Histiocytic sarcoma after acute lymphoblastic leukaemia: a common clonal origin

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.

Maintenance of Lineage Identity: Lessons from a B Cell

The maintenance of B cell identity requires active transcriptional control that enforces a B cell-specific program and suppresses alternative lineage genes. Accordingly, disrupting the B cell identity regulatory network compromises B cell function and induces cell fate plasticity by allowing derepression of alternative lineage-specific transcriptional programs. Although the B lineage is incredibly resistant to most differentiating factors, loss of just a single B lineage-specific transcription factor or the forced expression of individual non-B cell lineage transcription factors can radically disrupt B cell maintenance and allow dedifferentiation or transdifferentiation into entirely distinct lineages. B lymphocytes thereby offer an insightful and useful case study of how a specific cell lineage can maintain a stable identity throughout life and how perturbations of a single master regulator can induce cellular plasticity. In this article, we review the regulatory mechanisms that safeguard B cell identity, and we discuss how dysregulation of the B cell maintenance program can drive malignant transformation and enable therapeutic resistance.

Histiocytic Sarcoma With CCND1 Gene Rearrangement Clonally Related and Transdifferentiated From Mantle Cell Lymphoma

OBJECTIVES

Histiocytic neoplasms demonstrate shared gene translocations and clonal immunoglobulin gene rearrangements in cases of associated B-cell lymphomas. However, the evolution of these related disease processes remains largely uncertain, especially in the setting of a prior mantle cell lymphoma.

METHODS

We describe a unique case of a histiocytic sarcoma that transdifferentiated from blastoid mantle cell lymphoma after extensive therapy. Cytogenic and molecular studies were performed and provided evidence for clonal progression.

RESULTS

We present the first reported case of a patient with blastoid mantle cell lymphoma harboring a CCND1 rearrangement that progressed despite multiple therapeutic regimens and ultimately transdifferentiated into histiocytic sarcoma. The histiocytic sarcoma demonstrated a CCND1 rearrangement and targeted next-generation sequencing showed a pathogenic variant in NRAS, a gene involved in the RAS/MAPK pathway, known to play a role in the pathogenesis of histiocytic sarcomas. TP53, NOTCH2, CREBBP, and NFKBIE variants were also identified, which are often seen in B-cell lymphomas, while rarely described in histiocytic sarcoma.

CONCLUSIONS

To our knowledge, this is the first report to provide evidence for clonal evolution of histiocytic sarcoma from blastoid mantle cell lymphoma based on cytogenic and molecular findings. The patient's protracted therapeutic course may have acted as an evolutionary driver promoting this transdifferentiation process.

Cutaneous Langerhans Cell Histiocytosis as Presenting Sign of Systemic B-Cell Lymphoma

ABSTRACT

Langerhans cell histiocytosis (LCH) is a rare clonal proliferative disorder most commonly involving the bone and skin; however, it can arise in many other locations. It is predominantly a pediatric disease, but adult cases occur. Here, we present a case of adult-onset cutaneous LCH with systemic symptoms, believed to represent disseminated LCH. Further evaluation, however, revealed concomitant bone marrow involvement by a small B-cell lymphoma. An association between B-cell lymphoma and cutaneous LCH has only rarely been previously reported. This report adds to the growing body of literature, however, on associations of cutaneous LCH with hematologic malignancies, and it illustrates the need for a complete systemic evaluation including a bone marrow biopsy in suspected cases of disseminated LCH.

Insights into Potent Therapeutical Antileukemic Agent L-glutaminase Enzyme Under Solid-state Fermentation: A Review

AIM AND OBJECTIVE

To review the applications and production studies of reported antileukemic drug L-glutaminase under Solid-state Fermentation (SSF).

OVERVIEW

An amidohydrolase that gained economic importance because of its wide range of applications in the pharmaceutical industry, as well as the food industry, is L-glutaminase. The medical applications utilized it as an anti-tumor agent as well as an antiretroviral agent. L-glutaminase is employed in the food industry as an acrylamide degradation agent, as a flavor enhancer and for the synthesis of theanine. Another application includes its use in hybridoma technology as a biosensing agent. Because of its diverse applications, scientists are now focusing on enhancing the production and optimization of L-glutaminase from various sources by both Solid-state Fermentation (SSF) and submerged fermentation studies. Of both types of fermentation processes, SSF has gained importance because of its minimal cost and energy requirement. L-glutaminase can be produced by SSF from both bacteria and fungi. Single-factor studies, as well as multi-level optimization studies, were employed to enhance L-glutaminase production. It was concluded that L-glutaminase activity achieved by SSF was 1690 U/g using wheat bran and Bengal gram husk by applying feed-forward artificial neural network and genetic algorithm. The highest L-glutaminase activity achieved under SSF was 3300 U/gds from Bacillus sp., by mixture design. Purification and kinetics studies were also reported to find the molecular weight as well as the stability of L-glutaminase.

CONCLUSION

The current review is focused on the production of L-glutaminase by SSF from both bacteria and fungi. It was concluded from reported literature that optimization studies enhanced L-glutaminase production. Researchers have also confirmed antileukemic and anti-tumor properties of the purified L-glutaminase on various cell lines.

The mutational landscape of histiocytic sarcoma associated with lymphoid malignancy

Histiocytic sarcoma and tumors with dendritic cell differentiation (HDT) are uncommon neoplasms often with an aggressive clinical course that may occur in association with another hematologic malignancy or mediastinal germ cell tumor (secondary HDT, sHDT). Previous studies have shown mutations in the RAS/MAPK pathway in HDT and have demonstrated a clonal relationship between HDT and associated lymphoid malignancies through common translocations or identical immunoglobulin or T-cell receptor gene rearrangements. We performed whole exome sequencing on 16 cases of sHDT to further evaluate the spectrum of mutations that occur in sHDT in the context of an associated lymphoid malignancy, including cases associated with follicular lymphoma (FL), chronic lymphocytic leukemia/small lymphocytic lymphoma, B- and T-cell acute lymphoblastic leukemia/lymphoma and peripheral T-cell lymphoma, NOS. In addition, we assessed the clonal relationship between the HDT and the associated lymphoid malignancy in three cases for which matched samples were available. We found mutations in RAS/MAPK pathway genes in 14/16 cases of sHDT associated with diverse mature and precursor B-cell and T-cell neoplasms, involving KRAS (8/16), BRAF (2/16), NRAS (2/16), MAP2K1 (1/16), and NF1 (1/16). In addition, we note that FL-associated sHDT frequently shares a similar mutational profile to the associated malignancy, identifying mutations in CREBBP or KMT2D in all cases and "aberrant" somatic hypermutation in 5/6 cases. Our study confirms the role of the RAS/MAPK pathway in the pathogenesis of sHDT, provides further evidence of a common neoplastic precursor and, in the case of FL, gives additional insight into the stage in lymphomagenesis at which transdifferentiation may occur.

Atypical cutaneous histiocytic eruption in a patient with chronic myelomonocytic leukemia: A case report

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell malignancy with features of both a myeloproliferative neoplasm and a myelodysplastic syndrome. We present a case of 72-year-old man with CMML who presented with generalized hemorrhagic papules and plaques which on histopathology showed a peculiar infiltrate of atypical mature histiocytes. The immunohistochemical markers for Langerhans cells, indeterminate dendritic cells, and plasmacytoid dendritic cells were negative. Next generation sequencing performed on the paraffin block of the leg biopsy specimen revealed identical ASXL1, SRSF2, and KRAS mutations as seen in the CMML clone of the peripheral blood. Along with recent literature, this case illustrates the spectrum of histiocytic and dendritic cell proliferations in CMML, many of which may be clonally related to the hematopoietic malignancy.

Genome-wide analysis of acute leukemia and clonally related histiocytic sarcoma in a series of three pediatric patients

Pediatric histiocytic sarcoma (HS) clonally related to anteceding leukemia is a rare malignancy with poor outcome. We performed a molecular characterization of HS and the corresponding leukemia by methylation arrays and whole-exome sequencing and found a variety of aberrations in both entities with deletions of CDKN2A/B as a recurrent finding. Furthermore, data from genome-wide mutation analysis from one patient allowed the reconstruction of a sequence of tumorigenesis of leukemia and HS lesions including the acquisition of a putatively activating KRAS frameshift deletion (p.A66fs). Our results provide an insight into the genetic landscape of pediatric HS clonally related to anteceding leukemia.

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.

Genomic profiling of primary histiocytic sarcoma reveals two molecular subgroups

Histiocytic sarcoma is a rare malignant neoplasm that may occur de novo or in the context of a previous hematologic malignancy or mediastinal germ cell tumor. Here, we performed whole exome sequencing and RNA-sequencing (RNA-Seq) on 21 archival cases of primary histiocytic sarcoma. We identified a high number of genetic alterations within the RAS/RAF/MAPK pathway in 21 of 21 cases, with alterations in NF1 (6 of 21), MAP2K1 (5 of 21), PTPN11 (4 of 21), BRAF (4 of 21), KRAS (4 of 21), NRAS (1 of 21), and LZTR1 (1 of 21), including single cases with homozygous deletion of NF1, high-level amplification of PTPN11, and a novel TTYH3-BRAF fusion. Concurrent NF1 and PTPN11 mutations were present in 3 of 21 cases, and 5 of 7 cases with alterations in NF1 and/or PTPN11 had disease involving the gastrointestinal tract. Following unsupervised clustering of gene expression data, cases with NF1 and/or PTPN11 abnormalities formed a distinct tumor subgroup. A subset of NF1/PTPN11 wild-type cases had frequent mutations in B-cell lymphoma associated genes and/or clonal IG gene rearrangements. Our findings expand the current understanding of the molecular pathogenesis of this rare tumor and suggest the existence of a distinct subtype of primary histiocytic sarcoma characterized by NF1/PTPN11 alterations with predilection for the gastrointestinal tract.

Update on the classification of T-cell lymphomas, Hodgkin lymphomas, and histiocytic/dendritic cell neoplasms

Introduction: The classification of lymphomas is based on the postulated normal counterparts of lymphoid neoplasms and currently constitutes over 100 definite or provisional entities. As this number of entities implies, lymphomas show marked pathological, genetic, and clinical heterogeneity. Recent molecular findings have significantly advanced our understanding of lymphomas. Areas covered: The World Health Organization (WHO) classification of lymphoid neoplasms was updated in 2017. The present review summarizes the new findings that have been gained in the areas of mature T-cell neoplasms, Hodgkin lymphomas, and histiocytic/dendritic cell neoplasms since the publication of the 2017 WHO classification. Expert opinion: Although formal revisions to the WHO classification are published only periodically, our understanding of the pathologic, genetic, and clinical features of lymphoid neoplasms is constantly evolving, particularly in the age of -omics technologies and targeted therapeutics. Even in the relatively short time since the publication of the 2017 WHO classification, many significant findings have been identified in the entities covered in this review.

Clonal evolution of chronic lymphocytic leukemia to Langerhans cell histiocytosis: a case report

The traditional concept of unidirectional maturation of hematopoietic cells has been called into question due to the recognition of lineage plasticity, which is increasingly found also in the clonal evolution of hematopoietic and lymphoid malignancies. Here we present an unusual case of a patient with TP53-mutated chronic lymphocytic leukemia (CLL) treated with a PI3Kδ inhibitor evolving to clonally related Langerhans cell histiocytosis (LCH) with acquired BRAF V600E and STK11 mutations and loss of expression of PAX-5 and other examined B cell markers. In indolent B cell lymphoma, transformation to a more aggressive high-grade lymphoma occurs frequently during the course of disease and is thought to be caused by clonal evolution. Our case further supports the concept of significant lineage plasticity in lymphomas and raises the question of a potential role of novel pharmacologic agents in clonal evolution.

Case of primary central nervous system histiocytic sarcoma with prominent proliferation of histiocytic cells between the trabeculae of reactive glial cells

Histiocytic sarcoma (HS) is an extremely rare malignant neoplasm that exhibits morphologic and immune-phenotype evidence of histiocytic differentiation. The disease most commonly involves the lymph nodes, gastrointestinal tract, skin, and soft tissue, as well as in the central nervous system (CNS) being relatively rare. Here we report a case of primary CNS HS with unusual histopathological characteristics. A 65-year-old woman presented with CNS HS in the left frontal lobe region, showing two distinct histological patterns. Approximately half of the lesion displayed histological characteristics typical of HS, including diffuse invasion of large round-to-ovoid pleomorphic cells, with mitotic figures (Ki-67 index: 30%) and coagulative necrotic foci. The other half exhibited prominent proliferation of histiocytic cells between the trabeculae of reactive glial cells, with rare mitotic figures (Ki-67 index: < 1%) and no necrotic foci. There were transitions between two morphologies. The HS tumor cells and the histiocytic cells between the trabeculae of reactive glial cells possessed nearly identical histomorphologic and immunophenotypic features, although the HS tumor cells showed a more pronounced degree of cytologic atypia and mitotic activity. To our knowledge, this is the first reported case of HS with prominent proliferation of the histiocytic cells between the trabeculae of reactive glial cells. Here we present the detailed histological, immunohistochemical, and molecular findings. Investigating cases of HS may provide insight into the pathogenesis of this disease.

Myeloid transformation of plasma cell myeloma: molecular evidence of clonal evolution revealed by next generation sequencing

Background

Plasma cell myeloma (PCM) is a neoplasm of terminally differentiated B lymphocytes with molecular heterogeneity. Although therapy-related myeloid neoplasms are common in plasma cell myeloma patients after chemotherapy, transdifferentiation of plasma cell myeloma into myeloid neoplasms has not been reported in literature. Here we report a very rare case of myeloid neoplasm transformed from plasma cell myeloma.

Case presentation

A 60-year-old man with a history of plasma cell myeloma with IGH-MAF gene rearrangement and RAS/RAF mutations developed multiple soft tissue lesions one year following melphalan-based chemotherapy and autologous stem cell transplant. Morphological and immunohistochemical characterization of the extramedullary disease demonstrated that the tumor cells were derived from the monocyte-macrophage lineage. Next generation sequencing (NGS) studies detected similar clonal aberrations in the diagnostic plasma cell population and post-therapy neoplastic cells, including IGH-MAF rearrangement, multiple genetic mutations in RAS signaling pathway proteins, and loss of tumor suppressor genes. Molecular genetic analysis also revealed unique genomic alterations in the transformed tumor cells, including gain of NF1 and loss of TRAF3.

Conclusion

To our knowledge, this is the first case of myeloid sarcoma transdifferentiated from plasma cell neoplasm. Our findings in this unique case suggest clonal evolution of plasma cell myeloma to myeloma neoplasm and the potential roles of abnormal RAS/RAF signaling pathway in lineage switch or transdifferentiation.

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

The 2008 World Health Organization (WHO) diagnostic criteria of histiocytic and dendritic cell neoplasms from hematopoietic and lymphoid tissues no longer required the absence of clonal B-cell/T-cell receptor gene rearrangements. It is true that the clonal B-cell/T-cell receptor gene rearrangements have been identified in rare cases of histiocytic and dendritic cell neoplasms, such as those with or following lymphoma/leukemia or in some sporadic histiocytic/dendritic cell sarcomas, but the clonal features of such group of tumor are still not clear. Here we investigated the clonal status of 33 samples including Langerhans cell histiocytosis (LCH), Langerhans cell sarcoma (LCS), follicular dendritic cell sarcoma (FDCS), interdigitating dendritic cell sarcoma (IDCS) and histiocytic sarcoma (HS). Among them, twenty-eight cases were sporadic without current or past lymphoma/leukemia. Three cases were found with a past history of T-cell lymphoma, one case was followed by extraosseous plasmacytoma, and one case was found with diffuse large B-cell lymphoma (DLBCL). Our results showed that there was a high frequency of clonal IG and T-cell receptor gene rearrangements in these cases. Notably, 4 cases of LCH and 2 cases of FDCS showed both B and T cell receptor gene rearrangements concurrently. One case of FDCS synchronous with DLBCL showed identical clonal IGH in both tumor populations and clonal TCRβ in FDCS alone. No matter if the presence of clonal receptor gene rearrangements was associated with the tumor origin or tumorigenesis, it might serve as a novel tumor marker for developing target therapy.

Lymphoma classification update: T-cell lymphomas, Hodgkin lymphomas, and histiocytic/dendritic cell neoplasms

INTRODUCTION

Lymphomas are classified based on the normal counterpart, or cell of origin, from which they arise. Because lymphocytes have physiologic immune functions that vary both by lineage and by stage of differentiation, the classification of lymphomas arising from these normal lymphoid populations is complex. Recent genomic data have contributed additional depth to this complexity. Areas covered: Lymphoma classification follows the World Health Organization (WHO) system, which reflects international consensus and is based on pathological, genetic, and clinical factors. The present review focuses on the classification of T-cell lymphomas, Hodgkin lymphomas, and histiocytic and dendritic cell neoplasms, summarizing changes reflected in the 2016 revision to the WHO classification. These changes are critical to hematologists and other clinicians who care for patients with these disorders. Expert commentary: Lymphoma classification is a continually evolving field that needs to be responsive to new clinical, pathological, and molecular understanding of lymphoid neoplasia. Among the entities covered in this review, the 2016 revisions in the WHO classification particularly impact T-cell lymphomas, including a new umbrella category of T-follicular helper cell-derived lymphomas and evolving recognition of indolent T-cell lymphomas and lymphoproliferative disorders.

The Microscope as a Tool for Disease Discovery-A Personal Voyage

This review reflects the trajectory of my career in hematopathology, and my personal reflections on scientific advances in the field. During the course of more than 40 years, the approach to classification of hematological malignancies has evolved from descriptive approaches, based on either cytological or clinical features, to a modern approach, which incorporates cutting-edge technologies. My philosophy has focused on defining individual diseases, an approach that can best lead to an understanding of molecular pathogenesis. To quote Carolus Linnaeus ( 1 , p. 19), the father of taxonomy, "The first step in wisdom is to know the things themselves; this notion consists in having a true idea of the objects; objects are distinguished and known by classifying them methodically and giving them appropriate names. Therefore, classification and name-giving will be the foundation of our science."

Non-mesenchymal Mimics of Sarcoma

A variety of different non-mesenchymal neoplasms may mimic sarcoma, in particular sarcomatoid carcinoma and melanoma, but also mesothelioma and rarely some lymphomas. This article reviews the key clinical and histologic features of such neoplasms in different settings, along with the use of ancillary studies to help identify the tumor types most frequently misdiagnosed as sarcoma.

Secondary histiocytic sarcoma may cause apparent persistence or recurrence of minimal residual disease in childhood acute lymphoblastic leukemia

Histiocytic sarcoma (HS) is a rare disease with poor prognosis which may develop subsequent to acute lymphoblastic leukemia (ALL). Here we report two children treated within the AIEOP-BFM ALL 2009 trial: one patient succumbed to fulminant hemophagocytic lymphohistiocytosis triggered by HS during ALL maintenance therapy, the other patient had a smoldering course of HS for over 2 years, and subsequently died after allogeneic stem cell transplantation. In both cases, HS and ALL were clonally related and apparent return of minimal residual disease (MRD) was detected by qPCR in bone marrow. Thus, HS should be considered in ALL when MRD appears to persist or reappear.

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.

Histiocytic sarcoma with acute lymphoblastic leukemia a rare association: case report and literature review

Definition and diagnostic criteria for histiocytic sarcoma (HS) have changed over last two decades due to available new immunohistochemical markers, as well as better understanding of the biology of disease. We report here a case of 4 years old boy diagnosed as acute lymphoblastic leukemia (ALL), who later developed HS of pleura, when he was on maintenance phase of ALL protocol. HS constitutes less than 1 % of the haematolymphoid neoplasm, even more rare is association of HS with ALL. Thus reporting here a rare association of HS with ALL, will help in knowing the actual incidence of HS as well as association with ALL.

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.

The genetics of interdigitating dendritic cell sarcoma share some changes with Langerhans cell histiocytosis in select cases

Histiocytic disorders have been noted to have evidence of transdifferentiation; examples of cases with combinations of different lineages have been shown. In our index case, we identified interdigitating dendritic cell (IDC) differentiation in a case of Langerhans cell histiocytosis (LCH). Little is currently known about the genetics of IDC sarcoma (IDCS) because they are exceedingly rare. Using array comparative genomic hybridization (aCGH), we evaluated 4 cases of IDCS and compared them with our index case, as well as genetic abnormalities previously found in LCH. Four cases of paraffin-embedded samples of IDCS and 1 case of LCH with IDC differentiation were evaluated using aCGH. Array CGH results showed no abnormalities in a case of LCH with interdigitating cell differentiation. In 3 of 4 cases of IDCS, genetic abnormalities were identified; 1 case had no identifiable abnormalities. Interdigitating dendritic cell sarcoma case 1 had gains of 3q and 13q; IDCS case 2 had trisomy 12; IDCS case 3 had deletions of 7p, 12p, 16p, 18q, 19q, and 22q; and IDCS case 4 had no detectable abnormalities. Our index case, LCH with IDC differentiation, showed no abnormalities by aCGH. A number of LCH cases do not have detectable genetic abnormalities. In contrast, 3 of 4 cases of IDCS evaluated had identifiable abnormalities by aCGH. Furthermore, 2 of these shared abnormalities, albeit of large genetic regions, with published abnormalities seen in LCH. No recurrent abnormalities were identified in the IDCS cases. However, the possibility of a relationship between IDCS and LCH cannot be entirely excluded by these results.

Histiocytic/Dendritic Cell Transformation of B-Cell Neoplasms: Pathologic Evidence of Lineage Conversion in Differentiated Hematolymphoid Malignancies

B-cell lymphomas, such as low-grade follicular lymphoma and chronic lymphocytic leukemia/small lymphocytic lymphoma, can transform to histiocytic/dendritic cell sarcoma (H/DS) in rare cases. The diagnosis of this unconventional neoplastic evolution relies on a combination of immunophenotypic analysis and genotypic studies. A genotype identical to that of the primary B-cell neoplasm in a secondary neoplasm with H/DS immunophenotype supports the lineage conversion to H/DS. Putative mechanisms for this unusual phenomenon include dedifferentiation, common immature progenitor, and transdifferentiation models, the latter of which is suggested by clinical laboratory data at the present time. Elucidation of the molecular mechanisms governing this lineage conversion may facilitate the understanding of carcinogenesis of not only hematopoietic but also nonhematolymphoid neoplasms. The clinical outcome of secondary H/DS is dismal, as observed in sporadic cases, and the optimal treatment remains to be determined.

Xist RNA is a potent suppressor of hematologic cancer in mice

X chromosome aneuploidies have long been associated with human cancers, but causality has not been established. In mammals, X chromosome inactivation (XCI) is triggered by Xist RNA to equalize gene expression between the sexes. Here we delete Xist in the blood compartment of mice and demonstrate that mutant females develop a highly aggressive myeloproliferative neoplasm and myelodysplastic syndrome (mixed MPN/MDS) with 100% penetrance. Significant disease components include primary myelofibrosis, leukemia, histiocytic sarcoma, and vasculitis. Xist-deficient hematopoietic stem cells (HSCs) show aberrant maturation and age-dependent loss. Reconstitution experiments indicate that MPN/MDS and myelofibrosis are of hematopoietic rather than stromal origin. We propose that Xist loss results in X reactivation and consequent genome-wide changes that lead to cancer, thereby causally linking the X chromosome to cancer in mice. Thus, Xist RNA not only is required to maintain XCI but also suppresses cancer in vivo.

Interdigitating dendritic cell sarcoma presenting simultaneously with acute myelomonocytic leukemia: report of a rare case and literature review

Interdigitating dendritic cell sarcoma (IDCS) is an extremely rare tumor derived from interdigitating dendritic cells. We report the first case of a 64-year-old Chinese woman who was diagnosed with simultaneous IDCS and acute myelomonocytic leukemia (AML-M4). The patient had undergone chemotherapy for breast cancer 6 years previously. Based on the laboratory results, both the IDCS and the AML-M4 in this patient were determined to be of myelogenous origination. Furthermore, a review of 62 IDCS cases (Medline database, key word: IDCS) reported to date revealed that as many as 17 % of the patients had malignant disease and received radiotherapy and/or chemotherapy prior to developing IDCS, and that this group of patients showed worse prognosis compared with counterparts. The patient in the present report showed poor response to four cycles of sequential chemotherapy, and died 6 months after the initial diagnosis.

Unusual presentation of a rare cancer: histiocytic sarcoma in the brain 16 years after treatment for acute lymphoblastic leukemia

Histiocytic sarcoma (HS) is a very rare hematopoietic neoplasm that has been reported in association with other hematological malignancies. Presentation of HS in the central nervous system is even less common. Diagnosis of HS requires the presence of histiocytic markers and the systematic exclusion of markers of other cell lineages. Primary HS central nervous system tumors are aggressive and generally have poor outcomes. There are no standard treatment guidelines due to lack of clinical trials and a limited number of case reports. Here we present a unique case with two primary histiocytic lesions in the brain, refractory to systemic and radiation therapies, that developed after being treated for T-cell acute lymphoblastic leukemia 16 years prior.

Pediatric histiocytic sarcoma clonally related to precursor B-cell acute lymphoblastic leukemia with homozygous deletion of CDKN2A encoding p16INK4A

Histiocytic sarcoma (HS) is a rare malignancy of tissue histiocytes with a dismal prognosis. We report a 4-year-old male who developed HS during maintenance chemotherapy for precursor B-cell acute lymphoblastic leukemia (pre-B ALL). Both tumors showed identical clonal immunoglobulin and T-cell receptor gene re-arrangement patterns, as well as homozygous deletion of the CDKN2A gene encoding p16(INK4A). These data suggest a clonal relationship between the two neoplasms despite their distinct lineages. Since CDKN2A deletion predisposes to development of HS in experimental models, the cytogenetic features of the patient's pre-B ALL may have predisposed to this change in lineage.

Aggressive sporadic histiocytic sarcoma with immunoglobulin heavy chain gene rearrangement and t(14;18)

Histiocytic sarcoma (HS) is a rare but aggressive malignant neoplasm of histiocytic lineage with a poor prognosis. Immunohistochemically, the neoplastic cells are positive for CD163, CD68, and lysozyme, and negative for B and T cell markers. However, molecular studies on the origin of the neoplastic cells remain inconclusive. A 54-year-old woman was admitted to our hospital because of painful swelling of the left knee. Examination revealed generalized lymphadenopathy and splenomegaly. HS was diagnosed according to morphologic and immunohistochemical features observed on biopsy of the left inguinal lymph node. The tumor demonstrated a clonal immunoglobulin heavy chain gene rearrangement and a clonal cytogenetic abnormality including t(14;18) which was confirmed by fluorescence in situ hybridization analysis showing the IgH/BCL2 fusion gene. The neoplastic cells were negative for PAX5, a B cell associated transcription factor, and positive for CEBPβ, a transcription factor mediating macrophage and myeloid differentiation. Positron emission tomography showed disseminated areas of increased 18F-fluorodeoxyglucose uptake in multiple lymph nodes, the liver, spleen, both lungs, both kidneys, and many bony sites. The patient received localized irradiation therapy followed by chemotherapy, she failed to respond and died of the disease progression. The case findings suggest lineage promiscuity or plasticity related to the pathogenesis of HS.

Histiocytic sarcoma arising in indolent small B-cell lymphoma: report of two cases with molecular/genetic evidence suggestive of a 'transdifferentiation' during the clonal evolution

The biologic relationship between small B-cell lymphoma and histiocytic sarcoma (HS) when occurring in the same patient remains unclear, though recent data suggest a possible 'transdifferentiation' from follicular lymphoma (FL) to HS. We investigated the clonal relationship in two cases of small B-cell lymphoma with subsequent HS. Case 1: A 62-year-old female with splenic marginal zone lymphoma (SMZL) developed HS in a groin lymph node 1 year after the primary diagnosis. PCR/sequence analysis of the IGH gene showed a monoclonal rearrangement carrying an identical nucleotide sequence of PCR products from the spleen with SMZL and the lymph node with HS. Case 2: A 61-year-old female with a remote history of FL developed supraclavicular lymphadenopathy, which was confirmed to be HS. PCR analysis of the HS detected a monoclonal rearrangement of the IGH gene and FISH analysis revealed IGH/BCL2 fusion, a genetic hallmark for FL. The transformed HSs showed partial retention of their prior B-cell lymphomas' signatures, including expression of OCT2 in both cases and expression of BCL6 and enhanced expression of BCL2 in case 2. Both HSs demonstrated hypermutated IGH variable regions, arguing against a common progenitor mechanism of the transformation process. The data suggest a common clonal origin of B-cell lymphoma and subsequent HS occurring in the same patient, indicating that 'transdifferentiation' occurs in other small B-cell lymphomas, in addition to the previously reported FL or B-cell lymphoma with IGH/BCL2.

The histopathologic and molecular basis for the diagnosis of histiocytic sarcoma and histiocyte-associated lymphoma of mice

Histiocytic sarcoma (HS) and histiocyte-associated lymphoma (HAL) of mice are difficult to distinguish histologically. Studies of multiple cases initially diagnosed as HS or HAL allowed us to define HS as round, fusiform, or mixed cell types that were F4/80+, Mac-2+, and PAX5-; that lacked markers for other sarcomas; and that had immune receptor genes in germline configuration. Two other subsets had clonal populations of lymphocytes. The first, HAL, featured malignant lymphocytes admixed with large populations of normal-appearing histiocytes. The second appeared to be composites of lymphoma and HS. Several cases suggestive of B myeloid-lineage plasticity were also observed.

The phosphatidylserine receptors, T cell immunoglobulin mucin proteins 3 and 4, are markers of histiocytic sarcoma and other histiocytic and dendritic cell neoplasms

The T cell immunoglobulin mucin (TIM) proteins are a family of cell surface phosphatidyserine receptors that are important for the recognition and phagocytosis of apoptotic cells. Because TIM-4 is expressed by macrophages and dendritic cells in human tissue, we examined its expression in a range of histiocytic and dendritic cell neoplasms and found moderate to strong immunohistochemical staining in cases of juvenile xanthogranuloma and histiocytic sarcoma, and lower level staining in interdigitating dendritic cell sarcoma, Langerhans cell histiocytosis, acute monocytic leukemia (leukemia cutis), and blastic plasmacytoid dendritic cell neoplasm (hematodermic tumor). TIM-3 was first described on activated T(H)1 cells but was recently shown to also be a phosphatidylserine receptor and mediate phagocytosis. We found TIM-3 was expressed by peritoneal macrophages, monocytes and splenic dendritic cells. We found that it, like TIM-4, is expressed in a range of histiocytic and dendritic cell neoplasms, typically with strong immunohistochemical staining. Cases of diffuse large B cell lymphoma, anaplastic large cell lymphoma, metastatic malignant melanoma, and metastatic poorly differentiated carcinoma generally exhibited negative to minimal heterogenous staining for TIM-4 and TIM-3. We conclude that histiocytic and dendritic cell neoplasms consistently express TIM-3 and TIM-4 and that these molecules are new markers of neoplasms derived from histiocytic and dendritic cells.

Histiocytic sarcoma and underlying chronic myelomonocytic leukemia: a proposal for the developmental classification of histiocytic sarcoma

A 70-year-old male was admitted because of back pain due to peri-vertebral tumors. The histologic picture of a needle-biopsied tumor specimen showed pleomorphic large cell infiltration into the collagen fibers. On immunohistochemistry, these abnormal cells were positive for CD68, CD163 and lysozyme but negative for CD1a, 21, 30, and S100. Flow cytometric analysis also demonstrated that these cells were positive for CD13, 14, 38, 45, 56, and HLA-DR. A bone marrow aspirate showed the marked infiltration of abnormal large cells with the same surface antigens as described above. A diagnosis of HS was made. He showed monocytosis in the peripheral blood of more than 1.0 x 10(9)/L from presentation. The karyotype of bone marrow cells was 46,XY,+8. Fluorescent in situ hybridization (FISH) analysis with a probe for chromosome no. 8 showed that all these monocytes carried +8, indicating that he had another disorder of chronic myelomonocytic leukemia (CMML). FISH analysis with a probe for chromosome no. 12 demonstrated that the abnormal large cells in the bone marrow were all tetraploid, while analysis with the chromosome no. 8 probe showed more than 8 signals per cell, indicating that HS cells carried octasomy to decasomy of chromosome no. 8. These findings strongly suggest that HS in the present patient originated from underlying CMML.

Clinicopathologic features of histiocytic lesions following ALL, with a review of the literature

We describe the clinicopathologic features of 15 patients who had histiocytic lesions that followed acute lymphoblastic leukemia (ALL). Twenty-one separate histiocytic lesions were evaluated that covered a wide spectrum, some conforming to the usual categories of juvenile xanthogranulomas (5), Langerhans' cell histiocytosis (1), Langerhans' cell sarcoma (4), Rosai-Dorfman disease (1), and histiocytic sarcoma (4). Most were atypical for the category by histology, phenotype, or abnormally high turnover rate. Seven low-grade lesions defied easy categorization and were characterized only as "atypical histiocytic lesion" following ALL. For those evaluated, the molecular signature of the prior leukemia was present in the histiocytic lesion. In 3 of 15 patients, the leukemia and histiocytic lesion shared immunoglobulin H or monoclonal TCR gene rearrangements and, in 4 of 15 patients, clonal identity was documented by fluorescence in situ hybridization. Four patients died of progressive disease, 3 of whom had histiocytic sarcoma and 1 who had an atypical lesion. One patient died of recurrent ALL. The other 10 patients are alive, 7 after recurrences and treatment with surgery and/or chemotherapy. The post-ALL lesions are more aggressive than their native counterparts, but despite the demonstration of the presence of the leukemia signature in 7 of 15 patients, the prognosis is generally favorable, except for patients with histiocytic sarcoma. It remains unclear whether the histiocytic lesions arise as a line from the original ALL or whether transdifferentiation is involved.

Common clonal origin of an acute B-lymphoblastic leukemia and a Langerhans' cell sarcoma: evidence for hematopoietic plasticity

BACKGROUND

The hierarchical organization of hematopoiesis with unidirectional lineage determination has become a questionable tenet in view of the experimental evidence of reprogramming and transdifferentiation of lineage-determined cells. Clinical examples of hematopoietic lineage plasticity are rare. Here we report on a patient who presented with an acute B-lymphoblastic leukemia and developed a Langerhans' cell sarcoma 9 years later. We provide evidence that the second neoplasm is the result of transdifferentiation.

DESIGN AND METHODS

B-cell acute lymphoblastic leukemia was diagnosed in an 11-year old boy in 1996. Treatment according to the ALL-BFM-1995 protocol resulted in a complete remission. Nine years later, in 2005, Langerhans' cell sarcoma was diagnosed in a supraclavicular lymph node. Despite treatment with different chemotherapy protocols the patient had progressive disease. Finally, he received an allogeneic peripheral blood stem cell transplant and achieved a continuous remission. Molecular studies of IGH- and TCRG-gene rearrangements were performed with DNA from the Langerhans' cell sarcoma and the cryopreserved cells from the acute B-lymphoblastic leukemia. The expression of PAX5 and ID2 was analyzed with real-time reverse transcriptase polymerase chain reaction.

RESULTS

Identical IGH-rearrangements were demonstrated in the acute B-lymphoblastic leukemia and the Langerhans' cell sarcoma. The key factors required for B-cell and dendritic cell development, PAX5 and ID2, were differentially expressed, with a strong PAX5 signal in the acute B-lymphoblastic leukemia and only a weak expression in the Langerhans' cell sarcoma, whereas ID2 showed an opposite pattern.

CONCLUSIONS

The identical IGH-rearrangement in both neoplasms indicates transdifferentiation of the acute B-lymphoblastic leukemia into a Langerhans' cell sarcoma. Loss of PAX5 and the acquisition of ID2 suggest that these key factors are involved in the transdifferentiation from a B-cell phenotype into a Langerhans'/dendritic cell phenotype. (Clinical trial registration at: Deutsches KrebsStudienRegister, http://www.studien.de, study-ID:8).