NTRK expression is common in xanthogranuloma and is associated with the solitary variant.

BACKGROUND: Previously identified mutually-exclusive driver genes in juvenile xanthogranuloma (JXG) and adult xanthogranuloma (AXG) include mutations in MAP kinase pathway genes such as MAP2K1, BRAF, ARAF, KRAS, NRAS, PIK3CD as well as fusions in BRAF and ALK, with a subset of cases with no identified driver yet. NTRK fusion has been identified in rare cases. METHODS: We identified two consecutive index cases of localized JXG or AXG with NTRK1 fusion by next-generation sequencing (NGS) and confirmed by pan-NTRK immunostain. We expanded the study to a total of 50 cases of JXG and AXG using screening by pan-NTRK immunostain. We confirmed the specificity of our approach with negative results in 5 cases of histiocytic neoplasia lacking an NTRK fusion by NGS and 14 cases of non-neoplastic histiocytic disease. RESULTS: We found 23 cases of JXG or AXG with overexpression of NTRK by immunostain, and these cases were restricted to localized disease (23 of 43 cases, 53.5%) rather than disseminated disease (zero of seven cases). CONCLUSIONS: NTRK expression is common in JXG or AXG and associated with localized rather than disseminated disease. We speculate that the potential importance of this in JXG and AXG has not been previously appreciated due to the tendency to focus sequencing studies on disseminated disease. We confirm the presence of an NTRK1 fusion in two positive cases by NGS, however, additional genetic studies are necessary to further explore this.

Expanding Our Knowledge of Molecular Pathogenesis in Histiocytoses: Solitary Soft Tissue Histiocytomas in Children With a Novel CLTC::SYK Fusion.

The histiocytoses comprise a histopathologically and clinically diverse group of disorders bearing recurrent genomic alterations, commonly involving the BRAF gene and mitogen-activated protein kinase pathway. In the current study, a novel CLTC :: SYK fusion in 3 cases of a histopathologically distinct histiocytic neoplasm arising as solitary soft tissue lesions in children identified by next-generation sequencing and fluorescence in situ hybridization is described. Morphologically, all 3 neoplasms were composed of sheets of cells with round-oval nuclei and vacuolated eosinophilic cytoplasm but, in contrast to classic juvenile xanthogranuloma (JXG), Touton giant cells were absent. A separate cohort of classic JXG cases subsequently profiled by fluorescence in situ hybridization were negative for the presence of a CLTC::SYK fusion suggesting that CLTC::SYK fusion-positive histiocytoma is genetically and histologically distinct from JXG. We postulate that the CLTC::SYK fusion leads to aberrant activation of the SYK kinase, which is involved in variable pathways, including mitogen-activated protein kinase. The identification of a novel CLTC::SYK fusion may pave the way for the development of targeted therapeutic options for aggressive disease.

[Genetic diagnosis of a child with Café-au-lait macules and juvenile xanthogranuloma].

OBJECTIVE: To explore the genetic basis for a child with café-au-lait macules and juvenile xanthogranuloma. METHODS: Clinical data and peripheral blood samples of the patient and her family members were collected and subjected to targeted capture and high-throughput sequencing. Candidate variant was verified by Sanger sequencing. RESULTS: A deletional variant in exon 23 of the NF1 gene was detected in the proband. Sanger sequencing has verified it as a de novo variant, which was highly correlated with the clinical manifestations of the patient and her mother. The diagnosis of neurofibromatosis 1 (NF1) was established. The variant was unreported previously. CONCLUSION: Targeted capture and next-generation sequencing combined with Sanger sequencing can facilitate early diagnosis of NF1 and provide a basis for the clinical treatment, genetic counseling and prenatal diagnosis.

Histiocytic Disorders of Childhood.

Histiocytic disorders of childhood represent a wide spectrum of conditions that share the common histologic feature of activated or transformed "histiocytes." Langerhans cell histiocytosis (LCH) is the most common, with an incidence of approximately 5 per million children. LCH may be difficult to distinguish from more ubiquitous causes of skin rashes, bone pain, or fever. Current chemotherapy fails to cure more than 50% of children with multifocal disease, and treatment failure is associated with increased risks of long-term sequelae. Somatic activating mitogen-activated protein kinase (MAPK) pathway-activating mutations (most often BRAFV600E) have been identified in hematopoietic precursors in patients with LCH. Opportunities to improve outcomes with targeted therapies are under investigation. Juvenile xanthogranuloma (JXG) and Rosai-Dorfman disease (RDD) are less common than LCH and are distinguished by specific histologic and clinical features. Recurrent MAPK pathway gene mutations are also identified in JXG and RDD. In many cases, these conditions spontaneously resolve, but disseminated disease can be fatal. Although there has been historic debate regarding the nature of these conditions as inflammatory versus neoplastic, LCH, JXG, and RDD are now considered myeloid neoplastic disorders. In contrast, hemophagocytic lymphohistiocytosis (HLH) is clearly a disorder of immune dysregulation. HLH is characterized by extreme immune activation driven by hyperactivated T cells. HLH arises in approximately 1 child per million and is nearly universally fatal without prompt recognition and immune suppression. Outcomes of treated children are poor, with approximately 60% survival. Emapalumab, which targets interferon-γ signaling, was recently approved for patients with recurrent or refractory HLH, and additional cytokine-directed therapies are under investigation.

Oral Juvenile Xanthogranuloma: A Clinicopathological, Immunohistochemical and BRAF V600E Study of Five New Cases, with Literature Review.

Juvenile xanthogranuloma (JXG) is the most common form of non-Langerhans cell histiocytosis and oral mucosal involvement is exceedingly rare. Histiocytic disorders harbor activating mutations in MAPK pathway, including the report of BRAF V600E in JXG of extracutaneous site. However, no information is available for oral JXG. Herein, the clinicopathological and immunohistochemical features of five new oral JXG were evaluated in conjunction with literature review. Also, we assessed the BRAF V600E in oral samples. Five oral JXG were retrieved from pathology archives. Morphological and immunohistochemical analyses were performed. The BRAF V600E status was determined with TaqMan allele-specific qPCR. The series comprised of three female and two male patients, most of them adults, with a median age of 39 years (range 13-68 years). Clinically, the lesions appeared as asymptomatic solitary nodules, measuring until 2.5 cm, with more incident to the buccal mucosa. Morphologically, most of the cases presented classical histological features of JXG, with histiocytic cells consistent with the non-Langerhans cell immunophenotype. BRAF V600E was not detected in the cases tested. This is the first and largest published series of oral JXG affecting adults and a Brazilian population. The molecular pathogenesis of oral JXG remains unknown. Clinicians and pathologists must recognize JXG to avoid misdiagnoses with oral benign or malignant lesions.

Ocular Juvenile Xanthogranuloma With BRAF V600E Mutation in a Child.

The authors present a case of bilateral painless progressive proptosis. A diagnosis of ocular juvenile xanthogranuloma was made based on clinical manifestations, histopathology, and immunohistochemistrical staining. Genetic testing discovered the BRAF V600E mutation. This patient did not respond to standard chemotherapy; however, he demonstrated regression after anti-BRAF targeted therapy. [J Pediatr Ophthalmol Strabismus. 2021;58(4):e19-e21.].

Juvenile xanthogranuloma in Noonan syndrome.

Noonan syndrome (NS) is one of the common RASopathies. While the clinical phenotype in NS is variable, it is typically characterized by distinctive craniofacial features, cardiac defects, reduced growth, bleeding disorders, learning issues, and an increased risk of cancer. Several different genes cause NS, all of which are involved in the Ras/mitogen-activated protein kinase (Ras/MAPK) pathway. Juvenile xanthogranuloma (JXG) is an uncommon, proliferative, self-limited cutaneous disorder that affects young individuals and may be overlooked or misdiagnosed due to its transient nature. A RASopathy that is known to be associated with JXG is neurofibromatosis type 1 (NF1). JXG in NF1 has also been reported in association with a juvenile myelomonocytic leukemia (JMML). As RASopathies, both NS and NF1 have an increased incidence of JMML. We report a 10-month-old female with NS who has a PTPN11 pathogenic variant resulting in a heterozygous SHP2 p.Y62D missense mutation. She was found to have numerous, small, yellow-pink smooth papules that were histopathologically confirmed to be JXG. In understanding the common underlying pathogenetic dysregulation of the Ras/MAPK pathway in both NS and NF1, this report suggests a possible molecular association for why NS individuals may be predisposed to JXG.

Juvenile xanthogranuloma as a new type of skin lesions in tuberous sclerosis complex.

OBJECTIVE: Tuberous sclerosis complex (TSC) is a rare autosomal dominant genetic disease with many manifestations, and it involves any organ. In this study, we report a TSC patient with new type skin lesions. METHODS: A 7-month-old TSC boy with multiple cutaneous nodules was admitted in our hospital. We collected the clinical data of the patient. We performed biopsy of cutaneous nodules and whole-exome sequencing in both paraffin block tissue and blood samples. RESULTS: The patient presented with a 2 month history of gradual growth multiple cutaneous nodules. He had cardiac rhabdomyoma, subependymal giant cell astrocytoma (SEGA) and hypomelanotic macules. The pathological finding of cutaneous nodules was consistent with juvenile xanthogranuloma (JXG). After 3 months of sirolimus treatment, the multiple nodules disappeared. The whole-exome sequencing identified TSC1 (c.2356C > T, p.R786*) mutation in both paraffin block tissue and blood samples. We overturned the original pathological diagnosis and finally identified JXG as a new type of skin lesions in TSC. CONCLUSION: This is the first report on the occurrence of JXG skin lesions in TSC patient. Genetic testing is necessary in JXG. These findings expand the phenotype of skin in patients with TSC and contribute to the elucidation of JXG pathogenesis and treatment.

BRAF V600E mutation in Juvenile Xanthogranuloma family neoplasms of the central nervous system (CNS-JXG): a revised diagnostic algorithm to include pediatric Erdheim-Chester disease.

The family of juvenile xanthogranuloma family neoplasms (JXG) with ERK-pathway mutations are now classified within the "L" (Langerhans) group, which includes Langerhans cell histiocytosis (LCH) and Erdheim Chester disease (ECD). Although the BRAF V600E mutation constitutes the majority of molecular alterations in ECD and LCH, only three reported JXG neoplasms, all in male pediatric patients with localized central nervous system (CNS) involvement, are known to harbor the BRAF mutation. This retrospective case series seeks to redefine the clinicopathologic spectrum of pediatric CNS-JXG family neoplasms in the post-BRAF era, with a revised diagnostic algorithm to include pediatric ECD. Twenty-two CNS-JXG family lesions were retrieved from consult files with 64% (n = 14) having informative BRAF V600E mutational testing (molecular and/or VE1 immunohistochemistry). Of these, 71% (n = 10) were pediatric cases (≤18 years) and half (n = 5) harbored the BRAF V600E mutation. As compared to the BRAF wild-type cohort (WT), the BRAF V600E cohort had a similar mean age at diagnosis [BRAF V600E: 7 years (3-12 y), vs. WT: 7.6 years (1-18 y)] but demonstrated a stronger male/female ratio (BRAF V600E: 4 vs WT: 0.67), and had both more multifocal CNS disease ( BRAFV600E: 80% vs WT: 20%) and systemic disease (BRAF V600E: 40% vs WT: none). Radiographic features of CNS-JXG varied but typically included enhancing CNS mass lesion(s) with associated white matter changes in a subset of BRAF V600E neoplasms. After clinical-radiographic correlation, pediatric ECD was diagnosed in the BRAF V600E cohort. Treatment options varied, including surgical resection, chemotherapy, and targeted therapy with BRAF-inhibitor dabrafenib in one mutated case. BRAF V600E CNS-JXG neoplasms appear associated with male gender and aggressive disease presentation including pediatric ECD. We propose a revised diagnostic algorithm for CNS-JXG that includes an initial morphologic diagnosis with a final integrated diagnosis after clinical-radiographic and molecular correlation, in order to identify cases of pediatric ECD. Future studies with long-term follow-up are required to determine if pediatric BRAF V600E positive CNS-JXG neoplasms are a distinct entity in the L-group histiocytosis category or represent an expanded pediatric spectrum of ECD.

Genetic evaluation of juvenile xanthogranuloma: genomic abnormalities are uncommon in solitary lesions, advanced cases may show more complexity.

Juvenile xanthogranuloma is a rare histiocytic proliferation primarily affecting infants and young children, characterized by aberrant infiltration of histiocyte-derived cells in the skin, soft tissues and more rarely, visceral organs. Juvenile xanthogranuloma is generally considered to be a benign disorder; most lesions are solitary cutaneous nodules that resolve spontaneously without treatment. However, cases with extracutaneous involvement, multiple lesions, and/or systemic disease often require aggressive therapy. Though molecular studies have provided evidence of clonality in juvenile xanthogranuloma, in support of a neoplastic process, little is known about the genetic profile of juvenile xanthogranuloma. We used molecular inversion probe array technology to evaluate the genomic characteristics (copy number alterations or copy neutral-loss of heterozygosity) of 21 archived cases of juvenile xanthogranuloma (19 solitary, 1 diffuse cutaneous, 1 systemic). Four cases (19%) showed acquired, clonal alterations. Two lesions from a case of diffuse cutaneous juvenile xanthogranuloma showed distinct profiles: JXG-1a contained trisomy 5 and 17 and JXG-1b contained loss of heterozygosity in 5q. The systemic juvenile xanthogranuloma (JXG-2) showed multiple genomic alterations. Only two of 19 solitary juvenile xanthogranulomas showed abnormal genomic profiles: JXG-3 showed gains on 1q and 11q and JXG-4 showed a 7.2 Mb loss in 3p. No recurrent abnormalities were observed among these cases. The presence of non-recurrent copy number alterations in a subset of samples implies that copy number changes are unlikely driving pathogenesis in juvenile xanthogranuloma, but may be acquired during disease progression. The presence of genomic abnormalities in more advanced cases (ie, systemic and diffuse cutaneous juvenile xanthogranuloma) supports this notion, particularly as the advanced cases of juvenile xanthogranuloma presented more genomic complexity.

Activating MAPK1 (ERK2) mutation in an aggressive case of disseminated juvenile xanthogranuloma.

Juvenile xanthogranuloma (JXG) is a rare histiocytic disorder that is usually benign and self-limiting. We present a case of atypical, aggressive JXG harboring a novel mitogen-activated protein kinase (MAPK) pathway mutation in the MAPK1 gene, which encodes mitogen-activated protein kinase 1 or extracellular signal-regulated 2 (ERK2). Our analysis revealed that the mutation results in constitutive ERK activation that is resistant to BRAF or MEK inhibitors but susceptible to an ERK inhibitor. These data highlight the importance of identifying specific MAPK pathway alterations as part of the diagnostic workup for patients with histiocytic disorders rather than initiating empiric treatment with MEK inhibitors.

BRAF V600E mutation in pediatric intracranial and cranial juvenile xanthogranuloma.

Juvenile xanthogranuloma (JXG) is a cutaneous form of non-Langerhans cell histiocytosis, primarily affecting children. The lesion is presumed to originate from either macrophages or dermal dendritic cells. JXG can rarely present as an isolated intracranial lesion and, in contrast to the dismal outcome of patients with systemic disease, cranial JXG has been shown to carry a more favorable prognosis. Here, we report for the first time 3 pediatric cases of JXG with a BRAF V600E mutation, 2 with intracranial lesions and 1 with cranial lesions. Although these intracranial/cranial lesions have been referred to as JXG, they likely differ from cutaneous JXG in both the clinical features and BRAF status. It may be more appropriate to classify intracranial/cranial JXG in the same group as Langerhans cell histiocytosis and Erdheim-Chester disease, which also have a BRAF V600E mutation. Further study of BRAF status in a larger series of JXG is warranted.

New JAG1 Mutation Causing Alagille Syndrome Presenting With Severe Hypercholesterolemia: Case Report With Emphasis on Genetics and Lipid Abnormalities.

Context: Alagille syndrome is a rare autosomal-dominant genetic disorder caused by defects in the Notch signaling pathway, which involves multiple organ systems. Bile duct paucity is the main characteristic feature of the disease, which often leads to cholestatic hypercholesterolemia. Case Description: We report the case of a male infant who had developed failure to thrive, jaundice, intermittent pruritus, and multiple diffuse symmetrical skin xanthomas at 1 year of age. He was diagnosed with pulmonary stenosis, butterfly vertebrae of T4, T6, and T8; horseshoe kidney, and embryotoxon in the left eye. Laboratory workup revealed severe hypercholesterolemia. Alagille syndrome was suspected and confirmed by genetic testing, which identified a previously undescribed frameshift pathogenic heterozygous variant in the JAG1 gene, p.Arg486Lysfs*5. Conclusions: Here, we report a unique case of a patient diagnosed with Alagille syndrome who was found to have a previously undescribed frameshift pathogenic mutation in the JAG1 gene and who presented with xanthomatosis and levels of hypercholesterolemia more than 2 times higher than those previously reported in the literature. We also provide a review of the different pathophysiologic mechanisms associated with the increase in serum cholesterol and low-density lipoprotein cholesterol concentrations seen in cholestatic liver disease in general and in Alagille syndrome in particular.

Biological and clinical significance of somatic mutations in Langerhans cell histiocytosis and related histiocytic neoplastic disorders.

Langerhans cell histiocytosis (LCH), juvenile xanthogranuloma (JXG), and Erdheim-Chester disease (ECD) represent histiocytic disorders with a wide range of clinical manifestations. Until recently, mechanisms of pathogenesis have been speculative and debate has focused on classification of these conditions as reactive versus neoplastic. Genomic studies have been challenged by scarce tissue specimens, as well as heterogeneous nature of the lesions with variable infiltration of pathologic histiocytes. Whole-exome sequencing recently revealed a very low frequency of somatic mutations in LCH, JXG, and ECD compared to other neoplastic disorders. However, at least in the cases of LCH and ECD, there is a very high frequency of activating mutations in MAPK pathway genes, most notably BRAF-V600E, as well as MAP2K1, in LCH and NRAS in ECD. In ECD, recurrent mutations in the PI3K pathway gene PIK3CA have also been described. The heterogeneous clinical manifestations of these disorders may therefore be the cumulative result of activation of MAPK mutations (along with modifying signals from other pathways) at distinct stages of myeloid differentiation. Implications of this model include redefinition of LCH, JXG, and ECD as a group of clinically diverse myeloid neoplastic disorders with a common mechanism of pathogenesis. This model supports refocusing therapeutic strategies for these diseases on a personalized approach based on specific mutations and the cell(s) of origin.