Dasatinib induces a dramatic response in a child with refractory juvenile xanthogranuloma with a novel MRC1-PDGFRB fusion

Disseminated juvenile xanthogranulomas with underlying neurotrophic tyrosine receptor kinase fusion and response to larotrectinib

Recent molecular characterizations of histiocytoses, including juvenile xanthogranuloma (JXG), have identified diverse kinase gene mutations, suggesting that various targeted therapies may be promising treatments for these lesions. We herein present a case of an infant with disseminated JXG lesions with an underlying NTRK mutation who was successfully treated with larotrectinib.

Neuroimaging of pediatric tumors of the sellar region-A review in light of the 2021 WHO classification of tumors of the central nervous system

Sellar/suprasellar tumors comprise about 10% of all pediatric Central Nervous System (CNS) tumors and include a wide variety of entities, with different cellular origins and distinctive histological and radiological findings, demanding customized neuroimaging protocols for appropriate diagnosis and management. The 5th edition of the World Health Organization (WHO) classification of CNS tumors unprecedently incorporated both histologic and molecular alterations into a common diagnostic framework, with a great impact in tumor classification and grading. Based on the current understanding of the clinical, molecular, and morphological features of CNS neoplasms, there have been additions of new tumor types and modifications of existing ones in the latest WHO tumor classification. In the specific case of sellar/suprasellar tumors, changes include for example separation of adamantinomatous and papillary craniopharyngiomas, now classified as distinct tumor types. Nevertheless, although the current molecular landscape is the fundamental driving force to the new WHO CNS tumor classification, the imaging profile of sellar/suprasellar tumors remains largely unexplored, particularly in the pediatric population. In this review, we aim to provide an essential pathological update to better understand the way sellar/suprasellar tumors are currently classified, with a focus on the pediatric population. Furthermore, we intend to present the neuroimaging features that may assist in the differential diagnosis, surgical planning, adjuvant/neoadjuvant therapy, and follow-up of this group of tumors in children.

Treatment of Langerhans Cell Histiocytosis and Histiocytic Disorders: A Focus on MAPK Pathway Inhibitors

Histiocytic disorders are rare diseases defined by the clonal accumulation of a macrophage or dendritic cell origin. These disorders include Langerhans cell histiocytosis, Erdheim-Chester disease, juvenile xanthogranuloma, malignant histiocytoses, and Rosai-Dorfman-Destombes disease. These histiocytic disorders are a diverse group of disorders with different presentations, management, and prognosis. This review focuses on these histiocytic disorders and the role of pathological ERK signaling due to somatic mutations in the mitogen--activated protein kinase (MAPK) pathway. Over the last decade, there has been growing awareness of the MAPK pathway being a key driver in many histiocytic disorders, which has led to successful treatment with targeted therapies, in particular, BRAF inhibitors and MEK inhibitors.

Novel ANKRD26 and PDGFRB gene mutations in pediatric case of non-Langerhans cell histiocytosis: Case report and literature review

Cutaneous non-Langerhans cell histiocytosis (NLCH) is a rare and biologically benign entity that can be broadly classified into two categories: xanthogranuloma and non-xanthogranuloma. The xanthogranuloma family is characterized by a proliferation of histiocytes with both macrophage and dendritic cell differentiation, negative BRAF mutation, and rare Touton-type giant cells. Molecular studies have reported that mutations involved in the MAPK signaling pathways are implicated in the pathophysiology of histiocytoses. While LCH is associated with the somatic mutation of BRAF v600e, however, mutations and gene fusions in NLCH cases are undefined. We hereby present a 19-month-old female with recalcitrant nodular rashes diagnosed as NLCH with associated novel genetic mutation involving ANKRD26 and PDGFRB genes, as well as PDGFRB::CD74 fusion mRNA. Immunohistochemical staining showed strong and diffuse CD68 and CD163 positivity, and negative CD1a, CD207, ALK D5F3, S100 protein, and BRAF V600E (VE1). Albeit unknown significance, this case of an ANKRD26 and PDGFRB gene mutation in cutaneous NLCH has not been reported prior in the literature. Our case highlights the advantage of pathology and genetic studies in cutaneous NLCH to increase the understanding of this heterogeneous enigmatic disorder and identify further options in management.

Disseminated Juvenile Xanthogranuloma with a Novel MYH9-FLT3 Fusion Presenting as a Blueberry Muffin Rash in a Neonate

Juvenile xanthogranuloma (JXG) is a benign proliferative histiocytic disorder of the dendritic cell phenotype. It mostly presents in the pediatric age group as a solitary skin lesion. We describe a rare case of an infant born with disseminated JXG who presented with a blueberry muffin rash at birth. A term infant was noted to have multiple petechiae, purple nodules, and macules (1 mm-2 cm in diameter) and hepatosplenomegaly, at the time of birth. Further investigations revealed thrombocytopenia and direct hyperbilirubinemia and a magnetic resonance imaging showed scattered tiny foci of restricted diffusion in multiple areas of the brain. Patient received multiple platelet transfusions in the first few weeks with gradual improvement in thrombocytopenia. Ultimately, a biopsy of one of the lesions revealed the diagnosis of disseminated JXG with notable atypical features. Somatic mutation analysis showed a novel MYH9-FLT3 fusion, but a bone marrow biopsy was negative. The lesions faded over time, relative to patient's growth and normal neurodevelopment was noted at 18 months of age. JXG should be considered in the differentials of blueberry muffin rash in an infant. Although, JXG is mostly a self-limited condition, congenital disseminated JXG may be associated with significant morbidity and mortality.

Utility of Cyclin D1 Immunostaining in Cutaneous Xanthogranuloma

ABSTRACT

Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase pathway activation has recently been found to be associated with almost all Langerhans cell histiocytosis cases. In BRAF V600E mutation-positive cases, this activation is seen as a downstream activation. In addition, cyclin D1 is a downstream target of the MAPK pathway. Recent studies have argued in favor of using cyclin D1 as a potential neoplastic marker to differentiate Langerhans cell histiocytosis from other reactive Langerhans cell proliferations in the skin and lymph nodes. Therefore, we chose to study the immunohistochemical expression of cyclin D1 in cutaneous xanthogranuloma (XG) cases. Fifteen XG cases were retrieved and stained for cyclin D1, BRAF (v-raf murine sarcoma viral oncogene homolog B1), CD1a, and langerin (CD207). Twelve cases showed strong and diffuse nuclear positivity for cyclin D1, both in the XG cells and in the multinucleated osteoclast-like giant cells. Three cases showed focal weak nuclear staining for cyclin D1. All 15 cases showed negative immunoreactivity for BRAF, CD1a, and CD207. Although limited by small sample size, we conclude that most cases of cutaneous XG should show at least weak nuclear staining with cyclin D1. The histogenesis of XG is still largely unknown, and the finding of cyclin D1 positivity in a majority of cases may indicate a role for the MAPK/extracellular signal-regulated kinase pathway in cutaneous XG.