High frequency of clonal IG and T-cell receptor gene rearrangements in histiocytic and dendritic cell neoplasms

EBV-positive inflammatory follicular dendritic cell sarcoma of the colon with clonal immunoglobulin gene rearrangement: A case report and literature review

Introduction

Epstein-Barr virus-positive (EBV+) inflammatory follicular dendritic cell (FDC) sarcoma is a rare neoplasm characterized by spindle-shaped follicular dendritic cells, marked lymphoplasmacytic infiltration, and a consistent link to EBV. While it typically affects the liver and spleen, it is exceptionally rare in the digestive tract. We present a special case of EBV + inflammatory FDC sarcoma arising in the colon with clonal immunoglobulin (IG) gene rearrangement.

Case presentation

A 70-year-old man presented with a one-month history of abdominal distension. Colonoscopy revealed a pedunculated polyp in the ascending colon, which was subsequently removed via endoscopic polypectomy. Histological examination of the colonic polyp demonstrated a pronounced lymphoplasmacytic infiltrate with scattered EBV + neoplastic cells, as evidenced by EBV-encoded small RNA in situ hybridization (EBER ISH). The neoplastic cells were positive for FDC-specific markers, including CD21, CD35, and CD23. Additionally, the tumor exhibited clonal rearrangement of the immunoglobulin heavy chain (IGH) gene. The diagnosis was confirmed as EBV + inflammatory follicular dendritic cell sarcoma.

Conclusions

We described an exceptional case of EBV + inflammatory FDC sarcoma presenting as a colonic polyp, featuring a clonal IGH gene rearrangement not previously documented in this colonic tumor type. Heightened awareness of this rare neoplasm within the gastrointestinal tract is essential for both accurate diagnosis and effective patient management.

The changing landscape of pediatric histiocytoses: Birth, life, and transdifferentiation of pediatric histiocytes

Histiocytic neoplasms in the children are very rare, and histiocytoses can occur in the perinatal period. The presumed origins and presentation of specific histiocytoses in the pediatric age group are described. Common and newly described histiocytoses are presented including Langerhans cell histiocytosis, Rosai-Dorfman disease, histiocytic sarcoma, ALK positive histiocytosis, and hemophagocytic lymphohistiocytosis. Molecular findings common to pediatric histiocytoses are also discussed.

Progression in Myeloid Neoplasms: Beyond the Myeloblast

Disease progression in myelodysplastic syndromes (MDS), myelodysplastic-myeloproliferative neoplasms (MDS/MPN), and myeloproliferative neoplasms (MPN), altogether referred to as myeloid neoplasms (MN), is a major source of mortality. Apart from transformation to acute myeloid leukemia, the clinical progression of MN is mostly due to the overgrowth of pre-existing hematopoiesis by the MN without an additional transforming event. Still, MN may evolve along other recurrent yet less well-known scenarios: (1) acquisition of MPN features in MDS or (2) MDS features in MPN, (3) progressive myelofibrosis (MF), (4) acquisition of chronic myelomonocytic leukemia (CMML)-like characteristics in MPN or MDS, (5) development of myeloid sarcoma (MS), (6) lymphoblastic (LB) transformation, (7) histiocytic/dendritic outgrowths. These MN-transformation types exhibit a propensity for extramedullary sites (e.g., skin, lymph nodes, liver), highlighting the importance of lesional biopsies in diagnosis. Gain of distinct mutations/mutational patterns seems to be causative or at least accompanying several of the above-mentioned scenarios. MDS developing MPN features often acquire MPN driver mutations (usually JAK2), and MF. Conversely, MPN gaining MDS features develop, e.g., ASXL1, IDH1/2, SF3B1, and/or SRSF2 mutations. Mutations of RAS-genes are often detected in CMML-like MPN progression. MS ex MN is characterized by complex karyotypes, FLT3 and/or NPM1 mutations, and often monoblastic phenotype. MN with LB transformation is associated with secondary genetic events linked to lineage reprogramming leading to the deregulation of ETV6, IKZF1, PAX5, PU.1, and RUNX1. Finally, the acquisition of MAPK-pathway gene mutations may shape MN toward histiocytic differentiation. Awareness of all these less well-known MN-progression types is important to guide optimal individual patient management.

Potential role of MAP2K1 mutation in the trans-differentiation of interdigitating dendritic cell sarcoma: Case report and literature review

A 5-year-old male child was diagnosed with interdigitating dendritic cell sarcoma (IDCS) during his maintenance therapy for B-cell precursor acute lymphoblastic leukemia (B-ALL). Multiplex lymph node involvements of the neck were found by positron emission tomography CT (PET-CT). Treatments, including surgical and chemotherapy, resulted in complete remission. Four years later, systemic bone infiltration was discovered. Surgical resection of the IV rib and intensive chemotherapy led to a complete morphological remission, and allogeneic bone marrow transplantation was performed. Comprehensive genomic profiling of the formalin fixed the tumor tissue, and the cryopreserved leukemic cells revealed several common alterations and divergent clonal evolution with a novel MAP2K1 mutation of the IDCS, which is responsible for the trans-differentiation of the common lymphoid-committed tumor progenitor.

Follicular dendritic cell sarcoma

Follicular dendritic cells (FDC) are mesenchymal-derived dendritic cells located in B-follicles where they play a pivotal role in triggering and maintaining B-cell adaptive immune response. In 1986 Dr. Juan Rosai first reported a series of neoplasms showing features of FDC and defined it as Follicular Dendritic Cell Tumor, subsequently renamed as "sarcoma" (FDCS). In its seminal and subsequent articles Rosai and colleagues highlighted the heterogeneous microscopic appearance of FDCS and its immunohistochemical and ultrastructural features.

FDCS mostly occurs in extranodal sites (79.4% of cases) and lymph nodes (15.1%); in about 7%-10% of cases it is associated with hyaline-vascular Castleman disease. Given its significant growth pattern and cytological variability, FDCS can be confused with various neoplasms and even inflammatory processes. The diagnosis requires the use of a broad spectrum of FDC markers (e.g. CD21, CD23, CD35, clusterin, CXCL13, podoplanin), particularly considering that tumor antigen-loss is frequent. The inflammatory-pseudotumor-like (IPT-like) variant of FDCS, in addition to its peculiar histopathological and clinical features, is characterized by positivity of tumor cells for Epstein-Barr virus, representing a diagnostic requisite.

No distinctive genetic and molecular anomalies have been identified in FDCS. It often carries an aberrant clonal karyotype and chromosomal structural alterations, frequently involving onco-suppressor genes. Direct or next generation sequencing showed alterations on genes belonging to the NF-κB regulatory pathway and cell-cycle regulators. In contrast to hematopoietic-derived histiocytic and dendritic cells tumors, FDCS typically lacks mutations in genes related to the MAPK pathway.

FDCS recurs locally in 28% and metastasizes in 27% of cases. Extent of the disease, surgical resectability and histopathological features are significantly associated with the outcome. IPT-like FDCS behaves as an indolent tumor, even if it often recurs locally over years.

Complete surgical excision is the gold standard of treatment. Data on targeted therapies (e.g.: tyrosine kinase inhibitors) or immune checkpoint inhibitors are very limited and responses are variable. A better understanding of the molecular drivers of this tumor may lead to potential new therapeutic strategies.

A Pedigree Analysis and Clonal Correlations of the Coexistence of B-Cell Lymphoma and Histiocytic/Dendritic Cell Tumor

Histiocytic/dendritic cell tumors are rare in clinical practice. It is postulated that they originate from bone marrow stem cells. Accumulating evidence has established the existence of immunoglobulin gene and T-cell receptor gene rearrangements in these tumors. Cases of transdifferentiation across lineages from follicular lymphoma to histiocytic/dendritic cell tumors have also been reported. Herein, we report 2 adult males with histiocytic neoplasms coexisting with B-cell lymphoma. Laser capture microdissection and capillary electrophoresis polymerase chain reaction analysis revealed comparable immunoglobulin gene rearrangement in both patients. In one case, chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), Langerhans cell sarcoma, and histiocytic sarcoma coexisted in the lymph nodes. 11q22 deletion often present in CLL/SLL and expression of the BRAF V600E gene was detected in all the 3 components. In the other case, there diffuse large B-cell lymphoma and histiocytic sarcoma coexisted in the spleen. Forty-seven mutated genes commonly found in B-cell lymphoma were detected by next-generation sequencing. In the same line, DTX1, IRF8, KMT2D, MAP2K1, and TET2 genes were found to have similar mutation sites. The results of this study will contribute in providing new ideas for targeted treatment of these diseases.

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.

Original Observation of Primary Bladder Histiocytic Sarcoma: First Case Report

Histiocytic sarcoma (HS) is a rare malignant lymphohematopoietic neoplasm; it has been cited in the recent World Health Organization (WHO) classification as a malignant proliferation of cells exhibiting morphological and immunophenotypic features of mature histiocytes. To our knowledge, the present case is the first to be described in the bladder of a patient without a history of lymphoma. Only one case has been reported so far regarding a secondary bladder presentation in the setting of a previous diffuse large B-cell lymphoma. We discuss the case of a 68-year-old male who presented with hematuria and dysuria. CT scan revealed a 4-cm intravesical mass that histological examination defined as HS. Our objective was to describe the clinical, histological, immunophenotypical, molecular characteristics and discuss the differential diagnoses of this first case of primary bladder HS. Our research was based on a review of selected articles obtained via the PubMed database. This extremely rare experience provided us with the opportunity to depict an interesting case, highlight its uniqueness, and build up new pathological evidence.

Germinal Center Cells Turning to the Dark Side: Neoplasms of B Cells, Follicular Helper T Cells, and Follicular Dendritic Cells

Gaining knowledge of the neoplastic side of the three main cells—B cells, Follicular Helper T (Tfh) cells, and follicular dendritic cells (FDCs) —involved in the germinal center (GC) reaction can shed light toward further understanding the microuniverse that is the GC, opening the possibility of better treatments. This paper gives a review of the more complex underlying mechanisms involved in the malignant transformations that take place in the GC. Whilst our understanding of the biology of the GC-related B cell lymphomas has increased—this is not reviewed in detail here—the dark side involving neoplasms of Tfh cells and FDCs are poorly studied, in great part, due to their low incidence. The aggressive behavior of Tfh lymphomas and the metastatic potential of FDCs sarcomas make them clinically relevant, merit further attention and are the main focus of this review. Tfh cells and FDCs malignancies can often be misdiagnosed. The better understanding of these entities linked to their molecular and genetic characterization will lead to prediction of high-risk patients, better diagnosis, prognosis, and treatments based on molecular profiles.

Histiocytic and dendritic cell neoplasms: Reappraisal of a Japanese series based on t(14;18) and neoplastic PD-L1 expression

Histiocytic and dendritic cell (H/DC) neoplasms are heterogeneous, originating from myeloid- or stromal-derived cells. Multiple reports describe the cross-lineage transdifferentiation of neoplastic B cells into H/DC neoplasms. Most such cases are from Western countries, and rarely from Japan or East Asia. Here we report 17 cases of H/DC neoplasms in Japanese patients, with analysis of t(14;18) by fluorescence in situ hybridization, and of neoplastic programmed death-ligand 1 (PD-L1) expression by immunostaining (clones SP142, E1J2J, and 28-8). These 17 cases were diagnosed according to the 2017 World Health Organization (WHO) classification, and included two histiocytic sarcomas (HS), two interdigitating cell (IDC) sarcomas, one Langerhans cell sarcoma, two dendritic cell sarcomas, and 10 follicular dendritic cell (FDC) sarcomas. No case had any past history of follicular lymphoma (FL). Two cases of HS and one IDC sarcoma, all of which were myeloid-driven, were found to exhibit t(14;18). In the latter case, at 30 months after IDC sarcoma diagnosis, FL development was detected. Three (30%) FDC sarcoma cases exhibited neoplastic PD-L1 expression with all the three PD-L1 antibody clones. This is the first report of t(14;18) and neoplastic PD-L1 expression on H/DC neoplasms among Japanese patients, each of which appeared to be associated with HS and FDC sarcoma, respectively.

The association of gene rearrangement and lymphoma diagnosis: A prospective observational study

INTRODUCTION

To investigate the gene rearrangement and mutation of lymphoma biomarkers including (Immunoglobulin H (IgH), Immunoglobulin kappa (IGK), Immunoglobulin lambda (IGL), and TCR) in the lymphoma diagnosis.

METHODS AND ANALYSIS

Paraffin tissue samples from 240 cases diagnosed as suspected lymphoma in the department of pathology, Deyang City People's Hospital from June 2020 to June 2021 will be enrolled. Deoxyribonucleic acid extraction and Polymerase Chain Reaction (PCR) amplification will be performed in these paraffin tissue samples. Immunoglobulin and T cell receptor (TCR) rearrangement will be analyzed by hetero-double chain gel electrophoresis and BioMed-2 standardized immunoglobulin gene rearrangement detection system. In this study protocol IGH gene rearrangement, IGK gene rearrangement, both IGH and IGL gene rearrangement, both IGH and IGK gene rearrangement, both IGK and IGL gene rearrangement, both IGH, IGK and IGL gene rearrangement, TCR gene rearrangement and positive Ig/TCR rearrangement will be analyzed.

DISCUSSION

In this study, we will use B and T cell lymphoma analysis focusing on IgH, IGK, IGL, and TCR gene rearrangement, so as to provide early guidance for the diagnosis of lymphoma. Second generation sequencing technology is helpful in the differential diagnosis of lymphoma.

TRIAL REGISTRATION

Chinese Clinical trial registry: ChiCTR2000032366.

Histiocytic Sarcoma Following B-Lymphoblastic Leukemia/Lymphoma

OBJECTIVES

Rare cases of clonally related histiocytic sarcoma (HS) following B-lymphoblastic leukemia/lymphoma (B-ALL/LBL) have been reported to date.

METHODS

We present a patient with HS, which appeared as a breast mass 12 months after the initial diagnosis of B-ALL.

RESULTS

Both HS and the B-ALL shared IGH-MYC and IGK gene rearrangements. Next-generation sequencing and whole-exome sequencing (WES) studies detected 35 common mutations, as well as mutations unique to B-ALL (16) and HS (15), including BRAF D594G. The patient achieved complete remission of B-ALL, but HS failed to respond to many cycles of intensive chemotherapy regimens. A partial response was achieved with sorafenib, a BRAF-targeted therapy.

CONCLUSIONS

To our knowledge, this is the first study to demonstrate by WES that clonally related B-ALL and HS arise through divergent evolution from a common precursor. We present our findings together with a discussion of the previously reported cases of HS in patients with B-ALL.

Atypical Histiocytic Lesion Preceding a Peripheral T-Cell Lymphoma Involving the Skin Exhibiting the Same Molecular Alterations

Peripheral T-cell lymphoma (PTCL), not otherwise specified (NOS) is a diagnosis of exclusion, showing extreme cytological and phenotypic heterogeneity. Skin involvement of PTCL may be primary or secondary. Diagnosis of histiocytosis may be difficult, requiring clinical-pathological correlation. We describe a laryngeal atypical histiocytic lesion (AHL) and a nasal PTCL, NOS with cutaneous involvement in the same patient presenting with peculiar histopathologic and immunophenotypic features. The laryngeal neoplasm showed morphological and immunophenotypic evidence of histiocytic differentiation and does not fit any other category of the WHO classification nor the revised classification of histiocytosis. The nasal and cutaneous lesions presented features close to natural killer/T-cell lymphoma and gamma-delta T-cell lymphoma but did not meet accurately the WHO criteria. A somatic activating Q61K mutation was found on exon 3 of the NRAS gene in both AHL and PTCL, NOS. The mutation on NRAS gene in both AHL and PTCL, NOS may suggest a common origin from a precursor cell.

Histological type distribution and expression of nm23, VEGF, TOP2A and MUM-1 in peripheral T-cell and NK-cell lymphomas in Chinese: analysis of 313 cases

Peripheral T cell and natural killer cell lymphomas (PT/NKCLs) are rare malignant tumors of lymphoid tissue. The incidence varies by geographical region and race. We reclassified 313 cases of PT/NKCLs based on the 4th edition of the World Health Organization (WHO) classification to demonstrate the distribution of each histologic type of PT/NKCLs in Chinese populations. In our series, extranodal NK/T-cell lymphoma (ENKT) was the most common (37.1%) type, followed by peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) (31.3%) and angioimmunoblastic T-cell lymphoma (AITL) (12.8%). Also, we investigated the expression level of nm23, VEGF, TOP2A, and MUM-1 in all 313 cases. The positive rate of nm23, VEGF, TOP2A, and MUM-1 expression was more than 50% in most histologic types. Among the five common types, the expression rate of nm23 (34.5%) and TOP2A (27.6%) in ENKT were the lowest (P<0.05). VEGF expression was also lowest in ENKT (26.7%), but it was much higher in PTCL-NOS (54.1%), AITL (70.0%), and ALCL-ALK- (56.5%) and ALCL-ALK+ (42.9%). The difference of VEGF expression between ENKT and PTCL-NOS and AITL was significant (P<0.05). Fourteen of 23 (60.9%) cases of ALCL-ALK- and 9 of 14 (64.3%) cases of ALCL-ALK+ were positive for MUM-1, which was much higher than in ENKT (19.8%), PTCL-NOS (26.5%) and AITL (35.0%) (P<0.05). Although the significance of their expression in PT/NKCLs is not clear, we suggested that they may be novel tumor markers for developing targeted therapy in the future.

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.

[Histiocytic and dendritic cell neoplasms: Review of the literature]

Histiocytic and dendritic cell neoplasms (HDN) are rare and their biology, prognosis, treatment and terminology are still under discussion. They are composed of macrophage and dendritic-derived cells and show a wide range of clinical, morphological and prognostic features. Clinicopathological correlation and a broad immunohistochemical panel are required to establish a correct diagnosis. After the detection of BRAF mutations in Langerhans cell histiocytosis, the potential role of other molecular alterations is being studied. We have reviewed the literature published in the last 10 years to provide an overview of NHD, with particular emphasis their molecular features.

Expression of enhancer of zeste homolog 2 (EZH2) protein in histiocytic and dendritic cell neoplasms with evidence for p-ERK1/2-related, but not MYC- or p-STAT3-related cell signaling

EZH2 is an important enzymatic subunit of the epigenetic regulator polycomb repressive complex 2 (PRC2), which controls gene silencing through post-translational modification, and is overexpressed in various carcinomas and hematopoietic neoplasms. We found that the majority of cases of histiocytic and dendritic cell neoplasms, including histiocytic sarcoma, follicular dendritic cell sarcoma, Langerhans cell histiocytosis, and interdigitating dendritic cell sarcoma, show strong EZH2 expression by immunohistochemical staining, in contrast to benign histiocytic lesions and normal cellular counterparts, which did not show EZH2 expression, suggesting that this molecule may function as an oncogenic protein in these neoplasms. We correlated EZH2 expression with that of p-ERK1/2, MYC, and p-STAT3, potential regulators of EZH2, and found that 60-80% of these cases showed strong p-ERK1/2 expression, and only a minority of cases showed positivity for MYC or p-STAT3 in neoplastic cells. In cases of follicular dendritic cell sarcoma, Langerhans cell histiocytosis, histiocytic sarcoma, and interdigitating dendritic cell sarcoma with strong EZH2 expression, 90%, 89%, 70%, and 100% of cases showed co-expression of p-ERK1/2 with EZH2, respectively, while only a small percentage of these cases showed MYC or p-STAT3 co-expression with EZH2 (≤30%). These findings suggest that the p-ERK1/2 signaling cascade, but not the p-STAT3 and MYC signaling cascades, may regulate EZH2 expression in histiocytic and dendritic cell neoplasms, and that EZH2 and the p-ERK1/2 signaling cascade could serve as therapeutic targets for the treatment of these neoplasms. Interestingly, only a minority of cases of blastic plasmacytoid dendritic cell neoplasm exhibited high EZH2 expression, and only a minority of these cases showed p-ERK1/2 co-expression, suggesting that alternative mechanisms may contribute to tumorigenesis in this aggressive neoplasm.

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.

Histiocytic sarcoma with bladder involvement: Case report and literature review

We report an unusual case of histiocytic sarcoma with bladder involvement. An 80 year-old man with a previous history of diffuse large B-cell malignant lymphoma presented with hematuria and back pain. Serial urine cytologies revealed no urothelial malignant cells, but cystoscopy showed a large intravesical mass. The patient underwent transurethral resection (TUR) of the tumor. The bladder TUR specimen showed a widely infiltrating epithelioid neoplasm, with intense immunohistochemical positivity for CD45 and histiocytic markers (CD68, lysozime and fascin). Histopathological diagnosis was histiocytic sarcoma. As the patient's condition was progressively deteriorating, only palliative care was indicated and he died one month after TUR. Although histiocytic sarcoma can often be widespread at the time of diagnosis, to our knowledge, this is the first report of a case presenting with urinary symptoms. Histiocytic sarcoma can mimic many other malignant lesions, and only immunohistochemistry can define the tumor cells, allowing correct therapy. We discuss the differential diagnosis and possible associations.