Genetic homogeneity of adult Langerhans cell histiocytosis lesions: Insights from BRAFV600E mutations in adult populations

Incidence, Clinical Features, and Outcomes of Langerhans Cell Histiocytosis in the United States

Langerhans cell histiocytosis (LCH) is a disorder with highly diverse clinical manifestations. We explored if age, sex, race, organ system involved, and therapy approaches determine patient survival in the era of modern treatments. LCH patient data reported to the Surveillance, Epidemiology, and End Results (SEER) program in 2010-2016 (n=1282; age: 0 to 100 y) was analyzed. Age-specific LCH incidence flattening to a low level suggests an age cutoff for pediatric patients of 20 years. The overall survival probability is lower for patients 21 to 100 years old ( P <0.0001), irrespective of sex and race. The commonest sites involved in the 0- to 20-year age group were bone, skin, and bone marrow; this shifted to lung, bone, and skin as the commonest disease sites in patients 21 to 100 years of age. The treatments applied differed between age groups, as younger versus older patients were more likely to receive chemotherapy-based treatment (48.4% vs. 17%; P <0.0001). There also was a trend toward nonwhite versus white patients being less likely to receive chemotherapy-based treatment (31.7% vs. 38.2%; P =0.067). Whereas there are treatment disparities related to LCH patient age and perhaps race, patient age is the strongest predictor of survival, with patients 21 to 100 years of age with lung, lymph node, skin, and bone marrow disease having the worst outcomes ( P <0.0001).

Prevalence of the BRAF V600E mutation in Greek adults with Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a rare inflammatory myeloid neoplasia with a broad spectrum of clinical manifestations. The activation of the MAP kinase pathway plays an integral role in its pathogenesis with genetic alterations found in the majority of cases that most frequently involve a somatic mutation of the oncogenic BRAF^V600E variant. In this study we investigated the prevalence of the BRAF^V600E mutation and its clinical relevance in adult Greek patients with LCH. Among 37 patients studied, the BRAF^V600E mutation was identified in 12 out of 31 (38.7%), whereas in six patients (19.3%) the results were in conclusive. The presence of the mutation did not correlate with age at diagnosis, organ involvement, disease extent, response to initial treatment, development of diabetes insipidus and relapse risk. In our series the prevalence of the BRAF^V600E mutation is at the lower range of the relative percentage found in children, but in line to that obtained in previous studies of adult patients with LCH that have found an up to 50% prevalence of the BRAF^V600E mutation in these patients. Further studies with a larger number of adults are needed to identify the exact prevalence of mutations in the RAS-RAF-MEK-ERK pathway and their role on clinical parameters and disease outcomes.Supplemental data for this article is available online at https://doi.org/10.1080/08880018.2022.2029988 .

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.

Upper Gastrointestinal Langerhans Cell Histiocytosis: A Report of 2 Adult Cases and a Literature Review

Langerhans cell histiocytosis (LCH) with primary involvement of the upper gastrointestinal (GI) tract is rare. We report 2 adult cases of localized LCH in the upper-GI tract, including the second reported adult case of esophageal LCH and review 11 previously reported cases. Case 1 involved the esophagus of a 61-year-old man; histiocytosis was detected when endoscopy was performed for an examination of epigastric pain. Case 2 involved the stomach of a 56-year-old woman wherein the lesion was detected during a follow-up endoscopy after Helicobacter pylori infection. Both biopsy specimens exhibited diffuse proliferation of mononuclear cells with nuclear convolution and a background of eosinophilic infiltrate. The cells were immunohistochemically positive for CD1a and langerin, and BRAF V600E mutation was detected in Case 2. Follow-up endoscopy for both cases revealed that the lesions disappeared without any treatment. It is important to avoid misdiagnosing LCH of the upper-GI tract as a malignant neoplasm.

Custom pyrosequencing assay to detect short BRAF deletions in Langerhans cell histiocytic lesions

Langerhans cell histiocytosis (LCH) is a rare inflammatory myeloid neoplastic disease driven by activating mutations in the mitogen-activating protein kinase signalling pathway, including the BRAF ^V600E mutation and BRAF deletions (BRAFdel). Next-generation sequencing and whole exome sequencing (WES) are valuable and powerful approaches for BRAFdel identification, but these techniques are costly and time consuming. Pyrosequencing is an alternative method that has the potential to rapidly and reliably identify gene deletions. We developed a custom pyrosequencing assay to detect the exon-12 BRAFdel in 18 biopsies from adult patients with LCH, which were all genotyped in parallel using Sanger sequencing and WES. A BRAFdel was detected in 7/18 (39%), 6/18 (33%) and 3/18 (17%) LCH lesions using WES, pyrosequencing and Sanger, respectively, with good concordance between the WES and pyrosequencing results (Kappa-coefficient=0.88). Therefore, our pyrosequencing assay is reliable and useful for detecting BRAFdel, particularly in BRAF ^V600E-negative LCH lesions, for which targeted treatment is indicated.

Analysis of the BRAF and MAP2K1 mutations in patients with Langerhans cell histiocytosis in Japan

In Langerhans cell histiocytosis (LCH), somatic gene mutations in the mitogen-activated protein kinase pathway have been identified in more than 80% of cases in Western countries, in which mutually exclusive BRAF and MAP2K1 mutations are involved. Among them, BRAF V600E mutation is the major contributor (50-60%). In 59 patients (50 children and nine adults) with LCH (not including pulmonary LCH) in Japan, we first screened for BRAF V600E in all patients followed by target sequencing for other gene mutations in 17 of BRAF V600E-negative patients. As a result, BRAF V600E mutation was detected in 27/59 (46%) patients. We also identified BRAF mutations other than V600E in five and MAP2K1 mutations in nine patients. Thus, gene mutations in BRAF or MAP2K1 were identified in 41/44 (93%) of the fully tested patients. Regarding the correlation of clinical features and genotype in pediatric patients, we found that BRAF V600E mutation status was not correlated with sex, age at diagnosis, disease extent, response to first-line therapy, relapse, or CNS-related sequelae. Interestingly, MAP2K1 exon 2 in-frame deletion was related to the risk organ involvement; however, further studies are required to clarify the impact of these gene mutations on the clinical features of patients with LCH.

Genetic landscape of adult Langerhans cell histiocytosis with lung involvement

The clinical significance of the BRAF ^V600E mutation in adult Langerhans cell histiocytosis (LCH), including pulmonary Langerhans cell histiocytosis (PLCH), is not well understood. Similarly, the spectrum of molecular alterations involved in adult LCH has not been fully delineated. To address these issues, we genotyped a large number of adult LCH biopsies and searched for an association of identified molecular alterations with clinical presentation and disease outcome.Biopsies from 117 adult LCH patients, 83 with PLCH (median age 36.4 years, 56 females, 38 multisystem disease, 79 single system disease, 65 current smokers) were genotyped for the BRAF ^V600E mutation. In 69 cases, LCH lesions were also genotyped by whole-exome sequencing (WES) or targeted gene panel next-generation sequencing (NGS). Cox models were used to estimate the association of baseline characteristics with the hazard of LCH progression.MAPK pathway alterations were detected in 59 out of 69 cases (86%) (BRAF ^V600E mutation: 36%, BRAF ^N486_P490 deletion: 28%, MAP2K1 mutations: 15%, isolated NRAS ^Q61 mutations: 4%), while KRAS mutations were virtually absent in PLCH lesions. The BRAF ^V600E mutation was not associated with LCH presentation at diagnosis, including smoking status and lung function, in PLCH patients. BRAF ^V600E status did not influence the risk of LCH progression over time.Thus, MAPK alterations are present in most lesions from adult LCH patients, particularly in PLCH. Unlike reports in paediatric LCH, BRAF ^V600E genotyping did not provide additional information on disease outcome. The search for alterations involved in the MAPK pathway, including BRAF deletions, is useful for guiding targeted treatment in selected patients with refractory progressive LCH.

Characteristics of multiple nodules in a patient with pulmonary Langerhans cell histiocytosis: A case report

BACKGROUND

The common computed tomography findings of pulmonary Langerhans cell histiocytosis (PLCH) are multiple cysts and micronodules predominantly in middle to upper lung lobes. Non-cystic nodules and large nodules are atypical findings of PLCH.

CASE SUMMARY

The patient was a 48-year-old Japanese man with a smoking history (20 cigarettes/d, 28 years) and no symptoms. Multiple nodules existed in all lung lobes, predominantly in the right lower lobe. Some nodules seemed to be distributed randomly, and others were adjacent to bronchus. Most nodules were solid; some small ones were cystic. The largest nodule was 22 mm in diameter. Although metastatic lung tumors were suspected, thoracoscopic lung biopsy led to the diagnosis of PLCH. At 6 months after he quit smoking, all nodules had almost disappeared. We investigated the characteristics of nodules at diagnosis in detail. Of 349 nodules in total, 116 were in upper and 199 were in lower lobes. Ninety-six (27.5%) were cystic; the remaining 253 (72.5%) were non-cystic. The prevalence of cystic nodules was higher in upper lobes than in lower lobes (right upper 37.5% vs lower 18.2%, P = 0.0068; left upper 48.1% vs lower 24.4%, P = 0.0078). The average size (dia.) of cystic nodules was smaller than that of non-cystic nodules (5.03 mm vs 7.40 mm, respectively, P < 0.0001).

CONCLUSION

Although multiple non-cystic nodules including large nodules (over 20 mm) are atypical, PLCH should be included in differential diagnoses. The presence of small cystic nodules predominantly in upper lobes and asymptomatic situation are also important for differential diagnoses to distinguish from metastatic cancers.

Association between clinicopathologic characteristics and BRAFV600E expression in Chinese patients with Langerhans cell histiocytosis

Background

The identification of V‐raf murine sarcoma viral oncogene homolog B1 (BRAF)^V600E mutations has been recommended in patients with Langerhans cell histiocytosis (LCH) with difficult diagnosis and failure of first‐line treatment. The reported frequencies of BRAF^V600E mutations vary in Chinese patients with LCH.

Methods

We conducted a retrospective analysis of LCH patients with a definitive pathological diagnosis who were hospitalized between 2013 and 2017. The BRAF^V600E mutations were detected with the human BRAF^V600E amplification refractory mutation system‐PCR (ARMS‐PCR) kit from the collected tissue samples.

Results

This study consisted of 46 male (68.7%) and 21 female (31.3%) patients, with a mean age of 29.1 years (range, 2–76 years). Most were adults (45/67.2%) with the multisysytem‐LCH (MS‐LCH) disease subtype (49/61.3%). The overall frequency of BRAF^V600E mutations was 22.4% (15 of 67 patients), confirmed by PCR analysis. These mutations were not closely correlated with age (nonadults vs. adults = 5/22.7% vs. 10/22.2%, P = 0.54), gender (female vs. male = 9/19.6% vs. 6/28.6%, P = 0.61), LCH classification type (single system: MS‐risk organ⁺: MS‐risk organ⁻ = 3/16.7%: 12:28.6%: 0, P = 0.19) or prognosis (cured: improved/stable: exacerbated: died = 4/44.4%: 19.2%: 20%: 0, P = 0.37). There were 33 patients (49.2%) with lung involvement, and 12 patients (36.3%) underwent lung biopsies; after screening, four patients were diagnosed with solitary pulmonary LCH, all of whom were negative for BRAF^V600E mutations.

Conclusion

The BRAF^V600E mutation rate in patients with LCH was lower than those reported in other studies. In addition, BRAF^V600E mutations might not be correlated with age, gender, LCH classification type or prognosis for Chinese cases.

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.