Genotypic analysis of pulmonary Langerhans cell histiocytosis

Clinical-Radiologic-Pathologic Correlation of Smoking-Related Diffuse Parenchymal Lung Disease

The direct toxicity of cigarette smoke and the body's subsequent response to this lung injury leads to a wide array of pathologic manifestations and disease states that lead to both reversible and irreversible injury to the large airways, small airways, alveolar walls, and alveolar spaces. These include emphysema, bronchitis, bronchiolitis, acute eosinophilic pneumonia, pulmonary Langerhans cell histiocytosis, respiratory bronchiolitis, desquamative interstitial pneumonia, and pulmonary fibrosis. Although these various forms of injury have different pathologic and imaging manifestations, they are all part of the spectrum of smoking-related diffuse parenchymal lung disease.

Pulmonary langerhans cell histiocytosis: case series and literature review

Pulmonary Langerhans cell histiocytosis (PLCH) is a rare disease with insidious onset and nonspecific manifestations. The objective of this article was to characterize the clinical manifestations and features of PLCH by retrospectively analyzing clinical data of patients with PLCH in addition to simultaneous review of literature.A retrospective analysis was conducted on clinical data of patients with PLCH (n = 7), whose conditions were diagnosed by biopsy from pulmonary tissue (n = 6) or enlarged lymph nodes in the neck (n = 1) and confirmed by PLCH typical radiological features on computed tomography (CT) scan, between January 2001 and September 2012 at the Shanghai Pulmonary Hospital, Tongji University School of Medicine, Shanghai, China. The review of published reports was made to further emphasize the clinical manifestation and radiological features of PLCH.Long history of cigarette smoking was found in 6 patients. Two patients had recurrent pneumothorax and the other 2 had pulmonary arterial hypertension (World Health Organization group 5 pulmonary hypertension), diagnosed through ultrasonic cardiogram. The nodular shadows were revealed by chest CT scan in 5 patients, cystic shadows in 5 patients, and reticular shadows in 2 patients, as major manifestations, respectively; most of the lesions were located in the middle or upper segments of the lung. The obvious shrank of lesion was found in 1 patient after completely quitting smoking.The pathogenesis of PLCH might be closely associated with smoking. The cystic or nodular lesion was the typical radiological features. Further prospective studies with large sample size are required to further validate the study results and understand the clinical characteristics of PLCH to avoid misdiagnosis.

Pulmonary Langerhans cell histiocytosis: profiling of multifocal tumors using next-generation sequencing identifies concordant occurrence of BRAF V600E mutations

BACKGROUND

Pulmonary Langerhans cell histiocytosis is a localized proliferation of Langerhans cells in the lung that presents without systemic manifestations as bilateral nodular lung disease in adult cigarette smokers. The molecular basis for this proliferation is unknown.

METHODS

Twenty-two concurrent nodules in five patients were microdissected from formalin-fixed paraffin-embedded tissue and analyzed by next-generation sequencing for mutations in 46 cancer genes with the Ion AmpliSeq Cancer Panel on an Ion PGM (Personal Genome Machine) Sequencer (Life Technologies Corporation). Mutation confirmation was performed by conventional Sanger sequencing or by sensitive coamplification at lower denaturation polymerase chain reaction/fluorescence melting curve analysis.

RESULTS

Small amounts of DNA (10 ng) isolated from nodules were sufficient for successful interrogation of 740 mutational hot spots in 46 cancer genes by the Ion PGM Sequencer, with an average depth of coverage of 2,783 reads per hot spot and with uniformity of coverage of 92%. BRAF V600E mutation was detected in all concurrent nodules studied in two of the five patients, whereas in three of the five patients, no oncogene mutations were found.

CONCLUSIONS

Pulmonary Langerhans cell histiocytosis appears to be a clonal proliferation that may or may not have BRAF V600E mutations. For those with BRAF V600E mutations, new targeted therapies, such as vemurafenib, may be used in progressive cases.

Langerhans cell sarcoma with an aberrant cytoplasmic CD3 expression

Abstract

Langerhans cell sarcoma is a rare and aggressive high grade hematopoietic neoplasm with a dismal prognosis. It has a unique morphological and immunotypic profile with a CD1a/ langerin/S100 + phenotype. T cell lineage markers except for CD4 in Langerhans cell sarcoma have not been documented previously. We report a case of 86 year-old male of Caucasian descent who presented with an enlarging right neck mass over 2 months with an underlying unknown cause of anemia. Computed tomography scan of the neck, chest and abdomen revealed generalized lymphadenopathy and mild splenomegaly suspicious for lymphoma. Diagnostic core biopsy performed on right neck mass revealed a possible T cell lymphoma with expression of T cell lineage specific marker CD3 but conclusive diagnosis could not be made due to insufficient core biopsy sample. Further excisional biopsy performed on a left inguinal node showed a hematopoietic neoplasm with features of Langerhans cell sarcoma with a focal cytoplasmic CD3 expression in 30-40% of the tumor cells. PCR for T cell receptor (TCR) gene rearrangement failed to demonstrate a clonal gene rearrangement in the tumor cells arguing against a T cell lineage transdifferentiation, suggesting an aberrant CD3 expression. To the best of our knowledge, this case represents the first report of Langerhans cell sarcoma with an aberrant cytoplasmic CD3 expression.

Virtual slides

http://www.diagnosticpathology.diagnomx.eu/vs/2065486371761991

Use of the JL1 epitope, which encompasses the nonglycosylation site of CD43, as a marker of immature/neoplastic Langerhans cells

Langerhans cell histiocytosis (LCH) is the collective designation for a group of proliferative disorders of antigen-presenting cells in the epidermis. Over the past several decades, the etiology of LCH has been a controversial issue, particularly with respect to the pathologic process, that is, whether it is a neoplastic or inflammatory process. Recently, it was reported that the JL1 epitope, which encompasses the nonglycosylation site of CD43, is only exposed in the precursor stages of hematopoietic cells or in neoplastic conditions. We sought to investigate the possible utility of the JL1 monoclonal antibody as a diagnostic marker of LCH. In this study, we compared the staining characteristics of antibodies against the JL1 epitope with those of langerin and CD1a, which are widely used for the diagnosis of LCH. We found substantial differences in the staining patterns of these markers. The JL1 epitope could be bound by antibodies in cases of LCH and Langerhans cell (LC) sarcoma. In non-neoplastic lesions, JL1-positive LCs were found only in dermatitis, reflecting the immaturity of LCs in inflamed skin. However, anti-langerin antibodies were able to identify any form of LC, including those in normal skin, dermatitis, dermatopathic lymphadenopathy, and LCH. On the basis of these findings, we propose that the anti-JL1 antibody is a specific marker of immaturity, a feature that is shared in neoplastic LCs, and can be useful in the diagnosis of LCH.

Molecular cytogenetic characterization of canine histiocytic sarcoma: A spontaneous model for human histiocytic cancer identifies deletion of tumor suppressor genes and highlights influence of genetic background on tumor behavior

Background

Histiocytic malignancies in both humans and dogs are rare and poorly understood. While canine histiocytic sarcoma (HS) is uncommon in the general domestic dog population, there is a strikingly high incidence in a subset of breeds, suggesting heritable predisposition. Molecular cytogenetic profiling of canine HS in these breeds would serve to reveal recurrent DNA copy number aberrations (CNAs) that are breed and/or tumor associated, as well as defining those shared with human HS. This process would identify evolutionarily conserved cytogenetic changes to highlight regions of particular importance to HS biology.

Methods

Using genome wide array comparative genomic hybridization we assessed CNAs in 104 spontaneously occurring HS from two breeds of dog exhibiting a particularly elevated incidence of this tumor, the Bernese Mountain Dog and Flat-Coated Retriever. Recurrent CNAs were evaluated further by multicolor fluorescence in situ hybridization and loss of heterozygosity analyses. Statistical analyses were performed to identify CNAs associated with tumor location and breed.

Results

Almost all recurrent CNAs identified in this study were shared between the two breeds, suggesting that they are associated more with the cancer phenotype than with breed. A subset of recurrent genomic imbalances suggested involvement of known cancer associated genes in HS pathogenesis, including deletions of the tumor suppressor genes CDKN2A/B, RB1 and PTEN. A small number of aberrations were unique to each breed, implying that they may contribute to the major differences in tumor location evident in these two breeds. The most highly recurrent canine CNAs revealed in this study are evolutionarily conserved with those reported in human histiocytic proliferations, suggesting that human and dog HS share a conserved pathogenesis.

Conclusions

The breed associated clinical features and DNA copy number aberrations exhibited by canine HS offer a valuable model for the human counterpart, providing additional evidence towards elucidation of the pathophysiological and genetic mechanisms associated with histiocytic malignancies. Extrapolation of data derived from canine histiocytic disorders to human histiocytic proliferation may help to further our understanding of the propagation and cancerization of histiocytic cells, contributing to development of new and effective therapeutic modalities for both species.

Co-occurrence of Langerhans cell histiocytosis and Rosai-Dorfman disease: possible relationship of two histiocytic disorders in rare cases

Rosai-Dorfman disease and Langerhans cell histiocytosis are both disorders of accessory immune cells. Two cases have been previously reported of concurrent Langerhans cell histiocytosis and Rosai-Dorfman disease. In this report, we characterize the findings and selected molecular studies in nine additional cases. Histology was reviewed. Immunohistochemical stains were performed on all cases in which slides or blocks were available. A combination of CD1a, S-100, CD3, CD20, langerin, CD68, CD163, CD21, CD35 and CD123 immunohistochemical stains were performed. High-resolution array comparative genomic hybridization was performed on six samples from five cases. In these cases, seven were female and two male, with an average age of 25 years (15 months-59 years). A majority of the cases were identified in lymph node. Areas of Langerhans cell histiocytosis had a typical appearance with the existence of bland 'coffee-bean' nuclei, clear cytoplasm and associated eosinophils. The immunophenotype was typical, including expression of CD1a, S100, CD68 and langerin. In areas of Rosai-Dorfman disease, there was emperipolesis seen in all cases. Cells were intermediate-large in size with large round nuclei and ample clear or pale cytoplasm. The lesional cells were positive for S100, CD68, CD163, without expression of langerin or CD1a. Array comparative genomic hybridization showed gains and/or losses in four of the six samples. One case showed no gains or losses and one additional case showed gains and losses in the Langerhans cell histiocytosis, while no abnormalities were discovered in the Rosai-Dorfman disease component. These findings are comparable to those seen in previous studies of Langerhans cell histiocytosis. We report the clinical and pathologic findings of the combination of Langerhans cell histiocytosis and Rosai-Dorfman disease. Furthermore, we suggest on the basis of evidence from our cases that, when simultaneous, the two entities may be pathophysiologically related.

Clonal Status and Clinicopathological Features of Langerhans Cell Histiocytosis

Some studies have demonstrated that Langerhans cell histiocytosis (LCH) is a neoplastic hyperplasia of Langerhans cells, however some researchers consider that clonality should be assessed in more patients with LCH, both at disease presentation and during the disease course. Monoclonality is a major characteristic of most tumours, whereas normal tissue and reactive hyperplasia are polyclonal. To elucidate the nature of Langerhans cells further, the present study investigated the clinicopathological features and clonality of three cases of LCH in female patients using laser microdissection and a clonality assay, based on X-chromosomal inactivation mosaicism in somatic tissues and polymorphism of the androgen receptor gene. The results indicated that LCH was composed of Langerhans cells with a characteristic morphological appearance, eosinophils, giant cells, neutrophils and foamy cells. Immunohistochemically, the Langerhans cells were positive for CD1a, S-100 protein and vimentin. The clonality assay demonstrated that the Langerhans cells formed a monoclonal population, showing that LCH is neoplastic. We conclude that LCH is characterized by clonal proliferation, although additional studies with larger sample sizes are required to prove this conclusively.

Histiocytic disorders of the lung

Histiocytic proliferations involving the lung span a broad spectrum. Some proliferations are primary; others represent a histiocytic response secondary to conditions in which there may be isolated lung involvement or the lung may be involved as part of a systemic process. Primary histiocytic lung disorders, particularly those of uncertain histogenesis are a heterogeneous and intriguing group of disorders. Although they have been the focus of attention by clinicians and pathologists alike, much is unknown about their etiopathogenesis. Owing to this uncertainty, our understanding of these processes is in a state of flux, and is likely to change as more information is brought to light. This review will focus on pulmonary histiocytic proliferations of uncertain histogenesis. Other histiocytic lesions will be dealt with in brief.

Molecular Basis of Pulmonary Disease

Pulmonary pathology includes a large spectrum of both neoplastic and non-neoplastic diseases that affect the lung. Many of these are a result of the unusual relationship of the lung with the outside world. Every breath that a human takes brings the outside world into the body in the form of infectious agents, organic and inorganic particles, and noxious agents of all types. Although the lung has many defense mechanisms to protect itself from these insults, these are not infallible; therefore, lung pathology arises. Damage to the lung is particularly important given the role of the lung in the survival of the organism. Any impairment of lung function has widespread effects throughout the body, since all organs depend on the lungs for the oxygen they need. Pulmonary pathology catalogs the changes in the lung tissues and the mechanisms through which these occur. This chapter presents a review of lung pathology and the current state of knowledge about the pathogenesis of each disease. It suggests that a clear understanding of both morphology and mechanism is required for the development of new therapies and preventive measures.

Pulmonary Langerhans cell histiocytosis and other pulmonary histiocytic diseases: a review

CONTEXT

Pulmonary Langerhans cell histiocytosis is the most common and best known pulmonary histiocytic lesion; however, the realm of pulmonary histiocytic lesions also includes an assortment of uncommon diseases that may exhibit pulmonary involvement.

OBJECTIVE

To review pulmonary Langerhans cell histiocytosis and other pulmonary histiocytoses to better ensure correct diagnosis and optimal assessment of prognosis and treatment.

DATA SOURCES

Literature review and primary material from the author's institution.

CONCLUSIONS

This review discusses the most common pulmonary histiocytosis, pulmonary Langerhans cell histiocytosis, and also reviews the uncommon pulmonary histiocytic lesions, which are distinct from pulmonary Langerhans cell histiocytosis.

Expansion of regulatory T cells in patients with Langerhans cell histiocytosis

BACKGROUND

Langerhans cell histiocytosis (LCH) is a rare clonal granulomatous disease that affects mainly children. LCH can involve various tissues such as bone, skin, lung, bone marrow, lymph nodes, and the central nervous system, and is frequently responsible for functional sequelae. The pathophysiology of LCH is unclear, but the uncontrolled proliferation of Langerhans cells (LCs) is believed to be the primary event in the formation of granulomas. The present study was designed to further investigate the nature of proliferating cells and the immune mechanisms involved in the LCH granulomas.

METHODS AND FINDINGS

Biopsies (n = 24) and/or blood samples (n = 25) from 40 patients aged 0.25 to 13 y (mean 7.8 y), were studied to identify cells that proliferate in blood and granulomas. We found that the proliferating index of LCs was low ( approximately 1.9%), and we did not observe expansion of a monocyte or dendritic cell compartment in patients. We found that LCH lesions were a site of active inflammation, tissue remodeling, and neo-angiogenesis, and the majority of proliferating cells were endothelial cells, fibroblasts, and polyclonal T lymphocytes. Within granulomas, interleukin 10 was abundant, LCs expressed the TNF receptor family member RANK, and CD4(+) CD25(high) FoxP3(high) regulatory T cells (T-regs) represented 20% of T cells, and were found in close contact with LCs. FoxP3(+) T-regs were also expanded compared to controls, in the blood of LCH patients with active disease, among whom seven out of seven tested exhibited an impaired skin delayed-type hypersensitivity response. In contrast, the number of blood T-regs were normal after remission of LCH.

CONCLUSIONS

These findings indicate that LC accumulation in LCH results from survival rather than uncontrolled proliferation, and is associated with the expansion of T-regs. These data suggest that LCs may be involved in the expansion of T-regs in vivo, resulting in the failure of the host immune system to eliminate LCH cells. Thus T-regs could be a therapeutic target in LCH.

Immunohistochemical Analysis of Langerin in Langerhans Cell Histiocytosis and Pulmonary Inflammatory and Infectious Diseases

Pulmonary Langerhans cell histiocytosis (LCH) is an idiopathic condition affecting predominantly adult smokers. Histologically, LCH is characterized by a nodular, interstitial proliferation of Langerhans cells around the distal airways with associated eosinophils, lymphocytes, and macrophages. Associated findings, such as fibrosis, emphysematous change, and bronchiolitis can be reminiscent of other interstitial lung diseases. The markers CD1a and S100 have traditionally been used to distinguish LCH from other processes. Little is known about expression of the Langerhans cell-specific lectin, langerin, in pulmonary diseases. We examined the expression patterns of S100, CD1a, and langerin in LCH and other interstitial, inflammatory, and infectious processes in cases retrieved from the files at Brigham and Women's Hospital Department of Pathology. Immunoreactivity was scored according to the number of cells staining per high power field (400x) in areas of highest density, averaged over 4 fields. Cases diagnosed as LCH based on histomorphology and positive CD1a and S100 staining demonstrated strong langerin positivity in lesional tissue. All cases of LCH contained greater than 30 langerin and CD1a positive cells per high power field (HPF), with a mean of >100 cells per HPF, in lesional tissue. Of the other interstitial processes examined, only usual interstitial pneumonia demonstrated increased number of Langerhans cells within epithelium and interstitium (mean 14 cells per HPF) as compared with normal lung (mean 6 cells per HPF). Langerin and CD1a serve as specific diagnostic markers in distinguishing LCH from other interstitial and inflammatory processes.

Analysis of loss of heterozygosity in single-system and multisystem Langerhans' cell histiocytosis

The contribution of molecular mutations to the progression of Langerhans' cell histiocytosis (LCH) is not well understood. This study analyzes fractional allelic loss (FAL) across a series of tumor suppressor genes (TSGs) comparing LCH of various clinical stages and LCH involving organs of various degrees of prognostic risk. Polymerase chain reaction (PCR) amplification, using fluorescent-labeled primers targeting 6 TSGs, was performed on extracted DNA. The PCR products were analyzed using a capillary electrophoresis genetic analyzer. Ratios of the peak heights in informative cases were compared between unaffected and lesional tissue to identify loss of heterozygosity (LOH). Fisher's exact testing was used to analyze the results. Fourteen children with single-system involvement (SS-LCH) and 10 with multisystem involvement (MS-LCH) were included. High-risk or special-site organ involvement was seen in 13 children and low-risk organ involvement in 10. The mean FAL in MS-LCH (62.7%) was statistically significantly higher than in SS-LCH (40.3%). The FAL in children with risk or special-site LCH (53.2%) was also significantly higher than in children with low-risk LCH (39.6%). Markers on 5q had significantly higher FAL in MS-LCH (76.3%) and children with risk or special-site organ involvement (72.7%) compared with SS-LCH (46.2%) and children with low-risk organ involvement (37.5%). These data suggest that more extensive and higher-risk forms of LCH have evidence of more mutational events at TSGs. Further investigation of the potential use of LOH at 5q23 will be necessary to establish utility for this assay to predict disease progression and poor outcome.

Drug therapy for the treatment of Langerhans cell histiocytosis

Langerhans cell histiocytosis results from the abnormal accumulation of a class of dendritic cells normally found in the skin, which proliferate in many organ systems along with lymphocytes, macrophages and eosinophils. Standard therapy for Langerhans cell histiocytosis includes vinblastine and prednisone with or without methotrexate and mercaptopurine, depending on the extent of disease. Effective therapies for patients unresponsive to the above include cytosine arabinoside and cladribine. Thalidomide has proven useful for patients with Langerhans cell histiocytosis of the skin and/or bone. Emerging therapies include the use of monoclonal antibodies against the CD1a or CD52 epitopes found on Langerhans cells. Specific therapies directed against the cytokines that are apparently critical to the abnormal proliferation have not yet been defined.

Langerhans cell histiocytosis: current insights in a molecular age with emphasis on clinical oral and maxillofacial pathology practice

Langerhans cell histiocytosis (LCH) commonly involves the oral and maxillofacial region, and comes to the attention of dental practitioners when a patient presents with orofacial pain and a bony or soft tissue lesion. This is a relatively rare entity, which has made it difficult to investigate the clinical, biologic, and molecular aspects of the disease. Treatment protocols are not well defined, particularly in adults. During the past decade, the Histiocyte Society has formulated various LCH categories, based on risk stratification, and treatment protocols for the pediatric population. Adult trials are currently available through the Histiocyte Society. Although there has been considerable controversy, the neoplastic nature of LCH has been established by demonstrating clonality. LCH symptoms and the development and persistence of LCH lesions have been ascribed to a "chemokine/cytokine storm" due to autocrine and paracrine mechanisms. Discovery of biologic, cytogenetic, and molecular abnormalities in LCH have already affected treatment by providing novel therapeutic targets.

Biology of Langerhans cells and Langerhans cell histiocytosis

Langerhans cells (LC) are epidermal dendritic cells (DC). They play an important role in the initiation of immune responses through antigen uptake, processing, and presentation to T cells. Langerhans cell histiocytosis (LCH) is a rare disease in which accumulation of cells with LC characteristics (LCH cells) occur. LCH lesions are further characterized by the presence of other cell types, such as T cells, multinucleated giant cells (MGC), macrophages (MPhi), eosinophils, stromal cells, and natural killer cells (NK cells). Much has been learned about the pathophysiology of LCH by studying properties of these different cells and their interaction with each other through cytokines/chemokines. In this review we discuss the properties and interactions of the different cells involved in LCH pathophysiology with the hope of better understanding this enigmatic disorder.

The Nikolas Symposia and histiocytosis

Histiocytoses are a group of rare diseases that involve histiocytes (literally tissue cells (Greek), but in reality tissue-resident macrophages and dendritic cells), which are derived from bone-marrow stem cells. Histiocytoses pose problems similar to those of other rare diseases of childhood. Individual physicians see few cases, disease material is hard to collect and families suffer from lack of information and understanding. In this article, we describe how a series of 'think tank' meetings, the Nikolas Symposia, which have concentrated on Langerhans cell histiocytosis, have furthered our understanding of this enigmatic disease.

Pulmonary dendritic cells

Dendritic cells (DCs) are leukocytes that are emerging as chief orchestrators of immune responses. The crucial task of DCs is the continuous surveillance of antigen-exposed sites throughout the body, and their unique responsibility is to decide whether to present sampled antigen in an immunogenic or tolerogenic way. Any misstep can either lead to a flawed immune defense or to allergy, even autoimmunity. It comes as no surprise that the lungs become increasingly the subject of DC-related investigations, as they represent a vast interface between the body and the outer world. This constitutes an enormous challenge for the immune system: "firing up" immune responses inappropriately could have devastating results for the fragile gas exchange structures. Evidence accumulates that DCs play a pivotal role in maintaining the delicate balance between tolerance and active immune response in our respiratory system. The exponentially growing body of DC-related publications is a big challenge. This article aims to provide researchers and clinicians with an up-to-date view on DC biology and its relevance to pulmonary medicine. A developing trend in the field of DCs is the shift from fundamental immunologic research toward exciting clinical insights and applications. For the pulmonary clinician, this heralds the dawn of promising therapies in various domains such as infections, allergy, and cancer.

Atypical Cellular Disorders

Some immunologic diseases are characterized by profound loss or primary dysfunction of a given population of cells. The atypical cellular disorders discussed here all bear some similarities in that abnormal proliferations of lymphocytes and macrophages or dendritic cells result in lymphadenopathy, skin rashes, bone lesions and infiltrations of nearly any other organ system. What are the similarities and the differences between Langerhans cell histiocytosis (LCH), sinus histiocytosis with massive lymphadenopathy (SHML) or Rosai-Dorfman disease, and Castleman’s disease (CD)? Studies on LCH have some advantages since it was described before the others, and organized clinical trials have been done since the 1980s. The understanding of SHML benefited from a registry maintained by Drs. Rosai and Dorfman. CD was described fifty years ago and for one subtype has the most clearly defined etiology (HHV-8 infection) of the three atypical cellular disorders discussed here.

In Section I, Dr. Kenneth McClain examines the unanswered question of whether LCH is a malignant clonal disorder or an inflammatory response triggered by aberrant cytokine expression or a virus. Advocates of the malignant proliferation theory rest their case primarily on the following two points: Clonality of the CD1a+ Langerhans cells was demonstrated by analysis of the human androgen receptor in patients with single bone lesions (Low Risk) or multisystem disease including spleen, liver, bone marrow, or lung (High Risk). Although no consistent chromosomal abnormalities have been reported, loss of heterozygosity (LOH) has been defined by comparative genomic hybridization. Those in the “inflammatory response” camp note that non-clonal proliferation of Langerhans cells in adult pulmonary LCH also have LOH by the same method. The pathologic cells have not been successfully grown in culture or immune-deficient mice and don’t have a “malignant” morphology. While the basic scientific arguments continue, important advances in the treatment of LCH have been made by international collaborations of the Histiocyte Society. Risk groups have been clearly defined and the response to therapy after the initial 6 weeks is known to be the strongest prognostic variable for outcome.

In Section II, Dr. Yasodha Natkunam reviews the features of SHML, which most often presents as painless cervical lymphadenopathy, although many patients can have extranodal involvement as well. These sites include the skin, respiratory tract, bone, lung, gastrointestinal tract, and brain. The diagnosis rests on finding intact lymphocytes in the cytoplasm of activated macrophages as well as accumulation of mature plasma cells. Hemolytic or non-hemolytic anemias, hypergammaglobulinemia, and elevated erythrocyte sedimentatin rate (ESR) are often found with SHML. An intriguing finding of human herpesvirus (HHV)-6 viral proteins in SHML has been reported in several patients, but needs further study. SHML associated with lymphoproliferations triggered by defects in apoptosis are discussed since this mechanism may provide a clue to the etiology. Therapy for SHML varies greatly in reported case series. Many patients have spontaneous regression or resolution after surgical removal of isolated node groups. Others with systemic involvement may benefit from chemotherapy, but no clinical trials have been done.

In Section III, Dr. Steven Swerdlow clarifies key features of the four types of CD. Localized cases are divided into the hyaline vascular type and plasma cell type. Both are usually cured by surgical excision and have symptoms mainly of a mass lesion, although the latter often also has constitutional symptoms. The two types are distinguished largely by the nature of the follicles and the number of interfollicular plasma cells. Interleukin (IL)-6 expression is increased in the plasma cell type. Multicentric CD of the plasmablastic type is most often found in HIV-positive patients with coincident HHV-8 infection. Many have lymphomas or Kaposi sarcomas. Other cases of multicentric CD are also most like the plama cell type, however, with disseminated disease and constitutional symptoms. A wide variety of anti-neoplastic drugs, radiation therapy, anti-IL-6 and rituximab or atlizumab have been used with varying success in patients with multicentric CD. Clinical trials are needed for SHML and CD and registration of adult and pediatric patients on current LCH trials are encouraged.