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Background/aim: Hairy cell leukemia (HCL) is a well-known lymphoproliferative disease with very effective treatment approaches primarily relying on purine analogues. However, these treatments are associated with profound and prolonged immunosuppression. Merkel cell carcinoma (MCC) is a rare and extremely aggressive skin tumor with an increased incidence in immunocompromised patients., Case Report: We report a case of a patient with HCL who was diagnosed with MCC, while in remission following retreatment with pentostatin, which induced a profound decrease in CD4 (+) T-cells., Conclusion: Our case provides further evidence supporting the hypothesis of a significant association between immunosuppression and MCC pathogenesis., (Copyright © 2024, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

We report on the long-term efficacy and safety of a phase 2 trial of sequential cladribine and rituximab in hairy cell leukemia (HCL). One-hundred and thirty-nine patients were enrolled: 111 in the frontline setting, 18 in first relapse, and 10 with variant HCL (HCLv). A complete response (CR) was achieved in 133 of 137 evaluable participants (97%) with measurable residual disease (MRD) negativity in 102 (77%). MRD status was not associated with significant differences in event-free survival (EFS) or overall survival (OS). With a median follow-up of 7.8 years (range: 0.40-18.8), eight patients have experienced disease relapse (5.8%), 4/111 with newly diagnosed HCL (3·6%) and 4/10 with HCLv (40%) ( p  = 0.002). The 10-year EFS and OS rates were 86.7% and 91.1%, respectively. Grade 3 adverse events were observed in 28 participants (20·1%), mostly due to infections. Treatment of HCL with sequential cladribine followed by rituximab is associated with excellent efficacy and safety results both in the frontline and relapsed settings.

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., Competing Interests: Disclosure The authors declare they have no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Hairy cell leukemia (HCL) and HCL-like disorders have to be distinguished because of their different biology and treatment response. Thus, we conducted a retrospective study on patients with HCL and hairy cell leukemia variant (HCLv) to assess diagnostic algorithms and treatment outcomes in a real-world setting. We analyzed 225 HCL and 26 HCLv patients with median follow-up of 67.9 months (HCL) and 20.1 months (HCLv). Median age at diagnosis was 56.2 (HCL) and 69.5 years (HCLv), male predominance was observed in both groups (76.0% vs. 73.1%). Diagnostics was mostly based on morphological evidence of hairy cells in the peripheral blood and bone marrow. At diagnosis, BRAF V600E mutation was detected in 94.7% of examined HCL patients and in no HCLv patient. Front-line treatment was indicated in 205 (91.1%) HCL and 18 (69.2%) HCLv patients. The majority of HCL patients were administered a cladribine-based regimen (91.2%). Overall response rate (ORR) was higher in cladribine-treated patients compared to those given other treatments (97.7% vs. 81.3%), the same applied with achieving Complete remission (CR) (91.2% vs. 62.5%). HCLv treatment was heterogeneous, but cladribine remained the most frequent option (44.4%) with ORR 81.3% and CR rates 43.8%. Second-line treatment was indicated in 52 HCL and 8 HCLv patients, 25.4% and 44.4% of those treated in first-line. In the whole HCL group, median time to next treatment (TTNT) was not reached and 10-year TTNT was estimated at 74.1%. HCLv patients who underwent first-line treatment had a median TTNT of 56 months. The median overall survival (OS) in HCL patients was not reached compared to HCLv with a median OS of 9.5 years. These data confirm an excellent prognosis for HCL patients treated with cladribine-based therapy. On the contrary, HCLv with its aggressive behavior represents a group of patients in whom novel treatment approaches are needed., (© 2024 The Authors. Hematological Oncology published by John Wiley & Sons Ltd.)

Background: Hairy cell leukemia (HCL) is a rare mature B-cell malignancy that is primarily treated with purine analogues. However, relapse remains a significant challenge, prompting the search for alternative therapies. The BRAF V600E mutation prevalent in HCL patients provides a target for treatment with vemurafenib., Patients and Methods: This multicenter retrospective study included nine patients with relapsed/refractory (R/R) HCL from six different centers. Patient data included demographics, prior treatments, clinical outcomes, and adverse events., Results: Patients received different treatment regimens between centers, including vemurafenib alone or in combination with rituximab. Despite the differences in protocols, all patients achieved at least a partial response, with seven patients achieving a complete response. Adverse events were generally mild with manageable side effects. The absence of myelotoxic effects and manageable side effects make BRAF inhibitors attractive, especially for patients ineligible for purine analogues or those with severe neutropenia., Conclusion: Single agent vemurafenib or in combination with rituximab appears to be a promising therapeutic option for R/R HCL. Further research is needed to establish standardized treatment protocols and to investigate long-term outcomes., Competing Interests: Declaration of Competing Interest All of the authors declare that there is no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Haemophagocytic lymphohistiocytosis (HLH) is a rare, aggressive, excess immune activation syndrome. Diagnosis can be challenging due to its several clinical mimics including sepsis. There are multiple aetiologies of HLH; in adults, it is most commonly triggered by infection, malignancy, drugs and autoimmune processes. Failure to rapidly diagnose and treat this condition can be fatal. The management of HLH includes identifying and removing the trigger, supportive management and immunosuppression. Identifying the trigger is essential to inform the most appropriate type of immunosuppression. Here, we report a case of likely drug-induced HLH in a patient recently treated for hairy cell leukaemia. The culprit drug was thought to be co-trimoxazole and this case report highlights a very rare complication of this commonly used drug. We discuss our management approach with steroid monotherapy and withdrawal of co-trimoxazole., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

The association between Hairy Cell Leukemia (HCL) and non-tuberculous mycobacterial infections (NTMs) is well described, most notably Mycobacterium kansasii . The exact pathophysiology is not known. We report a case of a 31-year-old male with concomitantly diagnosed HCL and disseminated M kansasii infection who presented with rash, pancytopenia, and bulky axillary lymphadenopathy. The M kansasii was initially diagnosed through use of cell-free DNA detection and confirmed by bone marrow and lymph node cultures. Hairy Cell Leukemia was diagnosed with peripheral flow cytometry and confirmed via the same bone marrow sample. His HCL was put into remission with a single course of cladribine and rituximab chemotherapy; however, his M kansasii infection persisted for 6 months despite aggressive antimicrobial and surgical therapy. It was finally controlled using high-dose rifampin in combination with azithromycin and ethambutol. This case highlights the known link between HCL and M kansasii. Furthermore, it hints at potential causes beyond chemotherapy-induced immunocompromise. Notable possibilities include HCL cells acting as sanctuary sites for M kansasii to evade the immune system, and subclinical M kansasii infections causing NLRP3 inflammasome overactivation to trigger the oncogenic transformation to HCL. More research into the pathophysiologic link between HCL and M kansasii infections would allow for more effective prevention, diagnosis, and treatment of these severe atypical infections which are the major cause of morbidity in the cladribine era of HCL treatment., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Hairy cell leukemia (HCL), similar to its variant HCLv, is a B-cell malignancy associated with decreased humoral immunity. We prospectively monitored the largest cohort of patients with HCL/HCLv to date (n = 503) for COVID-19 by symptoms, antibody, and polymerase chain reaction (PCR) and/or antigen positivity. Fifty percent (253 of 503) of the patients with HCL/HCLv (238 HCL and 15 HCLv) had evidence of COVID-19, with 210 (83%) testing positive by PCR or rapid-antigen test. Of the 43 patients without positive tests, all had nucleocapsid antibodies indicating COVID-19 exposure, 7 recalled no symptoms, and 36 had mild symptoms. Of the 210 who tested positive, 23, 46, 129, and 12 cases occurred in 2020, 2021, 2022, and 2023, respectively. Among them, 175 began treatment for HCL/HCLv 0.4 to 429 (median, 66) months before, and 132 had their last dose of anti-CD20 monoclonal antibody 0.2 to 229 (median, 63) months before. Two patients died, including a young woman who began rituximab 2 months after first-line cladribine before vaccine availability. Nearly all patients with HCL/HCLv recovered uneventfully from COVID-19 including those without vaccination or those with significant immunosuppression and recent treatment. However, decreased normal B cells from HCL or treatment was associated with lower spike antibody levels as a response to COVID-19 (P = .0094) and longer recovery time (P = .0036). Thus, in a large cohort of patients with HCL/HCLv and in the first to determine relationships between COVID-19 outcome and immune markers, mortality was relatively low (∼1%), sequelae were uncommon, and recovery from COVID-19 was longer if normal B cells were low after recent treatment. The trials are registered at www.clinicaltrials.gov as #NCT01087333 and #NCT04362865., (Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution.)

Introduction: Hairy cell leukemia (HCL) is an indolent B-cell lymphoproliferative disease. BRAF V600E mutation is detected in nearly all classical HCL cases which offers the possibility of targeted therapy. Objective: The aim of our study was to assess the efficacy of low-dose vemurafenib as well as to assess the long term outcome of HCL patients treated with this drug at the Department of Internal Medicine and Oncology at Semmelweis University. Methods: We report on 10 patients with classical HCL treated with low-dose vemurafenib at our Department between 2013 and 2022. Results: As a result of fixed time low-dose vemurafenib treatment, 5 of 10 patients (5/10) achieved partial remission, 4 (4/10) had stable disease, and 1 (1/10) had MRD positivity. No patients achieved complete remission. The median progression-free survival was 28.5 months while the overall survival was 82 months. Conclusion: We confirm that low dose of vemurafenib is effective and safe in the vast majority of patients with HCL. This small-molecule oral treatment allows to gain valuable time-months or even years-before further, usually parenteral treatment options have to be given or before previous treatment has to be repeated. There are also promising data supporting the combination of vemurafenib with other drugs for the treatment of HCL patients which could provide even further possibility to bridge treatment., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Ferenczi, Nagy, Istenes, Eid, Bödör, Timár and Demeter.)

Since the recognition of BRAF V600E mutations in the majority of cases of hairy cell leukaemia, Erdheim-Chester disease and Langerhans cell histiocytosis, the targeted oral kinase inhibitors dabrafenib and vemurafenib have been adapted for their treatment. Like other targeted agents, these drugs produce high response rates and predictable but unique side effects. Physician familiarity is essential for the effective use of these agents. We review the Australian experience of BRAF/MEK inhibitor therapy in these rare haematological cancers., (© 2023 Royal Australasian College of Physicians.)

Introduction: Hairy cell leukemia (HCL) is a rare subtype of indolent lymphoid leukemia originating from a mature B lymphocyte. The standard first-line treatment for classic HCL, and HCL variant (HCLv), consists of purine nucleoside analogs (PNA), with or without rituximab. However, almost half of patients relapse and require subsequent therapy., Areas Covered: This article summarizes recent achievements in the treatment of relapsed and refractory HCL. A literature search was conducted of the PubMed and MEDLINE database for articles in English. Publications from 2010 through January 2023 were scrutinized. The search terms used were hairy cell leukemia in conjunction with BRAF inhibitors, Bruton's tyrosine kinase (BTK) inhibitors, CD20 monoclonal antibodies, relapsed, refractory and variant.The growing understanding of HCL biology has allowed the design of several new, chemotherapy-free targeted drugs which have demonstrated encouraging efficacy in early clinical trials., Expert Opinion: Novel drugs will soon be available to assist standard therapy for HCL and HCLv among patients with suboptimal results following PNA treatment. In particular, the BRAF inhibitors vemurafenib and dabrafenib, with or without rituximab, have revolutionized treatment of patients with relapsed or refractory disease.

Objective: To evaluate the clinical characteristics, treatment response, and outcomes in patients with classical hairy cell leukemia (cHCL) and HCL variant (HCL-V). Methods: This is a retrospective case series study. Between January 2011 and December 2021, clinical data of 30 patients newly with diagnosed HCL at Peking Union Medical College Hospital were analyzed. The main outcome measures include clinical characteristics, treatment efficacy and survival. The Kaplan-Meier method was used for survival analysis. Results: Twenty-one cases of cHCL and 9 cases of HCL-v were included. The median age at diagnosis was 55.5 (range, 30-86) years, with the ratio of male to female 2.75∶1. The main clinical manifestations included fatigue in 11 cases (36.7%), abdominal distension in 7 cases (23.3%), and infection in 4 cases, while 8 cases were asymptomatic. Splenomegaly was reported in 24 cases (80.0%), including 7 (23.3%) with megalosplenia. The white blood cell count, lymphocyte count, and the proportion of peripheral hairy cells in HCL-v group were significantly higher than those in cHCL group, whereas the development of anemia, thrombocytopenia, and monocytopenia in cHCL group was more remarkable than that in HCL-v group (all P< 0.05). The BRAF-V600E gene mutation was detected only in cHCL patients (11/14 vs. 0/9, P< 0.001). In terms of immunophenotype, the expression of CD25, CD103, CD123 and CD200 in cHCL group (20/20, 20/20, 4/7, 7/17) were all stronger than those in HCL-v group (3/9, 7/9, 0/4, 2/8). Twenty-two patients were treated, of which 13 cases (12 cases of cHCL and 1 case of HCL-v) with cladribine, and 9 cases (4 cHCL and 5 HCL-v) with interferon. Complete remission rate and overall response rate were comparable between cladribine and interferon treatment groups (both P< 0.05). The median follow-up time was 31 (range, 1-125) months, and the median overall survival (OS) of the entire group was 125 months. The 5-year OS rate in HCL-v patients represented a trend of inferior (50.0% vs. 95.0%, P= 0.207). Conclusions: The clinical features of HCL are unspecific, which includes fatigue, splenomegaly and recurrent infection. The clinical features, immunophenotype, treatment response and prognosis of HCL-v are different from those of cHCL. BRAF-V600E gene mutation is suggested as a key marker for differential diagnosis. Cladribine is recommended as front-line regimen of cHCL patients with satisfactory efficacy and prognosis. Conversely, response and clinical outcome in HCL-v patients still need to be improved.

Background: Hairy cell leukemia (HCL) is an indolent chronic lymphoproliferative disorder and first-line treatment with either intravenous or subcutaneous cladribine generally leads to long-lasting remissions., Method: All 131 patients with hairy-cell leukemia (HCL) were analyzed, with a median follow-up of 91 months. Data is from 2007 to 2020. We evaluated the response rate to cladribine as the first line and the response rate to cladribine with or without rituximab in relapsed patients. Further, we assessed relapse-free survival, complications, and secondary malignancy., Results: After a median follow-up of 91 months, the recurrence rate was 24%. The 5-year and 10-year RFS rates were 85% and 66%, respectively. Adding rituximab to 2-CDA leads to a better response rate than just cladribine (90% vs. 27.3%, p-value = 0.002) in the relapsed patients., Conclusion: HCL patients have long-term survival when cladribine is the first line of treatment. Furthermore, adding rituximab to cladribine leads to a higher response rate.

BRAF V600E is the key oncogenic driver mutation in hairy cell leukemia (HCL). We report the efficacy and safety of dabrafenib plus trametinib in patients with relapsed/refractory BRAF V600E mutation-positive HCL. This open-label, phase 2 study enrolled patients with BRAF V600E mutation-positive HCL refractory to first-line treatment with a purine analog or relapsed after ≥2 prior lines of treatment. Patients received dabrafenib 150 mg twice daily plus trametinib 2 mg once daily until disease progression, unacceptable toxicity, or death. The primary endpoint was investigator-assessed objective response rate (ORR) per criteria adapted from National Comprehensive Cancer Network-Consensus Resolution guidelines. Secondary endpoints included duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Fifty-five patients with BRAF V600E mutation-positive HCL were enrolled. The investigator-assessed ORR was 89.0% (95% confidence interval, 77.8%-95.9%); 65.5% of patients had a complete response (without minimal residual disease [MRD]: 9.1% [negative immunohistochemistry of bone marrow {BM} biopsy], 12.7% [negative BM aspirate flow cytometry {FC}], 16.4% [negative immunohistochemistry and/or FC results]; with MRD, 49.1%), and 23.6% had a partial response. The 24-month DOR was 97.7% with 24-month PFS and OS rates of 94.4% and 94.5%, respectively. The most common treatment-related adverse events were pyrexia (58.2%), chills (47.3%), and hyperglycemia (40.0%). Dabrafenib plus trametinib demonstrated durable responses with a manageable safety profile consistent with previous observations in other indications and should be considered as a rituximab-free therapeutic option for patients with relapsed/refractory BRAF V600E mutation-positive HCL. This trial is registered at www.clinicaltrials.gov as #NCT02034110., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

In classical hairy cell leukemia (HCL), standard treatments including purine analogs achieve a durable response (up to 90%), but lead to severe immunosuppression and long-lasting depletion of CD4 + T lymphocytes. The BRAF inhibitor vemurafenib is effective in HCL, but its use in first-line treatment is restricted to select clinical situations (e.g. active infection). Its impact on immune function or response to vaccines in HCL is unclear. We treated four HCL patients with vemurafenib during the COVID-19 pandemic and monitored immune reconstitution and response to SARS-CoV-2 immunization. All patients responded to HCL treatment with normalization of peripheral blood counts. No severe infections occurred. As an indication of limited immunosuppression by vemurafenib, stable CD4 + and CD8 + T lymphocyte counts and immunoglobulin levels were observed. Three out of four patients received SARS-CoV-2 vaccination (Pfizer-BioNTech) during treatment with vemurafenib. IgG antibody levels against the spike-protein of SARS-CoV-2 were detected (40-818 AE/ml). Our data suggest that vemurafenib has limited effects on cellular and humoral immune function in HCL, which allows for successful SARS-CoV-2 vaccination. These data support the use of BRAF inhibitors during the current pandemic where continued immune response is necessary for minimizing the COVID-19-related risk of non-vaccinated patients., (© 2022. The Author(s).)

Vemurafenib, an oral BRAF inhibitor, has demonstrated high response rates in relapsed/refractory (R/R) hairy cell leukemia (HCL). However, little is known about long-term outcomes and response to retreatment. Herein, we report the results of 36 patients with R/R HCL treated with vemurafenib from the United States arm of the phase 2 clinical trial (NCT01711632). The best overall response rate was 86%, including 33% complete response (CR) and 53% partial response (PR). After a median follow-up of 40 months, 21 of 31 responders (68%) experienced relapse with a median relapse-free survival (RFS) of 19 months (range, 12.5-53.9 months). There was no significant difference in the RFS for patients with CR vs PR. Fourteen of 21 (67%) relapsed patients were retreated with vemurafenib, with 86% achieving complete hematologic response. Two patients acquired resistance to vemurafenib with the emergence of new KRAS and CDKN2A mutations, respectively. Six of 12 (50%) responders to vemurafenib retreatment experienced another relapse with a median RFS of 12.7 months. Overall survival (OS) was 82% at 4 years, with a significantly shorter OS in patients who relapsed within 1 year of initial treatment with vemurafenib. Higher cumulative doses or a longer duration of treatment did not lengthen the durability of response. All adverse events in the retreatment cohort were grade 1/2 except for 1 case of a grade 3 rash and 1 grade 3 fever/pneumonia. Our data suggest that vemurafenib retreatment is a safe and effective option for patients with R/R HCL., (© 2022 by The American Society of Hematology.)

Cladribine is a purine analog used in first-line treatment of hairy cell leukemia and in relapsed/refractory chronic lymphocytic anemia. Although cladribine is typically associated with mild, self-limited skin reactions, there is increasing evidence that cladribine may increase the risk of severe cutaneous adverse reactions (SCAR) when combined with drugs classically associated with SCAR (e.g. allopurinol) beyond what would be expected for either drug alone, possibly due to cladribine-induced lymphopenia. We analyzed all SCAR cases reported for cladribine in Janssen's Global Safety Database and found that 26/35 (74.3%) reported concomitant drugs known to be associated with SCAR, most commonly sulfamethoxazole/trimethoprim (SMX/TMP) and allopurinol. In addition, a review of the WHO VigiBase showed that several drugs, including penicillins, SMX/TMP, and allopurinol had a statistically significant contribution to cladribine-associated SCAR. These results lend further support that cladribine may increase the propensity of these drugs to cause SCARs.

Hairy cell leukaemia (HCL) is a rare B cell malignancy that is associated with the BRAF V600E mutation and has good treatment response to purine analogues. Its presentation synchronously with other malignancies has been rarely reported. Here, we present a patient with HCL with hepatic involvement who was also found to have pancreatic adenocarcinoma concomitantly at the time of diagnosis. Treating these rare cases simultaneously is a challenge clinically. Throughout this case study, we provide our approach on how oncological care teams provided care for this complicated and rare disease state., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Hairy cell leukaemia (HCL) is an uncommon neoplasm of mature B-lymphoid cells which is characterized by cytopenias, commonly of all three cell lines, with typical hairy cells on peripheral smear and/or bone marrow along with organomegaly. Objective was to document the outcomes of HCL patients treated at a tertiary care hospital in Pakistan., Methods: Medical records of patients from 2004 to 2020 were reviewed and data was collected to assess patient's demographics, symptomatology, remission rate and overall survival. The record flies of all patients presenting to AFBMTC with HCL were included in the study. The record file with insufficient data were excluded., Results: 26 patients with a mean age of 48.12±11.43 years were diagnosed with HCL and treated at AFBMTC. Out of these, 23 (88.4%) were male and 03 (11.5%) females. The main presenting complaints were generalized body aches (34.6%), fever (15.4%), incidental finding of cytopenias (11.5%) and abdominal discomfort (26.9%). Splenomegaly was found in 76.92% while hepatomegaly was found in 46.15% of patients. A total of 12 (46.15%) patients received Cladribine (either intravenous or subcutaneous) and splenectomy was done in 7 (26.92%) as 1st line treatment. Eleven patients out of 12 (83.33%) who received Cladribine and 05 (71.42%) patients out of seven who underwent splenectomy; achieved complete remission (CR) after 1 st line of treatment. One patient received Cladribine as 1st line of treatment but did not respond and CHOP regimen was given as second line. Out of the 26 patients, 5 patients (19.23%) relapsed at a median interval of 5.83±6.6 years. Two patients received Cladribine + Rituximab while 03 patients received cladribine as their salvage therapy. Disease free survival (DFS) of 71.4% among the patients underwent splenectomy while 75.0% among the patients received Cladribine. DFS for combination therapy (included CHOP and CVP) was 66.7% while OS was calculated among patients who received cladribine, splenectomy and combination chemotherapy as 100%, 85.7%, 66.7% respectively., Conclusions: Cladribine has a significant efficacy and encouraging acute and long-term benefits when administered to patients with HCL. A single course of cladribine was able to induce CR in a vast majority of patients. At a median follow up of 4.6 years the OS was 100% with cladribine and 85% with splenectomy. Those who relapsed were successfully retreated with cladribine + Rituximab.

Purpose of Review: This article aims to bring an update on the recent discoveries in hairy cell leukemia (HCL), especially findings in pathophysiology and therapeutic advances., Recent Findings: Major discoveries have been made in genetics and epigenetics of HCL. Moreover, the importance of several signaling pathways and tumor microenvironment has been recently highlighted. These findings led to the development of new targeted therapies which have shown interesting results in recent clinical trials. HCL is a chronic B-cell lymphoproliferative disorder. Most patients respond to purine nucleoside analogs (PNA) like cladribine or pentostatin. However, relapses are frequent and the disease often becomes less sensitive to chemotherapy. Recent discoveries in pathophysiology, like the presence of the V600E mutation of the B-raf proto-oncogene (BRAF) gene and the importance of the B-cell receptor (BCR) pathway, led to the development of new drugs for relapsed/refractory (R/R) HCL patients. The variant-type of HCL (HCL-V) is usually less sensitive to PNA. Chemo-immunotherapy using PNA and rituximab (R), BRAF, MEK, or Bruton Tyrosine Kinase (BTK) inhibitors may be used. Good results were recently published and achieved with moxetumomab pasudotox (Moxe), an anti-CD22 immunoconjugate. In this review, we will present an update on HCL and HCL-V, focusing on pathophysiology and recent therapeutic advances., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The detailed clinical course of coronavirus disease 2019 (COVID-19) in patients with hairy cell leukemia (HCL) is rarely reported. We report the first case of HCL diagnosed with prolonged pancytopenia after COVID-19 infection in Japan. We describe the case of a 56-year-old man who was diagnosed with COVID-19. Computed tomography revealed ground-glass opacities in the bilateral lung lobes as well as splenomegaly. Remdesivir and dexamethasone were administered for the treatment of COVID-19. Since the pancytopenia persisted, bone marrow examination was performed, and he was diagnosed with HCL. Although pancytopenia can occur with COVID-19 alone, clinicians should be alerted regarding the presence of hematologic malignancies in patients in whom pancytopenia persists after COVID-19 treatment or in those with splenomegaly. Further, the condition of all previously reported patients with COVID-19 associated with HCL was severe enough to require mechanical ventilation. This is the first case in which the disease was not severe. The interleukin-6 (IL-6) level was lower in this case than in previous cases, suggesting that racial differences in IL-6 production may have contributed to COVID-19 severity.

Background: Hairy cell leukemia (HCL) is a rare chronic B cell malignancy, characterized by infiltration of bone marrow, blood and spleen by typical "hairy cells" that bear the BRAFV600E mutation. However, in addition to the intrinsic activation of the MAP kinase pathway as a consequence of the BRAFV600E mutation, the potential participation of other signaling pathways to the pathophysiology of the disease remains unclear as the precise origin of the malignant hairy B cells., Materials and Methods: Using mRNA gene expression profiling based on the Nanostring technology and the analysis of 290 genes with crucial roles in B cell lymphomas, we defined a 17 gene expression signature specific for HCL., Results: Separate analysis of samples from classical and variant forms of hairy cell leukemia showed almost similar mRNA expression profiles apart from overexpression in vHCL of the immune checkpoints CD274 and PDCD1LG2 and underexpression of FAS. Our results point to a post-germinal memory B cell origin and in some samples to the activation of the non-canonical NF-κB pathway., Conclusions: This study provides a better understanding of the pathogenesis of HCL and describes new and potential targets for treatment approaches and guidance for studies in the molecular mechanisms of HCL., (© 2022. The Author(s).)

Hairy cell leukemia (HCL) is a rare lymphoproliferative disease with an excellent prognosis after treatment with cladribine (2CDA), although relapse may occur during follow-up. The aim of the study is to review the efficacy, safety, long-term remission rate, and overall survival (OS) in those patients who received 2CDA as first-line treatment. We retrospectively reviewed data of HCL patients treated with 2CDA between March 1991 and May 2019 at 18 Italian Hematological centers: 513 patients were evaluable for study purpose. The median age was 54 years (range 24-88) and ECOG was 0 in 84.9% of cases. A total of 330 (64.3%) patients received 2CDA intravenously and 183 (35.7%) subcutaneously. ORR was 91.8%: CR was obtained in 335 patients (65.3%), PR in 96 (18.7%), and hematological response in 40 (7.8%) patients; in 42 (8.2%) no response was observed. Hemoglobin value (p = 0.044), frequency of circulating hairy cells (p = 0.039), recovery of absolute neutrophil count (p = 0.006), and normalization of spleen (p ≤ 0.001) were associated with CR compared to PR in univariable analysis. At a median follow-up of 6.83 years (range 0.04-28.52), the median time to relapse was 12.2 years. A significant difference in duration of response was identified between patients that obtained a CR and PR (19.4 years versus 4.8 years, p < 0.0001). Non-hematological grade 3 or higher early toxicity was reported in 103 (20.1%) patients. Median OS was not reached: 95.3%, 92.4%, and 81.8% of patients were estimated to be alive at 5, 10, and 15 years, respectively. Forty-nine patients died (9.5%), following an infection in 14 cases (2.7%), natural causes in 14 (2.7%), cardiovascular events in 13 (2.5%), a second neoplasm in 6 (1.2%), and progression of HCL in 2 cases (0.4%). Following treatment of HCL with 2CDA, 80% of patients are estimated to be alive 15 years after diagnosis., (© 2022. The Author(s).)

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., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Introduction: Frontline treatment of hairy cell leukemia (HCL) with a single course of the purine nucleoside analog (PNA) produces a high rate of complete remission (CR) with prolonged durations. At the time of relapse, although treatment guidelines recommend re-treatment with a PNA alone or in combination with rituximab (R), practice patterns vary and data supporting each approach are limited., Methods: We conducted a multisite outcomes analysis of patients treated for HCL between 1995 and 2018 at six US medical centers. All patients were treated with frontline PNA and subsequently required treatment with a PNA alone (PNA) or with R (+R)., Results: Of the 88 patients analyzed, 56 (63.6%) received second-line PNA and 22 (36.4%) received a PNA + R. Baseline characteristics of both groups were similar. There was no difference in median PFS [67 months (95% CI 43.8 non-reached (NR)) vs. 65 months (95% CI 60-NR)] or 5-year OS [98% (95% CI 0.94-1) vs. 94% (95% CI 0.83-1), p = .104] in the PNA versus PNA + R cohorts, respectively., Conclusion: To our knowledge, this is the largest study evaluating the role of R in treatment of relapsed HCL and suggests that there is no advantage to the addition of R to PNA therapy at the time of first re-treatment., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Hairy cell leukemia (HCL) responds very well to frontline chemotherapy with purine analogs (cladribine and pentostatine). However, approximately half of patients experience 1 or more relapses, which become progressively resistant to these myelotoxic and immunosuppressive agents. At progression, standard therapeutic options include a second course of purine analogs alone or in combination with rituximab and, upon second relapse, therapy with the anti-CD22 immunotoxin moxetumomab pasudotox. Furthermore, blockade of the mutant BRAF-V600E kinase (the pathogenetic hallmark of HCL) through orally available specific inhibitors (vemurafenib or dabrafenib) effaces the peculiar morphologic, phenotypic, and molecular identity of this disease and its typical antiapoptotic behavior and is emerging as an attractive chemotherapy-free strategy in various clinical scenarios. These include patients with, or at risk of, severe infections and, in a highly effective combination with rituximab, patients with relapsed or refractory HCL. Other treatments explored in clinical trials are BTK inhibition with ibrutinib and co-inhibition of BRAF (through dabrafenib or vemurafenib) and its downstream target MEK (through trametinib or cobimetinib). Here, we focus on our experience with BRAF inhibitors in clinical trials and as off-label use in routine practice by presenting 3 challenging clinical cases to illustrate their management in the context of all available treatment options., (© 2022 by The American Society of Hematology.)

Background: Hairy cell leukemia (HCL) is a rare chronic B-cell neoplasm with good long-term prognosis. First and second-line therapies include purine nucleoside analogues (PNAs) and rituximab, but until recently, limited alternative options were available for patients with two or more relapses., Aim: The aim of this study is to describe our real-life experience with HCL patients in third and fourth-line therapies., Methods and Results: Data from 49 HCL patients with two or more relapses, including 16 patients with three or more relapses, were collected from the French retrospective HCL cohort covering the period from 1980 until 2011. They were analyzed to assess hematological response, relapse free survival (RFS) and overall survival (OS) after third (L3) and fourth line (L4). The median age at diagnosis was 53 years. PNAs were the most frequently used treatments. As L3 therapy, 29 patients received PNAs (66%) and 15 (34%) other treatments (rituximab [11%] or interferon [7%] alone or in combination [16%]). The distribution of L4 treatments was similar. The overall hematological response rate (OHRR) after L3 was 97% (complete hematological response 86%) with a 40% five-year cumulative incidence of relapse (CIR), a median RFS of 104 months, and a median OS of 235 months. After L4, the OHRR was 94% with a two-year CIR of fourth relapse of 27%. Eleven secondary cancers (5-year cumulative incidence of 12%) were diagnosed in 10 patients. Patients with ≥2 relapses experience frequent further relapses, with increasingly shorter time to next treatment as the number of treatment lines increases. Furthermore, treatment strategies are associated with substantial toxicities., Conclusion: All these points lead to the need for novel treatments., (© 2021 The Authors. Cancer Reports published by Wiley Periodicals LLC.)

Introduction: This case report is presented to improve our understanding of the atypical immunophenotype of hairy cell leukemia., Patient Concerns: A 58-year-old woman presented to our department with fatigue for >10 days., Diagnosis: The patient was diagnosed with an increased proportion of abnormal lymphocytes in peripheral blood and bone marrow smear, positive for CD11c, CD19, CD20, CD22, CD25, CD123, CD200, and Kappa, partial expression of CD23, but no expression of CD103, positive for BRAF V600E mutation., Interventions and Outcomes: Cladribine combined with rituximab achieved complete remission of minor residual disease negativity., Conclusion: Hairy cell leukemia is rare, and the diagnosis and differential diagnosis should be made by combining the patient's medical history, clinical manifestations, immunophenotype, gene detection, and other means. Purine nucleoside analogs are the first-line treatments., Competing Interests: The authors report no conflicts of interest., (Copyright © 2021 the Author(s). Published by Wolters Kluwer Health, Inc.)

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., (© 2021 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Background: Polycythemia vera (PV) is one of the Philadelphia-negative myeloproliferative neoplasms (MPN), characterized by a pan-myelosis with an erythroid-predominant proliferation mainly driven by somatic JAK2 V617F gain-of-function mutation. Hairy cell leukemia (HCL) is a rare B-cell lineage lymphoproliferative disease (LPD) with a typic immunophenotypic profile. BRAF V600E, leading to constitutive activation of the RAF/MEK/ERK signalling pathway and increased cell proliferation, is identified as the driver mutation in almost all cases. Although the risk of developing an LPD is significantly increased in patients with MPN compared with the general population, few cases of co-occurring PV and HCL are reported to date. BRAF is one of the most frequently mutated oncogenes in human cancer and some point mutations were identified in multiple neoplasms in addition to HCL, including follicular and papillary thyroid adenoma and carcinoma., Case Presentation: Here we report a molecular diagnostic challenge in a woman with a concomitant diagnosis of JAK2 V617F PV, BRAF V600E HCL, and HRAS Q61K thyroid follicular adenoma., Conclusion: In the age of molecular and precision medicine, this case underlines the importance of integrating molecular results with clinical, radiologic, cytologic, and histopathologic investigations.

Background: Hairy cell leukemia (HCL) responds well to purine analogs with an overall median relapse free survival of 11-16 years. Most patients can be retreated with the same or a different purine analog however a subset of patients will become resistant or develop cumulative toxicities. Novel agents such as Vemurafenib (BRAF kinase inhibitor), Bendamustine/Rituximab (BR), Moxetumomab pasudotox (anti CD-22 recombinant immunotoxin) and Ibrutinib have emerging roles in patients with relapsed HCL., Methods: Five databases (PubMed, Embase, Cochrane Library, Web of Science and ClinicalTrials.gov) were searched using the following search terms: "hairy cell leukemia" or "leukemia, hairy cell" AND "relapse" or "recurrence". We included only prospective clinical trials with outcome data., Results: Vemurafenib monotherapy was evaluated in two separate arms of a phase 2 trial. In the US arm (n=24), the ORR was 100% (CR 42%; PR 58%). In the Italian arm (n=26), the ORR was 96% (CR 35%; PR 62%). In a phase 2 study (n=25), the combination of vemurafenib and rituximab showed CR of 100%. The combination of BR achieved an ORR of 100% whereas CR was 50% and 67% at a bendamustine dose of 70mg/m 2 (n=6) and 90 mg/m 2 (n=6) respectively. In a phase 3 trial, moxetumomab pasudotox (n=80) had an ORR of 75% (CR 41%). Single agent Ibrutinib (n=37) had an ORR of 54%. Therapies were generally well tolerated., Conclusion: Novel agents have good efficacy in HCL in patients with multiple relapses., Competing Interests: Disclosure All the authors have no disclosure or conflict of interest to report., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The treatment of hairy cell leukemia (HCL) has considerably changed over years. Purine analogues, namely cladribine, now represent the treatment of choice. One hundred and eighty-four patients were followed between 1986 and 2018 and treated according to era-specific guidelines. Responses were classified by combining Consensus Resolution criteria and marrow immunohistochemistry. Patients were grouped according to the number of treatment lines they received. Patients treated first line responded in 86% of cases, with complete response (CR) in 44% of cases. Response rates remained high throughout the first four lines (84%, 81%, 79% for the second line onward, with CR in 38%, 37%, 15% of cases respectively). One hundred and twenty-two patients received cladribine as first line treatment, with a response rate of 86% and a CR rate of 54%. Among the 66 CR patients, 45 (68%) have never received further therapy: 11 patients are in continuous CR between 5 and 10 years after treatment, 14 between 10 and 20 years and three patients at more than 20 years. Median time-to-next treatment (TTNT) for frontline cladribine-treated patients was 8.2 years: partial responders had a significantly shorter median TTNT than CR patients (5.3 years vs median not reached at 25.8 years, p < 0.001). Patients with HCL require subsequent lines of therapy in more than 50% of cases. Purine analogues allow significant response rates when applied first line and upon retreatment. Some patients may enjoy long lasting treatment-free intervals after one course of cladribine., (© 2021 Wiley Periodicals LLC.)

Moxetumomab pasudotox (Lumoxiti ® ), an anti-CD22 recombinant immunotoxin, is an important treatment option that is approved in adults with relapsed or refractory hairy cell leukaemia (HCL) who have received at least two prior lines of treatment with systemic therapies including purine nucleoside analogues. In a pivotal phase III trial, treatment with moxetumomab pasudotox resulted in approximately one third of patients achieving durable complete response lasting more than 6 months, as well as improvements in other haematological parameters and disease-related symptoms. Moxetumomab pasudotox had a generally manageable tolerability profile; the most common treatment-related adverse events (AEs) included nausea, peripheral oedema, headache and pyrexia. AEs of special interest (including haemolytic uraemic syndrome and capillary leak syndrome) were generally manageable and reversible with monitoring and supportive care., (© 2021. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Purpose of Review: This article provides a brief update on the recommended diagnosis and treatment strategies for patients with the classic form of hairy cell leukemia (HCL) and HCL variant (HCLv)., Recent Findings: HCL is a chronic B-cell malignancy with multiple treatment options. In recent years, many novel drugs have been assessed for HCL treatment with promising results. The investigated nonchemotherapy options include moxetumomab pasudotox, which targets CD22; vemurafenib or dabrafenib, which target the BRAFV600E protein; trametinib, which targets mitogen-activated protein kinase enzyme; and ibrutinib, which targets Bruton tyrosine kinase., Summary: Purine analogs significantly improve survival in patients with HCL. However, patients often relapse, require multiple treatments, and may become refractory. The introduction of novel agents has expanded the spectrum of therapy possibilities in those patients. In the coming years, they will assist standard therapy for patients with HCL who may currently have suboptimal results., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)