Hairy cell leukaemia-variant: Disease features and treatment

Detangling the Threads of Hairy Cell Leukemia, Beyond the Morphology and Into the Molecular

Hairy cell leukemia (HCL) makes up 2% of leukemias in the United States and encompasses great molecular heterogeneity. The standard treatment paradigm involves purine nucleoside analogues in the upfront setting with high complete response rate to initial therapy but frequent relapses. There is an increasing role for BRAF inhibitors, with or without rituximab, in refractory and even in untreated patients. The response to purine analogues in HCL variant cases, otherwise classified as splenic lymphoma with prominent nucleolus in the 5th WHO edition classification, is less robust. Several antibodies, small molecular inhibitors, and combination regimens have been explored in HCL but data is frequently limited by case reports or small case series. Here we review available treatment options including their efficacy and safety profiles. We also explore investigational agents and potential future targets. The goal is to present a comprehensive therapeutic review of this rare disease entity and outline the ever increasing and novel therapeutic management options which interrupt key pathways in the pathogenesis of this malignancy.

Untangling hairy cell leukaemia (HCL) variant and other HCL-like disorders: Diagnosis and treatment

The variant form of hairy cell leukaemia (HCL-V) is a rare disease very different from hairy cell leukaemia (HCL), which is a very well-defined entity. The 5th WHO edition (Leukemia, 36, 2022 and 1720) classification (WHO-HAEM5) introduced splenic lymphomas/leukaemias including four different entities: (1) HCL, (2) splenic marginal zone lymphoma (SMZL) with circulating villous cells in the peripheral blood, (3) splenic lymphoma with prominent nucleolus (SLPN), which replaced HCL-V and CD5 negative B-prolymphocytic leukaemia (B-PLL), and (4) splenic diffuse red pulp lymphoma (SDRPL). All these entities have to be distinguished because of a different clinical course and the need for a different treatment. The diagnosis can be challenging because of complex cases and overlap and/or grey zones between all the entities and needs integrating clinical, histologic, immunophenotypic, cytogenetic and molecular data. We review the diagnostic criteria including clinical, immunophenotypic and molecular characteristics of patients with HCL-V and other HCL-like disorders including HCL, SDRPL, SMZL, B-PLL and the Japanese form of HCL. We also discuss the different criteria allowing us to separate these different entities and we will update the recent therapeutic options that have emerged, in particular the advances with chemoimmunotherapy and/or targeted therapies.

Splenic B-cell lymphoma/leukemia with prominent nucleoli: A three-case series of the newly named old entity and review of literature

CONTEXT

Splenic B-cell lymphoma/leukemia with prominent nucleoli (SBLPN) aka hairy cell leukemia variant (HCL-v) is a rare B-cell chronic lymphoproliferative disorder. The main diagnostic challenge is to differentiate SBLPN from Classical hairy cell leukemia (HCL-c), as the former faces inferior responses to therapies and a poor prognosis.

AIMS

The aim is to discuss the clinic-hematological and immunophenotyping findings of three cases of SBLPN.

SETTINGS AND DESIGN

This is a retrospective observational study.

METHODS AND MATERIAL

From the year 2011 to 2021, flow cytometry of all the cases with HCL diagnosis was reviewed, and three cases with negative or dim CD25 and hematological presentation matching with SBLPN were picked up.

STATISTICAL ANALYSIS USED

Descriptive statistics is used.

RESULTS

All the cases were male. The age ranges from 43 to 64 years. Median hemoglobin concentration, total leucocyte count, and platelet count were 8.6 g/dL, 6.9 × 109/L, and 53 × 109/L, respectively. The atypical cells were medium to large. All three showed prominent nucleoli. Bone marrow biopsies showed an interstitial pattern of infiltration in all the cases. The hairy cells were positive for CD20, CD11c, and CD103. CD25 was dim positive in one case. Annexin A1 was negative in all three cases. BRAF V600E mutation analysis was done in one case and turned out negative for the mutation.

CONCLUSIONS

SBLPN is a rare entity, usually on-flow cytometry CD25 negative. However, in dim CD25-positive cases, BRAFV600E mutational analysis helps in discerning SBLPN diagnosis and differentiating it from HCL-c.

The many faces of nodal and splenic marginal zone lymphomas. A report of the 2022 EA4HP/SH lymphoma workshop

Session 3 of the lymphoma workshop of the XXI joint meeting of the European Association for Haematopathology and the Society for Hematopathology took place in Florence, Italy, on September 22, 2022. The topics of this session were splenic and nodal marginal zone lymphomas, transformation in marginal zone lymphomas, and pediatric nodal marginal zone lymphomas and their differential diagnosis as well as related entities. Forty-two cases in these categories were submitted to the workshop, including splenic lymphomas (marginal zone and diffuse red pulp lymphomas), transformed marginal zone lymphomas (splenic and nodal), nodal marginal zone lymphomas with increased TFH-cells, and pediatric nodal marginal zone lymphomas. The case review highlighted some of the principal problems in the diagnosis of marginal zone lymphomas, including the difficulties in the distinction between splenic marginal zone lymphoma, splenic diffuse red pulp lymphoma, and hairy cell leukemia variant/splenic B-cell lymphoma with prominent nucleoli which requires integration of clinical features, immunophenotype, and morphology in blood, bone marrow, and spleen; cases of marginal zone lymphoma with markedly increased TFH-cells, simulating a T-cell lymphoma, where molecular studies (clonality and mutation detection) can help to establish the final diagnosis; the criteria for transformation of marginal zone lymphomas, which are still unclear and might require the integration of morphological and molecular data; the concept of an overlapping spectrum between pediatric nodal marginal zone lymphoma and pediatric-type follicular lymphoma; and the distinction between pediatric nodal marginal zone lymphoma and "atypical" marginal zone hyperplasia, where molecular studies are mandatory to correctly classify cases.

The role of splenectomy in management of splenic B-cell lymphomas

INTRODUCTION

Splenic B-cell lymphomas are rare and understudied entities. Splenectomy is frequently required for specific pathological diagnosis in patients with splenic B-cell lymphomas other than classical hairy cell leukemia (cHCL), and can be effective and durable therapy. Our study investigated the diagnostic and therapeutic role of splenectomy for non-cHCL indolent splenic B-cell lymphomas.

METHODS

Observational study of patients with non-cHCL splenic B-cell lymphoma undergoing splenectomy between 1 August 2011 and 1 August 2021 at the University of Rochester Medical Center. The comparison cohort was patients categorized as having non-cHCL splenic B-cell lymphoma who did not undergo splenectomy.

RESULTS

Forty-nine patients (median age 68 years) had splenectomy (SMZL n = 33, HCLv n = 9, SDRPL n = 7) with median follow up of 3.9 years post splenectomy. One patient had fatal post-operative complications. Post-operative hospitalization was ≤ 4 days for 61% and ≤ 10 days for 94% of patients. Splenectomy was initial therapy for 30 patients. Of the 19 patients who had previous medical therapy, splenectomy changed their lymphoma diagnosis in 5 (26%). Twenty-one patients without splenectomy were clinically categorized as having non-cHCL splenic B-cell lymphoma. Nine required medical treatment for progressive lymphoma and of these 3 (33%) required re-treatment for lymphoma progression compared to 16% of patients following first line splenectomy.

CONCLUSION

Splenectomy is useful for the diagnosis of non-cHCL splenic B-cell lymphomas with comparable risk/benefit profile and remission duration to medical therapy. Patients with suspected non-cHCL splenic lymphomas should be considered for referral to a high-volume center with experience in performing splenectomies for definitive diagnosis and treatment.

The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Lymphoid Neoplasms

We herein present an overview of the upcoming 5^th edition of the World Health Organization Classification of Haematolymphoid Tumours focussing on lymphoid neoplasms. Myeloid and histiocytic neoplasms will be presented in a separate accompanying article. Besides listing the entities of the classification, we highlight and explain changes from the revised 4^th edition. These include reorganization of entities by a hierarchical system as is adopted throughout the 5^th edition of the WHO classification of tumours of all organ systems, modification of nomenclature for some entities, revision of diagnostic criteria or subtypes, deletion of certain entities, and introduction of new entities, as well as inclusion of tumour-like lesions, mesenchymal lesions specific to lymph node and spleen, and germline predisposition syndromes associated with the lymphoid neoplasms.

Purine nucleoside analogs plus rituximab are an effective treatment choice for hairy cell leukemia-variant

Both characteristics and optimal treatment strategy for hairy cell leukemia-variant (HCL-v) remain elusive due to its rarity. We retrospectively analyzed the clinical features of HCL-v and the efficacy of first-line treatment options in a large Chinese cohort. In this study, we recruited 33 HCL-v patients (23 males and 10 females) with a median age of 59 years (range, 34-79 years). The chief complaints included abdominal mass and relative signs (67%) and abnormal complete blood count (27%). Immunophenotyping showed monoclonal B-cells positive for pan B-cell antigens and CD11c, weakly positive for CD103 and CD200, while negative for CD5, CD10, CD25, CD123, and annexin A1. No BRAF V600E mutation was detected, but TP53 abnormality was recurrent. Treatment choices included interferon-α (IFN-α) in 11 patients, chlorambucil (CLB) in 5 patients, single purine nucleoside analogs (PNA) in 3 patients, PNA plus rituximab (PNA + R) in 9 patients, and others in 3 patients. Four patients who received IFN-α or CLB treatment also underwent splenectomy. Patients who received PNA + R had a higher complete response rate (88% versus 5%, P < 0.001) and longer progression-free survival (PFS, 3-year PFS rate 42% [95% CI 1-84] vs. 16% [95% CI 3-40], P = 0.042) than those who received other regimens. Overall, HCL-v is an indolent lymphoma with unique characteristics. The PNA + R regimen is the preferred choice in the first-line treatment for HCL-v.

Deciphering Genetic Alterations of Hairy Cell Leukemia and Hairy Cell Leukemia-like Disorders in 98 Patients

Simple Summary

The diagnosis of hairy cell leukemia (cHCL) and HCL-like disorders, including the variant form of HCL (vHCL) and splenic diffuse red pulp lymphoma (SDRPL) can be challenging, particularly in complex situations. The integration of all data, including molecular data, is essential for distinguishing the different entities. The BRAF^V600E mutation is identified in most cHCL cases, whereas it is absent in vHCL and SDRPL. MAP2K1 mutations are observed in half of vHCL cases and in cHCL BRAF^WT and they are associated with a worse prognosis. The interest in deep sequencing for the diagnosis and prognosis of hairy cell leukemia and HCL-like disorders is essential. Some KLF2 genetic alterations have been localized on the AID consensus motif, suggesting an AID-induced mutation mechanism. KLF2 is the second most altered gene in HCL, and mutations must be investigated to confirm whether AID could be responsible for the genetic alterations in this gene. Clonal evolution can be observed in half of the cases.

Abstract

Hairy cell leukemia (cHCL) patients have, in most cases, a specific clinical and biological presentation with splenomegaly, anemia, leukopenia, neutropenia, monocytopenia and/or thrombocytopenia, identification of hairy cells that express CD103, CD123, CD25, CD11c and identification of the V600E mutation in the B-Raf proto-oncogene (BRAF) in 90% of cases. Monocytopenia is absent in vHCL and SDRPL patients and the abnormal cells do not express CD25 or CD123 and do not present the BRAF^V600E mutation. Ten percent of cHCL patients are BRAF^WT and the distinction between cHCL and HCL-like disorders including the variant form of HCL (vHCL) and splenic diffuse red pulp lymphoma (SDRPL) can be challenging. We performed deep sequencing in a large cohort of 84 cHCL and 16 HCL-like disorders to improve insights into the pathogenesis of the diseases. BRAF mutations were detected in 76/82 patients of cHCL (93%) and additional mutations were identified in Krüppel-like Factor 2 (KLF2) in 19 patients (23%) or CDKN1B in 6 patients (7.5%). Some KLF2 genetic alterations were localized on the cytidine deaminase (AID) consensus motif, suggesting AID-induced mutations. When analyzing sequential samples, a clonal evolution was identified in half of the cHCL patients (6/12 pts). Among the 16 patients with HCL-like disorders, we observed an enrichment of MAP2K1 mutations in vHCL/SDRPL (3/5 pts) and genes involved in the epigenetic regulation (KDM6A, EZH2, CREBBP, ARID1A) (3/5 pts). Furthermore, MAP2K1 mutations were associated with a bad prognosis and a shorter time to next treatment (TTNT) and progression-free survival (PFS), independently of the HCL classification.

Immunophenotypic Analysis of Hairy Cell Leukemia (HCL) and Hairy Cell Leukemia-like (HCL-like) Disorders

Simple Summary

Hairy cell leukemia (HCL) is a rare B cell neoplasm that accounts for 2% of B-cell lymphomas. The diagnosis was based on the presence of abnormal lymphoid cells that expressed CD103, CD123, CD25 and CD11c. The aim of this retrospective study was to describe the immunophenotypic profile of HCL and HCL-like disorders using 13 markers and to assess the added value of immunophenotypic row data and unsupervised analysis. We confirmed that the immunological profile alone is not sufficient and that morphologic, phenotypic and molecular data need to be integrated.

Abstract

Hairy cell leukemia (HCL) is characterized by abnormal villous lymphoid cells that express CD103, CD123, CD25 and CD11c. HCL-like disorders, including hairy cell leukemia variant (vHCL) and splenic diffuse red pulp lymphoma (SDRPL), have similar morphologic criteria and a distinct phenotypic and genetic profile. We investigated the immunophenotypic features of a large cohort of 82 patients: 68 classical HCL, 5 vHCL/SDRPL and 9 HCL-like NOS. The HCL immunophenotype was heterogeneous: positive CD5 expression in 7/68 (10%), CD10 in 12/68 (18%), CD38 in 24/67 (36%), CD23 in 22/68 (32%) and CD43 in 19/65 (31%) patients. CD26 was expressed in 35/36 (97%) of HCL patients, none of vHCL/SDRPL and one of seven HCL-like NOS (14%). When adding CD26 to the immunologic HCL scoring system (one point for CD103, CD123, CD25, CD11c and CD26), the specificity was improved, increasing from 78.6% to 100%. We used unsupervised analysis of flow cytometry raw data (median fluorescence, percentage of expression) and the mutational profile of BRAF, MAP2K1 and KLF2. The analysis showed good separation between HCL and vHCL/SDRPL. The HCL score is not sufficient, and the use of unsupervised analysis could be promising to achieve a distinction between HCL and HCL-like disorders. However, these preliminary results have to be confirmed in a further study with a higher number of patients.

Advances in the Treatment of Hairy Cell Leukemia Variant

OPINION STATEMENT

Hairy cell leukemia variant (HCL-V) is a rare B cell lymphoproliferative disorder with a clinical-pathological distinction from the classic form of hairy cell leukemia (HCL-C). HCL-V is more aggressive in nature, has a higher tendency to be refractory to conventional purine analog pharmacotherapies, and leads to a poorer prognosis. Hence, these differing features bring paramount importance to the diagnosis and management of HCL-V. While there is no genetic mutation diagnostic of HCL-V, genetic profiling efforts have identified potential therapeutic targets (i.e., MAP2K1, KDM6A, CREBBP, ARID1A, CCND3, U2AF1, KMT2C) and yielded prognostic markers (i.e., IGHV4-34 rearrangements). To date, combination chemoimmunotherapies, such as cladribine and rituximab, have shown the best results in HCL-V. Future directions include targeted therapies such as moxetumomab pasudotox, ibrutinib, trametinib, and binimetinib and potentially anti-CD22 chimeric antigen receptor T cell therapy. The purpose of this review is to provide an outline of the diagnostic approach and an update on the therapeutic advancements in HCL-V.

Diagnosis and treatment of hairy cell leukemia as the COVID-19 pandemic continues

Hairy cell leukemia (HCL) is an indolent B-cell malignancy, usually driven by the BRAF V600E mutation. For 30 years, untreated and relapsed HCL was successfully treated with purine analogs, but minimal residual disease (MRD) remained in most patients, eventually causing relapse. Repeated purine analogs achieve decreasing efficacy and increasing toxicity, particularly to normal T-cells. MRD-free complete remissions (CRs) are more common using rituximab with purine analogs in both 1^st-line and relapsed settings. BRAF inhibitors and Ibrutinib can achieve remission, but due to persistence of MRD, must be used chronically to prevent relapse. BRAF inhibition combined with Rituximab can achieve high MRD-free CR rates. Anti-CD22 recombinant immunotoxin moxetumomab pasudotox is FDA-approved in the relapsed setting and is unique in achieving high MRD-free CR rates as a single-agent. Avoiding chemotherapy and rituximab may be important in ensuring both recovery from COVID-19 and successful COVID-19 vaccination, an area of continued investigation.

Long term follow-up of a phase II study of cladribine with concurrent rituximab with hairy cell leukemia variant

CDAR achieved 95% CR and 80% negative MRD, durable up to 10 years.

Carrying TP53 mutation and not achieving negative MRD after CDAR were associated with shorter survival outcomes.

Hairy cell leukemia variant (HCLv) responds poorly to purine analogue monotherapy. Rituximab concurrent with cladribine (CDAR) improves response rates, but long-term outcomes are unknown. We report final results of a phase 2 study of CDAR for patients with HCLv. Twenty patients with 0 to 1 prior courses of cladribine and/or rituximab, including 8 who were previously untreated, received cladribine 0.15 mg/kg on days 1 to 5 with 8 weekly rituximab doses of 375 mg/m² beginning day 1. Patients received a second rituximab course ≥6 months after cladribine, if and when minimal residual disease (MRD) was detected in blood. The complete remission (CR) rate from CDAR was 95% (95% confidence interval, 75-100). Sixteen (80%) of 20 patients (95% confidence interval, 56-94) became MRD negative according to bone marrow at 6 months. The median duration of MRD-negative CR was 70.1 months, and 7 of 16 are still MRD negative up to 120 months. With a median follow-up of 69.7 months, 11 patients received delayed rituximab, and the 5-year progression-free survival (PFS) and overall survival (OS) were 63.3% and 73.9%, respectively. Five patients with TP53 mutations had shorter PFS (median, 36.4 months vs unreached; P = .0024) and OS (median, 52.4 months vs unreached; P = .032). MRD-negative CR at 6 months was significantly associated with longer PFS (unreached vs 17.4 months; P < .0001) and OS (unreached vs 38.2 months; P < .0001). Lack of MRD in blood at 6 months was also predictive of longer PFS and OS (P < .0001). After progression following CDAR, median OS was 29.7 months. CDAR is effective in HCLv, with better outcomes in patients who achieve MRD-negative CR. This trial is registered at www.clinicaltrials.gov as #NCT00923013.

Mutation profiles of diffuse large B-cell lymphoma transformation of splenic B-cell lymphoma/leukemia, unclassifiable on whole-exome sequencing

A 58-year-old male was diagnosed with splenic B-cell lymphoma/leukemia, unclassifiable (SPLL-U). The lymphoma transformed into diffuse large B-cell lymphoma (DLBCL), and multidrug chemotherapy and autologous stem cell transplantation achieved complete remission. Two years later, the lymphoma relapsed as SPLL-U. Serial whole-exome sequencing indicated that the mutation profiles were similar between the onset and relapsed samples while those in DLBCL were partially distinctive, which was in line with the clinical course. Hierarchical clustering revealed that an IGLL5 mutation was the founder mutation proceeding the development of the diseases and suggested that KRAS and other mutations might contribute to the transformation.

Diagnostic and therapeutic challenges in hairy cell leukemia-variant: where are we in 2021?

INTRODUCTION

Hairy cell leukemia-variant (HCL-V) is a rare B-cell neoplasm arising or homing primarily in the spleen. It has been considered in the WHO classification of Hemopoietic and Lymphoid Tumors as a provisional entity since 2008 and included under the umbrella of unclassifiable splenomegalic B-cell leukemia/lymphomas. The diagnosis is a challenge to hematopathologists and management of these patients by the clinicians is difficult due to the lack of diagnostic and therapeutic guidelines and prospective studies.

AREAS COVERED

This manuscript is a comprehensive review of the clinical features, pathology, immunophenotypic profile, genomic alterations and therapeutic options of HCL-V. Diagnostic and therapeutic dilemmas are extensively outlined considering the information derived from a literature search covering from 1980 to 2019. Integration of all the data is needed and recommended for establishing the diagnosis of this leukemia.

EXPERT OPINION

More extensive information of genomic aberrations underlying the pathogenesis of the disease would be a solid stone for the diagnosis. To this end, a collaborative work among scientists and pathologists from different centers is required and expected. In turn, this might have a relevant clinical translation by allowing to identify putative targets for therapy and to improve the outlook of these patients.

Current and Emerging Therapeutic Options for Hairy Cell Leukemia Variant

Hairy cell leukemia variant (HCL-v) is a rare B-cell lymphoproliferative disorder with distinct immunophenotypic and molecular characteristics when compared to classical hairy cell leukemia (HCL-c). In contrast to the enormous progress in therapeutic options for HCL-c, HCL-v remains a therapeutic challenge due to inferior outcomes with standard chemoimmunotherapy and BCR signaling pathway inhibitors, and due to the fact that HCL-v has limited molecular therapeutic targets. In addition, because of the rarity of the disease, there is a paucity of later phase studies or multicenter trials to guide treatment decisions. In this article, we briefly review the diagnostic criteria and clinical characteristics of HCL-v and present a comprehensive overview of current therapeutic options in HCL-v.

CD43 in the malignant flow cytometry laboratory in 2020

Objectives: CD43 can be useful in routine flow cytometry. We conducted a systematic review aiming to describe when CD43 is used by flow cytometry in malignant hematology and to determine its value in these settings. Methods: Systematic review of MEDLINE (search 'CD43' AND 'flow cytometry,' starting in 2010). Results: Twenty-one of 103 entries retrieved were included in this systematic review. CD43 is used in three settings: 1) in the classification of mature B cell lymphoproliferative disorders, 2) as part of a strategy to quantify residual disease in chronic lymphocytic leukemia (CLL) and 3) to help classify CD10-positive B cell populations. In this section, the published data is summarized, the clinical usefulness in each of these settings is evaluated and illustrative cases are shown. Conclusion: CD43 has a growing role in the diagnosis and management of B cell malignancies; it has become essential for the classification of B cell lymphoproliferative disorders and may be of help in the differential diagnosis of CD10-positive lymphomas by FC. It is also required for optimal quantification of CLL residual disease, which will soon be used to guide therapeutic decisions.

Clonal dynamics in a composite chronic lymphocytic leukemia and hairy cell leukemia-variant

Composite lymphoma is the rare simultaneous manifestation of two distinct lymphomas. Chronic lymphocytic leukemia (CLL) has a propensity for occurring in composite lymphomas, a phenomenon that remains to be elucidated. We applied cytogenetics, droplet digital polymerase chain reaction, and massively parallel sequencing to analyze longitudinally a patient with CLL, who 3 years later showed transformation to a hairy cell leukemia-variant (HCL-V). Outgrowth of the IGHV4-34-positive HCL-V clone at the expense of the initially dominant CLL clone with trisomy 12 and MED12 mutation started before CLL-guided treatment and was accompanied by a TP53 mutation, which was already detectable at diagnosis of CLL. Furthermore, deep sequencing of IGH showed a composite lymphoma with presence of both disease components at all analyzed timepoints (down to a minor clone: major clone ratio of ~1:1000). Overall, our analyses showed a disease course that resembled clonal dynamics reported for malignancies with intratumoral heterogeneity and illustrate the utility of deep sequencing of IGH to detect distinct clonal populations at diagnosis, monitor clonal response to therapy, and possibly improve clinical outcomes.

A Rare Case of Hairy Cell Leukemia with Unusual Loss of CD123 Associated with COVID-19 at the Time of Presentation

Coronavirus disease 2019 (COVID-19) pandemic has been a serious threat and has been reported with different presentations and complications. Older age, along with comorbidities such as diabetes, hypertension, or cardiac disease, increases the risk factors for COVID-19 severity and death [N Engl J Med. 2020;382(18):1708–20 and Lancet Respir Med. 2020 05;8(5):475–81]. It is proposed that cancer patients have a significantly higher incidence of severe incidents including admission to the intensive care unit, the necessity for assisted ventilation, and even death after catching the virus compared with non-cancer patients [Lancet Oncol. 2020;21(3):335–7]. It is also described that cancer patients appear to be twice as likely to contract infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) [JAMA Oncol. 2020;6(7):1108–10]. Hairy cell leukemia (HCL) is a rare B-cell lymphoproliferative disorder, with patients typically presenting with cytopenias, marked splenomegaly in 80–90% of patients, circulating leukemia cells, bone marrow infiltration and the presence of BRAF V600E somatic mutation [Indian J Hematol Blood Transfus. 2014;30(Suppl 1):413–7]. Leukemic cells classically have central nuclei and abundant cytoplasm with hairy-like projections and express CD11c, CD25, CD103, and CD123 [Indian J Hematol Blood Transfus. 2014;30(Suppl 1):413–7]. Loss of CD123 in HCL has been rarely reported in the literature [Am J Hematol. 2019;94(12):1413–22]. We describe a unique case of a COVID-19-positive male who presented with severe respiratory symptoms, deteriorated quickly, and was intubated. Workup of severe progressive pancytopenia and bone marrow examination revealed HCL without splenomegaly and with atypical unusual loss of CD123. To our knowledge, this is the first case of CD123-negative HCL without splenomegaly associated with COVID-19 infection as the initial presentation.

Treatment of hairy cell leukemia

INTRODUCTION

Purine analogs made dramatic improvements for patients with hairy cell leukemia (HCL), but patients often relapse, require multiple treatments, and may become refractory. Major developments in treatment of relapsed/refractory HCL occurred with discovery of disease biology. New agents increase the complexity of clinical decision-making.

AREAS COVERED

Anti-CD22 recombinant immunotoxin Moxetumomab Pasudotox (Moxe), CD20 Mabs rituximab and obinutuzumab, BRAF/MEK inhibitors vemurafenib and dabrafenib-trametinib, and Bruton's tyrosine kinase (BTK) inhibitor ibrutinib have been tested in HCL. All show efficacy but with different treatment durations and response rates, including for eradicating minimal residual disease (MRD). Side effects differ and must be considered when selecting treatment. Studies from PubMed indexed papers and abstracts presented at major international conferences are included.

EXPERT OPINION

Rituximab with either purine analog or BRAF-inhibitor achieves high rates of MRD-free complete remission (CR). Moxe achieves MRD-free CR without chemotherapy toxicities. Moxe should be considered prior to splenectomy or development of adenopathy. BRAF/MEK inhibition and ibrutinib are effective options but most patients remain MRD+, requiring indefinite treatment or rituximab to prevent relapse. Under investigation is MRD elimination with CD20 antibody combined with Moxe or BRAF inhibitor. High-risk diseases including HCL variant and IGHV4-34+ unmutated HCL require further investigation.

Concurrent chronic lymphocytic leukemia/small lymphocytic lymphoma and hairy cell leukemia: clinical, pathologic and molecular features

Simultaneous occurrence of hairy cell leukemia (HCL) and chronic lymphocytic leukemia/small lymphocytic lymphoma (termed CLL) is very rare. Clinical characteristics, pathology and management of these cases have not been well described. We present six patients with CLL and HCL or HCL variant (HCL-v). Of six patients, three were initially diagnosed with CLL and later developed concurrent HCL. Two patients had concurrent HCL or HCL-v and CLL at initial diagnosis. One had HCL first, followed by concurrent CLL. Polymerase chain reaction analysis demonstrated B-cell clonality in all cases, with two distinct clonal populations in four cases, and three clonal populations in one case. Five patients were treated with a combination of a purine analog such as fludarabine, cladribine, and pentostastin with either rituximab or ibrutinib, while one received dabrefenib and trametinib. All patients achieved a durable response to either CLL or HCL-directed therapy with reduction or ablation of coexisting B-cell clones.

Development of Recombinant Immunotoxins for Hairy Cell Leukemia

Hairy cell leukemia (HCL) is an indolent B-cell malignancy with excellent initial response to purine analogs pentostatin or cladribine, but patients are rarely, if ever, cured. Younger patients will usually need repeat chemotherapy which has declining benefits and increasing toxicities with each course. Targeted therapies directed to the BRAF V600E mutation and Bruton's tyrosine kinase may be helpful, but rarely eradicate the minimal residual disease (MRD) which will eventually lead to relapse. Moxetumomab pasudotox (Moxe) is an anti-CD22 recombinant immunotoxin, which binds to CD22 on HCL cells and leads to apoptotic cell death after internalization and trafficking of the toxin to the cytosol. Phase I testing achieved a complete remission (CR) rate of 57% in relapsed/refractory HCL. Most CRs were without MRD and eradication of MRD correlated with prolonged CR duration. Patients were often MRD-free after five years. Important mild-moderate toxicities included capillary leak and hemolytic uremic syndromes which could be prevented and managed conservatively. A phase 3 trial met its endpoint of durable CR with acceptable toxicity, leading to FDA approval of Moxe for relapsed/refractory HCL, under the name Lumoxiti. Moxe combined with rituximab is currently being evaluated in relapsed/refractory HCL to improve the rate of MRD-free CR.

Hairy Cell Leukaemia

PURPOSE OF REVIEW

To summarise diagnostic clinical/laboratory findings and highlight differences between classical hairy cell leukaemia (HCLc) and hairy cell leukaemia variant (HCLv). Discussion of prognosis and current treatment indications including novel therapies, linked to understanding of the underlying molecular pathogenesis.

RECENT FINDINGS

Improved understanding of the underlying pathogenesis of HCLc, particularly the causative mutation BRAF V600E, leading to constitutive activation of the MEK/ERK signalling pathway and increased cell proliferation. HCLc is caused by BRAF V600E mutation in most cases. Purine nucleoside analogue (PNA) therapy is the mainstay of treatment, with the addition of rituximab, improving response and minimal residual disease (MRD) clearance. Despite excellent responses to PNAs, many patients will eventually relapse, requiring further therapy. Rarely, patients are refractory to PNA therapy. In relapsed/refractory patients, novel targeted therapies include BRAF inhibitors (BRAFi), anti-CD22 immunoconjugate moxetumomab and Bruton tyrosine kinase inhibitors (BTKi). HCLv has a worse prognosis with median overall survival (OS), only 7-9 years, despite the combination of PNA/rituximab improving front-line response. Moxetumomab or ibrutinib may be a viable treatment but lacks substantial evidence.

Difference of genomic copy numbers alterations between hairy cell leukemia-variant and classical hairy cell leukemia: a pilot retrospective study in Chinese

Background: Hairy cell leukemia (HCL) is a rare chronic B-cell lymphoproliferative disorder. It has two pathological subtypes: classical HCL (HCL-C) and HCL-variant (HCL-V). HCL-C and HCL-V are distinct in morphology and immunophenotype. Their differentiation is important for patient management and clinical outcome, with HCL-V responding poorly to conventional HCL treatments. Recently, whole genomic sequencing has been used to identify the difference between HCL-C and HCL-V and mutation of BRAF^V600E has been proved to be a molecular hallmark of HCL-C. However, BRAF inhibitors were not effective in all HCL-C cases and HCL-V seems be lack of the high-frequency mutations. Therefore, it is necessary to compare the genomic changes between HCL-C and HCL-V by high-resolution studies, especially in Chinese population, the genomic alterations of HCL have rarely be reported. Methods: In this study, the clinical features of a total of 18 Chinese HCL patients were described. Single nucleotide polymorphism (SNP) array analysis was performed to evaluate the genomic copy number alterations (CNA) and copy neutral loss of heterozygosity (CN-LOH) on six HCL-Vs with CD25^-/BRAF^V600E- and four HCL-Cs with CD25⁺/BRAF^V600E+. Results: A total of 24 CNAs including seven chromosomal gains and 17 chromosomal losses, and 22 CN-LOHs were revealed. Five of the six cases of HCL-V showed 15 CNAs including four cryptic chromosomal gains and 11 chromosomal losses. Overlapping regions involving micro-deletion of chromosome 2q13 and large chromosomal loss of 14q were showed in HCL-V. In HCL-C, a total of nine CNAs were revealed in three of the four cases including three chromosomal gains and six chromosomal losses. No overlapping area was observed among the CNVs. 15 CN-LOHs were showed in five of the six cases of HCL-V and seven CN-LOHs was demonstrated in all of the four HCL-Cs. Conclusions: Comparing to Westerners, a relatively higher proportion of HCL-V in all HCL is observed in this study. CNAs and CN-LOHs were common in both HCL-V and HCL-C but the CNAs were different in them. HCL-C was characterized with the higher ratio of large chromosomal changes but lacked of recurrent CNAs, while HCL-V was presented with the higher incidence of cryptic CNAs and recurrent CNAs involving tumor-associated genes. It is necessary to further investigate the association of the genes, such as NPHP1 and TRAF3 genes, and HCL-V in the future study.

Hairy cell leukemia: present and future directions

Hairy cell leukemia (HCL) is an indolent B-cell malignancy, with long-term responses to purine analogs, but with decreasing efficacy and increasing toxicity with repeated courses. Leukemic cells express CD22, CD20, CD25, tartrate-resistant acid phosphatase (TRAP), annexin 1A (Anxa1), and BRAF V600E mutation. HCLv, lacking CD25, Anxa1, TRAP, and BRAF V600E, is more aggressive and less purine analog-sensitive. A molecularly defined IGHV4-34+ variant is also resistant whether HCL or HCLv immunophenotypically. Traces of HCL cells, termed minimal residual disease (MRD), accompany most with complete remission (CR) and may cause relapse. Rituximab has limited single-agent activity, but frequent CR without MRD when combined with purine analog, albeit with chemotherapy toxicities. The anti-CD22 recombinant immunotoxin Moxetumomab Pasudotox can achieve MRD-negative CR in multiply relapsed HCL without chemotherapy toxicities and was FDA approved in 2018 as Lumoxiti. Investigational oral non-chemotherapy options also include Vemurafenib or Dabrafenib/Trametinib targeting BRAF V600E ± MEK, and Ibrutinib targeting Bruton's tyrosine kinase.

[Hairy cell leukemia]

Hairy cell leukemia (HCL) is a well-defined entity. Proliferation with hair cells, morphological aspects of hairy cells are easy to identify. Hairy cells express markers CD11c, CD25, CD103 and CD123. In 80% of cases, a BRAFV600E mutation is highlighted. In the absence of a BRAFV600E mutation, the differential diagnosis with other hair cell proliferations can be difficult, especially with the variant form of hairy leukemia, diffuse lymphoma of the red pulp of the spleen or splenic lymphoma of the marginal zone. Purine analogues (PNA) with or without anti-CD20 antibodies remain the first-line reference treatment. In case of relapse or resistance to PNA, BRAF inhibitors, with or without MEK inhibitors, are proposed in patients with the mutation. In the absence of BRAFV600E mutation, moxetumomab-pasudotox represents an interesting alternative. A multidisciplinary discussion is always necessary. In complex cases, expert advice is desirable.

Deciphering the genotype and phenotype of hairy cell leukemia: clues for diagnosis and treatment

Introduction: Hairy cell leukemia (HCL) is a rare, indolent B-cell neoplasm. The classical variant of the disease is characterized by the BRAF V600E mutation, which is present in virtually all cases. How this mutation leads to the signs and symptoms of the disease is currently not known. Areas covered: This review explores the genetic background of HCL, especially the BRAF V600E driver mutation, but passenger mutations and their effects are also included. The clinical significance of BRAF mutations in other cancer types is discussed, as well as BRAF- induced senescence. An overview of the major forms of treatment of HCL (cytostatic drugs, specific BRAF inhibitors, B cell-specific antibodies) is given. Finally, possible mechanisms of the monocytopenia and hairy morphology so typical of this disease are discussed. Expert opinion: Although being a rare disease, HCL and its pathogenesis can yield important information about BRAF-related cancer metabolism. Many aspects of the disease are still unclear, but with the right resources, this could change. This can lead to a more efficient and specific treatment, thus leading to decreased morbidity.

Outcomes and second neoplasms in hairy cell leukemia: A retrospective cohort

Hairy cell leukemia (HCL) is a rare chronic B-cell lymphoproliferative disease which is treated on the basis of small studies, making the literature still scarce of reports, especially of those conducted in Latin America. Here we intend to describe clinical characteristics, rates of response, survival and second neoplasms in HCL patients treated in a reference center in Brazil. All patients diagnosed with HCL between July/1987 and Jun/2018 were included in this analysis. Fifty-four patients were included in this analysis. Median age at diagnosis was 55 years (range, 26-88), with 37% being above 60 years-old. Most patients were treated with cladribine in our cohort (n = 36; 68%), administered through intravenous continuous infusion. Remaining patients were firstly managed with splenectomy (n = 7; 13%), IFN (n = 6; 11%) and rituximab (n = 2; 4%). In a univariate analysis, platelet count and B2M level at diagnosis were statistically associated with CR achievement (p = 0.004 and p = 0.024, respectively). A median follow-up time of 9 years was calculated. Estimated 10-year overall survival was 91.1% (95% confidence interval, 77-97). In this cohort, 10 patients had any second neoplasm, diagnosed before or after HCL. Regarding the sites of cancer, 69% were of skin - 8/16 carcinoma-type and 3/16 melanoma-type. Our response and survival data are similar to those reported by literature, which reaffirms the role of purine analogs in current HCL management. With a very long follow-up we also have observed a high incidence of second neoplasm.

Variant form of hairy cell leukemia

Mature lymphoid B-cell proliferations with hairy cells represent heterogeneous entities where specific diagnosis is difficult but important since it impacts therapeutic management. The clinical cases of variant hairy cell leukemia reported herein illustrate the persistence of a clear interest in the use of splenectomy as a therapeutic alternative. Furthermore, ibrutinib appears to be a promising treatment in patients with relapsed/refractory disease.

Moxetumomab pasudotox-tdfk for relapsed/refractory hairy cell leukemia: a review of clinical considerations

PURPOSE

Hairy cell leukemia (HCL) is a rare mature B cell leukemia. Purine analogs are the mainstay of treatment of HCL, but relapse after purine analog therapy is common. Outcomes of treatment of relapsed/refractory HCL typically diminish with each successive line of therapy. Moxetumomab pasudotox-tdfk is a novel recombinant immunotoxin approved for the treatment of patients with relapsed/refractory HCL who have received at least two prior therapies, including a purine analog. This article reviews HCL treatment, focusing on moxetumomab pasudotox-tdfk, its place in therapy, considerations for preparation and administration, and strategies for prevention and management of toxicities.

METHODS

A literature search was conducted in the PubMed database from inception to January 2019, using the following terms: moxetumomab, hairy cell leukemia, relapsed/refractory hairy cell leukemia, immunotoxin, and CD22. The package insert and available posters and abstracts were also reviewed.

RESULTS

FDA approval of moxetumomab pasudotox-tdfk was based on a phase III single-arm, open-label trial in 80 patients. Treatment with moxetumomab pasudotox-tdfk yielded a durable complete response rate of 30% with a median duration of response that had not yet been reached at a median follow-up of 16.7 months. The objective response rate was 75% based on blinded independent central review. The most common adverse reactions were infusion-related reactions, edema, nausea, fatigue, headache, pyrexia and anemia. Serious adverse events include capillary leak syndrome and hemolytic uremic syndrome.

CONCLUSIONS

Clinicians providing care for patients receiving moxetumomab pasudotox-tdfk should be aware of the strategies required for safe administration, including the management of serious adverse events.

Differential Expression of CD43, CD81, and CD200 in Classic Versus Variant Hairy Cell Leukemia

BACKGROUND

Hairy cell leukemia (HCL) and hairy cell leukemia variant (HCLv) are rare diseases with overlapping clinicopathological features. Features distinguishing HCL from HCLv include expression of CD25, CD123, CD200, annexin-A1, and the presence of BRAF V600E mutation. HCLv typically lacks these markers, but they may occur in a subgroup of HCL patients with an aggressive clinical course. We examined CD43, CD81, CD79b, and CD200 expression in HCL and HCLv.

METHODS

Multiparametric flow cytometry (FCM) was performed on blood from 59 HCL and 15 HCLv patients for protocol entry. Mean fluorescent intensity (MFI) of CD43, CD79b, CD81, and CD200 was determined (for CD200, n = 17 and 7, respectively).

RESULTS

Median MFI of HCL vs HCLv was 545 vs 272 for CD43, 602 vs 2,450 for CD81, 4,962 vs 1,969 for CD79b, and 11,652 vs 1,405 for CD200, respectively. Analysis of the median differences, HCL minus HCLv (and their 95% confidence intervals and P-values) indicated that CD43 MFI (estimated median difference (95% CI): 212 [72-413; P = 0.0027) and CD200 MFI (9,883 [3,514-13,434]; P < 0.0001) were higher in HCL than in HCLv, while CD81 MFI (-1,858 [-2,604 to -1,365]; P < 0.0001) was lower in HCL than in HCLv. CD79b MFI HCL median was more than double that of HCLv, but the observed difference (1,571 [-739 to 4,417]) was consistent with the null hypothesis of no difference (P = 0.13).

CONCLUSIONS

CD200, CD43, and CD81 are likely differentially expressed between HCL and HCLv, reflecting their differing disease biology. Inclusion of these markers in FCM is potentially informative. © 2019 International Clinical Cytometry Society.

Clinicopathologic and molecular features in hairy cell leukemia-variant: single institutional experience

Hairy cell leukemia-variant is rare. Only a small number of cases have been reported in the literature with little cytogenetic or molecular data available. In this study, we describe the clinicopathologic and genetic features of 23 patients with hairy cell leukemia-variant (16 men and 7 women) with a median age of 70 years. Most patients had splenomegaly (90%), leukocytosis (77%), and lymphocytosis (82%); no patients had monocytopenia. Histologically, the bone marrow biopsy specimens showed a mixed pattern of predominantly interstitial and lesser intrasinusoidal infiltration by leukemic cells. In bone marrow aspirate smears most cells had villous cytoplasmic features and a small nucleolus. We describe unusual sites of hairy cell leukemia-variant involvement in 4 patients, including brain, omentum, terminal ileum, and skin at the time of initial presentation. Immunophenotyping showed monotypic B-cells positive for pan B-cell antigens, CD11c, and CD103, and negative for CD25 and annexin A1. Conventional cytogenetic or fluorescence in situ hybridization analysis showed deletions of 17p13/TP53 and 11q22/ATM gene in 5/12 (42%) and 2/9 (22%) cases, respectively. Sequencing of the variable region of IGVH showed mutations (>2% deviation from germline) in 40% of the cases assessed. MAP2K1 mutation (p.C121S) was seen in 1 of 14 (7%) patients tested. No BRAF V600E mutations were detected. The patients were treated in a heterogeneous manner, but most often with therapies designed for classical hairy cell leukemia and the 5-year overall survival was 84%. In summary, hairy cell leukemia-variant exhibits a heterogeneous spectrum of clinical, morphologic, immunophenotypic, and genetic features that may overlap with classic hairy cell leukemia and other hairy cell-like B-cell neoplasms. A subset of patients can have an aggressive clinical course. In our experience MAP2K1 mutations are uncommon in this disease.

New generation sequencing of targeted genes in the classical and the variant form of hairy cell leukemia highlights mutations in epigenetic regulation genes

Classical hairy cell leukemia (HCL-c) is a rare lymphoid neoplasm. BRAF^V600E mutation, detected in more than 80% of the cases, is described as a driver mutation, but additional genetic abnormalities appear to be necessary for the disease progression. For cases of HCL-c harboring a wild-type BRAF gene, the differential diagnosis of the variant form of HCL (HCL-v) or splenic diffuse red pulp lymphoma (SDRPL) is complex. We selected a panel of 21 relevant genes based on a literature review of whole exome sequencing studies (BRAF, MAP2K1, DUSP2, MAPK15, ARID1A, ARID1B, EZH2, KDM6A, CREBBP, TP53, CDKN1B, XPO1, KLF2, CXCR4, NOTH1, NOTCH2, MYD88, ANXA1, U2AF1, BCOR, and ABCA8). We analyzed 20 HCL-c and 4 HCL-v patients. The analysis of diagnostic samples mutations in BRAF (n = 18), KLF2 (n = 4), MAP2K1 (n = 3), KDM6A (n = 2), CDKN1B (n = 2), ARID1A (n = 2), CREBBP (n = 2) NOTCH1 (n = 1) and ARID1B (n = 1). BRAF^V600E was found in 90% (18/20) of HCL-c patients. In HCL-c patients with BRAF^V600E, other mutations were found in 33% (6/18) of cases. All 4 HCL-v patients had mutations in epigenetic regulatory genes: KDM6A (n = 2), CREBBP (n = 1) or ARID1A (n = 1). The analysis of sequential samples (at diagnosis and relapse) from 5 patients (2 HCL-c and 3 HCL-v), showed the presence of 2 new subclonal mutations (BCOR^E1430X and XPO1^E571K) in one patient and variations of the mutated allele frequency in 2 other cases. In the HCL-v disease, we described new mutations targeting KDM6A that encode a lysine demethylase protein. This opens new perspectives for personalized medicine for this group of patients.

Bendamustine plus rituximab is an effective first-line treatment in hairy cell leukemia variant: a report of three cases

Hairy cell leukemia variant (HCLv) is a chronic lymphoproliferative disorder classified as a provisional entity in the 2016 WHO Classification of Lymphoid Tumors. HCLv is characterized by unfavorable prognosis, low complete remission rates and limited disease control following classical hairy cell leukemia-based regimens. In this study, we report 3 cases of elderly patients with treatment-naive, TP53 un-mutated HCLv, who were effectively treated with four cycles of bendamustine plus rituximab. The regimen was completed in all the patients with acceptable toxicity. All patients achieved a complete clinical response with no evidence of residual disease at bone marrow biopsy and flow-cytometry examination. After a median follow-up of 19 months, the 3 subjects are still in complete remission. In this work, bendamustine plus rituximab proved to be an effective and feasible first-line treatment strategy for elderly patients with TP53 un-mutated HCLv.

Genomic analysis of hairy cell leukemia identifies novel recurrent genetic alterations

Classical hairy cell leukemia (cHCL) is characterized by a near 100% frequency of the BRAFV600E mutation, whereas ∼30% of variant HCLs (vHCLs) have MAP2K1 mutations. However, recurrent genetic alterations cooperating with BRAFV600E or MAP2K1 mutations in HCL, as well as those in MAP2K1 wild-type vHCL, are not well defined. We therefore performed deep targeted mutational and copy number analysis of cHCL (n = 53) and vHCL (n = 8). The most common genetic alteration in cHCL apart from BRAFV600E was heterozygous loss of chromosome 7q, the minimally deleted region of which targeted wild-type BRAF, subdividing cHCL into those hemizygous versus heterozygous for the BRAFV600E mutation. In addition to CDKN1B mutations in cHCL, recurrent inactivating mutations in KMT2C (MLL3) were identified in 15% and 25% of cHCLs and vHCLs, respectively. Moreover, 13% of vHCLs harbored predicted activating mutations in CCND3 A change-of-function mutation in the splicing factor U2AF1 was also present in 13% of vHCLs. Genomic analysis of de novo vemurafenib-resistant cHCL identified a novel gain-of-function mutation in IRS1 and losses of NF1 and NF2, each of which contributed to resistance. These data provide further insight into the genetic bases of cHCL and vHCL and mechanisms of RAF inhibitor resistance encountered clinically.

CD11c+ T-bet+ memory B cells: Immune maintenance during chronic infection and inflammation?

CD11c+ T-bet+ B cells have now been detected and characterized in different experimental and clinical settings, in both mice and humans. Whether such cells are monolithic, or define subsets of B cells with different functions is not yet known. Our studies have identified CD11c+ IgM+ CD19^hi splenic IgM memory B cells that appear at approximately three weeks post-ehrlichial infection, and persist indefinitely, during low-level chronic infection. Although the CD11c+ T-bet+ B cells we have described are distinct, they appear to share many features with similar cells detected under diverse conditions, including viral infections, aging, and autoimmunity. We propose that CD11c+ T-bet+ B cells as a group share characteristics of memory B cells that are maintained under conditions of inflammation and/or low-level chronic antigen stimulation. In some cases, these cells may be advantageous, by providing immunity to re-infection, but in others may be deleterious, by contributing to aged-associated autoimmune responses.

Hairy cell leukaemia variant with periarticular joint infiltration and excellent radiotherapy response

Hairy cell leukaemia (HCL) is rare, accounting for only 2% of leukaemias. An even more infrequent variant has been described, HCL-V. The clinicopathologic features of these two entities overlap significantly, although they differ in a number of aspects, including demographics and immunophenotype. In this report, we present the case of a man with HCL-V diagnosed 12 years previously, who is currently haematologically stable with an unusual complication of joint pain due to extensive bony expansion secondary to leukaemic infiltration, and atypical skeletal imaging. His painful joint disease responded dramatically to radiotherapy.

Issues in diagnosis of small B cell lymphoid neoplasms involving the bone marrow and peripheral blood. Report on the Bone Marrow Workshop of the XVIIth meeting of the European Association for Haematopathology and the Society for Hematopathology

Small B cell lymphoid neoplasms are the most common lymphoproliferative disorders involving peripheral blood (PB) and bone marrow (BM). The Bone Marrow Workshop (BMW) organized by the European Bone Marrow Working Group (EBMWG) of the European Association for Haematopathology (EAHP) during the XVIIth EAHP Meeting in Istanbul, October 2014, was dedicated to discussion of cases illustrating how the recent advances in immunophenotyping, molecular techniques and cytogenetics provide better understanding and classification of these entities. Submitted cases were grouped into following categories: (i) cases illustrating diagnostic difficulties in chronic lymphocytic leukaemia (CLL); (ii) cases of BM manifestations of small B cell lymphoid neoplasms other than CLL; (iii) transformation of small B cell lymphoid neoplasms in the BM; and (iv) multiclonality and composite lymphomas in the BM. This report summarizes presented cases and conclusions of the BMW and provides practical recommendations for classification of the BM manifestations of small B cell lymphoid neoplasms based on the current state of knowledge.

CD5 positive hairy cell leukemia: A rare case report with brief review of literature

OBJECTIVE

The aberrant expression of CD5 in both HCL and HCL-v is a very rare event. Although a number of CD5 positive HCL and HCL-v cases have been reported, but these are far and few in between. We aimed to review the reported cases of CD5 positive HCL and its variant.

METHOD

We hereby report a case of CD5 positive HCL, with variations in PIK3CA and PDGFRA gene, along with a brief review of literature of the cases of CD5 positive HCL and its variant.

RESULTS AND CONCLUSION

The current case was positive for CD103, CD11c, CD25, and CD123 which has led the diagnosis to be of typical HCL. With the extensive literature review we found that only 26 cases of hairy cell leukemia [HCL and HCL-v] bearing CD5 expression have been reported so far. The positivity of CD5 is more common in HCL-v as compared to HCL. Additional prospective studies of CD5+ HCL and its variants are required to show whether they are a clinically significant subgroup of lymphoid malignancies. © 2016 International Clinical Cytometry Society.