Efficacy of BRAF-Inhibitor Therapy in BRAFV600E -Mutated Adult Langerhans Cell Histiocytosis

Dabrafenib and trametinib in Langerhans cell histiocytosis and other histiocytic disorders

The standard treatment for Langerhans cell histiocytosis (LCH) is chemotherapy, although the failure rates are high. Since MAP-kinase activating mutations are found in most cases, BRAF- and MEK-inhibitors have been used successfully to treat patients with refractory or relapsed disease. However, data on long-term responses in children are limited and there are no data on the use of these inhibitors as first-line therapy. We treated 34 patients (26 with LCH, 2 with juvenile xanthogranuloma, 2 with Rosai-Dorfman disease, and 4 with presumed single site-central nervous system histiocytosis) with dabrafenib and/or trametinib, either as first line or after relapse or failure of chemotherapy. Sixteen patients, aged 1.3-21 years, had disease that was recurrent or refractory to chemotherapy, nine of whom had multisystem LCH with risk-organ involvement. With a median treatment duration of 4.3 years, 15 (94%) patients have sustained favorable responses. Eighteen patients, aged 0.2-45 years, received an inhibitor as first-line treatment. All of these have had sustained favorable responses, with a median treatment duration of 2.5 years. Three patients with presumed isolated central nervous system/pituitary stalk histiocytosis had stabilization or improvement of their disease. Overall, inhibitors were well tolerated. Five patients with single-system LCH discontinued therapy and remain off therapy without recurrence. In contrast, all four patients with multisystem disease who discontinued therapy had to restart treatment. Our data suggest that children suffering from histiocytoses can be treated safely and effectively with dabrafenib or trametinib. Additional studies are, however, needed to determine the long-term safety and optimal duration of therapy.

Langerhans cell histiocytosis: promises and caveats of targeted therapies in high-risk and CNS disease

Langerhans cell histiocytosis (LCH) is a rare myeloid neoplasm driven by activating mutations in the MAPK pathway, most commonly BRAF-V600E and MAP2K1. It affects children and adults, with a wide spectrum of clinical presentations ranging from self-limited to multisystem (MS) life-threatening forms. LCH is defined by the accumulation of CD1a+/CD207+ cells in different organs, and patients with liver, spleen, or hematopoietic system involvement have a higher risk of mortality. Patients with neurodegeneration (ND) have devastating outcomes and are resistant to systemic therapies. MS-LCH is treated with risk-adapted therapy, but many patients require multiple salvage regimens that are myelosuppressive and expensive. MAPK inhibitors are increasingly being used, but most patients relapse upon discontinuation of therapy. Here, we review the management of central nervous system disease and how novel cerebrospinal fluid biomarkers might predict patients at high risk of ND who could benefit from early MAPK inhibition. Further, we discuss treatment strategies for refractory/relapsed (R/R) LCH, with a focus on MAPK inhibitors' efficacy and challenges (ie, the unknown): long-term toxicity in children, optimal duration, if they are curative, whether it is safe to combine them with chemotherapy, and their high price tag. Lastly, emerging strategies, such as the new panRAF inhibitor (Day 101) in patients with R/R LCH, ERK1/2 or CSF1R inhibition in patients with MEK1/2 inhibitor resistance, and targeting the microenvironment (checkpoint plus MEK inhibition) or senescent cells (mTOR or BCL-XL inhibitors) in R/R patients, are also examined.

Long-term outcomes among adults with Langerhans cell histiocytosis

Advances in the treatment of Langerhans cell histiocytosis (LCH) have resulted in a growing survivor population. There is a lack of data on long-term outcomes among adults with LCH. We conducted a retrospective record review of 219 adults (aged ≥18 years) with LCH. Most common presentation was multisystem (34.2%), followed by single-system pulmonary (32%), unifocal (28.3%), and single-system multifocal (5.5%) LCH. Risk organ involvement (the liver, spleen, or bone marrow) was seen in 8.7% of cases, and 40 of 88 (45.5%) tested cases were BRAFV600E. At a median follow-up of 74 months, 5-year progression-free survival (PFS) was 58.3% and estimated median PFS was 83 months. Median overall survival (OS) was not reached; 5- and 10-year OS rates were 88.7% and 74.5%, respectively. Risk organ involvement was associated with worse PFS (hazard ratio [HR], 4.5) and OS (HR, 10.8). BRAFV600E was not associated with risk organ involvement or survival. When compared with matched unaffected US population, individuals with LCH had a significantly higher risk of overall mortality (standardized mortality ratio [SMR], 2.66), specifically among those aged <55 years at diagnosis (SMR, 5.94) and those with multisystem disease (SMR, 4.12). Second cancers occurred in 16.4% cases, including diverse hematologic and solid organ malignancies. LCH-associated deaths constituted 36.1% of deaths and occurred within 5 years of diagnosis. After 5 years, non-LCH causes of death, including second cancers, chronic obstructive pulmonary disease, and cardiovascular diseases, predominated. Our study highlights, to our knowledge, for the first time, that adults with LCH experience early and late mortality from non-LCH causes and the need for development of targeted survivorship programs to improve outcomes.

BRAF testing modalities in histiocytic disorders: Comparative analysis and proposed testing algorithm

OBJECTIVES

Understanding of histiocytic disorders has been revolutionized by demonstration of mitogen-activated protein kinase (MAPK) pathway mutations, most commonly BRAFV600E. The optimal testing strategy to assess BRAFV600E is unknown. We aimed to compare performance of testing modalities, to propose a framework for evaluation of BRAFV600E mutation status in histiocytic disorders.

METHODS

We retrospectively reviewed patients with histiocytic disorders and BRAF mutation testing on a lesional tissue specimen.

RESULTS

In 120 patients, BRAF assessment included immunohistochemistry (IHC) in 97 (80.2%), polymerase chain reaction (PCR) in 35 (28.9%), and next-generation sequencing (NGS) in 62 (51.2%). Forty-five underwent both NGS and IHC. With NGS as the gold standard, the sensitivity and specificity of IHC were 82.4% and 96.4%. Three false negatives were observed in biopsy specimens with low BRAFV600E variant allele frequency or decalcified tissue. One false-positive IHC was observed in a lung biopsy specimen, likely due to antibody cross-reactivity with respiratory cilia. Among 14 with successful NGS and PCR, a single discordance was observed. Two PCR-to-IHC discrepancies were observed, including one other false-positive IHC.

CONCLUSIONS

Immunohistochemistry was highly specific for detection of BRAFV600E. Main caveats were false negatives and lack of detection of non-BRAFV600E mutations. We propose the use of IHC as initial screening in general practice with reflex molecular testing if negative.

Lineage switching of the cellular distribution of BRAFV600E in multisystem Langerhans cell histiocytosis

Most children with high-risk Langerhans cell histiocytosis (LCH) have BRAFV600E mutation. BRAFV600E alleles are detectable in myeloid mononuclear cells at diagnosis but it is not known if the cellular distribution of mutation evolves over time. Here, the profiles of 16 patients with high-risk disease were analyzed. Two received conventional salvage chemotherapy, 4 patients on inhibitors were tracked at intervals of 3 to 6 years, and 10 patients, also given inhibitors, were analyzed more than 2 years after diagnosis. In contrast to the patients responding to salvage chemotherapy who completely cleared BRAFV600E within 6 months, children who received inhibitors maintained high BRAFV600E alleles in their blood. At diagnosis, mutation was detected predominantly in monocytes and myeloid dendritic cells. With time, mutation switched to the T-cell compartment, which accounted for most of the mutational burden in peripheral blood mononuclear cells, more than 2 years from diagnosis (median, 85.4%; range, 44.5%-100%). The highest level of mutation occurred in naïve CD4+ T cells (median, 51.2%; range, 3.8%-93.5%). This study reveals an unexpected lineage switch of BRAFV600E mutation in high-risk LCH, which may influence monitoring strategies for the potential withdrawal of inhibitor treatment and has new implications for the pathogenesis of neurodegeneration, which occurred in 4 patients.

Spectrum of second primary malignancies and cause-specific mortality in pediatric and adult langerhans cell histiocytosis

With the advent of targeted therapeutics in Langerhans cell histiocytosis (LCH), there is a growing survivor population that might be at risk for late mortality from non-LCH causes, including second primary malignancies (SPMs). We undertook a large study using the Surveillance, Epidemiology, and End Results (SEER) database to evaluate the patterns of SPMs and cause-specific mortality among individuals with LCH (2000-2016) from the US. We found an increased risk of SPMs in the cohort (standardized incidence ratio [SIR] 2.07). The pediatric group was at a high risk of developing Hodgkin lymphoma (SIR 60.93) and non-Hodgkin lymphoma (SIR 60.88). People with adult-onset LCH were found to have a high risk of developing miscellaneous malignant cancers (SIR 11.43), which primarily included myelodysplastic syndrome. Adults were also at a high risk of developing carcinoma in-situ of vulva at 2-11 months [SIR 62.72] and B-ALL at 60-119 months [SIR 66.29] after LCH diagnosis. Additionally, 5% and 1% of the patients developed prior or concomitant malignancies with LCH, respectively. The 5 yr overall survival (OS) was 96.6% for pediatric and 88.5% for adult LCH cohorts. Most common cause of death was infections in pediatric and SPMs in adult LCH. Our study highlights that despite advances in treatments, people with LCH have an increased mortality risk from non-LCH causes when compared with the general population, including a high risk of SPMs.

Efficacy and safety of vemurafenib in Langerhans cell histiocytosis (LCH): A systematic review and meta-analysis

Almost half of the patients with Langerhans cell histiocytosis (LCH) are refractory to primary induction chemotherapy or undergo reactivation. The ideal treatment modality for refractory/relapsed LCH is yet not evidenced. This review aimed to determine the efficacy and safety of vemurafenib (a BRAF pathway inhibitor) in LCH, particularly the refractory/relapsed cases. The literature search was conducted using PubMed, Embase, CENTRAL, and abstracts published in the SIOP meetings. Studies that described the outcome of patients of LCH being treated with vemurafenib, alone or in combination, were included. A total of 416 studies were screened, and after applying exclusion criteria, 22 studies (n = 107) were included in the final analysis. The first-line therapy was prednisolone plus vinblastine for most patients (n = 92, 86%), and vemurafenib was started upfront in 3 patients (3%). The median time to first clinical response with vemurafenib was one week. The median time to best response was 5.25 months. Out of 107 patients, 62 patients (58%) had ultimately no active disease (NAD) while 39 (36%) had active disease better (ADB), making the overall response rate (ORR) of 101/107, ie, 94.4% (CI 0.88; 0.98). The main adverse effects of vemurafenib were rash or photosensitivity (47%) and other cutaneous adverse events (15%). Vemurafenib is highly efficacious and safe in the treatment of refractory LCH; however, the timing of its commencement and duration of therapy is yet to be established. Larger prospective collaborative trials are needed to answer the appropriate treatment duration and effective maintenance therapy approach.

PUVA therapy in persistent cutaneous histiocytosis: Case report and literature review

BACKGROUND

Cutaneous and mucocutaneous histiocytosis (group C) comprise a wide variety of entities affecting skin and/or mucosae. Although they are considered as reactive proliferations, their exact pathophysiology remains unknown and, therefore, they lack a specific treatment.

AIMS

The aim of this study is to review the evidence on cases of histiocytosis treated with UVB and/or UVA and to report a new case of relapsing group C histiocytosis that has been successfully treated with PUVA therapy.

MATERIALS & METHODS

We have conducted a review of the literature published over the last 40 years on the treatment of histiocytosis with phototherapy in the online PubMed database. We also describe a new case of successful treatment of histiocytosis with PUVA therapy.

RESULTS

Our patient was a 27-year-old man with persistent outbreaks of cutaneous histiocytosis over the previous 8 years. He responded successfully to PUVA therapy, and no relapse has been detected after one year of follow-up.

DISCUSSION

Self-involution is usual in group C histiocytosis, so conservative management is usually the first approach. Relapsing cases pose a therapeutic challenge. Reported treatment options for these patients include isotretinoin, cryotherapy, immunosuppressants, low-dose chemotherapy, CO2 laser, radiotherapy, and surgery. Phototherapy and photochemotherapy have been used in a small number of patients with considerable success. The main limitation to provide firm recommendations on histiocytosis therapy is the absence of solid evidence, as the articles published are mainly case reports with a short follow-up. In our patient, despite the short follow-up we have considered photochemotherapy to be effective since no spontaneous remission had been achieved in the previous 8 years.

CONCLUSION

PUVA therapy could be a safe and effective option to treat persistent cutaneous manifestations in patients with histiocytosis, although more evidence is required to support this statement.

Biomodulatory therapy induces durable remissions in multi-system Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is rare hematological neoplasia originating from the aberrant proliferation of CD207-positive dendritic cells. Refractory multi-system LCH is difficult to treat necessitating the continuous development of different salvage therapies. At our medical center, eleven patients (age 11 months to 77 years) with multi-system LCH were treated on a compassionate use basis with metronomic biomodulation therapy (MBT) involving the daily oral application of low-dose trofosfamide, etoricoxib, pioglitazone and low-dose dexamethasone. Overall, four patients including two heavily pretreated pediatric patients achieved ongoing complete remission. Moreover, partial disease remission was observed in three patients, and four patients attained stable disease. MBT demonstrated high activity against multi-system LCH even in patients, refractory to multiple systemic chemotherapies. Further confirmation of efficacy should be systematically evaluated in prospective trials.

Langerhans cell histiocytosis in adults: literature review

Langerhans cells histiocytosis is a variant of malignant histiocytosis. The course and symptoms vary. patients with localized forms have a better prognosis, because local therapy is effective. patients with multifocal forms of histiocytosis receive systemic drug therapy, which cures some of the patients. This review provides up-to-date data about typical presentation of the organ involvement, diagnosis, course and therapy of various forms of Langerhans cells histiocytosis.

Phase 2 study of oral thalidomide-cyclophosphamide-dexamethasone for recurrent/refractory adult Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a clonal histiocytic neoplasm with various clinical manifestations and heterogeneous prognoses. No standard therapy is available for recurrent/refractory LCH patients. This single-center, single-arm, phase 2 study enrolled 32 patients diagnosed with recurrent/refractory LCH. The TCD regimen (thalidomide 100 mg daily, cyclophosphamide 300 mg/m² Day 1, 8, 15, and dexamethasone 40 mg Day 1, 8, 15, 22 every 4 weeks) was administered for 12 cycles and thalidomide alone as maintenance for 12 months. The primary endpoint was event-free survival (EFS). Events were defined as progression during or after TCD therapy or death from any cause. After a median follow-up of 22 months (range 5-24 months), no patient died of all causes. The overall response rate was 87.5%, including 18 patients (56.3%) achieving complete remission and 10 patients (31.3%) as partial remission. The estimated 24-month EFS was 64.0%. Patients with risk organ involvement had similar EFS compared to patients without risk organ involvement (P = 0.38). The common toxicities of TCD regimen include grade 1-2 neutropenia (18.8%), grade 1-2 constipation (12.5%), grade 1-2 tiredness (9.4%) and grade 2 peripheral neuropathy (12.5%). Oral thalidomide, cyclophosphamide and dexamethasone are effective and safe regimen for recurrent/refractory LCH patients, particularly for patients with risk organ involvement.

Cyclin D1 expression and molecular genetic findings in periocular histiocytoses and neoplasms of macrophage-dendritic cell lineage

PURPOSE

Frequent activating mutations in the mitogen-activated protein kinase (MAPK) pathway genes have been identified in histiocytoses. MAPK signaling consistently upregulates Cyclin D1. The goal of this study was to determine whether Cyclin D1 expression by immunohistochemistry is a useful diagnostic marker for periocular histiocytoses and to further characterize their genetic basis.

DESIGN

Retrospective observational case series.

METHODS

Pathology records were searched for all patients with histiocytoses diagnosed between 1995-2020. Eleven histiocyte-rich inflammatory lesions and 10 xanthelasma served as controls. Cyclin D1 immunohistochemistry was performed on all tissues. A subset of histiocytoses was evaluated by next-generation sequencing (NGS) and droplet digital PCR (ddPCR).

RESULTS

There were 36 patients, 15 (42%) males and 21 (58%) females, with histiocytoses: 9 (25%) juvenile xanthogranuloma, 8 (22%) adult-onset asthma and periocular xanthogranuloma, 7 (19%) Langerhans cell histiocytosis, 5 (14%) Rosai-Dorfman disease, 5 (14%) xanthogranuloma not otherwise specified, 1 (3%) Erdheim-Chester disease, and 1 (3%) histiocytic sarcoma. Moderate-to-strong nuclear Cyclin D1 expression was present in ≥50% of lesional cells in histiocytoses (23/36, 64%), significantly more when compared to histiocyte-rich inflammatory lesions (0/11, 0%, P<.001) and xanthelasma (0/10, 0%, P<.001). Cyclin D1 was expressed in <10% of lesional cells in all 11 histiocyte-rich inflammatory lesions (P<.001) and all 10 xanthelasma lesions (P<.001). MAPK pathway gene mutations were detected in 12 of 14 (86%) histiocytoses successfully assayed by NGS and/or ddPCR.

CONCLUSIONS

Our study confirms that the Cyclin D1 immunohistochemical stain is a useful diagnostic marker for periocular histiocytoses, correlating with underlying mutations in MAPK pathway genes.

International expert consensus recommendations for the diagnosis and treatment of Langerhans cell histiocytosis in adults

Langerhans cell histiocytosis (LCH) can affect children and adults with a wide variety of clinical manifestations, including unifocal, single-system multifocal, single-system pulmonary (smoking-associated), or multisystem disease. The existing paradigms in the management of LCH in adults are mostly derived from the pediatric literature. Over the last decade, the discovery of clonality and MAPK-ERK pathway mutations in most cases led to the recognition of LCH as a hematopoietic neoplasm, opening the doors for treatment with targeted therapies. These advances have necessitated an update of the existing recommendations for the diagnosis and treatment of LCH in adults. This document presents consensus recommendations that resulted from the discussions at the annual Histiocyte Society meeting in 2019, encompassing clinical features, classification, diagnostic criteria, treatment algorithm, and response assessment for adults with LCH. The recommendations favor the use of 18F-Fluorodeoxyglucose positron emission tomography-based imaging for staging and response assessment in the majority of cases. Most adults with unifocal disease may be cured by local therapies, while the first-line treatment for single-system pulmonary LCH remains smoking cessation. Among patients not amenable or unresponsive to these treatments and/or have multifocal and multisystem disease, systemic treatments are recommended. Preferred systemic treatments in adults with LCH include cladribine or cytarabine, with the emerging role of targeted (BRAF and MEK inhibitor) therapies. Despite documented responses to treatments, many patients struggle with a high symptom burden from pain, fatigue, and mood disorders that should be acknowledged and managed appropriately.

A Novel GAB2::BRAF Fusion in Cutaneous Non-Langerhans Cell Histiocytosis with Systemic Involvement

Several mutations and gene fusions involved in the mitogen-activated protein kinase (MAPK) pathway have been reported in histiocytic neoplasms including Langerhans cell histiocytosis (LCH) and non-Langerhans cell histiocytosis (NLCH). We identified a GAB2::BRAF fusion in a cutaneous lesion from a 22-year-old woman who presented with central diabetes insipidus and red/brown papules on her face, oral mucosa, axilla, and groin. Skin biopsies showed a CD68+, S100-, and CD1a- histiocytic proliferation consistent with NLCH, best clinically classified as xanthoma disseminatum. Next-generation sequencing identified a GAB2::BRAF fusion involving exon 2 of GAB and exon 10 of BRAF. This case implicates a novel fusion in the MAPK signaling pathway, not previously reported in histiocytic neoplasms, as a possible driver of NLCH. Our findings underscore the utility of performing molecular studies on skin biopsies with NLCH to help identify potential targets for therapy. This article is protected by copyright. All rights reserved.

Adult Langerhans Cell Histiocytosis and the Skeleton

Langerhans cell histiocytosis (LCH) is a rare inflammatory neoplasia in which somatic mutations in components of the MAPK/ERK pathway have been identified. Osseous involvement is evident in approximately 80% of all patients and may present as a single osteolytic lesion, as a multi-ostotic single system disease or as part of multisystem disease. Both exogenous, such as treatment with glucocorticoids, and endogenous parameters, such as anterior pituitary hormone deficiencies and inflammatory cytokines, may severely affect bone metabolism in LCH. Computed tomography (CT) or magnetic resonance imaging (MRI) are usually required to precisely assess the degree of bone involvement; 18F-fluorodeoxyglucose (FDG) positron emission tomography-CT can both detect otherwise undetectable LCH lesions and differentiate metabolically active from inactive or resolved disease, while concomitantly being useful in the assessment of treatment response. Treatment of skeletal involvement may vary depending on location, extent, size, and symptoms of the disease from close observation and follow-up in unifocal single-system disease to chemotherapy and gene-targeted treatment in cases with multisystem involvement. In any case of osseous involvement, bisphosphonates might be considered as a treatment option especially if pain relief is urgently needed. Finally, a patient-specific approach is suggested to avoid unnecessary extensive surgical interventions and/or medical overtreatment.

Diagnosis, treatment and recurrence of a mandibular Langerhans cell histiocytosis: a three-year follow-up case report

Introduction: Langerhans cell histiocytosis (LCH) is an abnormal clonal proliferation of Langerhans cells secondary to immune process, mutation of oncogene or genetic predispositions. It preferentially affects bone, lung and skin. The incidence is 2–6 cases per million per year. Prognosis is variable and depends on number and location of lesions, and impact of the initial treatment. Oral lesions may be the first sign of LCH as illustrated by the present case. Observation: A 24-year-old male consulted first for severe gingival inflammation, teeth mobilities and alveolar bone loss with a suspicion of LCH. A pulmonary involvement was secondarily revealed by tomodensitometry. Histological examination, from gingival biopsy, confirmed the diagnostic of LCH, showing cells positive for the anti-CD1A antibody. The patient was managed by oral surgery and chemotherapy approaches. Alveolar bone loss significantly reduced. But 2 years and a half after the diagnosis, a recurrence was noted and managed by surgical approach. After a three-year follow-up, no recurrence was noted. Conclusion: Oral lesions can be inaugural manifestations of LCH. The dentist has an essential role in the early detection of these lesions.

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.

Mitogen-activating protein kinase pathway alterations in Langerhans cell histiocytosis

PURPOSE OF REVIEW

Langerhans cell histiocytosis (LCH) is a rare disorder characterized by the infiltration of involved tissues by specialized dendritic cells. The demonstration of the constant activation of the mitogen-activated protein kinase (MAPK) pathway in LCH lesions has been a breakthrough in the understanding of the pathogenesis of this rare disease. We will summarize the current knowledge on MAPK alterations in LCH and the new therapeutic options indicated by these findings.

RECENT FINDINGS

Since the description of the B-Raf proto-oncogene, serine/threonine kinase (BRAF)V600E mutation in LCH lesions, several other molecular alterations affecting the MAPK pathway have been identified in most cases. Based on these driver alterations, LCH cells were shown to be derived from hematopoietic precursors, which yielded the current concept of LCH as a myeloid inflammatory neoplasia. MAPK pathway inhibitors have emerged as an innovative therapy in severe forms of LCH, resulting in virtually no acquired resistance. However, although they are highly effective, their effect is only temporary, as the disease relapses upon discontinuation of the treatment.

SUMMARY

LCH is an inflammatory myeloid neoplastic disorder, driven by mutations activating the MAPK pathway. MAPK-targeted treatments represent an important stepforward in the management of patients with severe progressive LCH.

Update on Pulmonary Langerhans Cell Histiocytosis

Pulmonary Langerhans cell (LC) histiocytosis (PLCH) has unknown cause and is a rare neoplastic disorder characterized by the infiltration of lungs and various organs by bone marrow-derived Langerhans cells with an accompanying strong inflammatory response. These cells carry somatic mutations of BRAF gene and/or NRAS, KRAS, and MAP2K1 genes, which cause activation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling pathway. PLCH occurs predominantly in young smokers, without gender predominance. Lungs might be involved as an isolated organ or as part of a multiorgan disease. High-resolution computed chest tomography plays an outstanding role in PLCH diagnosis. The typical radiological picture of PLCH is the presence of small intralobular nodules, “tree in bud” opacities, cavitated nodules, and thin- and thick-walled cysts, frequently confluent. Histological examination of the lesion and demonstration of characteristic eosinophilic granulomas with the presence of LCs that display antigen CD1a or CD207 in immunohistochemistry are required for definite diagnosis. Smoking cessation is the most important recommendation for PLCH patients, but treatment of progressive PLCH and multisystem disease is based on chemotherapy. Recently, new targeted therapies have been implemented.