Lesions resembling Langerhans cell histiocytosis in association with other lymphoproliferative disorders: a reactive or neoplastic phenomenon?

Thyroid Langerhans cell histiocytosis concurrent with papillary thyroid carcinoma: A case report and literature review

Langerhans cell histiocytosis (LCH) is a clonal neoplasm of myeloid dendritic cells, rarely involving the thyroid gland. Papillary thyroid carcinoma (PTC) is the most common histological subtype of thyroid cancer. We report a rare case of a 34-year-old Chinese woman who has LCH with PTC and cervical lymph node metastasis of LCH, with a review of the literature. The patient has thyroid nodules and cervical lymph node enlargement detected by neck ultrasound during physical examination. Fine needle aspiration cytology (FNAC) showed PTC with Hashimoto's thyroiditis and BRAF V600E mutation after thyroidectomy and lymph node dissection. Histopathological examination suggests that LCH was concurrent with classical PTC, accompanied by LCH cervical lymph node metastasis. No BRAF, HRAS, and TERT promoter mutations were detected in LCH metastatic lesions. The patient is in stable clinical condition currently.

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.

Cutaneous Pseudolymphoma With Langerhans Cell Hyperplasia-A Rare Case With Clinical Presentation Mimicking Malignancy and Potential Diagnostic Pitfall

ABSTRACT

We describe a rare case of cutaneous pseudolymphoma with Langerhans cell hyperplasia. An 84-year-old female patient presented with erythematous and pernicious-looking plaques on her scalp that had been present for months. Histologically, lymphoid follicles consisting of mixed-type lymphocytes and Langerhans cells were aggregated focally. The diagnosis was verified by several immunohistochemical stains and by clinical evaluation. Skin lesions were steadily resolved with low-dose corticosteroid and hydroxychloroquine.

Co-existence of BRAF V600E-mutated malignant melanoma and BRAF V600E-mutated Langerhans cell histiocytosis: A case report

Langerhans cell histiocytosis (LCH) is a neoplastic condition of Langerhans cells, and can be associated with other neoplasms, especially BRAF-mutant hematological tumors and papillary thyroid carcinoma. Here we present the first case of co-existing LCH and low cumulative sun damage (low-CSD) melanoma, both of which had a BRAF V600E mutation. A 49-year-old man had a 45 × 43 × 15 mm semi-pedunculated, pigmented tumor in his back but had no other systemic symptoms. Histopathology revealed a 2-mm-sized incidental focus of LCH within a large lesion of low-CSD melanoma. Diffuse immunoexpression of CD1a, langerin/CD207, S100 protein, and BRAF (VE1) was observed in the focus of LCH. Sanger sequencing with microdissection confirmed BRAF V600E mutation in the component of LCH. Interestingly, the advanced melanoma also harbored the same BRAF V600E mutation, although the significance of this tumor combination is still unknown.

Reactive Langerhans Cell Proliferation Mimicking Langerhans Cell Histiocytosis in Association with Sézary Syndrome: A Case Report and Literature Review

Sézary syndrome (SS) is a rare type of cutaneous T-cell lymphoma (CTCL) that is characterized by erythroderma, lymphadenopathy and circulating clonal T-cells (Sézary cells). However, to our knowledge, reactive Langerhans cell (LC) proliferation mimicking Langerhans cell histiocytosis (LCH) associated with SS has not been reported. In this report, we describe an unusual case of reactive LC proliferation mimicking LCH associated with SS in a 57-year-old female patient. With complaints of recurrent skin symptoms and enlarged lymph nodes (LNs), she was admitted to our center with a presumptive diagnosis of LCH as demonstrated by LN biopsy pathology. However, other than adenopathy, no lesions were noted in any organ system commonly involved in LCH. Typical Sézary cells were identified through morphology and further confirmed by flow cytometric immunophenotyping in peripheral blood (PB) and bone marrow (BM). In addition, T-cell receptor gene rearrangement was positive, whereas the BRAF V600E gene mutation was negative in skin, LN, PB and BM. The patient was ultimately diagnosed with SS with reactive LC proliferation. This case should remind clinicians to be wary of diagnosing LCH if LCH-like pathology occurs exclusively in LNs. Moreover, morphologic, immunologic, cytogenetic and molecular biologic studies should be performed to avoid misdiagnosis.

[Langerhans cell histiocytosis revealed by a temporomandibular joint disorder: Report of a case and review of the craniofacial expressions]

INTRODUCTION

Langerhans cell histiocytosis (HL) is a rare disease that can affect all tissues. Oral manifestations such as mucosal ulcer and tooth mobility are often the first signs of the disease. We report a rare case of mandibular condyle unifocal HL mimicking a temporomandibular joint disorder.

CASE REPORT

A 44-year-old patient presented with a left temporomandibular disorder with painful left preauricular swelling. The imaging assessment found a bone lesion of the left mandibular condyle. A curettage with biopsy was used to diagnose HL. Six months later, the patient had no more pain.

DISCUSSION

The craniofacial clinical expressions of HL mainly concern the bones, which can cause: pain, swelling, fracture, compression of noble organs. The other sites are: oral cavity, skin, lymph nodes, or eyes. Isolated forms are generally benign, and their treatment is discussed between abstention and non-aggressive surgery.

[Multisystem histiocytosis of Langerhans cells associated with Lymphomatoid papulosis: An accidental finding? Case report and literature review]

Langerhans cell histiocytosis (LCH) is a disease characterized by proliferation of CD1a+dendritic cells with local or diffuse organ compromise. The identification of recurrent gene mutations has confirmed the hypothesis of LCH as a true neoplasm. Lymphomatoid papulosis (LyP) belongs to the spectrum of CD30+primary cutaneous lymphomas. LCH has been described in association with other lymphoproliferative disorders. However, lesions constituted by Langerhans cells (LC) have been commonly considered reactive, related to cytokines produced by the lymphoma-microenvironment interaction. Some authors designate these lesions as "Langerhans cells-like lesions". We present the case of a 28-years-old woman with multisystem LCH and simultaneous PyL lesions with reactive LC hyperplasia.

Langerhans Cell Histiocytosis Associated With Underlying Hematolymphoid Disorders in Adults: Report of 2 Cases and Review of the Literature

Langerhans cell histiocytosis (LCH) is an uncommon disorder characterized by proliferation of abnormal LCs usually affecting children and adolescents. LCH in adults first presenting in the skin is rare. Although LCH and even LCH with a second malignancy may be more common in children, cutaneous LCH with a second hematologic malignancy has been more commonly identified in adults. The authors report 2 new cases of LCH in adult patients with underlying myelodysplasia and follicular lymphoma. The specimens were examined by routine microscopy and immunohistochemical stains for S100 protein and CD1a. Patients were elderly men with established diagnoses of follicular lymphoma and myelodysplasia, presented with follicular lesions and erythematous plaques involving intertriginous areas. Histologic examination revealed collections of mononuclear cells in upper dermis, which demonstrated strong positivity for S100 and CD1a, confirming their identity as LCs. BRAF analysis returned negative for detection of BRAF V600E mutation in both patients. The authors have recently encountered 2 cases of adult patients with skin-limited LCH predated by other lymphoproliferative disorders. The association between LCH and hematopoietic disorders may be explained by a common bone marrow precursor that is differentiating along different cell lines. Cutaneous LCH may be associated with underlying lymphoproliferative disorders and should be considered in the differential diagnosis of cutaneous eruptions in patients with hematopoietic disorders. Clinical follow-up evaluation of patients diagnosed with LCH for peripheral blood abnormalities and lymphadenopathy or "B symptoms" may be prudent in patients not already carrying a diagnosis of an underlying hematologic disorder.

Histiocytic cell neoplasms involving the bone marrow: summary of the workshop cases submitted to the 18th Meeting of the European Association for Haematopathology (EAHP) organized by the European Bone Marrow Working Group, Basel 2016

The bone marrow is a preferential site for both reactive and neoplastic histiocytic proliferations. The differential diagnosis ranges from reactive histiocyte hyperplasia in systemic infections, vaccinations, storage diseases, post myeloablative therapy, due to increased cell turnover, and in hemophagocytic lymphohistiocytosis, through extranodal Rosai-Dorfman disease to neoplasms derived from histiocytes, including histiocytic sarcomas (HS), Langerhans cell histiocytoses (LCH), Erdheim-Chester disease (ECD), and disseminated juvenile xanthogranuloma (JXG). One of the most important recent developments in understanding the biology of histiocytic neoplasms and in contributing to diagnosis was the detection of recurrent mutations of genes of the Ras/Raf/MEK/ERK signaling pathway, in particular the BRAF^V600E mutation, in LCH and ECD. Here, we summarize clinical and pathological findings of 17 histiocytic neoplasms that were presented during the bone marrow symposium and workshop of the 18th European Association for Haematopathology (EAHP) meeting held in Basel, Switzerland, in 2016. A substantial proportion of these histiocytic neoplasms was combined with clonally related lymphoid (n = 2) or myeloid diseases (n = 5, all ECD). Based on the latter observation, we suggest excluding co-existent myeloid neoplasms at initial staging of elderly ECD patients. The recurrent nature of Ras/Raf/MEK/ERK signaling pathway mutations in histiocytic neoplasms was confirmed in 6 of the 17 workshop cases, illustrating their diagnostic significance and suggesting apotential target for tailored treatments.

Non-neoplastic histiocytic and dendritic cell disorders in lymph nodes

Benign and malignant proliferations of histiocytes and dendritic cells may be encountered in lymph nodes. Reactive histiocytic and dendritic cell infiltrates occur in response to diverse stimuli and in addition to causing lymphadenopathy, may be present unexpectedly in lymph nodes excised for other indications. This review summarizes the pathogenesis and histopathological features of the various non-neoplastic histiocytic and dendritic cell infiltrates that can occur in lymph nodes.

Histiocytic and dendritic cell neoplasms: what have we learnt by studying 67 cases

Tumors derived from histiocytic and dendritic cells encompass a large and heterogeneous group of neoplastic and reactive conditions, and their diagnosis is challenging both for pathologists and clinicians. Diagnosis is based on morphological and phenotypical findings, but hybrid features are not uncommon. Furthermore, recent studies uncovered the molecular mechanisms driving some of these tumors, improving diagnostic adequacy, and providing the basis for effective therapeutic breakthroughs.Sixty-seven cases were submitted to the accessory cell and histiocytic neoplasms session at the European Association of Haematopathology/Society for Hematopathology workshop 2016 held in Basel, Switzerland. The cases included histiocytic sarcomas (HS), Langerhans cell tumors (LCT), Erdheim-Chester disease, interdigitating dendritic cell sarcomas (IDCS), indeterminate dendritic cell tumors (IND-DCT), follicular dendritic cell sarcomas, and blastic plasmacytoid dendritic cell neoplasms. Rosai-Dorfman disease and, more rare, conditions such as ALK-positive histiocytosis were also submitted. These cases illustrated classical and unexpected features at morphological, phenotypical, and molecular levels, providing a valuable compendium for pathologists confronting with these tumors.The paper summarizes the most notable features of every single group of diseases, with comments about the most challenging issues, in the attempt to provide practical indications for their recognition.

Langerhans cell histiocytosis associated with lymphoma: an incidental finding that is not associated with BRAF or MAP2K1 mutations

Langerhans cell histiocytosis is characterized by a localized or systemic proliferation of Langerhans cells. BRAF mutations have been reported in 40-70% of cases and MAP2K1 mutations have been found in BRAF-negative cases, supporting that Langerhans cell histiocytosis is a true neoplasm, at least in mutated cases. In a small subset of patients, Langerhans cell histiocytosis is detected incidentally in a biopsy involved by lymphoma. These lesions are usually minute and rarely have been assessed for mutations. We assessed for BRAF and MAP2K1 mutations in seven cases of Langerhans cell histiocytosis detected incidentally in biopsies involved by lymphoma. We performed immunohistochemical analysis for phosphorylated (p)-ERK. There were four men and three women (median age, 54 years; range, 28-84). The biopsies included lymph nodes (n=6) and chest wall (n=1). The lymphomas included five classical Hodgkin lymphoma, one mantle cell lymphoma, and one angioimmunoblastic T-cell lymphoma. All cases were negative for BRAF V600E and MAP2K1 mutations. Nevertheless, three of seven cases showed ERK activation as shown by expression of p-ERK. We performed mutation analysis using a panel of 134 commonly mutated genes (including BRAF and MAP2K1) by next-generation sequencing on three cases, including two cases positive for p-ERK by immunohistochemistry. No mutations were detected in any of the three cases assessed. Six patients received therapy appropriate for their lymphoma. With a median follow-up of 21 months (range, 6-89), no patients developed disseminated or recurrent Langerhans cell histiocytosis. We conclude that lymphoma-associated Langerhans cell histiocytosis is a clinically benign process that is not associated with BRAF V600E or MAP2K1 mutations and, as suggested by others, the designation Langerhans cell hyperplasia may be more appropriate. Nevertheless, the expression of p-ERK in three cases suggests that the RAS-RAF-MAP2K-ERK pathway is activated, perhaps by non-mutational mechanisms induced by the presence of lymphoma or lymphoma-microenvironment interactions.

Langerhans cell histiocytosis: a comprehensive review

Langerhans cell histiocytosis (LCH) is currently regarded as a myeloid neoplasm, with remarkably broad clinical spectrum, ranging from isolated skin or bone lesions to a disseminated disease that can involve nearly any organ. LCH is generally regarded as a sporadic disease that occurs predominantly in the paediatric population. The diagnosis of LCH is confirmed by immunohistochemistry (IHC) by demonstrating the presence of dendritic cell markers such as S100 protein, in addition to CD1a and langerin. Contrary to previous beliefs, recent literature reveals that the pathogenesis of LCH might involve a clonal process implicating BRAF c.1799T>A (p.Val600Glu) and other mutations [(600DLAT) B-RAF and (T599A) B-RAF, somatic MAP2K1 mutations].Through this review article, we have summarised the latest understanding of the biological and salient histological characteristics of LCH and its potential morphological mimics.

Concomitant nodal involvement by Langerhans cell histiocytosis and Hodgkin's lymphoma

A 10-year-old girl with a family history of Hodgkin's lymphoma presented with a 2 month history of cervical lymphadenopathy and weight loss. Biopsy indicated concomitant nodal involvement by Langerhans cell histiocytosis and Hodgkin's lymphoma. Such an association is rare, especially so in children, but is not an isolated phenomenon, thereby prompting the question of whether Langerhans cell histiocytosis is a reactive or a neoplastic process.

A case of Langerhans' cell histiocytosis associated with Hodgkin's lymphoma: Fine-needle aspiration cytologic and histopathological features

Langerhans cell histiocytosis (LCH) can be associated with a variety of malignant neoplasms, the most common being malignant lymphoma, especially Hodgkin's lymphoma (HL). In this report, we describe the fine needle aspiration (FNA) cytologic features of a case with concurrent LCH and HL in a lymph node. A 20-year-old man presented with an enlarged left upper cervical lymph node. FNA smears from the swelling revealed numerous CD1a+ and S-100+ Langerhans-type cells (LCs) along with many eosinophils, neutrophils, and lymphocytes; there were also large atypical cells with enlarged nuclei having prominent nucleoli. The cytodiagnosis was LCH and the possibility of association with or trans-differentiation into a lymphoma was suggested. The histopathological diagnosis of the excised left cervical lymph node was classical HL-nodular sclerosis type (CHL-NS) with LCH. The lacunar type Reed-Sternberg (RS) cells were positive for CD30 and CD15, and the LCs were positive for CD1a and S-100 protein. PET/CT imaging demonstrated hypermetabolic lymph nodes in neck, abdomen, thorax and pelvis as well as pulmonary nodules and a splenic mass. The patient received 13 courses of chemotherapy and two years later, the enhanced CT revealed regressive course of the disease.

Langerhans cell sarcoma following marginal zone lymphoma: expanding the knowledge on mature B cell plasticity

The concept of unidirectional differentiation of the haematopoietic stem cell has been challenged after recent findings that human B cell progenitors and even mature B cells can be reprogrammed into histiocytic/dendritic cells by altering expression of lineage-associated transcription factors. The conversion of mature B cell lymphomas to Langerhans cell neoplasms is not well documented. Three previous reports have described clonally related follicular lymphoma and Langerhans cell tumours, whereas no case has been published of clonally related marginal zone lymphoma and Langerhans cell sarcoma. We describe the case of a 77-year-old patient who developed a Langerhans cell sarcoma and 6 years later a nodal marginal zone lymphoma. Mutation status examination showed 100 % gene identity to the germline sequence, suggesting direct trans-differentiation or dedifferentiation of the nodal marginal zone lymphoma to the Langerhans cell sarcoma rather than a common progenitor. We found inactivation of paired box 5 (PAX-5) in the lymphoma cells by methylation, along with duplication of part of the long arm of chromosomes 16 and 17 in the sarcoma cells. The absence of PAX-5 could have triggered B cells to differentiate into macrophages and dendritic cells. On the other hand, chromosomal imbalances might have activated genes involved in myeloid lineage maturation, transcription activation and oncogenesis. We hypothesize that this occurred because of previous therapies for nodal marginal zone lymphoma. Better understanding of this phenomenon may help in unravelling the molecular interplay between transcription factors during haematopoietic lineage commitment and may expand the spectrum of clonally related mature B cell neoplasms and Langerhans cell tumours.

Evidence of BRAF V600E in indeterminate cell tumor and interdigitating dendritic cell sarcoma

BRAF V600E mutations have been reported in several histiocytic and dendritic cell neoplasms. In this case series, we report BRAF V600E-positive histiocytic and dendritic cell neoplasms in association with lymphomas and lymphoid proliferations. This is a review of cases with immunohistochemistry for BRAF V600E, with additional immunohistochemistry to categorize tumors. We report the first case of BRAF V600E-positive indeterminate cell tumor in association with angioimmunoblastic T-cell lymphoma. We also report a case of BRAF V600E-positive interdigitating dendritic cell sarcoma in a patient with positive B-cell polymerase chain reaction. It is unclear if these neoplasms developed as transdifferentiation of lymphoid neoplasms or if they developed independently. These cases illustrate the expanding spectrum of BRAF V600E-positive histiocytic and dendritic cell tumors and suggest that attention should be paid to lymphomas for possible coincident presentation of these disorders.

Histologic patterns of thymic involvement in Langerhans cell proliferations: a clinicopathologic study and review of the literature

Thymic involvement by Langerhans cell histiocytosis (LCH) has been described mainly in isolated case reports. A description of the histopathologic patterns of LCH proliferations in the thymus, together with therapeutic implications, has not, to our knowledge, been previously addressed. The pathology consultation files at Children's Hospital of Pittsburgh of the University of Pennsylvania Medical Center were reviewed for cases of thymic involvement by LCH. Relevant cases in the literature were also reviewed, and the histopathology and clinical course of those cases were collected. Nine consultation cases of thymic involvement were reviewed, together with 23 cases in the literature, which provided adequate pathologic description and ancillary confirmation (n  =  32), revealing 4 distinct pathologic groups. Group 1 showed microscopic collection of hyperplastic LCH-like cells in incidental thymectomies of patients without LCH disease, requiring no further treatment (n  =  7; 22%). Group 2 showed solitary and/or cystic LCH of the thymus with gland disruption, and at least 3 cases resolved without systemic therapy (n  =  10; 31%). Group 3 showed more variable thymic involvement in multisystemic LCH disease, with either a medullary restricted pattern or more diffuse gland involvement, requiring adjuvant therapy and having a higher mortality rate (n  =  13; 41%). Group 4 showed a mixed histiocytic lesion with a concurrent LCH and juvenile xanthogranuloma-like proliferation (n  =  2; 6%). Thymic involvement in LCH is quite rare. Based on our cases and those in the literature, we propose 4 distinct pathologic groups of thymic involvement in Langerhans cell proliferations with relevance for diagnosis and treatment.

Polyclonal T-cells express CD1a in Langerhans cell histiocytosis (LCH) lesions

Langerhans cell histiocytosis (LCH) is a complex and poorly understood disorder that has characteristics of both inflammatory and neoplastic disease. By using eight-colour flow cytometry, we have identified a previously unreported population of CD1a(+)/CD3(+) T-cells in LCH lesions. The expression of CD1a is regarded as a hallmark of this disease; however, it has always been presumed that it was only expressed by pathogenic Langerhans cells (LCs). We have now detected CD1a expression by a range of T-cell subsets within all of the LCH lesions that were examined, establishing that CD1a expression in these lesions is no longer restricted to pathogenic LCs. The presence of CD1a(+) T-cells in all of the LCH lesions that we have studied to date warrants further investigation into their biological function to determine whether these cells are important in the pathogenesis of LCH.

A colonization of a different kind

An unusual morphological pattern in the lymph node can at times, pose a diagnostic problem. We report a case of a 55 year old male whose cervical lymph node biopsy showed an unusual pattern of follicular colonization by T-lymphoblasts. The interfollicular area showed a diffuse infiltrate of Langerhans cells. A diagnosis of a T lymphoblastic lymphoma coexisting with Langerhans cell histiocytosis like lesion was made, keeping in mind lack of clinical evidence for the latter.

Langerhans cell histiocytosis in acute leukemias of ambiguous or myeloid lineage in adult patients: support for a possible clonal relationship

Four patients presented with acute leukemia of ambiguous or myeloid lineage in association with Langerhans cell histiocytosis and provide evidence suggesting a common origin of the two neoplasms. One patient had a non-constitutional trisomy 21 in both the leukemic blasts and the Langerhans cells indicative of a clonal relationship. A second case expressed CD2, CD13, and CD117 on both the Langerhans cells and the blasts suggesting a possible clonal relationship. All four cases exhibited geographic intermingling of the Langerhans cell histiocytosis and acute leukemia and shared unique features including extramedullary leukemia involving lymph nodes in all cases with Langerhans cell histiocytosis only present in sites involved by acute leukemia. T-cell antigen expression was present in all cases with one meeting criteria for mixed phenotype acute leukemia, T/myeloid, not otherwise specified. These findings support the concept that coexistent Langerhans cell histiocytosis and acute leukemia is clonally related in some cases. Furthermore, these cases of acute myeloid or acute leukemia of ambiguous lineage with Langerhans cell histiocytosis share some unique features suggesting a common underlying neoplastic hematopoietic stem cell.

Clonal Relationships Between Malignant Lymphomas and Histiocytic/Dendritic Cell Tumors

Tumors of histiocytic or dendritic cell origin appear to occur with increased frequency in patients with lymphoma. Recent molecular data have demonstrated clonal relationships between the lymphoma and the histiocytic/dendritic cell tumor in some of these cases. Clinical, pathologic, and experimental data suggest that this phenomenon probably represents transdifferentiation of the lymphoma clone to a histiocytic/dendritic cell lineage in most cases. Awareness of this entity is necessary to prompt comparative molecular studies in appropriate cases.

Fibrohistiocytic tumors and related neoplasms in children and adolescents

Fibrohistiocytic tumors (FHTs) in children and adolescents range from the benign fibrous histiocytoma, or dermatofibroma, to a variety of intermediate and malignant neoplasms, such as dermatofibrosarcoma protruberans and high-grade undifferentiated pleomorphic sarcoma (malignant fibrous histiocytoma). Those tumors as a group are comprised of fibroblasts, myofibroblasts, and histiocytes-dendritic cells with a variably prominent inflammatory infiltrate consisting of lymphocytes and eosinophils. Dendritic cells are also a major constituent of another group of neoplasms that include Langerhans cell histiocytosis, follicular and interdigitating cell sarcomas, and juvenile xanthogranuloma. These latter tumors are considered in this discussion for the sake of differential diagnosis and their possible histogenetic relationship to FHTs. Recent studies have suggested that the relationship between the fibroblast and histiocyte in the FHTs may reflect the intrinsic capacity to transdifferentiate from one to the other morphologic and functional state. The so-called "facultative fibroblast," as a cell with fibroblastic and histiocytic properties, was discussed in the context of the fibrous xanthoma 50 years ago. Possibly the entire histogenetic concept of FHTs should be reconsidered in light of current studies.

A case of coexisting Warthin tumor and langerhans cell histiocytosis associated with necrosis, eosinophilic abscesses and a granulomatous reaction in intraparotid lymph nodes

We present a patient (50-year-old male) with coexisting Warthin tumor and involvement of two intraparotid lymph nodes by Langerhans cell histiocytosis associated with necrosis, eosinophilic abscesses and a granulomatous reaction. This is the second documented case of this unusual combination of histological changes in nodal Langerhans cell histiocytosis and the first case involving intraparotid lymph nodes occurring together with an ipsilateral Warthin tumor.

Intestinal Langerhans cell histiocytosis-like lesion in an adult presented with diverticulitis: a reactive or neoplastic condition?

The involvement of the gut by Langerhans cell histiocytosis (LCH) is very rare in adults; however this is usually observed with a disseminated disease in children. We report a 75-year-old male patient who underwent right hemicolectomy for a complicated intestinal diverticular disease. The surgical specimen revealed LCH-like proliferative lesion associated with diverticulitis. The overall morphological and immunohistochemical findings are indistinguishable from LCH. Systemic scans and subsequently performed bone marrow biopsies were free of disease. Although the HUMARA clonality assay cannot be assessed, the lack of evidence of LCH progression or disease elsewhere in the whole body strongly supported the possibility of an atypical reactive phenomenon probably due to the underlying intestinal diverticular disease. Therefore, it is important to avoid diagnosing such a unifocal Langerhans cell proliferation as LCH in patients with underlying pathologies in the absence of systemic involvement. Therefore, without knowledge of clonal status of a unifocal Langerhans cell proliferation, we recommend using the terminology of LCH-like lesion.