopt Weighted Gene Co-expression Network Analysis (WGCNA) to screen potential biomarkers for early-stage STAD using RNA-Seq and clinical data from TCGA database. We find six gene clusters (or modules) are significantly correlated with the stage-I STADs. Among these, five hub genes, i.e., MS4A1, THBS2, VCAN, PDGFRB, and KCNA3 are identified and significantly de-regulated in the stage-I STADs compared with the normal stomach gland tissues, which suggests they can serve as potential early diagnostic biomarkers. Moreover, we show that high expression of VCAN and PDGFRB is associated with poor prognosis of STAD. VCAN encodes a large chondroitin sulfate proteoglycan that is the main component of the extracellular matrix, and PDGFRB encodes a cell surface tyrosine kinase receptor for members of the platelet-derived growth factor (PDGF) family. Consistently, Gene Ontology (GO) analysis of differentially expressed genes in the STADs indicates terms associated with extracellular matrix and receptor ligand activity are significantly enriched. Protein-protein network interaction analysis (PPI) and Gene Set Enrichment Analysis (GSEA) further support the core role of VCAN and PDGFRB in the tumorigenesis. Collectively, our study identifies the potential biomarkers for early detection and prognosis of STAD.

Aggressive infantile myofibromatosis with intestinal involvement

Background

Infantile myofibromatosis (IM) is the most common cause of multiple fibrous tumors in infancy. Multicentric disease can be associated with life-threatening visceral lesions. Germline gain-of-function mutations in PDGFRB have been identified as the most common molecular defect in familial IM.

Case presentation

We here describe an infant with PDGFRB-driven IM with multiple tumors at different sites, including intestinal polyposis with hematochezia, necessitating temporary chemotherapy.

Conclusions

PDGFRB-driven IM is clinically challenging due to its fluctuating course and multiple organ involvement in the first years of life. Early molecular genetic analysis is necessary to consider tyrosine kinase inhibitor treatment in case of aggressive visceral lesions.

PDGF receptor mutations in human diseases

PDGFRA and PDGFRB are classical proto-oncogenes that encode receptor tyrosine kinases responding to platelet-derived growth factor (PDGF). PDGFRA mutations are found in gastrointestinal stromal tumors (GISTs), inflammatory fibroid polyps and gliomas, and PDGFRB mutations drive myofibroma development. In addition, chromosomal rearrangement of either gene causes myeloid neoplasms associated with hypereosinophilia. Recently, mutations in PDGFRB were linked to several noncancerous diseases. Germline heterozygous variants that reduce receptor activity have been identified in primary familial brain calcification, whereas gain-of-function mutants are present in patients with fusiform aneurysms, Kosaki overgrowth syndrome or Penttinen premature aging syndrome. Functional analysis of these variants has led to the preclinical validation of tyrosine kinase inhibitors targeting PDGF receptors, such as imatinib, as a treatment for some of these conditions. This review summarizes the rapidly expanding knowledge in this field.

Segmental overgrowth and aneurysms due to mosaic PDGFRB p.(Tyr562Cys)

Activating variants in the platelet-derived growth factor receptor β gene (PDGFRB) have been associated with Kosaki overgrowth syndrome, infantile myofibromatosis, and Penttinen premature aging syndrome. A recently described phenotype with fusiform aneurysm has been associated with mosaic PDGFRB c.1685A > G p.(Tyr562Cys) variant. Few reports however have examined the vascular phenotypes and mosaic effects of PDGFRB variants. We describe clinical characteristics of two patients with a recurrent mosaic PDGFRB p.(Tyr562Cys) variant identified via next-generation sequencing-based genetic testing. We observed intracranial fusiform aneurysm in one patient and found an additional eight patients with aneurysms and phenotypes associated with PDGFRB-activating variants through literature search. The conditions caused by PDGFRB-activating variants share overlapping features including overgrowth, premature aged skin, and vascular malformations including aneurysms. Aneurysms are progressive and can result in morbidities and mortalities in the absence of successful intervention. Germline and/or somatic testing for PDGFRB gene should be obtained when PDGFRB activating variant-related phenotypes are present. Whole-body imaging of the arterial tree and echocardiography are recommended after diagnosis. Repeating the imaging study within a 6- to 12-month period after detection is reasonable. Finally, further evaluation for the effectiveness and safety profile of kinase inhibitors in this patient population is warranted.

Solitary adult orbital myofibroma: Report of a case and review of the literature

Purpose

Myofibromas are benign soft tissue tumors commonly encountered in infancy and childhood. Developing usually within the first two years of life, they can be multicentric and involve deep visceral organs.

Observations

We present the rare occurrence of a solitary orbital myofibroma in an adult patient. The clinical, histopathologic and immunohistochemical findings of the tumor are documented.

Conclusions

A comprehensive review of pediatric and adult orbital and periocular involvement by myofibroma is presented. Its characteristic pathologic and molecular findings are reviewed.

Importance

Myofibromas are uncommon but important tumors that can occur in the head and neck region, including the orbit. Seen more often in children, they can rarely be encountered in adult patients. Diagnosis is possible with a panel of immunostains and molecular analysis can be further confirmatory.

Genetic testing and surveillance in infantile myofibromatosis: a report from the SIOPE Host Genome Working Group

Infantile myofibromatosis (IM), which is typically diagnosed in young children, comprises a wide clinical spectrum ranging from inconspicuous solitary soft tissue nodules to multiple disseminated tumors resulting in life-threatening complications. Familial IM follows an autosomal dominant mode of inheritance and is linked to PDGFRB germline variants. Somatic PDGFRB variants were also detected in solitary and multifocal IM lesions. PDGFRB variants associated with IM constitutively activate PDGFRB kinase activity in the absence of its ligand. Germline variants have lower activating capabilities than somatic variants and, thus, require a second cis-acting hit for full receptor activation. Typically, these mutant receptors remain sensitive to tyrosine kinase inhibitors such as imatinib. The SIOPE Host Genome Working Group, consisting of pediatric oncologists, clinical geneticists and scientists, met in January 2020 to discuss recommendations for genetic testing and surveillance for patients who are diagnosed with IM or have a family history of IM/PDGFRB germline variants. This report provides a brief review of the clinical manifestations and genetics of IM and summarizes our interdisciplinary recommendations.

Activating variants in PDGFRB result in a spectrum of disorders responsive to imatinib monotherapy

More than 50 individuals with activating variants in the receptor tyrosine kinase PDGFRB have been reported, separated based on clinical features into solitary myofibromas, infantile myofibromatosis, Penttinen syndrome with premature aging and osteopenia, Kosaki overgrowth syndrome, and fusiform aneurysms. Despite their descriptions as distinct clinical entities, review of previous reports demonstrates substantial phenotypic overlap. We present a case series of 12 patients with activating variants in PDGFRB and review of the literature. We describe five patients with PDGFRB activating variants whose clinical features overlap multiple diagnostic entities. Seven additional patients from a large family had variable expressivity and late-onset disease, including adult onset features and two individuals with sudden death. Three patients were treated with imatinib and had robust and rapid response, including the first two reported infants with multicentric myofibromas treated with imatinib monotherapy and one with a recurrent p.Val665Ala (Penttinen) variant. Along with previously reported individuals, our cohort suggests infants and young children had few abnormal features, while older individuals had multiple additional features, several of which appeared to worsen with advancing age. Our analysis supports a diagnostic entity of a spectrum disorders due to activating variants in PDGFRB. Differences in reported phenotypes can be dramatic and correlate with advancing age, genotype, and to mosaicism in some individuals.

Oncogenic and drug-sensitive RET mutations in human epithelial ovarian cancer

Background

Epithelial ovarian cancer (EOC) is a highly lethal malignancy. Improvement in genetic characterization of EOC patients is required to propose new potential targets, since surgical resection coupled to chemotherapy, presents several limits such as cancer recurrence and drug resistance. Targeted therapies have more efficacy and less toxicity than standard treatments. One of the most relevant cancer-specific actionable targets are protein tyrosine kinases (PTKs) whose role in EOC need to be better investigated.

Methods

EOC genomic datasets are retrieved and analyzed. The biological and clinical significance of RET genomic aberrations in ovarian cancer context are investigated by a series of in vitro and in vivo experiments.

Results

Epithelial ovarian cancer sequencing projects identify recurrent genomic RET missense mutations in 1.98% of patients, ranking as the top-five hit among the 100 receptor tyrosine kinases-encoding genes. RET mutants R693H and A750T show oncogenic transformation properties in NIH3T3 cells. Introduction of the RET mutants into human EOC cells increases RET signaling, cell viability, anchorage-independent cell growth and tumor xenograft growth in nude mice, demonstrating that they are activating mutations. RET mutants significantly enhance the activation of RET and its downstream MAPK and AKT signaling pathway in ovarian cancer cells. Vandetanib, a clinical approved RET inhibitor, inhibits the cell viability and decreases the activation of RET-MAPK signaling pathways in EOC cells expressing oncogenic RET mutants.

Conclusions

The discovery of RET pathogenic variants in the EOC patients, suggests a previously underestimated role for RET in EOC tumorigenesis. The identification of the gain-of-function RET mutations in EOC highlights the potential use of RET in targeted therapy to treat ovarian cancer patients.

Dysregulated mesenchymal PDGFR-β drives kidney fibrosis

Kidney fibrosis is characterized by expansion and activation of platelet-derived growth factor receptor-β (PDGFR-β)-positive mesenchymal cells. To study the consequences of PDGFR-β activation, we developed a model of primary renal fibrosis using transgenic mice with PDGFR-β activation specifically in renal mesenchymal cells, driving their pathological proliferation and phenotypic switch toward myofibroblasts. This resulted in progressive mesangioproliferative glomerulonephritis, mesangial sclerosis, and interstitial fibrosis with progressive anemia due to loss of erythropoietin production by fibroblasts. Fibrosis induced secondary tubular epithelial injury at later stages, coinciding with microinflammation, and aggravated the progression of hypertensive and obstructive nephropathy. Inhibition of PDGFR activation reversed fibrosis more effectively in the tubulointerstitium compared to glomeruli. Gene expression signatures in mice with PDGFR-β activation resembled those found in patients. In conclusion, PDGFR-β activation alone is sufficient to induce progressive renal fibrosis and failure, mimicking key aspects of chronic kidney disease in humans. Our data provide direct proof that fibrosis per se can drive chronic organ damage and establish a model of primary fibrosis allowing specific studies targeting fibrosis progression and regression.

Novel PDGFRB rearrangement in multifocal infantile myofibromatosis is tumorigenic and sensitive to imatinib

Infantile myofibromatosis (IM) is an aggressive neoplasm composed of myofibroblast-like cells in children. Although typically localized, it can also present as multifocal disease, which represents a challenge for effective treatment. IM has previously been linked to activating somatic and germline point mutations in the PDGFRβ tyrosine kinase encoded by the PDGFRB gene. Clinical panel-based targeted tumor sequencing of a tumor from a newborn with multifocal IM revealed a novel PDGFRB rearrangement, which was reported as being of unclear significance. Additional sequencing of cDNA from tumor and germline DNA confirmed a complex somatic/mosaic PDGFRB rearrangement with an apparent partial tandem duplication disrupting the juxtamembrane domain. Ectopic expression of cDNA encoding the mutant form of PDGFRB markedly enhanced cell proliferation of mouse embryo fibroblasts (MEFs) compared to wild-type PDGFRB and conferred tumor-forming capacity on nontumorigenic 10T1/2 fibroblasts. The mutated protein enhanced MAPK activation and retained sensitivity to the PDGFRβ inhibitor imatinib. Our findings reveal a new mechanism by which PDGFRB can be activated in IM, suggest that therapy with tyrosine kinase inhibitors including imatinib may be beneficial, and raise the possibility that this receptor tyrosine kinase might be altered in a similar fashion in additional cases that would similarly present annotation challenges in clinical DNA sequencing analysis pipelines.

A Distinctive Genomic and Immunohistochemical Profile for NOTCH3 and PDGFRB in Myofibroma With Diagnostic and Therapeutic Implications

Introduction. Myofibromas are rare tumors of pericytic lineage, typically affecting children, and are sometimes aggressive. A subset of sporadic and familial myofibromas have activating variants in PDGFRB. The relationship of myofibroma and PDGFRB to the NOTCH pathway has not yet been described. Methods. Ten myofibroma cases were sequenced with a targeted panel of 447 genes, including copy number variation and selected fusions. Immunohistochemical analysis of total NOTCH3 and activated NOTCH3 was assessed for all 10 myofibroma cases, and a series of histologic mimics (n = 20). Results. Alterations identified by next-generation sequencing included PDGFRB sequence variants in 8/10 cases (80%), a NOTCH3 variant in 1/10 cases (10%), and a NOTCH2 variant in 1/10 cases (10%). All 10 cases also showed a pattern of low-amplitude (1.5- to 2-fold) copy number alterations including gains in PDGFRB and NOTCH3. Ten of 10 myofibromas (100%) showed cytoplasmic staining for total NOTCH3 and 9 of 10 cases (90%) showed nuclear staining for activated NOTCH3. Within the control cohort of histologic mimics, 3 of 3 nodular fasciitis cases (100%) were positive for activated and total NOTCH3, and the remaining 17 cases were negative for pan NOTCH3, while 3 of 3 desmoid-type fibromatosis cases (100%) showed patchy weak nuclear staining for activated NOTCH3. Discussion. Our findings suggest a common pathway of PDGFRB/NOTCH3 activation in myofibromas, even in cases that lack PDGFRB sequence variants. These results support the pericytic lineage of myofibroma. Identification of the characteristic genomic alterations or immunohistochemical staining pattern may facilitate a difficult pathologic diagnosis, and support the use of targeted treatments.

Association of PDGFRB Mutations With Pediatric Myofibroma and Myofibromatosis

Importance

Myofibroma is the most frequent fibrous tumor in children. Multicentric myofibroma (referred to as infantile myofibromatosis) is a life-threatening disease.

Objective

To determine the frequency, spectrum, and clinical implications of mutations in the PDGFRB receptor tyrosine kinase found in sporadic myofibroma and myofibromatosis.

Design, Setting, and Participants

In this retrospective study of 69 patients with sporadic myofibroma or myofibromatosis, 85 tumor samples were obtained and analyzed by targeted deep sequencing of PDGFRB. Mutations were confirmed by an alternative method of sequencing and were experimentally characterized to confirm gain of function and sensitivity to the tyrosine kinase inhibitor imatinib.

Main Outcomes and Measures

Frequency of gain-of-function PDGFRB mutations in sporadic myofibroma and myofibromatosis. Sensitivity to imatinib, as assessed experimentally.

Results

Of the 69 patients with tumor samples (mean [SD] age, 7.8 [12.7] years), 60 were children (87%; 29 girls [48%]) and 9 were adults (13%; 4 women [44%]). Gain-of-function PDGFRB mutations were found in samples from 25 children, with no mutation found in samples from adults. Mutations were particularly associated with severe multicentric disease (13 of 19 myofibromatosis cases [68%]). Although patients had no familial history, 3 of 25 mutations (12%) were likely to be germline, suggesting de novo heritable alterations. All of the PDGFRB mutations were associated with ligand-independent receptor activation, and all but one were sensitive to imatinib at clinically relevant concentrations.

Conclusions and Relevance

Gain-of-function mutations of PDGFRB in myofibromas may affect only children and be more frequent in the multicentric form of disease, albeit present in solitary pediatric myofibromas. These alterations may be sensitive to tyrosine kinase inhibitors. The PDGFRB sequencing appears to have a high value for diagnosis, prognosis, and therapy of soft-tissue tumors in children.

PDGRFB mutation-associated myofibromatosis: Response to targeted therapy with imatinib

Heterozygous activating mutations in platelet-derived growth factor receptor B (PDGFRB) have been recently identified as a cause of autosomal-dominant infantile myofibromatosis. We describe a 36-year-old man with PDGFRB c.1681C>T (p.R561C) mutation. Upon progressive disease, the patient received treatment with imatinib and showed a remarkable response with remission of multiple lesions after 12 months. This is the first report of an adult patient with PDGFRB c.1681C>T mutation treated with imatinib.

Naturally occurring and synthetic constitutive-active cytokine receptors in disease and therapy

Cytokines control immune related events and are critically involved in a plethora of patho-physiological processes including autoimmunity and cancer development. Mutations which cause ligand-independent, constitutive activation of cytokine receptors are quite frequently found in diseases. Many constitutive-active cytokine receptor variants have been directly connected to disease development and mechanistically analyzed. Nature's solutions to generate constitutive cytokine receptors has been recently adopted by synthetic cytokine receptor biology, with the goal to optimize immune therapeutics. Here, CAR T cell immmunotherapy represents the first example to combine synthetic biology with genetic engineering during therapy. Hence, constitutive-active cytokine receptors are therapeutic targets, but also emerging tools to improve or modulate immunotherapeutic strategies. This review gives a comprehensive insight into the field of naturally occurring and synthetic constitutive-active cytokine receptors.

Infantile Myofibromatosis With Intracranial Extradural Involvement and PDGFRB Mutation: A Case Report and Review of the Literature

Infantile myofibroma is a rare benign mesenchymal tumor that presents as solitary or multiple lesions (myofibromatosis) in the skin, soft tissue, bone, or internal organs. It most commonly affects the head and neck of infants and young children, but it can also affect adults. Intracranial involvement is reported to be extremely rare, and its clinical picture has been poorly characterized. Recently, it has been demonstrated that germline and somatic mutations in the platelet-derived growth factor receptor beta (PDGFRB) are associated with familial infantile myofibromatosis. We report a case of infantile myofibromatosis with predominant posterior fossa extradural involvement in a 14-year-old adolescent girl with a confirmed mutation in the PDGFRB gene.

A novel de novo PDGFRB variant in a child with severe cerebral malformations, intracerebral calcifications, and infantile myofibromatosis

The spectrum of clinical consequences of variants in the Platelet derived growth factor receptor beta (PDGFRB) gene is wide. Missense variants leading to variable loss of signal transduction in vitro have been reported in the idiopathic basal ganglia calcification (IBGC) syndrome Type 4. In contrast, gain-of-function variants have been reported in infantile myofibromatosis, Penttinen syndrome, and Kosaki overgrowth syndrome. Here, we report a patient harboring a novel postzygotic variant in PDGFRB (c.1682_1684del, p.[Arg561_Tyr562delinsHis]) and presenting severe cerebral malformations, intracerebral calcifications, and infantile myofibromatosis. This observation expands the phenotype associated with PDGFRB variants and illustrates the wide clinical spectrum linked to dysregulation of PDGFRB.

A tyrosine kinase-activating variant Asn666Ser in PDGFRB causes a progeria-like condition in the severe end of Penttinen syndrome

Missense variants located to the "molecular brake" in the tyrosine kinase hinge region of platelet-derived growth factor receptor-β, encoded by PFGFRB, can cause Penttinen-type (Val665Ala) and Penttinen-like (Asn666His) premature ageing syndromes, as well as infantile myofibromatosis (Asn666Lys and Pro660Thr). We have found the same de novo PDGFRB c.1997A>G p.(Asn666Ser) variants in two patients with lipodystrophy, acro-osteolysis and severely reduced vision due to corneal neovascularisation, reminiscent of a severe form of Penttinen syndrome with more pronounced connective tissue destruction. In line with this phenotype, patient skin fibroblasts were prone to apoptosis. Both in patient fibroblasts and stably transduced HeLa and HEK293 cells, autophosphorylation of PDGFRβ was observed, as well as increased phosphorylation of downstream signalling proteins such as STAT1, PLCγ1, PTPN11/SHP2-Tyr580 and AKT. Phosphorylation of MAPK3 (ERK1) and PTPN11/SHP2-Tyr542 appeared unaffected. This suggests that this missense change not only weakens tyrosine kinase autoinhibition, but also influences substrate binding, as both PTPN11 tyrosines (Tyr542 and Tyr580) usually are phosphorylated upon PDGFR activation. Imatinib was a strong inhibitor of phosphorylation of all these targets, suggesting an option for precision medicine based treatment.

Atomistic mechanism of the constitutive activation of PDGFRA via its transmembrane domain

Single-point mutations in the transmembrane (TM) region of receptor tyrosine kinases (RTKs) can lead to abnormal ligand-independent activation. We use a combination of computational modeling, NMR spectroscopy and cell experiments to analyze in detail the mechanism of how TM domains contribute to the activation of wild-type (WT) PDGFRA and its oncogenic V536E mutant. Using a computational framework, we scan all positions in PDGFRA TM helix for identification of potential functional mutations for the WT and the mutant and reveal the relationship between the receptor activity and TM dimerization via different interfaces. This strategy also allows us design a novel activating mutation in the WT (I537D) and a compensatory mutation in the V536E background eliminating its constitutive activity (S541G). We show both computationally and experimentally that single-point mutations in the TM region reshape the TM dimer ensemble and delineate the structural and dynamic determinants of spontaneous activation of PDGFRA via its TM domain. Our atomistic picture of the coupling between TM dimerization and PDGFRA activation corroborates the data obtained for other RTKs and provides a foundation for developing novel modulators of the pathological activity of PDGFRA.

Effects of Sunitinib and Other Kinase Inhibitors on Cells Harboring a PDGFRB Mutation Associated with Infantile Myofibromatosis

Infantile myofibromatosis represents one of the most common proliferative fibrous tumors of infancy and childhood. More effective treatment is needed for drug-resistant patients, and targeted therapy using specific protein kinase inhibitors could be a promising strategy. To date, several studies have confirmed a connection between the p.R561C mutation in gene encoding platelet-derived growth factor receptor beta (PDGFR-beta) and the development of infantile myofibromatosis. This study aimed to analyze the phosphorylation of important kinases in the NSTS-47 cell line derived from a tumor of a boy with infantile myofibromatosis who harbored the p.R561C mutation in PDGFR-beta. The second aim of this study was to investigate the effects of selected protein kinase inhibitors on cell signaling and the proliferative activity of NSTS-47 cells. We confirmed that this tumor cell line showed very high phosphorylation levels of PDGFR-beta, extracellular signal-regulated kinases (ERK) 1/2 and several other protein kinases. We also observed that PDGFR-beta phosphorylation in tumor cells is reduced by the receptor tyrosine kinase inhibitor sunitinib. In contrast, MAPK/ERK kinases (MEK) 1/2 and ERK1/2 kinases remained constitutively phosphorylated after treatment with sunitinib and other relevant protein kinase inhibitors. Our study showed that sunitinib is a very promising agent that affects the proliferation of tumor cells with a p.R561C mutation in PDGFR-beta.

STAT1 modulates tissue wasting or overgrowth downstream from PDGFRβ

In this study, He et al. investigated how gain-of-function PDGFRβ mutations cause human disease, specifically whether PDGFRB mutations alone are responsible for genetic diseases characterized by musculoskeletal wasting or overgrowth. Using a genetic approach, their findings suggest a molecular mechanism by which STAT1 suppresses PDGFRβ-driven fibrosis and bone growth.

Platelet-derived growth factor (PDGF) acts through two conserved receptor tyrosine kinases: PDGFRα and PDGFRβ. Gain-of-function mutations in human PDGFRB have been linked recently to genetic diseases characterized by connective tissue wasting (Penttinen syndrome) or overgrowth (Kosaki overgrowth syndrome), but it is unclear whether PDGFRB mutations alone are responsible. Mice with constitutive PDGFRβ signaling caused by a kinase domain mutation (D849V) develop lethal autoinflammation. Here we used a genetic approach to investigate the mechanism of autoinflammation in Pdgfrb^+/D849V mice and test the hypothesis that signal transducer and activator of transcription 1 (STAT1) mediates this phenotype. We show that Pdgfrb^+/D849V mice with Stat1 knockout (Stat1^−/−Pdgfrb^+/D849V) are rescued from autoinflammation and have improved life span compared with Stat1^+/−Pdgfrb^+/D849V mice. Furthermore, PDGFRβ–STAT1 signaling suppresses PDGFRβ itself. Thus, Stat1^−/−Pdgfrb^+/D849V fibroblasts exhibit increased PDGFRβ signaling, and mice develop progressive overgrowth, a distinct phenotype from the wasting seen in Stat1^+/−Pdgfrb^+/D849V mice. Deletion of interferon receptors (Ifnar1 or Ifngr1) does not rescue wasting in Pdgfrb^+/D849V mice, indicating that interferons are not required for autoinflammation. These results provide functional evidence that elevated PDGFRβ signaling causes tissue wasting or overgrowth reminiscent of human genetic syndromes and that the STAT1 pathway is a crucial modulator of this phenotypic spectrum.

Analysis of acquired mutations in transgenes arising in Ba/F3 transformation assays: findings and recommendations

The identification and functional validation of potentially oncogenic mutations in leukemia is an essential step toward a future of personalized targeted therapy. To assess the oncogenic capacity of individual mutations, reliable and scalable in vitro experimental approaches are required. Since 1988, researchers have used the IL-3 dependent Ba/F3 transformation assay to validate the oncogenic potential of mutations to drive factor-independent growth. Here we report a previously unrecognized phenomenon whereby Ba/F3 cells, engineered to express weakly transforming mutations, present with additional acquired mutations in the expressed transgene following factor withdrawal. Using four mutations with known transformative capacity in three cytokine receptors (CSF2RB, CSF3R and IL7R), we demonstrate that the mutated receptors are highly susceptible to acquiring additional mutations. These acquired mutations of unknown functional significance are selected by factor withdrawal but appear to exist prior to the removal of growth factor. This anomaly has the potential to confound efforts to both validate and characterize oncogenic mutations in leukemia, particularly when it is not standard practice to sequence validate cDNAs from transformed Ba/F3 lines. We present specific recommendations to detect and mitigate this phenomenon in future research using Ba/F3 transformation assays, along with methods to make the Ba/F3 assay more quantitative.

A patient with germ-line gain-of-function PDGFRB p.N666H mutation and marked clinical response to imatinib

PurposeHeterozygous germ-line activating mutations in PDGFRB cause Kosaki and Penttinen syndromes and myofibromatosis. We describe a 10-year-old child with a germ-line PDGFRB p.N666H mutation who responded to the tyrosine kinase inhibitor imatinib by inhibition of PDGFRB.MethodsThe impact of p.N666H on PDGFRB function and sensitivity to imatinib was studied in cell culture.ResultsCells expressing the p.N666H mutation showed constitutive PDGFRB tyrosine phosphorylation. PDGF-independent proliferation was abolished by imatinib at 1 μM concentration. Patient fibroblasts showed constitutive receptor tyrosine phosphorylation that was also abrogated by imatinib with reduced proliferation of treated cells.This led to patient treatment with imatinib at 400 mg daily (340 mg/m²) for a year with objective improvement of debilitating hand and foot contractures, reduced facial coarseness, and significant improvement in quality of life. New small subcutaneous nodules developed, but remained stable. Transient leukopenia, neutropenia, and fatigue resolved without intervention; however, mildly decreased growth velocity resulted in reducing imatinib dose to 200 mg daily (170 mg/m²). The patient continues treatment with ongoing clinical response.ConclusionTo our knowledge, this is one of the first personalized treatments of a congenital disorder caused by a germ-line PDGF receptor mutation with a PDGFRB inhibitor.

STAT6 Reliably Distinguishes Solitary Fibrous Tumors from Myofibromas

Solitary fibrous tumors (SFT) and myofibromas (MF) historically have belonged to the same morphologic spectrum and have been lumped together under the nonspecific umbrella term, "hemangiopericytoma" along with other pericytic/myoid tumors. While current evidence shows clear distinction between the two entities, they frequently remain in the same histopathologic differential diagnosis. This diagnostic dilemma especially is common for smaller incisional biopsies from the oral cavity. STAT6 immunohistochemistry (IHC) recently was established as a reliable method to detect solitary fibrous tumor; however, the literature is sparse regarding STAT6 reactivity in MFs. The authors report ten new cases of oral solitary fibrous tumor, discuss histopathologic similarities and differences between the two tumors, and list respective STAT6 IHC expressivity. After IRB approval, 10 cases diagnosed as SFT and 24 cases of MF were collected from the University of Florida Oral and Maxillofacial Pathology Biopsy Service between the years 1994 and 2016. The original hematoxylin and eosin slides and related IHC were reviewed. IHC with STAT6 antibody was performed on all 34 samples, and the findings were analyzed. All cases were from the oral cavity or perioral regions. 10/10 SFTs expressed STAT6 nuclear reactivity, while no cases of MF showed nuclear expression of STAT6. STAT6 is a dependable marker to differentiate SFTs from MFs.