Genomic Alterations in Langerhans Cell Histiocytosis

Advancements in the understanding and management of histiocytic neoplasms

Histiocytic neoplasms are rare diseases involving macrophages, dendritic cells, and monocytes. They include Langerhans cell histiocytosis (LCH), Erdheim-Chester disease (ECD), Rosai-Dorfman disease (RDD), juvenile xanthogranuloma (JXG), and histiocytic sarcoma. Histiocytic neoplasms are characterized by varied clinical courses and prognoses, necessitating a nuanced understanding of their classification, epidemiology, and clinical manifestations. Genetic studies have revealed somatic mutations, predominantly in the MAPK pathway, suggesting a clonal neoplastic nature. This review covers the current understanding of histiocytic neoplasms, molecular pathophysiology, with a particular focus on mutations in genes such as BRAF, MAP2K1, and the PI3K-AKT signaling pathways, and evolving treatment strategies, especially focusing on LCH, ECD, RDD, and JXG. The treatment landscape has evolved with advancements in targeted therapies. BRAF inhibitors, such as vemurafenib and dabrafenib, have shown efficacy, especially in high-risk LCH cases; however, challenges remain, including relapse post-treatment discontinuation, and adverse effects. MEK inhibitors have also demonstrated effectiveness, and cobimetinib has recently been approved for use in adults. Further research is required to determine the optimal treatment duration and strategies for managing therapy interruptions. Advancements in molecular genetics and targeted therapies have revolutionized the management of histiocytic neoplasms. However, ongoing research is crucial for optimizing patient outcomes.

One Health: Therapies Targeting Genetic Variants in Human and Canine Histiocytic and Dendritic Cell Sarcomas

The precise cause of HS/DCS is still unknown. The relatively low incidence in humans urges for an animal model with a high incidence to accelerate knowledge about genetics and optimal treatment of HS/DCS. Namely, until now, the therapies targeting genetic variants are still more experimental and sparsely used, while consensus is missing. In addition, the literature about variants and possible mutation-targeted therapies in humans and dogs consists mainly of case reports scattered throughout the literature. Therefore, an overview is provided of all currently known genetic variants in humans and dogs with HS/DCS and its subtypes, their possible mutation-targeted therapies, their efficacy, and a contemplation about the future. Several genetic variants have already been discovered in HS/DCS, of which many are shared between canine and human HS/DCS, but unique variants exist as well. Unfortunately, none of these already found variants seem to be specifically causal for HS/DCS, and the puzzle of its landscape of genetic variation is far from complete. The use of mutation-targeted therapies, including MAPK-/MEK-inhibitors and the future use of PTPN11-, CDK4/6- and PD-1-inhibitors, seems to be promising for these specific variants, but clearly, clinical trials are needed to determine optimal inhibitors and standardised protocols for all variants. It can be concluded that molecular analysis for variants and subsequent mutation-targeted therapy are an essential addition to cancer diagnostics and therapy. A joint effort of humans and dogs in research is urgently needed and will undoubtedly increase knowledge and survival of this devastating disease in dogs and humans.

Molecular Mutations in Histiocytosis: A Comprehensive Survey of Genetic Alterations

Histiocytosis represents a group of uncommon disorders characterized by the abnormal accumulation of specialized immune cells, such as macrophages, dendritic cells, or monocyte-derived cells, in various tissues and organs. Over 100 distinct subtypes have been documented, each displaying a broad spectrum of clinical presentations and histological characteristics. Till today, histiocytosis has been addressed through a combination of chemotherapy, radiotherapy, and surgery, with varying responses from individual patients. Due to its atypical symptoms, it has been prone to misdiagnosis. Advances in our understanding of the cellular and molecular aspects of these conditions are paving the way for improved diagnostic methods and targeted therapies. Researchers have extensively investigated various mutations in patient samples. However, no paper has yet provided a comprehensive summary of the collective analysis of mutations and pathways. Hence, this paper consolidates research efforts that specifically concentrate on gene mutations identified in patient samples of different subtypes of histiocytosis. These insights are essential for developing targeted therapies and improving diagnosis. Further, it provides potential insights to enhance the development of more effective therapeutic approaches for rare diseases.

Vemurafenib combined with chemotherapy achieved sustained remission in pediatric LCH: a multi-center observational study

BACKGROUND

Langerhans cell histiocytosis (LCH) is a myeloid neoplasia with potentially fatal consequences, and about 2/3 of cases involve the BRAFV600E kinase-activated mutation. Vemurafenib, a BRAF inhibitor, has demonstrated significant clinical improvements in LCH. However, the high relapse rate of LCH following cessation of vemurafenib therapy remains a major challenge, and alternative treatment strategies require further investigation.

METHODS

In this retrospective multi-center study, we evaluated the efficacy and safety of vemurafenib combined with conventional chemotherapy in patients with severe or refractory LCH.

RESULTS

Seventeen patients were enrolled in the study, with eleven classified as risk organ involvement (RO +). Six received the combination therapy as the primary treatment, and eleven after being refractory to prior chemotherapy. The overall response rate was 94.1%. Progression-free survival among all 17 patients was 70.6% (12/17) at a median follow-up of 32 months, and relapse-free survival among the 15 patients with discontinuation after a response was 73.3%(11/15) at a median follow-up of 34 months. Five of six patients (83.3%) with myeloid BRAFV600E mutations demonstrated molecular remission. The overall survival rate was 100%. Adverse events were mostly classified as grades 1 or 2.

CONCLUSION

Our data suggest that the combination of vemurafenib and chemotherapy can achieve sustained clinical and molecular level relief in children with LCH, and side effects are tolerable.

Multiple Langerhans cell histiocytosis with spinal involvement

Aims

The aim of this study was to report the long-term prognosis of patients with multiple Langerhans cell histiocytosis (LCH) involving the spine, and to analyze the risk factors for progression-free survival (PFS).

Methods

We included 28 patients with multiple LCH involving the spine treated between January 2009 and August 2021. Kaplan-Meier methods were applied to estimate overall survival (OS) and PFS. Univariate Cox regression analysis was used to identify variables associated with PFS.

Results

Patients with multiple LCH involving the spine accounted for 15.4% (28/182 cases) of all cases of spinal LCH: their lesions primarily involved the thoracic and lumbar spines. The most common symptom was pain, followed by neurological dysfunction. All patients presented with osteolytic bone destruction, and 23 cases were accompanied by a paravertebral soft-tissue mass. The incidence of vertebra plana was low, whereas the oversleeve-like sign was a more common finding. The alkaline phosphatase was significantly higher in patients with single-system multifocal bone LCH than in patients with multisystem LCH. At final follow-up, one patient had been lost to follow-up, two patients had died, three patients had local recurrence, six patients had distant involvement, and 17 patients were alive with disease. The median PFS and OS were 50.5 months (interquartile range (IQR) 23.5 to 63.1) and 60.5 months (IQR 38.0 to 73.3), respectively. Stage (hazard ratio (HR) 4.324; p < 0.001) and chemotherapy (HR 0.203; p < 0.001) were prognostic factors for PFS.

Conclusion

Pain is primarily due to segmental instability of the spine from its destruction by LCH. Chemotherapy can significantly improve PFS, and radiotherapy has achieved good results in local control. The LCH lesions in some patients will continue to progress. It may initially appear as an isolated or single-system LCH, but will gradually involve multiple sites or systems. Therefore, long-term follow-up and timely intervention are important for patients with spinal LCH.

Langerhans Cell Histiocytosis in Children: Literature Review

Relevant information on Langerhans cell histiocytosis development and course in children is presented. The current concepts of disease pathogenesis, principles of its severity evaluation, patients stratification into risk groups, as well as of clinical course features are described. Modern approaches to the disease treatment via targeted therapy are summarized and analyzed. 

Solid-variant aneurysmal bone cysts in the craniofacial skeleton: the role of genomic analysis

BACKGROUND

Solid variant aneurysmal bone cysts (SVABCs) are a rare but well-described subtype of ABCs. While classic ABCs are readily identified radiographically, SVABCs lack these characteristic radiographic features and thus have a wide differential diagnosis on presentation (including Ewing sarcoma, Langerhans cell histiocytosis, osteosarcoma, metastasis, and giant cell tumor). Genomic/molecular analyses are often necessary for the diagnosis of SVABCs, with USP6 rearrangements being a characteristic finding. We present two cases in which genomic analysis was critical in the diagnosis of SVABCs and revealed unique gene fusions that may provide insight into SVABC pathogenesis.

CASE DESCRIPTIONS

Two 13-year old male children presented to our institution with new mass lesions involving the craniofacial skeleton. Magnetic resonance imaging (MRI) in both cases revealed predominantly solid, avidly enhancing masses, one of the squamous portion of the temporal bone, and the other arising from the sphenopalatine foramen with extension into the ipsilateral maxillary and ethmoid sinuses. Histopathology displayed predominantly solid morphology, and next generation sequencing (NGS) revealed a FAT1-USP6 gene fusion in the temporal lesion, and a MIR22HG-USP6 gene fusion in the maxillofacial lesion, the latter of which was not identified on fluorescence in situ hybridization (FISH). These findings were most consistent with a diagnosis of SVABC in each case.

CONCLUSIONS

These two cases highlight novel gene fusions in atypically located SVABCs and emphasize the ability of NGS to more accurately and consistently identify USP6 gene fusions, particularly in SVABCs that may otherwise be indistinguishable from alternative pathologies.

Skull Base Tumors: Neuropathology and Clinical Implications

Tumors that arise in and around the skull base comprise a wide range of common and rare entities. Recent studies have advanced our understanding of their pathogenesis, which in some cases, have significantly influenced clinical practice. The genotype of meningiomas is strongly associated with their phenotype, including histologic subtype and tumor location, and clinical outcome. A single molecular alteration, NAB2-STAT6 fusion, has redefined the category of solitary fibrous tumors to include the previous entity hemangiopericytomas. Schwannomas, both sporadic and familial, are characterized by near ubiquitous alterations in NF2 , with additional mutations in SMARCB1 or LZTR1 in schwannomatosis. In pituitary adenohypophyseal tumors, cell lineage transcription factors such as SF-1, T-PIT, and PIT-1 are now essential for classification, providing a more rigorous taxonomy for tumors that were previously considered null cell adenomas. The pituicyte lineage transcription factor TTF-1 defines neurohypophyseal tumors, which may represent a single nosological entity with a spectrum of morphologic manifestations (ie, granular cell tumor, pituicytoma, and spindle cell oncocytoma). Likewise, the notochord cell lineage transcription factor brachyury defines chordoma, discriminating them from chondrosarcomas. The identification of nonoverlapping genetic drivers of adamantinomatous craniopharyngiomas and papillary craniopharyngiomas indicates that these are distinct tumor entities and has led to successful targeted treatment of papillary craniopharyngiomas using BRAF and/or mitogen-activated protein kinase inhibitors. Similarly, dramatic therapeutic responses have been achieved in patients with Langerhans cell histiocytosis, both with BRAF -mutant and BRAF -wildtype tumors. Familiarity with the pathology of skull base tumors, their natural history, and molecular features is essential for optimizing patient care.

Histiocytic Neoplasms, Version 2.2021, NCCN Clinical Practice Guidelines in Oncology

Histiocytic neoplasms are rare hematologic disorders accounting for less than 1% of cancers of the soft tissue and lymph nodes. Clinical presentation and prognosis of these disorders can be highly variable, leading to challenges for diagnosis and optimal management of these patients. Treatment often consists of systemic therapy, and recent studies support use of targeted therapies for patients with these disorders. Observation ("watch and wait") may be sufficient for select patients with mild disease. These NCCN Guidelines for Histiocytic Neoplasms include recommendations for diagnosis and treatment of adults with the most common histiocytic disorders: Langerhans cell histiocytosis, Erdheim-Chester disease, and Rosai-Dorfman disease.

From the archives of MD Anderson Cancer Center: A case of concurrent follicular lymphoma and Langerhans cell sarcoma with a review of the literature

Transdifferentiation of follicular lymphoma to a Langerhans cell neoplasm is rarely reported and not well understood. Here we present a case, review the literature and discuss some of the biological underpinnings of lineage switch of B cells to histiocytes/Langerhans cells. A 31-year-old woman had follicular lymphoma (FL) and Langerhans cell sarcoma (LCS) co-localized above and below diaphragm. The FL was low-grade, had typical morphologic features, and was positive for CD10, BCL-2, and BCL-6. The LCS was cytologically atypical with necrosis and a high mitotic rate, and the immunophenotype supported Langerhans cell lineage positive for CD1a, CD207/langerin, and S-100 protein. Both tumors carried IGH-BCL2 and the LCS cells had immunophenotypic evidence of a residual B cell program, supporting the notion that these neoplasms are clonally related. The case reported is unusual because the patient was young and both diseases presented simultaneously, before any therapy. In addition, immunohistochemical analysis showed that the LCS was negative for BRAF V600E and phospho-ERK, suggesting that the LCS belongs to the known subset of Langerhans cell tumors lacking BRAF V600E and MAP2K1 mutations. Concurrent occurrence of FL and Langerhans cell neoplasm is an unusual phenomenon, with 10 cases reported previously: 4 Langerhans cell histiocytosis and 6 Langerhans cell sarcoma, including this case.

Solitary juvenile xanthogranuloma of the hypopharynx. Clinico-pathologic study in a child with β-Thalassemia Major and Cutaneous Mastocytosis

Juvenile Xanthogranuloma (JXG), the most common pediatric non-Langerhans cell histiocytosis, may rarely occur in association with Neurofibromatosis (types 1 and 2), Juvenile Myelomonocytic Leukemia and Cutaneous Mastocytosis (CM) and, morphologically, mimics Erdheim-Chester Disease tissue lesions and ALK-positive histiocytosis. We describe a 4-year-old girl with Beta-Thalassemia Major who developed an hypopharyngeal BRAFV600E- and ALK-negative JXG and CM. JXG has been rarely reported in the aerodigestive tract and in association with CM. In this molecular era, knowledge of genetic heterogeneity of JXG and clinical scenarios in which it may develop is essential for the appropriate diagnosis and treatment of each individual patient.

Sclerosing epithelioid mesenchymal neoplasm of the pancreas - a proposed new entity

We have encountered pancreatic tumors with unique histologic features, which do not conform to any of the known tumors of the pancreas or other anatomical sites. We aimed to define their clinicopathologic features and whether they are characterized by recurrent molecular signatures. Eight cases were identified; studied histologically and by immunohistochemistry. Selected cases were also subjected to whole-exome sequencing (WES; n = 4), RNA-sequencing (n = 6), Archer FusionPlex assay (n = 5), methylation profiling using the Illumina MethylationEPIC (850k) array platform (n = 6), and TERT promoter sequencing (n = 5). Six neoplasms occurred in females. The mean age was 43 years (range: 26-75). Five occurred in the head/neck of the pancreas. All patients were treated surgically; none received neoadjuvant/adjuvant therapy. All patients are free of disease after 53 months of median follow-up (range: 8-94). The tumors were well-circumscribed, and the median size was 1.8 cm (range: 1.3-5.8). Microscopically, the unencapsulated tumors had a geographic pattern of epithelioid cell nests alternating with spindle cell fascicles. Some areas showed dense fibrosis, in which enmeshed tumor cells imparted a slit-like pattern. The predominant epithelioid cells had scant cytoplasm and round-oval nuclei with open chromatin. The spindle cells displayed irregular, hyperchromatic nuclei. Mitoses were rare. No lymph node metastases were identified. All tumors were positive for vimentin, CD99 and cytokeratin (patchy), while negative for markers of solid pseudopapillary neoplasm, neuroendocrine, acinar, myogenic/rhabdoid, vascular, melanocytic, or lymphoid differentiation, gastrointestinal stromal tumor as well as MUC4. Whole-exome sequencing revealed no recurrent somatic mutations or amplifications/homozygous deletions in any known oncogenes or tumor suppressor genes. RNA-sequencing and the Archer FusionPlex assay did not detect any recurrent likely pathogenic gene fusions. Single sample gene set enrichment analysis revealed that these tumors display a likely mesenchymal transcriptomic program. Unsupervised analysis (t-SNE) of their methylation profiles against a set of different mesenchymal neoplasms demonstrated a distinct methylation pattern. Here, we describe pancreatic neoplasms with unique morphologic/immunophenotypic features and a distinct methylation pattern, along with a lack of abnormalities in any of key genetic drivers, supporting that these neoplasms represent a novel entity with an indolent clinical course. Given their mesenchymal transcriptomic features, we propose the designation of "sclerosing epithelioid mesenchymal neoplasm" of the pancreas.

Apparent Lack of BRAF V600E Derived HLA Class I Presented Neoantigens Hampers Neoplastic Cell Targeting by CD8+ T Cells in Langerhans Cell Histiocytosis

Langerhans Cell Histiocytosis (LCH) is a neoplastic disorder of hematopoietic origin characterized by inflammatory lesions containing clonal histiocytes (LCH-cells) intermixed with various immune cells, including T cells. In 50-60% of LCH-patients, the somatic BRAF ^V600E driver mutation, which is common in many cancers, is detected in these LCH-cells in an otherwise quiet genomic landscape. Non-synonymous mutations like BRAF ^V600E can be a source of neoantigens capable of eliciting effective antitumor CD8⁺ T cell responses. This requires neopeptides to be stably presented by Human Leukocyte Antigen (HLA) class I molecules and sufficient numbers of CD8⁺ T cells at tumor sites. Here, we demonstrate substantial heterogeneity in CD8⁺ T cell density in n = 101 LCH-lesions, with BRAF ^V600E mutated lesions displaying significantly lower CD8⁺ T cell:CD1a⁺ LCH-cell ratios (p = 0.01) than BRAF wildtype lesions. Because LCH-lesional CD8⁺ T cell density had no significant impact on event-free survival, we investigated whether the intracellularly expressed BRAF ^V600E protein is degraded into neopeptides that are naturally processed and presented by cell surface HLA class I molecules. Epitope prediction tools revealed a single HLA class I binding BRAF ^V600E derived neopeptide (KIGDFGLATEK), which indeed displayed strong to intermediate binding capacity to HLA-A^*03:01 and HLA-A^*11:01 in an in vitro peptide-HLA binding assay. Mass spectrometry-based targeted peptidomics was used to investigate the presence of this neopeptide in HLA class I presented peptides isolated from several BRAF ^V600E expressing cell lines with various HLA genotypes. While the HLA-A^*02:01 binding BRAF wildtype peptide KIGDFGLATV was traced in peptides isolated from all five cell lines expressing this HLA subtype, KIGDFGLATEK was not detected in the HLA class I peptidomes of two distinct BRAF ^V600E transduced cell lines with confirmed expression of HLA-A^*03:01 or HLA-A^*11:01. These data indicate that the in silico predicted HLA class I binding and proteasome-generated neopeptides derived from the BRAF ^V600E protein are not presented by HLA class I molecules. Given that the BRAF ^V600E mutation is highly prevalent in chemotherapy refractory LCH-patients who may qualify for immunotherapy, this study therefore questions the efficacy of immune checkpoint inhibitor therapy in LCH.

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.

Langerhans cell histiocytosis in an adult patient

Aim: to present a clinical case of a rare dermatosis — Langerhans cell histiocytosis (LCH) in an adult patient.

Materials and methods. A clinical and laboratory examination of a 64-year-old woman who had complained of rashes on the skin of the scalp, neck, trunk and lower extremities accompanied by itching was carried out. A histological study of skin biopsy samples from the lesion area, as well as an immunohistochemical study of Langerhans cell markers — langerin and S-100 protein — were performed.

Results. Clinical manifestations of the disease, the presence of histiocytic infiltrate in the epidermis and dermis during the histological study and immunohistochemical detection of langerin infiltrate cells and S-100 protein were all consistent with the diagnosis of LCH. The therapy with methotrexate subcutaneously significantly improved the patient’s condition.

Conclusion. Verification of the LCH diagnosis requires a histological study of skin biopsy samples and an immunohistochemical study of Langerhans cell markers. The efficacy of methotrexate in the treatment of this disease has been confirmed.

Trametinib in the treatment of multiple malignancies harboring MEK1 mutations

The aberrant activation of RAS-derived mitogen-activated protein kinase (MAPK) signaling pathway plays a prominent role in tumorigenesis of an array of malignancies. The reasons are usually the upstream activated mutations including mitogen-activated protein kinase kinase 1/2 (MEK1/2). As oncogenic mutations, MEK1 mutations have been observed in a variety of malignancies including melanoma, histiocytic neoplasms, colorectal cancer and lung cancer. Presently, the use of trametinib, a highly selective MEK1/2 inhibitor, was limited to BRAF mutations, according to the approvals of FDA. Therefore, we consider that this is a question worth studying that whether malignancies with MEK1 mutations are sensitive to the treatment of trametinib. This review discussed the function of MEK1 mutations, retrieved the frequency and distribution of MEK1 mutations in various malignancies, and reviewed the basic experiments and clinical case reports on trametinib in the treatment of cell lines or patients with MEK1 mutations. Most studies have demonstrated that trametinib was effective to cells or tumor patients harboring MEK1 mutations, which suggest that the MEK1 mutations might be potential indications of trametinib therapy. In addition, it was also reported that resistance was observed in the treatment of trametinib, suggesting that different MEK1 mutations may have different response to trametinib, and further studies are necessary to distinguish that which MEK1 mutations are appropriate for the treatment with trametinib and which are not.

Dental-craniofacial manifestation and treatment of rare diseases

Rare diseases are usually genetic, chronic and incurable disorders with a relatively low incidence. Developments in the diagnosis and management of rare diseases have been relatively slow due to a lack of sufficient profit motivation and market to attract research by companies. However, due to the attention of government and society as well as economic development, rare diseases have been gradually become an increasing concern. As several dental-craniofacial manifestations are associated with rare diseases, we summarize them in this study to help dentists and oral maxillofacial surgeons provide an early diagnosis and subsequent management for patients with these rare diseases.

Langerhans Cell Histiocytosis Causing Central Nervous System Vasculitis Leading to Stroke in a Two-year-old Boy: A Case Report

Here, the authors present the first documented case of a patient developing central nervous system (CNS) vasculitis secondary to Langerhans cell histiocytosis (LCH) ultimately leading to stroke. LCH is a rare histiocytic disorder affecting males and females equally and typically presents in pediatric patients with a median age of 30 months. Presentation of the disease can be single-site or multisystem; and, classification of treatment is further demarcated by high risk and low risk depending on the organ systems involved. Treatment of LCH typically involves vinblastine and prednisone, as well as salvage treatment as needed.

Atypical presentation of isolated orbital Langerhans cell histiocytosis

Background

A 9-year old female presented with one month of waxing and waning upper eyelid swelling. An excisional biopsy via anterior orbitotomy was performed.

Objective

To describe a patient presenting atypically with symptoms concerning for orbital cellulitis who was diagnosed with Langerhans cell histiocytosis (LCH).

Methods

Description of case report.

Results

We report a case of a 9-year old female with one month of periorbital edema and erythema suspected to be orbital cellulitis. A complete ophthalmological exam, subsequent imaging, and an excisional biopsy revealed the diagnosis of LCH. With a confirmed diagnosis, the patient started chemotherapy indicated by the Histiocyte Society Evaluation and Treatment Guidelines.

Conclusion

Langerhans cell histiocytosis (LCH) embodies a spectrum of diseases with the primary pathologic process being the abnormal proliferation of polyclonal Langerhans cells. In children with isolated bony involvement, the most common presenting symptom is pain. Rarely is orbital involvement with associated periorbital edema and erythema the primary presentation.

Langerhans cell histiocytosis in adults: Advances in pathophysiology and treatment

Langerhans cell histiocytosis (LCH) is a rare systemic disorder characterized by the accumulation of CD1a+/Langerin+ LCH cells and wide-ranging organ involvement. Langerhans cell histiocytosis was formerly referred to as histiocytosis X, until it was renamed in 1987. Langerhans cell histiocytosis β was named for its morphological similarity to skin Langerhans cells. Studies have shown that LCH cells originate from myeloid dendritic cells rather than skin Langerhans cells. There has been significant debate regarding whether LCH should be defined as an immune disorder or a neoplasm. A breakthrough in understanding the pathogenesis of LCH occurred in 2010 when a gain-of-function mutation in BRAF (V600E) was identified in more than half of LCH patient samples. Studies have since reported that 100% of LCH cases show ERK phosphorylation, indicating that LCH is likely to be a clonally expanding myeloid neoplasm. Langerhans cell histiocytosis is now defined as an inflammatory myeloid neoplasm in the revised 2016 Histiocyte Society classification. Randomized trials and novel approaches have led to improved outcomes for pediatric patients, but no well-defined treatments for adult patients have been developed to date. Although LCH is not fatal in all cases, delayed diagnosis or treatment can result in serious impairment of organ function and decreased quality of life. This study summarizes recent advances in the pathophysiology and treatment of adult LCH, to raise awareness of this "orphan disease".

Imaging of Histiocytosis in the Era of Genomic Medicine

Histiocytosis describes a group of diseases that have long been considered enigmatic in the history of medicine. Recently, novel genomic analyses have identified somatic oncogenic driver mutations responsible for the pathogenesis of these entities. These discoveries have led to the recharacterization of histiocytoses as neoplastic diseases and have opened a new era of precision medicine approaches for treatment. The histiocytic disorders demonstrate a variety of imaging manifestations involving multiple organ systems, and radiologists play a major role in diagnosis and monitoring. An up-to-date knowledge of the novel genomic discoveries and their implications is essential for radiologists to understand the new approaches to treating histiocytic disorders and to contribute as key members of the multidisciplinary treatment team. This article provides a cutting-edge review of the novel concepts in histiocytosis, with a focus on recent genomic discoveries and precision medicine approaches to treating the disease, and describes imaging manifestations with correlative histologic and genomic findings, with an emphasis on adult-onset cases and uncommon subtypes. ^©RSNA, 2018.

Cutaneous Hematolymphoid and Histiocytic Proliferations in Children

This article focuses on cutaneous hematopoietic neoplasms that are more likely to be encountered in the pediatric age-group and includes both lymphoproliferative and histiocytic disorders. The cutaneous hematologic disorders in children have a different epidemiologic profile to what is seen during adulthood. Although mycosis fungoides is the most frequent form of cutaneous lymphoma in adults, it is very rare in children. Because lymphoblastic leukemias and lymphomas are more frequent in the pediatric setting, cutaneous leukemic infiltrates are relatively common in this age-group. Similarly, histiocytic disorders are more common in children, particularly Langerhans cell histiocytosis and juvenile xanthogranuloma. Notably, the histiocytic disorders have undergone significant modifications on their nomenclature in the basis of the molecular characteristics that are present in them. A summary of the most frequent cutaneous hematopoietic disorders in children will be discussed further in this review.

Novel activating BRAF fusion identifies a recurrent alternative mechanism for ERK activation in pediatric Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasm characterized by constitutive activation of extracellular signal-regulated kinase (ERK). Genomic characterization has identified activating point mutations including mutually exclusive BRAFV600E and activating MAP2K1 mutations to be responsible for ERK activation in a majority of pediatric LCH patients. Here, we report the discovery of a novel BRAF kinase fusion, PACSIN2-BRAF, in a child with multisystem LCH. This is the second reported case of an activating BRAF kinase fusion and indicates a recurrent pathologic mechanism. Genomic evaluation for activating kinase fusions should be strongly considered in pediatric LCH patients lacking more common mutations.

Evaluation and treatment of Langerhans cell histiocytosis patients with central nervous system abnormalities: Current views and new vistas

Central nervous system (CNS) involvement in Langerhans cell histiocytosis (LCH) can include mass lesions of the hypothalamic pituitary axis, choroid plexus, cerebrum, and cerebellum or magnetic resonance imaging (MRI) signal abnormalities of the cerebellum, pons, and basal ganglia. The term neurodegenerative (ND) CNS-LCH has been given to the MRI signal abnormalities and neurologic dysfunction, although initially patients may have no clinical symptoms. Standardized evaluations to better understand the natural history and response to therapy are needed. We propose guidelines for clinical, radiologic, and physiologic tests as a framework for developing the best methods of evaluation, which can then be tested in prospective treatment protocols.

Histiocytic neoplasms in the era of personalized genomic medicine

PURPOSE OF REVIEW

Since the discovery of B-Raf proto-oncogene (BRAF) V600E mutations in histiocytic neoplasms, diverse kinase alterations have been uncovered in BRAF V600E-wildtype histiocytoses. The purpose of this review is to outline recent molecular advances in histiocytic neoplasms and discuss their impact on the pathogenesis and treatment of these disorders.

RECENT FINDINGS

Activating kinase alterations discovered in BRAF V600E-wildtype Langerhans (LCH) and non-Langerhans cell histiocytoses (non-LCH) result in constitutive activation of the mitogen-activated protein kinase and/or phosphoinositide 3-kinases-Akt murine thymoma pathways. These kinase alterations include activating mutations in A-Raf proto-oncogene, mitogen-activated protein kinase kinase 1, neuroblastoma rat sarcoma viral oncogene homolog, Kirsten rat sarcoma viral oncogene homolog, and phosphatidylinositol-4,5-bisphosphate 3 kinase, catalytic subunit α kinases in LCH and non-LCH; BRAF, anaplastic lymphoma receptor tyrosine kinase, and neurotrophic tyrosine kinase, receptor type 1 fusions, as well as the Ets variant 3-nuclear receptor coactivator 2 fusion in non-LCH; and mutations in the mitogen-activated protein kinase kinase kinase 1 and Harvey rat sarcoma viral oncogene homolog kinases in LCH and histiocytic sarcoma, respectively. These discoveries have refined the understanding of the histiocytoses as clonal, myeloid neoplasms driven by constitutive mitogen-activated protein kinase signaling and identified molecular therapeutic targets with promising clinical responses to rapidly accelerated fibrosarcoma and mitogen-activated protein kinase kinase inhibition.

SUMMARY

Genomic analyses over the last 6 years have identified targetable kinase alterations in BRAF V600E-wildtype histiocytic neoplasms. However, despite this progress, the molecular pathogenesis and therapeutic responsiveness of non-BRAF V600E kinase alterations are still poorly defined in these disorders.

Histiocytoses: emerging neoplasia behind inflammation

Histiocytoses are disorders characterised by inflammation and the accumulation of cells derived from the monocyte and macrophage lineages, which results in tissue damage. Although they are often considered rare disorders with protean clinical manifestations, considerable advances in the understanding of their genetics have led to increased clinical recognition of these conditions, and fuelled further insights into their pathogenesis. In this Review, we describe insights into the cells of origin, molecular pathology, clinical features, and treatment strategies for some of the most common histiocytic disorders, including Langerhans cell histiocytosis, Erdheim-Chester disease, and Rosai-Dorfman disease. With the discovery of recurrent mutations affecting the mitogen-activated protein kinase and mTOR-AKT pathways in some of these histiocytoses, our understanding of these diseases has now evolved from the concept of a primary inflammatory condition to that of a clonal neoplastic disease. This understanding has led to the development of effective mechanism-based therapeutic strategies for patients with histiocytic diseases.

Identification and Targeting of Kinase Alterations in Histiocytic Neoplasms

Histiocytic disorders represent clonal disorders of cells believed to be derived from the monocyte, macrophage, and/or dendritic cell lineage presenting with a range of manifestations. Although their nature as clonal versus inflammatory nonclonal conditions have long been debated, recent studies identified numerous somatic mutations that activate mitogen-activated protein kinase signaling in clinically and histologically diverse forms of histiocytosis. Clinical trials and case series have revealed that targeting aberrant kinase signaling using BRAF and/or MEK inhibitors may be effective. These findings suggest that a personalized approach in which patient-specific alterations are identified and targeted may be a critically important therapeutic approach.

[Adult Langerhans cell histiocytosis]

Langerhans cell histiocytosis (LCH) is a rare disease affecting both genders and can occur at any age. It often evolves through successive flares, and its severity varies from benign forms that don't require treatment to life threatening disease. Some patients have important functional impairment with psychological and social consequences and prolonged disability. LCH may affect only one organ, with uni- or multifocal involvement or be multisystem disease involving multiple organs. The organs most frequently involved are bones, lung, skin and the endocrinal system. Pulmonary LCH is strongly related to smoking. Some patients have mixed histocytosis combining LCH and other histiocytic disorders. The diagnosis relies on the histological study of tissues samples, and shows tissue infiltration with large cell with pale cytoplasm and reniform nucleus, staining for CD1a and Langerin (CD207) on immunohistochemistry. The BRAF^V600E mutation is observed in tissue samples in approximately half of patients and the activation of the RAS-RAF-MEK-ERK pathway has been shown to be constantly activated in LCH lesions, regardless the BRAF status. These findings represent an important forward step in the understanding of the physiopathology of the disease. Treatment must be adapted to the severity of the disease and goes from conservative observation to systemic chemotherapy. Therapies targeting the RAS-RAF-MEK-ERK pathway are promising treatments for progressive disease.

Insights into the pathogenesis of Langerhans cell histiocytosis: the development of targeted therapies

More than a century after its first description, Langerhans cell histiocytosis (LCH) still remains an intriguing disease. Considerable progress in understanding its biology has been achieved recently. Description of the V600E BRAF mutation in samples of LCH tissue in 2010 was followed by description of additional mutations, all leading to constitutive ERK activation. Current experimental data suggest that LCH is a myeloid neoplasia with inflammatory properties, yet the exact pathophysiology remains poorly understood. Disease management paradigms have changed over time, closely reflecting the evolving view of the nature of the disease. The international Histiocyte Society have conducted three prospective clinical studies on multisystem LCH since the early 1990s. The standard frontline therapy for patients with multisystem LCH based on the cumulative knowledge of those trials consists of 6–12 weeks of initial therapy (daily oral steroids and weekly vinblastine injections), followed by pulses of prednisolone/vinblastine every 3 weeks, for a total treatment duration of 12 months. A currently ongoing study (LCH-IV) with a complex design (five interventional and two observational strata) targets further reduction of mortality and morbidity by tailoring treatment intensity depending on expected risk, as well as by exploring treatment regimens for special locations. Current knowledge on LCH pathobiology opens opportunities for improvement in the patient outcome. The activating BRAF and MAP2K1 mutations collectively accounting for about 75% of the LCH population as well as the resulting constitutive activation of downstream ERK offer an opportunity for targeted treatment. Related issues (eg, finding most effective and less toxic drugs or combinations, appropriate dosage, and optimal treatment duration) must be addressed in controlled prospective trials. Additional mechanisms, such as the interactions of the mutated dendritic cell clone with other inflammatory cells and key cytokines and chemokines, still remain attractive targets for therapeutic intervention, particularly in patients with localized, less aggressive disease.

Alternative genetic mechanisms of BRAF activation in Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is characterized by inflammatory lesions containing pathologic CD207⁺ dendritic cells with constitutively activated ERK. Mutually exclusive somatic mutations in MAPK pathway genes have been identified in ∼75% of LCH cases, including recurrent BRAF-V600E and MAP2K1 mutations. To elucidate mechanisms of ERK activation in the remaining 25% of patients, we performed whole-exome sequencing (WES, n = 6), targeted BRAF sequencing (n = 19), and/or whole-transcriptome sequencing (RNA-seq, n = 6) on 24 LCH patient samples lacking BRAF-V600E or MAP2K1 mutations. WES and BRAF sequencing identified in-frame BRAF deletions in the β3-αC loop in 6 lesions. RNA-seq revealed one case with an in-frame FAM73A-BRAF fusion lacking the BRAF autoinhibitory regulatory domain but retaining an intact kinase domain. High levels of phospho-ERK were detected in vitro in cells overexpressing either BRAF fusion or deletion constructs and ex vivo in CD207⁺ cells from lesions. ERK activation was resistant to BRAF-V600E inhibition, but responsive to both a second-generation BRAF inhibitor and a MEK inhibitor. These results support an emerging model of universal ERK-activating genetic alterations driving pathogenesis in LCH. A personalized approach in which patient-specific alterations are identified may be necessary to maximize benefit from targeted therapies for patients with LCH.

Critical Pitfalls in the use of BRAF Mutation as a Diagnostic Tool in Thyroid Nodules: a Case Report

Thyroid fine-needle aspiration (FNA) cytology is the primary tool for the diagnostic evaluation of thyroid nodules. BRAF mutation analysis is employed as an ancillary tool in indeterminate cases, as recommended by the American Thyroid Association management guidelines. Hereby, we report the case of a 73-year-old woman who presented an 8-mm-size, ill-defined, left thyroid nodule. FNA resulted "suspicious for papillary thyroid carcinoma". BRAF mutation status was analyzed, and somatic BRAF (V600E) mutation identified. The patient underwent a total thyroidectomy. At histological examination, the nodule was composed of Langerhans cells, admixed with many eosinophils. A final diagnosis of Langerhans cell histiocytosis of the thyroid was made. Our case emphasizes the critical diagnostic pitfalls due to the use of BRAF (V600E) mutation analysis in thyroid FNA. Notably, BRAF (V600E) mutation is common in melanoma, colorectal carcinoma, lung carcinoma, ovarian carcinoma, brain tumors, hairy cell leukemia, multiple myeloma, and histiocytoses. Therefore, in cases of indeterminate FNA with unclassifiable atypical cells BRAF (V600E) mutated, the possibility of a localization of hystiocytosis or a secondary thyroid malignancy should be taken into account.

Recurrent NRAS mutations in pulmonary Langerhans cell histiocytosis

The mitogen-activated protein kinase (MAPK) pathway is constantly activated in Langerhans cell histiocytosis (LCH). Mutations of the downstream kinases BRAF and MAP2K1 mediate this activation in a subset of LCH lesions. In this study, we attempted to identify other mutations which may explain the MAPK activation in nonmutated BRAF and MAP2K1 LCH lesions.We analysed 26 pulmonary and 37 nonpulmonary LCH lesions for the presence of BRAF, MAP2K1, NRAS and KRAS mutations. Grossly normal lung tissue from 10 smoker patients was used as control. Patient spontaneous outcomes were concurrently assessed.BRAF(V600E) mutations were observed in 50% and 38% of the pulmonary and nonpulmonary LCH lesions, respectively. 40% of pulmonary LCH lesions harboured NRAS(Q61K) (/R) mutations, whereas no NRAS mutations were identified in nonpulmonary LCH biopsies or in lung tissue control. In seven out of 11 NRAS(Q61K) (/R)-mutated pulmonary LCH lesions, BRAF(V600) (E) mutations were also present. Separately genotyping each CD1a-positive area from the same pulmonary LCH lesion demonstrated that these concurrent BRAF and NRAS mutations were carried by different cell clones. NRAS(Q61K) (/R) mutations activated both the MAPK and AKT (protein kinase B) pathways. In the univariate analysis, the presence of concurrent BRAF(V600E) and NRAS(Q61K) (/R) mutations was significantly associated with patient outcome.These findings highlight the importance of NRAS genotyping of pulmonary LCH lesions because the use of BRAF inhibitors in this context may lead to paradoxical disease progression. These patients might benefit from MAPK kinase inhibitor-based treatments.

Cell(s) of Origin of Langerhans Cell Histiocytosis

Langerhans cell histiocytosis (LCH) is heterogeneous disease characterized by common histology of inflammatory lesions containing Langerin(+) (CD207) histiocytes. Emerging data support a model in which MAPK activation in self-renewing hematopoietic progenitors may drive disseminated high-risk disease, whereas MAPK activation in more differentiated committed myeloid populations may induce low-risk LCH. The heterogeneous clinical manifestations with shared histology may represent the final common pathway of an acquired defect of differentiation, initiated at more than one point. Implications of this model include re-definition of LCH as a myeloid neoplasia and re-focusing therapeutic strategies on the cells and lineages of origin.