References

1. Rodriguez-Galindo C, Allen CE: Langerhans cell histiocytosis. Blood 135 (16): 1319-1331, 2020. [PubMed: 32106306]
2. Emile JF, Abla O, Fraitag S, et al.: Revised classification of histiocytoses and neoplasms of the macrophage-dendritic cell lineages. Blood 127 (22): 2672-81, 2016. [PMC free article: PMC5161007] [PubMed: 26966089]
3. Berres ML, Lim KP, Peters T, et al.: BRAF-V600E expression in precursor versus differentiated dendritic cells defines clinically distinct LCH risk groups. J Exp Med 211 (4): 669-83, 2014. [PMC free article: PMC3978272] [PubMed: 24638167]
4. Allen CE, Merad M, McClain KL: Langerhans-Cell Histiocytosis. N Engl J Med 379 (9): 856-868, 2018. [PMC free article: PMC6334777] [PubMed: 30157397]
5. Willman CL, Busque L, Griffith BB, et al.: Langerhans'-cell histiocytosis (histiocytosis X)--a clonal proliferative disease. N Engl J Med 331 (3): 154-60, 1994. [PubMed: 8008029]
6. Yu RC, Chu C, Buluwela L, et al.: Clonal proliferation of Langerhans cells in Langerhans cell histiocytosis. Lancet 343 (8900): 767-8, 1994. [PubMed: 7510816]

Cell of Origin and Biological Correlates

The pathological histiocyte or Langerhans cell histiocytosis (LCH) cell has a gene expression profile closely resembling that of a myeloid dendritic cell. Studies have also demonstrated that the BRAF V600E variant can be identified in mononuclear cells in peripheral blood and cell-free DNA, usually in patients with disseminated disease.[1-3] This suggests that multisystem LCH arises from a somatic variant within the marrow or a circulating precursor cell, while localized disease arises from a variant occurring in a precursor cell at the local site.[2]

Modern classification of the histiocytic diseases subdivides them into dendritic cell–related, monocyte/macrophage-related, or true malignancies. LCH is a dendritic cell disease.[4,5] Comprehensive data analysis on gene expression array of LCH cells is consistent with the concept that the skin Langerhans cell (LC) is not the cell of origin for LCH.[1] Rather, the origin is likely to be a hematopoietic progenitor cell before being a committed myeloid dendritic cell, which expresses the same antigens (CD1a and CD207) as the skin LC.[6,7] This concept was further supported by reports that the transcription profile of LCH cells was distinct from myeloid and plasmacytoid dendritic cells, as well as epidermal LCs.[1,6,8,9]

LCH is now considered a myeloid neoplasm. However, some controversy remains as to whether it is a true malignancy or a neoplasm with varying clinical behavior. The same BRAF V600E variant has been found in many cancers; however, V600E-altered BRAF is also present in benign nevi, possibly indicating that malignant transformation requires additional variants.[10] These findings have raised the possibility of treatment with targeted therapies. Several trials of BRAF and MEK inhibitors are open for adults and children with LCH.

For more information, see the sections on Cytogenetic and Genomic Studies and Cytokine Analysis.

Histopathology

The Langerhans histiocytosis cells in LCH lesions (LCH cells) are immature dendritic cells, making up fewer than 10% of the cells present in the lesion.[9,11] These cells are classically large oval cells with abundant pink cytoplasm and a bean-shaped nucleus on hematoxylin and eosin stain. LCH cells stain positively with antibodies to S100, CD1a, and/or anti-Langerin (CD207). Staining with CD1a or Langerin confirms the diagnosis of LCH, but care should be taken to correlate with clinical presentation in organs in which normal LC cells occur.[12]

Because LCH cells activate other immunologic cells, LCH lesions also contain other histiocytes, lymphocytes, macrophages, neutrophils, eosinophils, and fibroblasts, and they may contain multinucleated giant cells.

In the brain, the following three types of histopathological findings have been described in LCH:

1. Mass lesions in the meninges or choroid plexus with CD1a-positive LCH cells and predominantly CD8-positive lymphocytes.
2. Mass lesions in connective tissue spaces with CD1a-positive LCH cells and predominantly CD8-positive lymphocytes that cause an inflammatory response and neuronal loss.
3. Neurodegenerative lesions, consisting of cells staining for the altered BRAF protein with positive CD14, CD33, and CD163, identifying these as hematopoietic myeloid/monocytic cells. These are the pathological LCs that have migrated into the brain and do not stain with CD1a or CD207 and have become microglia-like.[13]

Immunologic Abnormalities

Normally, the LC is a primary presenter of antigen to naïve T lymphocytes. However, in LCH, the pathological dendritic cell does not efficiently stimulate primary T-lymphocyte responses.[14] Antibody staining for the dendritic cell markers, including CD80, CD86, and class II antigens, has shown that in LCH, the abnormal cells are immature dendritic cells. These cells present antigen poorly and are proliferating at a low rate.[11,14,15]

An expansion of regulatory T cells in patients with LCH has been reported.[15] The population of CD4-positive, CD25(high), FoxP3(high) cells was reported to comprise 20% of T cells and appeared to be in contact with LCH cells in the lesions. These T cells were present in peripheral blood in higher numbers in patients with LCH than in controls and returned to a normal level when patients were in remission.[15] Poorly functioning T cells expressing inhibitor receptors PD-1, TIM3, and LAG-3 have been found in LCH lesions but not in the peripheral blood of patients.[16] The dysfunctional T cells accumulate in LCH lesions, because PD-1 on the cell surface engages with the PD-L1 on the pathological dendritic cells.

Cytogenetic and Genomic Studies

Genomics of LCH

BRAF, NRAS, and ARAF variants

The genomic basis of LCH was advanced by a 2010 report of an activating variant of the BRAF oncogene (V600E) that was detected in 35 of 61 cases (57%).[17] Multiple subsequent reports have confirmed the presence of BRAF V600E variants in 50% or more of LCH cases in children.[2,18,19] Other BRAF variants that result in signal activation have been described.[18,20] ARAF variants are infrequent in LCH but, when present, can also lead to RAS-MAPK pathway activation.[21]

The presence of the BRAF V600E variant in blood and bone marrow was studied in a series of 100 patients, 65% of whom tested positive for the BRAF V600E variant by a sensitive quantitative polymerase chain reaction technique.[2] Circulating cells with the BRAF V600E variant could be detected in all high-risk patients and in a subset of low-risk multisystem patients. The BRAF V600E allele was detected in circulating cell-free DNA in 100% of patients with risk-organ–positive multisystem LCH, 42% of patients with risk-organ–negative LCH, and 14% of patients with single-system LCH.[22]

The myeloid dendritic cell origin of LCH was confirmed by finding CD34-positive stem cells with the variant in the bone marrow of high-risk patients. In those with low-risk disease, the variant was found in more mature myeloid dendritic cells, suggesting that the stage of cell development at which the somatic variant occurs is critical in defining the extent of disease in LCH.

Pulmonary LCH in adults was initially reported to be nonclonal in approximately 75% of cases,[23] while a later study of BRAF variants showed that 25% to 50% of adult patients with lung LCH had evidence of BRAF V600E variants.[23,24] Another study of 26 pulmonary LCH cases found that 50% had BRAF V600E variants and 40% had NRAS variants.[25] Approximately the same number of variants are polyclonal as are monoclonal. It has not been determined whether clonality and BRAF pathway variants are concordant in the same patients, which might suggest a reactive rather than a neoplastic condition in smoker's lung LCH and a clonal neoplasm in other types of LCH.

In a study of 117 patients with LCH, 83 adult patients with pulmonary LCH underwent molecular analysis. Nearly 90% of these patients had variants in the MAPK pathway.[26][Level of evidence C3] Of the 69 patients who had their biopsy samples further analyzed using a next-generation sequencing panel of 74 genes, 36% had BRAF V600E variants, 29% had BRAF N486-P490 deletions, 15% had MAP2K1 variants or deletions, and 4% had NRAS variants. Only one patient had a KRAS variant. Additionally, 11 patients had their biopsy samples analyzed using whole-exome sequencing. An average of 14 variants were found per patient, which is markedly higher than the average of one variant found per pediatric patient.[27] There were no clinical correlates, including presence of a BRAF V600E variant and smoking status. Of the 117 patients with LCH, 60% experienced a relapse.

Figure 1. Courtesy of Rikhia Chakraborty, Ph.D. Permission to reuse the figure in any form must be obtained directly from Dr. Chakraborty.

The RAS-MAPK signaling pathway (see Figure 1) transmits signals from a cell surface receptor (e.g., a growth factor) through the RAS pathway (via one of the RAF proteins [A, B, or C]) to phosphorylate MEK and then the extracellular signal-regulated kinase (ERK), which leads to nuclear signals affecting cell cycle and transcription regulation. The V600E variant of BRAF leads to continuous phosphorylation, and thus activation, of MEK and ERK without the need for an external signal. Activation of ERK occurs by phosphorylation, and phosphorylated ERK can be detected in virtually all LCH lesions.[17,28]

In a mouse model of LCH, the BRAF V600E variant was shown to inhibit a chemokine receptor (CCR7)–mediated migration of dendritic cells, forcing them to accumulate in the LCH lesion.[29] This variant also causes an increased expression of BCL2L1, which results in resistance to apoptosis. This process leads to the cells being less responsive to chemotherapy. The BRAF V600E variant also causes growth arrest of hematopoietic progenitor cells and a senescence-associated secretory phenotype that further promotes accumulation of the pathological cells.[30]

Another mouse model with the BRAF V600E variant under control of Scl or Map17 gene promoters added additional insights into the biology of neurodegenerative LCH.[31] These studies confirmed the hematopoietic origin of CD11a-positive macrophages with BRAF V600E variants. This process disrupts the blood-brain barrier and causes loss of Purkinje cells and progressive neurodegeneration by resistance to apoptosis and production of senescent associated secretory proteins, which include inflammatory cytokines IL-1, IL-6, and matrix metalloproteinases. Treatment with a MAP kinase inhibitor and a senolytic agent (navitoclax) decreased the pathogenic cell numbers and led to clinical improvement in the mice.

In summary, LCH is now considered a myeloid neoplasm primarily driven by activating variants of the MAPK pathway. Fifty percent to 60% of the activating variants are caused by BRAF V600E variants, which are enriched in patients with multisystem risk organ–positive LCH and in patients with neurodegenerative-disease LCH.[32] Ongoing studies are assessing whether low-level variant detection in peripheral blood can be used as a minimal residual disease marker to assist in therapeutic decisions.

Other RAS-MAPK pathway alterations

Because RAS-MAPK pathway activation (elevated phosphor-ERK) can be detected in all LCH cases, including those without BRAF variants, the presence of genomic alterations in other components of the pathway was suspected. The following genomic alterations were identified:

• MAP2K1 variants. Whole-exome sequencing on biopsy samples of BRAF-altered versus BRAF–wild-type LCH tissue revealed that 7 of 21 BRAF–wild-type specimens had MAP2K1 variants, while no BRAF-altered specimens had MAP2K1 variants.[28] The variants in MAP2K1 (which codes for MEK1) were activating, as indicated by their induction of ERK phosphorylation.[28]
  Another study showed MAP2K1 variants exclusively in 11 of 22 BRAF–wild-type cases.[33] One study showed that MAP2K1 and other variants associated with pediatric and adult LCH were mutually exclusive of BRAF variants.[34] The authors found a variety of variants in other pathways (e.g., JNK, RAS-ERK, and JAK-STAT) in pediatric and adult patients with BRAF V600E or MAP2K1 variants. Another study evaluated the kinase alterations and myeloid-associated variants in 73 adult patients with LCH.[35] They reported a median of two variants per adult patient, as opposed to children who usually have only one variant. BRAF V600E was found in 31%, BRAF indel in 29%, and MAP2K1 in 19% of patients with LCH. A variety of other protein kinase and related pathways were found in 89% of adult patients with LCH. MAP2K1 variants were exclusive of BRAF variants.
• In-frame BRAF deletions and FAM73A::BRAF gene fusions. In-frame BRAF deletions and in-frame FAM73A::BRAF gene fusions have occurred in the group of BRAF V600E and MAP2K1 variant–negative cases.[27]

In summary, studies support the universal activation of ERK in LCH. ERK activation in most cases of LCH is explained by BRAF and MAP2K1 alterations.[17,27,28] Altogether, these variants in the MAP kinase pathway account for nearly 80% of the causes of the universal activation of ERK in LCH.[17,27,28] The remaining cases have a range of variants that include small deletions in BRAF, BRAF gene fusions (discussed above), as well as variants in ARAF, MAP3K1, NRAS, ERBB3, PI3CA, CSF1R, and other rare targets.[34 ,32][Level of evidence C1]

Clinical implications

Clinical implications of the described genomic findings include the following:

• LCH is included in a group of other pediatric tumors with activating BRAF variants, such as select nonmalignant conditions (e.g., benign nevi) [36] and low-grade malignancies (e.g., pilocytic astrocytoma).[37,38] All of these conditions have a generally indolent course, with spontaneous resolution occurring in some cases. This distinctive clinical course may be a manifestation of oncogene-induced senescence.[36,39]
• In some pediatric studies, BRAF V600E variants have been associated with more severe multisystem disease, treatment failure, increased reactivations, and an increased risk of neurodegeneration (see below).[40] These clinical correlates were recently investigated for non-BRAF V600E variants in an international study. Similar to the BRAF V600E cohort, all patients with multisystem risk organ–positive LCH had detectable variants in peripheral blood mononuclear cells. Of seven patients with multisystem risk organ–negative LCH, four had detectable variants. No patients with single-system disease had detectable variants in peripheral blood mononuclear cells. The authors concluded that other MAPK pathway variants are associated with risk status, similar to BRAF V600E variants.[32]
  BRAF V600E variants can be targeted by BRAF inhibitors (e.g., vemurafenib and dabrafenib) or by the combination of BRAF inhibitors plus MEK inhibitors (e.g., dabrafenib/trametinib and vemurafenib/cobimetinib). These agents and combinations are approved for adults with melanoma. Treatment of melanoma in adults with combinations of a BRAF inhibitor and a MEK inhibitor showed significantly improved progression-free survival outcomes compared with treatment using a BRAF inhibitor alone.[41,42]
  Several case reports and two case series have also demonstrated the efficacy of BRAF inhibitors for the treatment of LCH in children.[43-48] However, the long-term role of this therapy is complicated because most patients will relapse when the inhibitors are discontinued. For more information, see the sections on Treatment of recurrent, refractory, or progressive high-risk disease: multisystem LCH and Targeted therapies for the treatment of single-system and multisystem disease.
• Circulating BRAF V600E–altered cells have been found in 59% of patients who developed neurodegenerative-disease LCH, compared with 15% of patients who did not develop neurodegenerative-disease LCH. Detectable altered circulating cells had a sensitivity of 0.59 and specificity of 0.86 for developing the neurodegenerative disease. Even after therapy, some patients with neurodegenerative-disease LCH had circulating BRAF V600E–altered cells.[13]
• With additional research, the observation of the BRAF V600E variant (or potentially MAP2K1 variants) in circulating cells or cell-free DNA may become a useful diagnostic tool to define high-risk versus low-risk disease.[2] Additionally, for patients who have a somatic variant, persistence of circulating cells with the variant may be useful as a marker of residual disease.[2]

Cytokine Analysis

Immunohistochemical staining has shown upregulation of many different cytokines/chemokines, both in LCH lesions and in the serum/plasma of patients with LCH.[49,50] In an analysis of gene expression in LCH by gene array techniques, 2,000 differentially expressed genes were identified. Of 65 genes previously reported to be associated with LCH, only 11 were found to be upregulated in the array results. The most highly upregulated gene in both CD207-positive and CD3-positive cells was SPP1 (encoding the osteopontin protein); other genes that activate and recruit T cells to sites of inflammation are also upregulated.[1] The expression profile of the T cells was that of an activated regulatory T-cell phenotype with increased expression of FOXP3, CTLA4, and SPP1. These findings support a previous report on the expansion of regulatory T cells in LCH.[1] There was pronounced expression of genes associated with early myeloid progenitors such as CD33 and CD44, which is consistent with an earlier report of elevated myeloid dendritic cells in the blood of patients with LCH.[51] A model of Misguided Myeloid Dendritic Cell Precursors has been proposed, whereby myeloid dendritic cell precursors are recruited to sites of LCH by an unknown mechanism, and the dendritic cells, in turn, recruit lymphocytes by excretion of osteopontin, neuropilin-1, and vannin-1.[1]

One study evaluated possible biomarkers for central nervous system LCH. The study examined 121 unique proteins in the cerebrospinal fluid (CSF) of 40 pediatric patients with LCH and compared them with controls, which included 29 patients with acute lymphoblastic leukemia, 25 patients with brain tumors, 28 patients with neurodegenerative diseases, and 9 patients with hemophagocytic lymphohistiocytosis. Only osteopontin proved to be significantly increased in the CSF of LCH patients with either neurodegeneration or mass lesions (pituitary), compared with all of the control groups. Analysis of osteopontin expression in these tissues confirmed an upregulation of the SPP1 gene.[13]

Several investigators have published studies evaluating the level of various cytokines or growth factors in the blood of patients with LCH. These studies have included many of the genes found not to be upregulated by the gene expression results discussed above.[1] One explanation for elevated levels of these proteins is a systemic inflammatory response, with the cytokines/growth factors being produced by cells outside the LCH lesions. A second possible explanation is that macrophages in the LCH lesions produce the cytokines measured in the blood or are concentrated in lesions.

IL-1 beta and prostaglandin GE₂ levels were measured in the saliva of patients with oral LCH lesions or multisystem high-risk patients with and without oral lesions. Levels of both were higher in patients with active disease and decreased after successful therapy.[52]

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General Information About Childhood LCH

Special Considerations for the Treatment of Children With Cancer

Cancer in children and adolescents is rare, although the overall incidence has slowly increased since 1975.[41] Children and adolescents with cancer should be referred to medical centers that have a multidisciplinary team of cancer specialists with experience treating the cancers that occur during childhood and adolescence. This multidisciplinary team approach incorporates the skills of the following pediatric specialists and others to ensure that children receive treatment, supportive care, and rehabilitation to achieve optimal survival and quality of life:

• Primary care physicians.
• Pediatric surgeons.
• Transplant surgeons.
• Pathologists.
• Pediatric radiation oncologists.
• Pediatric medical oncologists and hematologists.
• Ophthalmologists.
• Rehabilitation specialists.
• Pediatric oncology nurses.
• Social workers.
• Child-life professionals.
• Psychologists.
• Nutritionists.

For specific information about supportive care for children and adolescents with cancer, see the summaries on Supportive and Palliative Care.

The American Academy of Pediatrics has outlined guidelines for pediatric cancer centers and their role in the treatment of children and adolescents with cancer.[42] At these centers, clinical trials are available for most types of cancer that occur in children and adolescents, and the opportunity to participate is offered to most patients and their families. Clinical trials for children and adolescents diagnosed with cancer are generally designed to compare potentially better therapy with current standard therapy. Other types of clinical trials test novel therapies when there is no standard therapy for a cancer diagnosis. Most of the progress in identifying curative therapies for childhood cancers has been achieved through clinical trials. Information about ongoing clinical trials is available from the NCI website.

Low-Risk Disease: Single-System or Multisystem LCH

High-Risk Disease: Multisystem LCH

Recurrent, Refractory, or Progressive Childhood LCH

Assessment of Response to Treatment

Response assessment remains one of the most difficult areas in LCH therapy. It is easier when there is a specific area that can be monitored clinically or with ultrasonography, CT, PET, or MRI scans, such as the skin, hepato/splenomegaly, and other mass or lytic bone lesions. Clinical judgment, including evaluation of pain and other symptoms, remains important.

Bone lesions may take many months to heal and are difficult to evaluate on plain radiographs, although sclerosis around the periphery of a bone lesion suggests healing. CT or MRI scans are useful in assessing response of a soft tissue mass associated with a bone lesion, but are not particularly helpful in assessing the response of lytic bone lesions. Technetium Tc 99m bone scans remain positive in healing bone. PET scans may be helpful in monitoring the response to therapy because the intensity of the PET image diminishes with the response of lesions and healing of bone.[17]

For children or adults with lung LCH, pulmonary function testing and high-resolution CT scans are sensitive methods for detecting disease progression.[20] Residual interstitial changes reflecting residual fibrosis or residual inactive cysts must be distinguished from active disease; somatostatin analog scintigraphy may be useful in this regard.[162]

Treatment Options No Longer Considered Effective for Childhood LCH

Treatments that have been used in the past but are no longer recommended for pediatric patients with LCH include cyclosporine [163] and interferon-alpha.[164]

Extensive surgery is also not indicated. For lesions of the mandible, extensive surgery may destroy any possibility of secondary tooth development. Surgical resection of groin or genital lesions is contraindicated because these lesions can be healed by chemotherapy.

Radiation therapy use in LCH has been significantly reduced in pediatric patients, and even low-dose radiation therapy should be limited to single-bone, vertebral body lesions or other single-bone lesions compressing the spinal cord or optic nerve that do not respond to chemotherapy or are painful and not amenable to other therapy.[94,101,165]

Late Disease and Treatment Effects of Childhood LCH

The reported frequency of long-term consequences of LCH has ranged from 20% to 70%. Children with low–risk-organ involvement (skin, bones, lymph nodes, or pituitary gland) have an approximately 20% chance of developing long-term sequelae.[30,166]; [167][Level of evidence B4] Patients with multisystem involvement have a reported rate of long-term complications of approximately 70% when treatment was only 6 months.[30,101,168,169] However, the extent of long-term sequelae in patients who are treated for a year has not been reported.

This wide variation in frequency results from case definition, sample size, therapy used, method of data collection, and follow-up duration. Quality-of-life studies have reported the following:

• In one study of long-term survivors of skeletal LCH, the quality-of-life scores were not significantly different from those of healthy control children and adults.[104] In addition, the quality-of-life scores were very similar between those with and without permanent sequelae.
• In another study of 40 patients who were carefully screened for late effects, adverse quality-of-life scores were found in more than 50% of patients.[40] Seventy-five percent of patients had detectable long-term sequelae. Hypothalamic/pituitary dysfunction (50%), cognitive dysfunction (20%), and cerebellar involvement (17.5%) were the most common side effects.

The late effects of LCH may occur in the following body systems:

• Endocrine. Patients with diabetes insipidus are at risk of panhypopituitarism and should be monitored carefully for adequacy of growth and development. In a retrospective review of 141 patients with LCH and diabetes insipidus, 43% developed growth hormone (GH) deficiency.[101,168,169] The 5-year risk of GH deficiency among children with LCH and diabetes insipidus was 35%, and the 10-year risk was 54%. There was no increased reactivation of LCH in patients who received GH compared with those who did not.[168] Growth and development problems are more frequent because of the young age at presentation and the more toxic effects of long-term prednisone therapy in the very young child.
• Special senses (hearing loss). Hearing loss has been found in 38% of children who were treated for LCH.[101] Seventy percent of patients with LCH in this study had ear involvement, which included aural discharge, mastoid swelling, and hearing loss. Of those with CT or MRI abnormalities in the mastoid, 59% had hearing loss.[170][Level of evidence C1]
• Neurological. Neurological symptoms secondary to vertebral compression of cervical lesions have been reported in 3 of 26 patients with LCH and spinal lesions.[101] CNS LCH occurs most often in children with LCH of the pituitary or CNS-risk skull bones (mastoid, orbit, or temporal bone). Significant cognitive defects and MRI abnormalities may develop in some long-term survivors with CNS-risk skull lesions.[171] Some patients have markedly abnormal cerebellar function and behavior abnormalities, while others have subtle deficits in short-term memory and brain stem–evoked potentials.[83]
• Skeletal. Orthopedic problems from lesions of the spine, femur, tibia, or humerus may be seen in 20% of patients. These problems include vertebral collapse or instability of the spine that may lead to scoliosis and facial or limb asymmetry.
• Respiratory. Diffuse pulmonary disease may result in poor lung function with higher risk of infections and decreased exercise tolerance. These patients should be monitored with pulmonary function testing, including the diffusing capacity of carbon monoxide and ratio of residual volume to total lung capacity.[39]
• Digestive. Liver disease may lead to sclerosing cholangitis, which rarely responds to any treatment other than liver transplant.[129] Dental problems characterized by loss of teeth have been significant for some patients, usually related to overly aggressive dental surgery.[172]
• Subsequent neoplasms. Bone marrow failure secondary to LCH or from therapy is rare and is associated with a higher risk of malignancy. Patients with LCH have a higher-than-normal risk of developing secondary cancers.[173,174]
  Leukemia (usually acute myeloid leukemia) occurs after treatment, as does lymphoblastic lymphoma. Concurrent LCH and malignancy has been reported in a few patients, and some patients had their malignancy first, followed by development of LCH. Three patients with T-cell acute lymphoblastic leukemia (ALL) and aggressive LCH were reported and, as with all histiocytic disorders associated with or following lymphoblastic malignancies, the same genetic changes were found in both diseases, suggesting a shared clonal origin.[175-177] One study reported two cases in which clonality with the same T-cell receptor gamma genotype was found.[176] The authors of this study emphasized the plasticity of lymphocytes developing into Langerhans cells. The second study described one patient with LCH after T-cell ALL who had the same T-cell receptor gene rearrangements and activating variants of the NOTCH1 gene.[177]

A publication based on surveying Histiocyte Society members and a literature review reported 116 cases of childhood LCH-malignancy pairs. Leukemias and myeloproliferative disorders (n = 58; 50.0%) prevailed over solid tumors (n = 43; 37.1%) and lymphomas (n = 15; 12.9%). In most children, malignancy followed LCH (n = 69; 59.5%). However, ALL, including T-cell ALL, was sometimes seen preceding the onset of LCH or histiocytic neoplasms. The histiocytic disorder commonly carried the same underlying genetic findings as the preceding leukemia.[178]

Another study reported a population-based analysis of subsequent malignancies in pediatric patients in the Surveillance, Epidemiology, and End Results (SEER) Program database from 2000 to 2016.[179] Of the 936 pediatric cases, there were 2 cases of non-Hodgkin lymphoma, 2 cases of Hodgkin lymphoma, and 1 case of T-cell ALL. However, the median follow-up was 38 months, which may not be sufficient to capture secondary solid tumors.

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139. Simko SJ, McClain KL, Allen CE: Up-front therapy for LCH: is it time to test an alternative to vinblastine/prednisone? Br J Haematol 169 (2): 299-301, 2015. [PMC free article: PMC4791956] [PubMed: 25400231]
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Incidence

A population-based study in England found that the incidence of LCH in patients older than 15 years was 1.05 cases per 1 million people.[3] Of these individuals, 44% were younger than 45 years. A higher incidence of LCH in economically disadvantaged areas was associated with a higher incidence of smoking in those areas.

More than 90% of adult pulmonary LCH cases occur in young adults who smoke, often more than 20 cigarettes per day.[4,5]

Clinical Presentation

Adult patients may have signs and symptoms of LCH for many months before receiving a definitive diagnosis and treatment. LCH in adults is often similar to that in children and appears to involve the same organs, although the incidence in each organ may be different. There is a predominance of lung disease in adults, usually occurring as single-system disease and closely associated with smoking and some unique biological characteristics. Most isolated lung LCH cases in adults are polyclonal and possibly reactive, while fewer lung LCH cases are monoclonal.[6,7]

A German registry with 121 registrants showed that 62% had single-organ involvement and 38% had multisystem involvement. Pulmonary LCH occurred in 34% of the total study population. Lungs are the most common site, followed by bone and skin involvement. The median age at diagnosis was 44 years (±12.8 years). All organ systems found in childhood LCH were seen in these adults, including endocrine and central nervous system (CNS), liver, spleen, bone marrow, and gastrointestinal tract. The major difference is the much higher incidence of isolated pulmonary LCH in adults, particularly in young adults who smoke. Other differences appear to be the more frequent involvement of genital and oral mucosa.[8]

Presenting signs and symptoms from published studies include the following:

• Dyspnea or tachypnea.
• Polydipsia and polyuria.
• Bone pain.
• Soft tissue swelling near bone lesions.
• Skin rash or scalp nodules.
• Lymphadenopathy.
• Weight loss.
• Fever.
• Gingival hypertrophy.
• Ataxia.
• Memory problems.
• Hepatosplenomegaly.

Patients who present with isolated diabetes insipidus should be carefully observed for the onset of other signs or symptoms characteristic of LCH. At least 80% of patients with diabetes insipidus had involvement of other organ systems, including bone (68%), skin (57%), lung (39%), and lymph nodes (18%).[9] However, isolated diabetes insipidus in adults is similar to that in pediatric patients, with progression from posterior to anterior pituitary/hypothalamus and to cerebellar involvement. For more information, see the Endocrine system section.

Diagnostic Evaluation

Positron emission tomography (PET) scans are the most sensitive modality for finding affected sites and are done to diagnose people with LCH.[1,44] MRI of the brain is indicated for patients with pituitary-associated symptoms and those with evidence of neurodegeneration. Spine MRIs are indicated for people with vertebral pain or lower motor neuropathy.

Treatment of Adult LCH

References

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Purpose of This Summary

This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about the treatment of childhood and adult Langerhans cell histiocytosis. It is intended as a resource to inform and assist clinicians in the care of their patients. It does not provide formal guidelines or recommendations for making health care decisions.

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Changes to the summaries are made through a consensus process in which Board members evaluate the strength of the evidence in the published articles and determine how the article should be included in the summary.

The lead reviewers for Langerhans Cell Histiocytosis Treatment are:

• Louis S. Constine, MD (James P. Wilmot Cancer Center at University of Rochester Medical Center)
• Thomas G. Gross, MD, PhD (National Cancer Institute)
• Michael Jeng, MD (Stanford Medicine Children's Health)
• Kenneth L. McClain, MD, PhD (Texas Children's Cancer Center and Hematology Service at Texas Children's Hospital)
• Carlos Rodriguez-Galindo, MD (St. Jude Children's Research Hospital)

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The preferred citation for this PDQ summary is:

PDQ® Pediatric Treatment Editorial Board. PDQ Langerhans Cell Histiocytosis Treatment. Bethesda, MD: National Cancer Institute. Updated <MM/DD/YYYY>. Available at: https://www.cancer.gov/types/langerhans/hp/langerhans-treatment-pdq. Accessed <MM/DD/YYYY>. [PMID: 26389240]

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