P2X receptor- and postsynaptic NMDA receptor-mediated long-lasting facilitation of inhibitory synapses in the rat insular cortex.

Adenosine triphosphate (ATP) changes the efficacy of synaptic transmission. Despite recent progress in terms of the roles of purinergic receptors in cerebrocortical excitatory synaptic transmission, their contribution to inhibitory synaptic transmission is unknown. To elucidate the effects of α,ß-methylene ATP (αß-mATP), a selective agonist of P2X receptors (P2XRs), on inhibitory synaptic transmission in the insular cortex (IC), we performed whole-cell patch-clamp recording from IC pyramidal neurons (PNs) and fast-spiking neurons (FSNs) in either sex of VGAT-Venus transgenic rats. αß-mATP increased the amplitude of miniature IPSCs (mIPSCs) under conditions in which NMDA receptors (NMDARs) are recruitable. αß-mATP-induced facilitation of mIPSCs was sustained even after the washout of αß-mATP, which was blocked by preincubation with fluorocitrate. The preapplication of NF023 (a P2X1 receptor antagonist) or AF-353 (a P2X3 receptor antagonist) blocked αß-mATP-induced mIPSC facilitation. Intracellular application of the NMDAR antagonist MK801 blocked the facilitation. d-serine, which is an intrinsic agonist of NMDARs, mimicked αß-mATP-induced mIPSC facilitation. The intracellular application of BAPTA a Ca2+ chelator, or the bath application of KN-62, a CaMKII inhibitor, blocked αß-mATP-induced mIPSC facilitation, thus indicating that mIPSC facilitation by αß-mATP required postsynaptic [Ca2+]i elevation through NMDAR activation. Paired whole-cell patch-clamp recordings from FSNs and PNs demonstrated that αß-mATP increased the amplitude of unitary IPSCs without changing the paired-pulse ratio. These results suggest that αß-mATP-induced IPSC facilitation is mediated by postsynaptic NMDAR activations through d-serine released from astrocytes. Subsequent [Ca2+]i increase and postsynaptic CaMKII activation may release retrograde messengers that upregulate GABA release from presynaptic inhibitory neurons, including FSNs. (250/250 words).

Clinical and prognostic features of Langerhans cell histiocytosis in adults.

Langerhans cell histiocytosis (LCH) is a rare disease characterized by clonal expansion of CD1a+ CD207+ myeloid dendritic cells. The features of LCH are mainly described in children and remain poorly defined in adults; therefore, we conducted a nationwide survey to collect clinical data from 148 adult patients with LCH. The median age at diagnosis was 46.5 (range: 20-87) years with male predominance (60.8%). Among the 86 patients with detailed treatment information, 40 (46.5%) had single system LCH, whereas 46 (53.5%) had multisystem LCH. Moreover, 19 patients (22.1%) had an additional malignancy. BRAF V600E in plasma cell-free DNA was associated with a low overall survival (OS) rate and the risk of the pituitary gland and central nervous system involvement. At a median follow-up of 55 months from diagnosis, six patients (7.0%) had died, and the four patients with LCH-related death did not respond to initial chemotherapy. The OS probability at 5 years post-diagnosis was 90.6% (95% confidence interval: 79.8-95.8). Multivariate analysis showed that patients aged ≥60 years at diagnosis had a relatively poor prognosis. The probability of event-free survival at 5 years was 52.1% (95% confidence interval: 36.6-65.5), with 57 patients requiring chemotherapy. In this study, we first revealed the high rate of relapse after chemotherapy and mortality of poor responders in adults as well as children. Therefore, prospective therapeutic studies of adults with LCH using targeted therapies are needed to improve outcomes in adults with LCH.

Non-operative Management of Spontaneous Gastropleural Fistula Caused by Primary Gastric Diffuse Large B-cell Lymphoma.

We herein report a 79-year-old man diagnosed with primary gastric diffuse large B-cell lymphoma (DLBCL) with gastropleural fistula (GPF), successfully treated by chemotherapy without surgery. If primary gastric DLBCL perforates during chemotherapy, surgery is often warranted. Our patient's computed tomography findings showed loculated pleural effusion with air foci in the left lower lobe, suggesting GPF. After six cycles of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) chemotherapy, the fistula fully closed, and complete remission was achieved. In conclusion, while gastric DLBCL can exhibit spontaneous GPF, it can be treated with chemotherapy alone, which was well-tolerated in our patient.

HTLV-1 bZIP factor impairs DNA mismatch repair system.

Adult T-cell leukemia (ATL) is a peripheral T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1). Microsatellite instability (MSI) has been observed in ATL cells. Although MSI results from impaired mismatch repair (MMR) pathway, no null mutations in the genes encoding MMR factors are detectable in ATL cells. Thus, it is unclear whether or not impairment of MMR causes the MSI in ATL cells. HTLV-1 bZIP factor (HBZ) protein interacts with numerous host transcription factors and significantly contributes to disease pathogenesis and progression. Here we investigated the effect of HBZ on MMR in normal cells. The ectopic expression of HBZ in MMR-proficient cells induced MSI, and also suppressed the expression of several MMR factors. We then hypothesized that the HBZ compromises MMR by interfering with a transcription factor, nuclear respiratory factor 1 (NRF-1), and identified the consensus NRF-1 binding site at the promoter of the gene encoding MutS homologue 2 (MSH2), an essential MMR factor. The luciferase reporter assay revealed that NRF-1 overexpression enhanced MSH2 promoter activity, while co-expression of HBZ reversed this enhancement. These results supported the idea that HBZ suppresses the transcription of MSH2 by inhibiting NRF-1. Our data demonstrate that HBZ causes impaired MMR, and may imply a novel oncogenesis driven by HTLV-1.

[Endoscopic variceal ligation and percutaneous transhepatic obliteration difficulty in esophageal variceal bleeding: a case report].

A 48-year-old male patient with a history of alcoholic cirrhosis was admitted to our hospital due to hematemesis with a 7-day history of melena. Emergency esophagogastroduodenoscopy revealed esophageal variceal bleeding. We attempted hemostasis with endoscopic variceal ligation (EVL). The esophageal mucosa was not aspirated into the EVL device although the patient had no history of endoscopic injection sclerotherapy or EVL. Percutaneous transhepatic obliteration (PTO) was performed and esophageal variceal bleeding was successfully hemostasis. PTO is a viable option for refractory esophageal bleeding.

Insular cortical descending projections facilitate neuronal responses to noxious but not innoxious stimulation in rat trigeminal spinal subnucleus caudalis.

The insular cortex (IC) receives orofacial nociceptive information. Pyramidal neurons in IC layer V send their axons to various brain regions, such as the trigeminal spinal subnucleus caudalis (Sp5C), parabrachial nucleus, and periaqueductal gray. However, little information has been available about the functions of these descending projections from the IC. This study aimed to elucidate the effect of IC â†’ Sp5C on neuronal spike firings responding to noxious and innoxious stimuli to the face of the rat receiving an injection of adeno-associated virus encoding modified channelrhodopsin-2 (ChR2) fused to mCherry under the control of the human synapsin promotor. We classified Sp5C neurons responding to mechanical stimuli into three groups: low-threshold (LT), nociceptive specific (NS), and wide dynamic range (WDR) neurons, which respond to innoxious stimuli (brushing) only, noxious mechanical stimuli (pinching) only, and both noxious and innoxious stimuli, respectively. Neuronal activities of IC neurons were activated by photostimulation (repetitive pulses at 20 Hz for 5 Hz) to the IC that consistently induced action potentials in IC layer V pyramidal neurons. LT neurons showed comparable spike firing rates to brushing the facial skin before and during ChR2 activation induced by photostimulation. In contrast, NS neurons showed an increase in their firing frequency to pinching during ChR2 activation. On the other hand, WDR neurons increased their Sp5C neuronal firing to pinching during ChR2 activation without changing their firing rates to innoxious mechanical stimuli. These results suggest that the IC descending projections facilitate nociception by increasing Sp5C neuronal activities responding to noxious mechanical stimuli.

Determination of Venetoclax Concentration in Plasma Using High-Performance Liquid Chromatography.

Venetoclax is an oral B-cell lymphoma-2 protein inhibitor. It is a key drug for the treatment of chronic lymphocytic leukemia and acute myeloid leukemia. However, venetoclax is administered at a fixed dose, irrespective of body surface area or weight. Furthermore, the plasma concentration of venetoclax varies widely between individuals and is influenced by diet. Therefore, individualized dosing using therapeutic drug monitoring (TDM) may help to optimize treatment in clinical practice. In this study, we aimed to develop a simple method to determine venetoclax concentrations in plasma. The analysis required the extraction of a 50-µL plasma sample and precipitation of proteins using acetonitrile extraction. Venetoclax and the internal standard (12.5-µg/mL ibrutinib) were separated by high-performance liquid chromatography (HPLC). The calibration curve was linear over the plasma venetoclax concentration range 0.25-10 µg/mL with a coefficient of determination (r2) of 0.9999. The coefficients of intra-day and inter-day validation were 0.8-4.1% and 1.3-3.3%, respectively. The assay accuracy was -2.8 to 1.6%, and the recovery was >97.2%. These results demonstrate a very simple, novel and sensitive HPLC-UV-based method for determining the concentration of plasma venetoclax, and confirm its applicability to the TDM of venetoclax in a clinical setting.

Descending projections from the insular cortex to the trigeminal spinal subnucleus caudalis facilitate excitatory outputs to the parabrachial nucleus in rats.

ABSTRACT: Nociceptive information from the orofacial area projects to the trigeminal spinal subnucleus caudalis (Sp5C) and is then conveyed to several nuclei, including the parabrachial nucleus (PBN). The insular cortex (IC) receives orofacial nociceptive information and sends corticofugal projections to the Sp5C. The Sp5C consists of glutamatergic and GABAergic/glycinergic interneurons that induce excitatory postsynaptic currents and inhibitory postsynaptic currents, respectively, in projection neurons. Therefore, quantification of glutamatergic IC inputs in combination with identifying postsynaptic neuronal subtypes is critical to elucidate IC roles in the regulation of Sp5C activities. We investigated features of synaptic transmission from the IC to glutamatergic and GABAergic/glycinergic Sp5C neurons of laminae I/II using vesicular GABA transporter-Venus transgenic rats that received an injection of adeno-associated virus-channelrhodopsin-2-mCherry into the IC. Selective stimulation of IC axon terminals in Sp5C slice preparations induced monosynaptic excitatory postsynaptic currents in both excitatory glutamatergic and inhibitory GABAergic/glycinergic Sp5C neurons with a comparable amplitude. Paired whole-cell patch-clamp recordings showed that unitary inhibitory postsynaptic currents from inhibitory neurons influencing excitatory neurons, including neurons projecting to the PBN, exhibited a high failure rate and were suppressed by both bicuculline and strychnine, suggesting that excitatory neurons in the Sp5C receive both GABAergic and glycinergic inhibition with low impact. Moreover, selective stimulation of IC axons increased the firing rate at the threshold responses. Finally, we demonstrated that selective stimulation of IC axons in the Sp5C by a chemogenetic approach decreased the thresholds of both mechanical and thermal nociception. Thus, IC projection to the Sp5C is likely to facilitate rather than suppress excitatory outputs from the Sp5C.

Utility of therapeutic drug monitoring of venetoclax in acute myeloid leukemia.

The favorable outcomes of venetoclax-based regimens in older adults with acute myeloid leukemia (AML) may result in its regimen becoming the standard treatment. However, the dosage of venetoclax is fixed, irrespective of body surface area (BSA) or weight. Therefore, individualized dosing using therapeutic drug monitoring (TDM) may help optimize treatment in a safe and effective manner. Twelve patients with AML who received venetoclax-based treatment were enrolled in this study. Blood samples were collected before venetoclax administration, and the minimum plasma concentration (Cmin) was evaluated. The concentration of venetoclax was evaluated using a simple, sensitive, and cost-effective assay using high-performance liquid chromatography, as described previously. The median age was 74 (70-85) years. Ten patients received venetoclax in combination with azacitidine and one patient received low-dose cytarabine (LDAC). The patients BSA ranged from 1.345 to 1.912 m2 (median 1.543). The dose of venetoclax was 400 mg with azacitidine, and 600 mg with LDAC. In four patients who were taking CYP3A4 inhibitors, venetoclax was reduced to 50 mg according to the prescribing information. The Cmin ranged from 0.39 to 2.49, and the patient taking itraconazole showed highest Cmin regardless of the reduction of venetoclax. Most patients showed higher Cmin compared to the data from previous clinical trials, and BSA and venetoclax concentrations showed a negative correlation. Many Asian AML patients > 75 years old are petite and receive CYP3A4 inhibitors. Therefore, the TDM of venetoclax may be useful.

The mouse homolog of the mutant WASp responsible for human X-linked neutropenia renders granulopoiesis ineffective.

Severe congenital neutropenia (SCN) is characterized by severe neutropenia and recurrent critical infections. X-linked neutropenia (XLN) is caused by a gain-of-function mutation in the Wiskott-Aldrich syndrome gene (WAS), the product of which (WASp) is expressed only in blood cells, especially during neutrophil maturation. To investigate the mechanism of neutropenia, we established a novel knock-in mouse line expressing WASp-I292T. WASp-I292T neutrophils exhibited activated (dysregulated) actin polymerization. Although WASp-I292T mice did not recapitulate neutropenia, neutrophil levels were increased in the bone marrow, and extramedullary hematopoiesis was observed. Bone marrow neutrophils from WASp-I292T mice exhibited attenuated transmigration. These abnormalities were associated with downregulation of NFκB and TP53 and faulty activation of their downstream pathways.

Primary splenic histiocytic sarcoma successfully treated with splenectomy: a case report and literature review.

A 61-year-old woman was referred to our hospital with refractory thrombocytopenia and splenomegaly. She was diagnosed with immune thrombocytopenia 3 years prior to admission and received steroid therapy. However, her platelet count started decreasing six months prior to admission. A diagnostic and therapeutic splenectomy was performed, which led to the diagnosis of histiocytic sarcoma. The patient's platelet count recovered promptly after splenectomy, and she was in complete remission for over a year.

Challenging Diagnosis of Pure Erythroid Leukemia: A Case Report and Literature Review.

Pure erythroid leukemia (PEL) is an extremely rare type of acute myeloid leukemia (AML), accounting for fewer than 1% of all AML cases. A 72-year-old man presented with severe fatigue. His bone marrow aspiration contained myeloperoxidase negative abnormal cells that were aggregating and depicting epithelial adhesion, suggesting the possibility of solid tumor metastasis. His general condition deteriorated during medical diagnosis, and he died soon after starting chemotherapy. PEL appeared to be the definitive diagnosis after evaluating the histopathological findings, which were obtained after his death. With atypical morphological features, immunophenotypic and karyotypic approaches must be integrated for PEL assessment.

Bortezomib-cyclophosphamide-dexamethasone induction/consolidation and bortezomib maintenance for transplant-eligible newly diagnosed multiple myeloma: phase 2 multicenter trial.

OBJECTIVES: We conducted a phase II trial to prospectively evaluate the efficacy and safety of bortezomib-cyclophosphamide-dexamethasone (VCD) induction, autologous stem cell transplantation (ASCT), VCD consolidation, and bortezomib maintenance in transplant-eligible newly diagnosed multiple myeloma (NDMM) patients in Japan (UMIN000010542). METHODS: From 2013 to 2016, 42 patients with a median age of 58 (range 42-65) years with NDMM were enrolled in 15 centers. The primary endpoint was the complete response (CR) /stringent CR (sCR) rate after transplantation, and overall/progression-free survival rates were also evaluated. RESULTS: Following induction therapy, the overall response rate was obtained in 71% of patients, including a CR/sCR of 10% and a very good partial response (VGPR) of 26%. Twenty-six of the 42 patients completed ASCT following the protocol and CR/sCR and VGPR rate 100 days after ASCT was 26% and 17%, respectively. During consolidation therapy, 3 of the 24 patients achieved deeper responses. Eight of the 18 patients completed 2-year bortezomib maintenance without disease progression and grade 3/4 toxicities. Five patients were VGPR or partial response after ASCT but maintained response with 2-year bortezomib maintenance. Two-year overall and progression-free survival rates were 92.5% (95% confidence interval [CI]: 78.5%-97.5%) and 62.6% (95% CI: 45.8%-75.5%), respectively. Grade 3/4 toxicities (≥ 10%) included neutropenia (19%) and anemia (17%) in induction, and thrombocytopenia (29%) in consolidation. CONCLUSION: VCD induction/consolidation and bortezomib maintenance with ASCT for NDMM resulted in a high CR/sCR rate and provided good overall/progression-free survival in Japan.

Remdesivir and Human Milk: A Case Study.

INTRODUCTION: Remdesivir was originally developed to treat Ebola hemorrhagic fever, and its efficacy in treating coronavirus disease 2019 was detected during a preliminary analysis of a randomized controlled trial. It is known that Severe Acute Respiratory Syndrome Coronavirus 2 is not transmitted through human milk, but data about the presence of remdesivir in human milk have been lacking. MAIN ISSUE: In this case study, we determined the human milk-to-serum drug concentration ratio and the relative dose of Remdesivir in one participant. MANAGEMENT: The participant, a 28-year-old primipara, was found to have Coronavirus 2 infection in 2019, 2 days after delivery. She was given Remdesivir. The Remdesivir concentration in maternal serum and human milk was measured, and the milk-to-serum drug concentration ratio was found to be low (0.089), as was the relative infant dose (0.0070). The participant could not breastfeed her infant during her Coronavirus 2 infection treatment because in Japan anyone with COVID-19 was completely quarantined. However, she was able to resume breastfeeding after discharge and breastfed her infant for 6 months with supplements. CONCLUSION: Given the low amount of Remdesivir in the participant's milk, the inclusion of antibodies to Severe Acute Respiratory Syndrome Coronavirus 2, which can be expected to protect the infant from infection, and various other benefits of human milk, suggests that breastfeeding is safe during treatment with Remdesivir.

Circulating cell-free DNA in the peripheral blood plasma of patients is an informative biomarker for multiple myeloma relapse.

BACKGROUND: Multiple myeloma (MM) is an incurable hematological malignancy. Despite the introduction of several novel drugs, most patients relapse. Biomarkers to identify the early signs of relapse will make it possible to adjust the therapeutic strategy before the disease worsens. Although understanding genetic changes is important for the treatment of MM, currently known biomarkers of relapse, including serum free-light chains and monoclonal paraproteins, are not associated with genetic changes. METHODS: We therefore performed a multicenter study to examine the usefulness of circulating cell-free DNA (cfDNA) present in the peripheral blood (PB) plasma of patients as a biomarker for MM relapse. RESULTS: We identified several driver mutations by combined analysis of next-generation sequencing and existing databases of candidate oncogenes. Furthermore, relapse was detected more sensitively by monitoring the circulating cfDNA with these driver mutations than by conventional serum free-light chain examination. CONCLUSION: These results suggest the potential utility of cfDNA in the PB plasma of patients as a relevant early biomarker for MM relapse.

Electrostatic charge controls the lowest LH1 Qy transition energy in the triply extremophilic purple phototrophic bacterium, Halorhodospira halochloris.

Halorhodospira (Hlr.) halochloris is a unique phototrophic purple bacterium because it is a triple extremophile-the organism is thermophilic, alkalophilic, and halophilic. The most striking photosynthetic feature of Hlr. halochloris is that the bacteriochlorophyll (BChl) b-containing core light-harvesting (LH1) complex surrounding its reaction center (RC) exhibits its LH1 Qy absorption maximum at 1016 nm, which is the lowest transition energy among phototrophic organisms. Here we report that this extraordinarily red-shifted LH1 Qy band of Hlr. halochloris exhibits interconvertible spectral shifts depending on the electrostatic charge distribution around the BChl b molecules. The 1016 nm band of the Hlr. halochloris LH1-RC complex was blue-shifted to 958 nm upon desalting or pH decrease but returned to its original position when supplemented with salts or pH increase. Resonance Raman analysis demonstrated that these interconvertible spectral shifts are not associated with the strength of hydrogen-bonding interactions between BChl b and LH1 polypeptides. Furthermore, circular dichroism signals for the LH1 Qy transition of Hlr. halochloris appeared with a positive sign (as in BChl b-containing Blastochloris species) and opposite those of BChl a-containing purple bacteria, possibly due to a combined effect of slight differences in the transition dipole moments between BChl a and BChl b and in the interactions between adjacent BChls in their assembled state. Based on these findings and LH1 amino acid sequences, it is proposed that Hlr. halochloris evolved its unique and tunable light-harvesting system with electrostatic charges in order to carry out photosynthesis and thrive in its punishing hypersaline and alkaline habitat.

[CLINICAL STUDY OF OPEN RADICAL CYSTECTOMY AND ILEAL CONDUIT CONSTRUCTION FOR BLADDER CANCER: RESULTS OF 15-YEAR SINGLE CENTER EXPERIENCE].

(Objective) We retrospectively analyzed clinical outcome, prognostic factors and adjuvant chemotherapy for bladder cancer patients with open radical cystectomy (ORC) combined with ileal conduit construction (ICC). (Patients and methods) From February 2005 to February 2019, 179 patients underwent ORC and ICC for invasive bladder cancer or BCG unresponsive non-muscle invasive bladder cancer. We investigated intraoperative and early postoperative complications, overall survival (OS), cancer-specific survival (CSS), and poor prognostic factors affecting OS. Furthermore, we evaluated the prognosis of patients with pT3,4 or pN1-3 depending on adjuvant chemotherapy. (Results) Clavien-Dindo Grade 4 or 5 complications were not occurred. The 5-year and 10-year OS probability were 71.1% and 57.4%, respectively, while the 5-year and 10-year CSS probability were 76.5% and 71.5%, respectively. Multivariate analysis revealed that male (HR = 2.70, 95%CI [0.97-7.51]), pT3,4 (HR = 1.83, 95%CI [1.05-3.21]), and pN1-3 (HR = 2.85, 95%CI [1.62-5.03]) were independent poor prognostic factors. Adjuvant chemotherapy significantly improved OS (p = 0.03) and CSS (p = 0.017) in pN1-3 patients. (Conclusion) ORC combined with ICC was an effective operative method, and good results were obtained. Adjuvant chemotherapy may be effective for patients with positive regional lymph nodes.

Myostatin deficiency not only prevents muscle wasting but also improves survival in septic mice.

Sepsis remains a leading cause of mortality in critically ill patients. Muscle wasting is a major complication of sepsis and negatively affects clinical outcomes. Despite intense investigation for many years, the molecular mechanisms underlying sepsis-related muscle wasting are not fully understood. In addition, a potential role of muscle wasting in disease development of sepsis has not been studied. Myostatin is a myokine that downregulates skeletal muscle mass. We studied the effects of myostatin deficiency on muscle wasting and other clinically relevant outcomes, including mortality and bacterial clearance, in mice. Myostatin deficiency prevented muscle atrophy along with inhibition of increases in muscle-specific RING finger protein 1 (MuRF-1) and atrogin-1 expression and phosphorylation of signal transducer and activator of transcription protein 3 (STAT3; major players of muscle wasting) in septic mice. Moreover, myostatin deficiency improved survival and bacterial clearance of septic mice. Sepsis-induced liver dysfunction, acute kidney injury, and neutrophil infiltration into the liver and kidney were consistently mitigated by myostatin deficiency, as indicated by plasma concentrations of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and neutrophil gelatinase-associated lipocalin (NGAL) and myeloperoxidase activity in the organs. Myostatin deficiency also inhibited sepsis-induced increases in plasma high-mobility group protein B1 (HMGB1) and macrophage inhibitory cytokine (MIC)-1/growth differentiation factor (GDF)-15 concentrations. These results indicate that myostatin plays an important role not only in muscle wasting but also in other clinically relevant outcomes in septic mice. Furthermore, our data raise the possibility that muscle wasting may not be simply a complication, but myostatin-mediated muscle cachexia and related changes in muscle may actually drive the development of sepsis as well.NEW & NOTEWORTHY Muscle wasting is a major complication of sepsis, but its role in the disease development is not known. Myostatin deficiency improved bacterial clearance and survival and mitigated damage in the liver and kidney in septic mice, which paralleled prevention of muscle wasting. These results raise the possibility that muscle wasting may not simply be a complication of sepsis, but myostatin-mediated cachexic changes may have a role in impaired bacterial clearance and mortality in septic mice.

[Pathophysiology and treatment of adult Langerhans cell histiocytosis].

Langerhans cell histiocytosis (LCH) is a rare disease characterized by tissue infiltration of clusters of CD1a+/CD207+ histiocyte-like cells and a resultant surrounding inflammatory reaction. Because of its morphological similarity to cutaneous Langerhans cells, LCH was formerly named histiocytosis X in 1987. However, its cell lineage appears closely related to myeloid dendritic cells. In 2010, BRAF-V600E was detected in biopsy specimens from the majority of LCH patients. The subsequent observation of extracellular signal-regulated kinase phosphorylation in almost all LCH samples suggested that LCH was a neoplasm provoked by activation of the mitogen-activated protein (MAP) kinase pathway. Therefore, the 2016 Revised Classification by the Histiocyte Society defined LCH as an inflammatory myeloid neoplasm. Although a series of global and domestic clinical trials have improved the prognosis of pediatric LCH patients, no standard therapy with a high level of evidence for adult cases exists. Generally, LCH patients have a favorable prognosis, but delayed diagnosis and intervention may cause severe damage to the involved organs, resulting in a poor quality of life. Here we present recent advances in the pathophysiology and treatment of LCH to enlighten the understanding of this orphan disease.