Potential genetic mechanisms driving B/myeloid conversion in patients with follicular lymphoma and Langerhans cell neoplasms.

Transformation of follicular lymphoma (FL) to a Langerhans cell (LC) neoplasm is extremely uncommon. The shared IGH::BCL2 rearrangement is a robust finding in most transformed tumors underscoring that the cell of origin is perhaps a pre-B cell harboring IGH::BCL2 with the propensity to undergo further genetic alterations in the germinal centers of lymph nodes: does IGH::BCL2 in pre-B cells set off a plasticity cell state? Do FL and LC neoplasms develop separately through a common progenitor or via a multistep process of transdifferentiation or dedifferentiation/redifferentiation? Here, we review the literature and relevant cases presented in the Society for Hematopathology/European Association of Haematopathology 2021 Workshop to better understand this rare and complex phenomenon. We discuss clinical data, clonal relationship, and the mutational profile of these tumors and review proposed mechanisms of B/myeloid conversion based on in vitro and in vivo models.

Malignant Histiocytosis Comprises a Phenotypic Spectrum That Parallels the Lineage Differentiation of Monocytes, Macrophages, Dendritic Cells, and Langerhans Cells.

Malignant histiocytoses (MHs), or the 'M group' of the Histiocyte Society classification, are characterized by neoplastic histiocytes with large pleomorphic nuclei. MH encompasses the diagnoses of histiocytic sarcoma, interdigitating dendritic cell sarcoma, and Langerhans cell sarcoma. We aimed to define the phenotypic spectrum of MH and examine the genotypic features across this spectrum. Using immunohistochemistry, we arranged the 22 cases into 4 subtypes that correspond to the lines of differentiation from monocytic and dendritic cell precursors as follows: (1) macrophage (n = 5): CD68+, CD163+, CD14+, and Factor 13a+; (2) monocyte-macrophage (n = 5): CD68+, CD163+, CD14+, S100+, and OCT2+; (3) dendritic cell (n = 6): CD68+, CD11c+, S100+, lysozyme+, ZBTB46+, and CD1a/langerin < 5%; and (4) Langerhans cell (n = 6): CD68+, CD11c+, S100+, ZBTB46+, CD1a+, and langerin+. The phenotypic subtypes align with those seen in low-grade histiocytic neoplasms as follows: MH-macrophage type correlates with Erdheim-Chester disease phenotype; MH-monocyte-macrophage type with Rosai-Dorfman disease phenotype, and MH-Langerhans cell type with Langerhans cell histiocytosis. Activating mutations in MAPK-pathway genes were identified in 80% of MH cases; 29% had mutations in the PI3k-AKT-mTOR pathway and 59% had mutations in epigenetic modulating genes. Strong expression of cyclin D1 was present in all cases, whereas p-ERK and p-AKT were not uniformly expressed. Eight of 22 (36%) MH cases were proven to be clonally related to a prior B-cell lymphoma. Defining the phenotypic spectrum of MH provides a guide to diagnosis and allows further exploration into the potential biological and clinical significance.

Primary Langerhans cell sarcoma in the urinary bladder: Case report and literature review.

Langerhans cell sarcoma (LCS) is a rare malignancy of dendritic cells and usually results in a poor oncological outcome. Thus, LCS is usually given a positive administration. Herein, we presented the first case of primary LCS in the urinary bladder staged T1N0M0 and treated by TURBT and short-term local chemotherapy. Our experience in this unique case may suggest that LCS in the urinary bladder with a non-muscle-invasive stage may be managed according to the treatment model of non-muscle-invasive urothelial carcinoma of the urinary bladder.

Langerhans cell sarcoma with BRAF-V600E mutation and hemophagocytosis: An autopsy report.

Langerhans cell sarcoma (LCS) is a rare high-grade neoplasm of langerhans cell phenotype having unambiguous malignant cytological features. We report such a rare case in a 20-year-old man who presented with dyspnea and high-grade fever. On evaluation, he had generalized lymphadenopathy, hepatosplenomegaly, and a large anterior mediastinal mass. Fine needle aspiration from the mediastinal mass and bone marrow aspirate showed numerous atypical cells, many of which showed grooved nuclei. In addition, the bone marrow showed prominent hemophagocytosis. The patient had a stormy hospital stay and succumbed to the illness. The autopsy revealed a rare multisystem involvement by LCS involving the lymph nodes, liver, spleen, lungs, and intestine, which harbored a BRAFV600E mutation and was associated with hemophagocytosis.

Case Report: Langerhans Cell Sarcoma With Intracranial and Extracranial Communication on the Left Frontal Bone.

Background: Langerhans cell sarcoma (LCS) is an extremely rare type of malignant tumor that originates from Langerhans cells (LC). It is characterized by the malignant proliferation and dissemination of LC and is extremely invasive, with rapid progression and a poor prognosis. Treatment includes resection of lesions, radiotherapy, chemotherapy, immunotherapy, and transplantation of hematopoietic stem cells. However, a unified and optimized treatment plan is lacking, and individualized treatment is accepted. Case presentation: We report an 18-year-old man with intracranial and extracranial communicative LCS that occurred in only the left forehead without metastasis to other regions. Clinical and hematological data were normal. We undertook complete resection of diseased tissue, which was pathologically examined. Staining (hematoxylin and eosin) showed positivity for cluster of differentiation (CD)1a (++), S-100 protein (++), P53 (++), CD68 (+), cyclin D1 (+), cyclin A (+), cyclin B1 (+), IGF2BP3 (+), and Ki-67 (45%-50%). Recurrence or metastasis were not observed after long-term follow-up. Conclusion: LCS is a rare malignant tumor, and one that occurs with intracranial and extracranial communication is even rarer. Active adoption of an individualized treatment plan is crucial.

A Patient with Sequential Diseases of Langerhans Cell Sarcoma, Langerhans Cell Histiocytosis, and Acute Lymphoblastic Leukemia / 罕见病研究

Langerhans cell histiocytosis(LCH)and Langerhans cell sarcoma(LCS)are characterized by clone proliferation of Langerhans-type cells, which may occur concurrently or sequentially with T-cell acute lymphoblastic leukemia (T-ALL) and other Lymphoid neoplasms. A 15-year old female patient diagnosed with T-ALL developed LCH involving multiple systems during maintenance chemotherapy of T-AL. After treated with chemotherapy with improved result, the patient showed progression of the illness and refractory to the second-line treatment. We found c.G35A (p.G12D)mutation in the KRAS gene and used the targeted drug Trametinib for treatment. The treatment proved effective, leading to partial remission within a week. Three months after Trametinib treatment, the patient developed new lymphadenopathy. Biopsy revealed the existence of LCS. The disease progressed quickly, and the patient died 7 days after diagnosis of LCS. The case of patients with T-ALL then developing LCH and LCS sequentially is extraordinarily rare. The causes of the case is unclear and may be related to cell transdifferentiation, clonal evolution, and chemotherapy. Targeted drugs can contain this disease for a short time.

The Expression of Insulin-Like Growth Factor 2 Messenger RNA-Binding Protein 3 in Langerhans Cell Histiocytosis and Langerhans Cell Sarcoma.

Langerhans cell neoplasms, which include Langerhans cell histiocytosis and Langerhans cell sarcoma, are tumors that originate from dendritic cells. Langerhans cell sarcoma is defined as a high-grade neoplasm with overtly malignant cytological features and the Langerhans cell-like phenotype, and generally has a poorer prognosis and more aggressive phenotype than Langerhans cell histiocytosis. Insulin-like growth factor 2 messenger RNA-binding protein 3 (IGF2BP3 or IMP3) is an oncofetal protein that is expressed in various cancer types; its expression is often associated with a poor prognosis and aggressive phenotype. Here, we used immunohistochemistry to evaluate IGF2BP3 expression in Langerhans cell neoplasms. IGF2BP3 expression was scored as negative (< 1%) or positive (≥ 1%) by immunohistochemistry. All 4 patients with Langerhans cell sarcoma (100%) and 6 of 22 pediatric (age < 18 years) patients with Langerhans cell histiocytosis (27.3%) had positive results for IGF2BP3; however, 16 of 22 pediatric patients with Langerhans cell histiocytosis (72.7%) and all 15 adult (age ≥ 18 years) patients with Langerhans cell histiocytosis (100%) had a negative result. Among patients with Langerhans cell histiocytosis, IGF2BP3 expression was independent of sex, location, prognosis, and BRAF V600E staining results. Taken together, these results indicate that IGF2BP3 expression may be a helpful marker for distinguishing Langerhans cell sarcoma from Langerhans cell histiocytosis in adult patients.

Adult-onset perianal Langerhans cell histiocytosis presenting as pruritus ani: a case report and review of the literature.

BACKGROUND: Langerhans cells belong to the histiocytic system and give rise to two tumors: Langerhans cell histiocytosis and Langerhans cell sarcoma. Clinical aggressiveness and degree of atypia distinguish the two neoplasms. Langerhans cell histiocytosis can infiltrate a single or multiple organ systems and particularly affects bone, skin, and lymph nodes. Perianal cutaneous Langerhans cell histiocytosis is a rare condition in adults, with 15 cases reported in the literature. CASE: We present the case of a 50-year-old hispanic man who presented with a 9-month history of pruritus ani and a personal history of diabetes insipidus. Punch biopsy confirmed a lesion of Langerhans cells origin but could not exclude Langerhans cell sarcoma because of limited sample size. An additional biopsy was planned as well as a positron emission tomography scan to determine the extent of disease spread. While the patient failed to follow up for repeat biopsy, the positron emission tomography scan was performed and was negative for metastatic disease. A stable perianal lesion of Langerhans cell histiocytosis with benign clinical features in a 50-year-old male despite lack of treatment is extremely rare and has not been described in the literature so far. Here, we review the presentation and workup of patients with Langerhans cell histiocytosis, review the relevant literature, and discuss treatment planning. CONCLUSION: Perianal Langerhans cell histiocytosis is rare, and there should be a high index of suspicion with chronic or new perianal lesions, especially in a patient with a history of diabetes insipidus. It is also important to consider the patient's full clinical course when it is not possible to reach a definitive pathological diagnosis before management.

From the archives of MD Anderson Cancer Center: A case of concurrent follicular lymphoma and Langerhans cell sarcoma with a review of the literature.

Transdifferentiation of follicular lymphoma to a Langerhans cell neoplasm is rarely reported and not well understood. Here we present a case, review the literature and discuss some of the biological underpinnings of lineage switch of B cells to histiocytes/Langerhans cells. A 31-year-old woman had follicular lymphoma (FL) and Langerhans cell sarcoma (LCS) co-localized above and below diaphragm. The FL was low-grade, had typical morphologic features, and was positive for CD10, BCL-2, and BCL-6. The LCS was cytologically atypical with necrosis and a high mitotic rate, and the immunophenotype supported Langerhans cell lineage positive for CD1a, CD207/langerin, and S-100 protein. Both tumors carried IGH-BCL2 and the LCS cells had immunophenotypic evidence of a residual B cell program, supporting the notion that these neoplasms are clonally related. The case reported is unusual because the patient was young and both diseases presented simultaneously, before any therapy. In addition, immunohistochemical analysis showed that the LCS was negative for BRAF V600E and phospho-ERK, suggesting that the LCS belongs to the known subset of Langerhans cell tumors lacking BRAF V600E and MAP2K1 mutations. Concurrent occurrence of FL and Langerhans cell neoplasm is an unusual phenomenon, with 10 cases reported previously: 4 Langerhans cell histiocytosis and 6 Langerhans cell sarcoma, including this case.

Spectrum of histiocytic neoplasms associated with diverse haematological malignancies bearing the same oncogenic mutation.

Histiocytic disorders are a spectrum of rare diseases characterised by the accumulation of macrophage-, dendritic cell-, or monocyte-differentiated cells in various tissues and organs. The discovery of recurrent genetic alterations in many of these histiocytoses has led to their recognition as clonal neoplastic diseases. Moreover, the identification of the same somatic mutation in histiocytic lesions and peripheral blood and/or bone marrow cells from histiocytosis patients has provided evidence for systemic histiocytic neoplasms to originate from haematopoietic stem/progenitor cells (HSPCs). Here, we investigated associations between histiocytic disorders and additional haematological malignancies bearing the same genetic alteration(s) using the nationwide Dutch Pathology Registry. By searching on pathologist-assigned diagnostic terms for the various histiocytic disorders, we identified 4602 patients with a putative histopathological diagnosis of a histiocytic disorder between 1971 and 2019. Histiocytosis-affected tissue samples of 187 patients had been analysed for genetic alterations as part of routine molecular diagnostics, including from nine patients with an additional haematological malignancy. Among these patients, we discovered three cases with different histiocytic neoplasms and additional haematological malignancies bearing identical oncogenic mutations, including one patient with concomitant KRAS p.A59E mutated histiocytic sarcoma and chronic myelomonocytic leukaemia (CMML), one patient with synchronous NRAS p.G12V mutated indeterminate cell histiocytosis and CMML, and one patient with subsequent NRAS p.Q61R mutated Erdheim-Chester disease and acute myeloid leukaemia. These cases support the existence of a common haematopoietic cell-of-origin in at least a proportion of patients with a histiocytic neoplasm and additional haematological malignancy. In addition, they suggest that driver mutations in particular genes (e.g. N/KRAS) may specifically predispose to the development of an additional clonally related haematological malignancy or secondary histiocytic neoplasm. Finally, the putative existence of derailed multipotent HSPCs in these patients emphasises the importance of adequate (bone marrow) staging, molecular analysis and long-term follow-up of all histiocytosis patients.

Epstein-Barr Virus-Positive Langerhans Cell Sarcoma: Is There a Link? A Case Report.

Langerhans cell sarcoma (LCS) is an extremely rare, malignant neoplasm that originates from Langerhans cells (LCs). Fewer than 70 cases have been reported in the English-language literature. LCS typically involves multiple organs, including the skin, lymph nodes, lungs, bone, bone marrow, liver, spleen, and soft tissues. Several etiological factors for LCS have been proposed, including immunosuppression, virus infection, and prior hematological disease. We report a rare case of LCS with Epstein-Barr virus (EBV) infection; bilateral cervical giant cysts were the initial manifestation. To our knowledge, this is the first report of LCS with EBV infection. The case information was complete, and the relevant literature was reviewed to gain insight into LCS. The case raises new questions on the oncogenic character of EBV.

Langerhans cell sarcoma involving skin and showing epidermotropism: A comprehensive review.

Langerhans cell sarcoma (LCS) is rare and aggressive; patients have an overall survival rate of less than 50%. We present a 62-year-old man with a history of superficial spreading melanoma of the upper back with sentinel lymph node metastasis, Langerhans cell histiocytosis, and LCS. The patient presented with erythematous papules and scaly areas on his face, neck, arms, chest, abdomen, and legs. A skin biopsy revealed a proliferation of large neoplastic cells involving the dermis and with epidermotropism. These cells had atypical bean-shaped nuclei, with ample cytoplasm and abundant mitotic figures including atypical forms. Immunohistochemical studies showed the tumor to be diffusely positive for CD1a, S100 protein, and langerin (CD207) and negative for melanocytic markers. Some tumor cells were positive for cyclin D1. A diagnosis of LCS involving the skin was established. The present study is a very unusual case of LCS showing epidermotropism. The patient's history of metastatic melanoma posed additional challenges for diagnosis, underlying the need of immunophenotyping in these cases. Consensus for optimal standard therapy has not been established in LCS, and thus, early recognition is important since these neoplasms tend to recur and metastasize. LCS in skin is discussed and published cases are comprehensively reviewed.

Adult Langerhans cell histiocytosis presenting with multisystem involvement and sarcomatoid features: a case report.

BACKGROUND: Langerhans cell tumors are rare clonal disorders characterized by neoplastic proliferation of dendritic cells that can be further classified into the subtypes Langerhans cell histiocytosis and Langerhans cell sarcoma, which are rare neoplasms exhibiting aggressive features and a poor prognosis. In addition to illustrating the refractoriness and poor outcomes of multisystem Langerhans cell histiocytosis in adults, specific events in this case highlight important characteristics of disease biology that warrant detailed discussion and exposition to a wider audience. CASE PRESENTATION: We describe the case of a 42-year-old Caucasian man with Langerhans cell histiocytosis diagnosed from a lesion on the left arm that presented with constitutional symptoms, early satiety, and weight loss. Esophagogastroduodenoscopy showed extensive esophageal and duodenal involvement by Langerhans cell histiocytosis with features of Langerhans cell sarcoma. He was initially treated for Langerhans cell histiocytosis with low doses of cytarabine until he eventually presented clear transformation to acute monoblastic leukemia with complex karyotype that could not be properly controlled, leading eventually to death. CONCLUSIONS: Langerhans cell histiocytosis remains an exceedingly rare entity in adults, frequently presenting as multisystem disease with risk organ involvement. Langerhans cell sarcoma represents an aggressive subtype with extremely poor prognosis for which intensive acute myeloid leukemia induction should be strongly considered.

Immunophenotyping of Nonneoplastic and Neoplastic Histiocytes in Cats and Characterization of a Novel Cell Line Derived From Feline Progressive Histiocytosis.

Histiocytic proliferative diseases are rare in cats, and their pathogenesis is poorly understood. In the present study, 25 cases of histiocytic sarcoma (HS) and 6 of feline progressive histiocytosis (FPH) were examined, and survival times were recorded in 19 cases. The immunophenotypes of tumor cells in these cases as well as of nonneoplastic feline histiocytes were characterized using formalin-fixed, paraffin-embedded tissues. An FPH cell line (AS-FPH01) and xenotransplant mouse model of FPH were also established. The median survival time of HS (150 days) was significantly shorter than that of FPH (470 days). Immunohistochemically, nonneoplastic histiocytes were immunopositive for various combinations of Iba-1, HLA-DR, E-cadherin, CD204, CD163, CD208, and MAC387. By immunohistochemistry, dermal interstitial dendritic cells (iDCs) and macrophages were CD204+/E-cadherin-, while epidermal Langerhans cells (LCs) were CD204-/E-cadherin+. Neoplastic cells of 4 FPH and 18 HS were CD204+/E-cadherin- (iDC/macrophage immunophenotype), while 2 FPH and 2 HS were CD204-/E-cadherin+ (LC immunophenotype), and 5 HS were CD204+/E-cadherin+ (LC-like cell immunophenotype). Furthermore, immunohistochemical and western blot analyses of AS-FPH01 cells derived from E-cadherin-negative FPH revealed that cultured cells were immunopositive for both CD204 and E-cadherin in vitro and in vivo. These results indicate that the neoplastic cells of feline HS and FPH were variably positive for iDC/macrophage and LC markers, and their immunophenotype changed in different microenvironments. The novel cell line established in the present study may serve as an experimental model of FPH that will enable further molecular and therapeutic studies on this disease.

Langerhans cell sarcoma of the vulva: Case report and review of the literature.

Langerhans cell sarcoma (LCS) is a rare, malignant neoplastic disorder of Langerhans cells thought to arise from antecedent Langerhans cell histiocytosis (LCH) or de novo. There are less than 70 cases of LCS reported in the medical literature, with this case being the first report of primary vulvar LCS. We present the case of a 73-year-old female with a painful 2 cm ulcerated lesion of the right labia majora. The patient was treated with oral antibiotics without resolution. On referral to gynecologic oncology an office biopsy showed LCS. Surgical excision was performed with clear margins and diagnostic confirmation of LCS by histopathological features and immunohistochemical evaluation. The patient received adjuvant radiation therapy (45.6 Gy). After 33 months of surveillance, the patient remains with no evidence of disease. Due to the rarity of this disease, there is a lack of standardized recommendations for adjuvant therapy, including radiotherapy and chemotherapy regimens for both localized and systemic LCS. This case report supports the management of localized disease by surgical excision followed by radiotherapy as effective for preventing recurrence and metastatic progression. Early recognition and treatment are critical for cure, and can be accomplished by prompt referral to a specialist as well as low threshold for biopsy. Further investigation is needed for establishing a standardized management guideline for LCS.

A case of Langerhans cell sarcoma on the scalp: Whole-exome sequencing reveals a role of ultraviolet in the pathogenesis.

Langerhans cell sarcoma (LCS) is a high-grade neoplasm with overtly malignant cytological features and a Langerhans cell phenotype. The underlying genetic features are poorly understood, and only a few alterations, such as those of the MARK pathway-related genes, CDKN2A and TP53 have been reported. Here we present a 70-year-old male with LCS on the scalp and pulmonary metastasis. The multinodular tumor, 3.0 cm in diameter, consisted of diffusely proliferated pleomorphic cells with numerous mitoses (53/10 HPFs). Immunohistochemically, the tumor cells were positive for CD1a, Langerin and PD-L1, and the Ki-67 labeling index was 50%. These pathological features were consistent with LCS, and were also observed in the metastatic tumor. Whole-exome sequencing revealed that both the primary and metastatic tumors harbored a large number of mutations (>20 mutations/megabase), with deletion of CDKN2A and TP53 mutation, and highlighted that the mutational signature was predominantly characteristic of ultraviolet (UV) exposure (W = 0.828). Our results suggest, for the first time, that DNA damage by UV could accumulate in Langerhans cells and play a role in the pathogenesis of LCS. The high mutational burden and PD-L1 expression in the tumor would provide a rationale for the use of immune checkpoint inhibitors for treatment of unresectable LCS.

Concurrent cutaneous localization of Langerhans cell sarcoma and chronic lymphocytic leukemia/small lymphocytic lymphoma in a patient with a history of chronic lymphocytic leukemia/small lymphocytic lymphoma.

The phenomenon of histiocytic/dendritic cell sarcomas arising through transformation of a pre-existed lymphoproliferative disease is called transdifferentiation. Langerhans cell sarcoma transdifferentiating from chronic lymphocytic leukemia/small lymphocytic lymphoma is extremely rare and all the reported cases were localized in lymph nodes. We present a case of concurrent cutaneous localization of Langerhans cell sarcoma and chronic lymphocytic leukemia/small lymphocytic lymphoma, in which the chronic lymphocytic leukemia/small lymphocytic lymphoma preceded the development of the Langerhans cell sarcoma. A cutaneous lesion from a 63-year-old patient with a history of chronic lymphocytic leukemia/small lymphocytic lymphoma was biopsied. The histologic examination revealed a mixture of two cell populations infiltrating diffusely the dermis. The first was composed of small lymphoid cells with somewhat monotonous appearance and mild nuclear atypia positive for PAX5, CD79a, CD20, CD23, CD5, and LEF1. The second was composed of large cells with abundant cytoplasm and pleomorphic nuclei. These cells were positive for CD1a, CD207, and S100 protein and exhibited a high mitotic rate and a high MIB-1 immunostaining index. Therefore, two different entities, chronic lymphocytic leukemia/small lymphocytic lymphoma and Langerhans cell sarcoma, were detected in the same skin fragment. The patient died 3 years after initial diagnosis of chronic lymphocytic leukemia/small lymphocytic lymphoma.

Combined Tumors in Hematolymphoid Neoplasms: Case Series of Histiocytic and Langerhans Cell Sarcomas Arising From Low-Grade B-Cell Lymphoma.

We report an index case of histiocytic sarcoma arising in a 70-year-old patient with long-standing chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). The patient presented in 2017 with painful, enlarging swelling of the left neck. He had remote history of cutaneous squamous cell carcinoma with no sign of recurrence, and his CLL/SLL was thought to be in remission. Computed tomography showed mild splenomegaly and multifocal lymphadenopathy including a 3-cm left neck mass. Biopsy of the left neck mass showed CLL/SLL with associated histiocytic sarcoma. Flow cytometry demonstrated a B cell neoplasm with CLL/SLL phenotype. Despite radiation therapy, he expired 3 months after presentation. Two similar cases (CLL/SLL and histiocytic sarcoma, follicular lymphoma and Langerhans cell sarcoma) from another institution are also illustrated. The pathological features of combined tumors in lymphoid neoplasms, a general framework to the work-up to determine interrelatedness of tumor components, and the clinical relevance are discussed.

[Durable remission of Langerhans cell sarcoma attained by autologous hematopoietic stem cell transplantation following surgical resection].

Langerhans cell sarcoma (LCS) is a rare neoplastic proliferation of Langerhans cells with a poor prognosis. Owing to its rarity, standard treatment for LCS has not been established to date. Here, we report a case of LCS occurring in multiple lymph nodes in the right cervix in which remission is maintained by autologous hematopoietic stem cell transplantation (auto-HSCT) after surgical resection. A 58-year-old male presented with enlarged right submandibular lymph nodes. Positron-emission tomography/computed tomography (PET/CT) revealed multiple lymphadenopathies in his right cervix. We performed a lymph node biopsy, and he was diagnosed with LCS. We selected the CHOP regimen as the first-line chemotherapy; however, rapid disease progression was observed soon after the first cycle of the therapy. The neck dissection was performed on day 16 of the CHOP therapy. As the residual tumor was suspected, we started the second-line chemotherapy with a combination of etoposide, cisplatin, ifosfamide, and gemcitabine; complete remission was confirmed by PET/CT. Subsequently, the patient was administered high-dose chemotherapy with auto-HSCT. After 2 years of auto-HSCT, complete remission has been maintained. Although there is no report of auto-HSCT for LCS, it could be an effective therapeutic tool for the disease.

Establishment of cell line and in vivo mouse model of canine Langerhans cell histiocytosis.

A cell line named FB-LCH01, derived from a dog diagnosed with Langerhans cell histiocytosis (LCH), was established and characterized. FB-LCH01 had C-shaped nucleoli, characterized by modal chromosome aberrations. The original tumour cells as well as established FB-LCH01 cells were immunopositive for human leukocyte antigen-DR, Iba-1 and E-cadherin, and immunonegative for CD163 and CD204, suggesting Langerhans cell origin. Furthermore, the characteristics of FB-LCH01 were compared with those of two canine histiocytic sarcoma cell lines (PWC-HS01 and FCR-HS02) established previously. Expression of E-cadherin was detected only in FB-LCH01, but not in PWC-HS01 and FCR-HS02. All (n = 9) the severe combined immunodeficiency mice inoculated with the FB-LCH01 cells developed subcutaneous tumour masses after 3 weeks. Eight of nine mice also developed metastatic lesions in the lymph nodes (8/8; 100%), lung (5/8; 62.5%), stomach (5/8; 62.5%), heart (4/8; 50%), pancreas (4/8; 50%), kidney (3/8; 37.5%), skin (3/8; 37.5%) and bone marrow (1/8; 12.5%). Tumour cells were pleomorphic and round- to polygonal-shaped with prominent anisocytosis and anisokaryosis. The xenotransplanted tumour cells maintained the immunohistochemical features of the original tumour with persistent E-cadherin expression at injection site and some visceral organs. In conclusion, the established cell line as well as the mice xenotransplant model in this study reflect the nature of canine LCH and may serve as promising models for investigating the patho-tumorigenesis and therapy of the disease.