The significance of minimal residual disease in hairy cell leukaemia treated with deoxycoformycin: a long-term follow-up study

Consensus opinion from an international group of experts on measurable residual disease in hairy cell leukemia

A significant body of literature has been generated related to the detection of measurable residual disease (MRD) at the time of achieving complete remission (CR) in patients with hairy cell leukemia (HCL). However, due to the indolent nature of the disease as well as reports suggesting long-term survival in patients treated with a single course of a nucleoside analog albeit without evidence of cure, the merits of detection of MRD and attempts to eradicate it have been debated. Studies utilizing novel strategies in the relapse setting have demonstrated the utility of achieving CR with undetectable MRD (uMRD) in prolonging the duration of remission. Several assays including immunohistochemical analysis of bone marrow specimens, multi-parameter flow cytometry and molecular assays to detect the mutant BRAF V600E gene or the consensus primer for the immunoglobulin heavy chain gene (IGH) rearrangement have been utilized with few comparative studies. Here we provide a consensus report on the available data, the potential merits of MRD assessment in the front-line and relapse settings and recommendations on future role of MRD assessment in HCL.

Measurable residual disease in hairy cell leukemia: Technical considerations and clinical significance

Hairy cell leukemia (HCL) is a rare type of chronic lymphoid leukemia originating from a mature B lymphocyte. A diagnosis of HCL is based on cytology, confirmed by multiparametric flow cytometry (MFC) studies using anti-B-cell monoclonal antibodies, together with a panel of antibodies more specific to HCL, such as CD11c, CD25, CD103 and CD123. Recently, the BRAF V600E mutation has been described as a disease-defining genetic event. Measurable residual disease (MRD) is defined as the lowest level of HCL cells that can be detected accurately and reproducibly using validated methods; as MRD negativity is associated with high rates of durable complete response, by clearing MRD, the long-term outcome may be improved in patients with advanced HCL. MRD is typically detected using bone marrow, and in some cases, peripheral blood; however, in HCL, discrepancies frequently exist between MRD results obtained from blood, bone marrow aspirate and core biopsy. Among the methods used for MRD detection, MFC appears to be a more sensitive technique than immunohistochemistry. Molecular tests are also used, such as real-time quantitative PCR for unique immunoglobulin heavy chain (IgH) gene rearrangements and PCR techniques with clone specificity for BRAF V600E. Clone-specific PCR (spPCR) is able to detect one HCL cell in 106 normal cells, and is particularly suitable for patients found to be negative for MRD by MFC. Recently, the Hairy Cell Leukemia Consortium created a platform to work on a definition for MRD, and establish the optimal time point, tissue type and method for measuring MRD. This

Minimal Residual Disease, Its Detection and Significance in Hairy-Cell Leukemia

As minimal residual disease (MRD) is considered the detection of hairy cells (HCs) in a patient with hairy cell leukemia (HCL) in complete remission with the absence of detectable HCs by routine morphology of peripheral blood, aspirates and bone marrow core sections, using more sensitive methods of identification as immunohistological staining or polymerase chain reaction (PCR) to detect immunoglobulin heavy chain genes rearrangement. Various monoclonal antibodies (MoAbs) as CD20, DBA.44, B ly-7, HC2, CD25 and CD11c have been applied using immunological staining. There is no standardized technique for identification of MRD. According to the technique used the MRD has been detected in 13% to 100% of patients in complete remission (CR). It may be concluded that many patients, if not all, in stable CR may have residual HCs. Whether MRD will have impact on early relapse or on long term outcome, or whether patients in CR with persistant MRD will remain so, is a matter of a longer follow-up.

How I manage patients with hairy cell leukaemia

Patients with hairy cell leukaemia (HCL) have highly favourable outcomes after purine analogue therapy. However, most patients subsequently relapse and require re-treatment. A minority of patients develop purine analogue-refractory disease. Targeted therapies have improved outcomes for such patients. Recently, the BRAF V600E mutation was identified in most patients with classical HCL, resulting in constitutive mitogen-activated protein kinase pathway activation; impressive responses are achieved in heavily pre-treated patients with BRAF inhibition. The CD22-targeted immunoconjugate moxetumomab pasudotox and BTK inhibitor ibrutinib also achieve responses in relapsed and refractory patients. HCL variant and the IGHV4-34 molecular variant of HCL lack BRAF mutation and have inferior outcomes with standard purine analogue therapy. The addition of rituximab to purine analogues achieves very high rates of minimal residual disease-negative complete remission and improves outcomes for patients with HCL variant. Given the rarity of HCL, optimal integration of novel therapies into treatment algorithms will require well-designed, collaborative studies.

Bone marrow and splenic histology in hairy cell leukaemia

Hairy cell leukaemia is a rare chronic neoplastic B-cell lymphoproliferation that characteristically involves blood, bone marrow and spleen with liver, lymph node and skin less commonly involved. Histologically, the cells have a characteristic appearance with pale/clear cytoplasm and round or reniform nuclei. In the spleen, the infiltrate involves the red pulp and is frequently associated with areas of haemorrhage (blood lakes). The cells stain for B-cell related antigens as well as with antibodies against tartrate-resistant acid phosphatase, DBA44 (CD72), CD11c, CD25, CD103, CD123, cyclin D1 and annexin A1. Mutation of BRAF -V600E is present and antibody to the mutant protein can be used as a specific marker. Bone marrow biopsy is essential in the initial assessment of disease as the bone marrow may be inaspirable or unrepresentative of degree of marrow infiltration as a result of the tumour associated fibrosis preventing aspiration of the tumour cell component. Bone marrow biopsy is important in the assessment of therapy response but in this context staining for CD11c and Annexin A1 is not helpful as they are also markers of myeloid lineage and identification of low level infiltration may be obscured. In this context staining for CD20 may be used in conjunction with morphological assessment and staining of serial sections for cyclin D1 and DBA44 to identify subtle residual infiltration. Staining for CD79a and CD19 is not recommended as these antibodies will identify plasma cells and can lead to over-estimation of disease. Staining for CD20 should not be used in patients following with anti-CD20 based treatments. Down regulation of cyclin D1 and CD25 has been reported in patients following BRAF inhibitor therapy and assessment of these antigens should not be used in this context. Histologically, hairy cell leukaemia needs to be distinguished from other B-cell lymphoproliferations associated with splenomegaly including splenic marginal zone lymphoma, splenic diffuse red pulp small B-cell lymphoma and hairy cell leukaemia variant. This can be done by assessment of the spleen but as this is now rarely performed in this disorder distinction is almost always possible by a combination of morphological and immunophenotypic studies on bone marrow trephine biopsy, which can be supplemented by assessment of BRAF-V600E mutation assessment in borderline cases.

Current and emerging treatment options for hairy cell leukemia

Hairy cell leukemia (HCL) is a lymphoproliferative B-cell disorder characterized by pancytopenia, splenomegaly, and characteristic cytoplasmic hairy projections. Precise diagnosis is essential in order to differentiate classic forms from HCL variants, such as the HCL-variant and VH4-34 molecular variant, which are more resistant to available treatments. The current standard of care is treatment with purine analogs (PAs), such as cladribine or pentostatin, which provide a high rate of long-lasting clinical remissions. Nevertheless, ~30%–40% of the patients relapse, and moreover, some of these are difficult-to-treat refractory cases. The use of the monoclonal antibody rituximab in combination with PA appears to produce even higher responses, and it is often employed to minimize or eliminate residual disease. Currently, research in the field of HCL is focused on identifying novel therapeutic targets and potential agents that are safe and can universally cure the disease. The discovery of the BRAF mutation and progress in understanding the biology of the disease has enabled the scientific community to explore new therapeutic targets. Ongoing clinical trials are assessing various treatment strategies such as the combination of PA and anti-CD20 monoclonal antibodies, recombinant immunotoxins targeting CD22, BRAF inhibitors, and B-cell receptor signal inhibitors.

Peripheral blood 8 colour flow cytometry monitoring of hairy cell leukaemia allows detection of high-risk patients

Although purine analogues have significantly improved the outcome of hairy cell leukaemia (HCL) patients, 30-40% relapse, illustrating the need for minimal residual disease (MRD) markers that can aid personalized therapeutic management. Diagnostic samples from 34 HCL patients were used to design an 8-colour flow cytometry (8-FC) tube for blood MRD (B/RD) analysis (188 samples) which was compared to quantitative IGH polymerase chain reaction (Q-PCR) on 83 samples and to qualitative consensus IGH PCR clonality analysis on 165 samples. Despite heterogeneous HCL phenotypes at diagnosis, discrimination from normal B lymphocytes was possible in all cases using a single 8-FC tube, with a robust sensitivity of detection of 10(-4) , comparable to Q-PCR at this level, but preferable in terms of informativeness, simplicity and cost. B/RD assessment of 15 patients achieving haematological complete remission after purine analogues was predictive of a clinically significant relapse risk: with a median follow-up of 95 months; only one of the nine patients with reproducible 8-FC B/RD levels below 10(-4) (B/RD(neg) ) relapsed, compared to 5/6 in the B/RD(pos) group (P = 0.003). These data demonstrate the clinical interest of a robust 8-FC HCL B/RD strategy that could become a surrogate biomarker for therapeutic stratification and new drug assessment, which should be evaluated prospectively.

Successful Treatment of Aplastic Variant of Hairy-cell Leukaemia with Deoxycoformycin

The case of a patient with the aplastic variant of hairy cell leukaemia, successfully treated with the drug Deoxycoformycin(Pentostatin), is presented. It is very important to be aware of this rare variant of a rare disease so that the right treatment can be offered.

Implications of minimal residual disease in hairy cell leukemia after cladribine using immunohistochemistry and immunophenotyping

Hairy cell leukemia (HCL) is a highly treatable, but generally incurable B-cell lymphoproliferative disorder with a long natural history. The purine analogs cladribine and pentostatin are the treatments of choice and both induce complete remission (CR) by peripheral blood counts and morphologic examination of the marrow in the large majority of patients. However, some patients, otherwise in apparent CR, have evidence of minimal residual disease (MRD) as detected by a number of different techniques, including immunohistochemistry, immunophenotypying by flow cytometry, and polymerase chain reaction (PCR). Immunohistochemistry is readily available, but precise criteria which constitute MRD are not uniform. Immunophenotyping can identify a characteristic immunophenotype, but leukemia cells may be difficult to obtain from a fibrotic bone marrow. Patient-specific PCR, while highly specific, is not readily available. Furthermore, the introduction of newer effective therapies such as the monoclonal antibody rituximab and immunoconjugate BL22 following a purine analog or concurrently with a purine analog may eradicate MRD. However, the optimal method for detecting MRD is not known. Furthermore, whether the eradication of MRD improves overall survival has not been established.

Approach to the patient after relapse of hairy cell leukemia

The current hairy cell leukemia (HCL) treatment is excellent, but evidence of cure with purine analogs cladribine and pentostatin, is lacking. Significant long-term immune suppression, particularly to CD4+ T-cells, and declining complete remission rates with each course, make the identification of new therapies an important goal. The anti-CD20 monoclonal antibody (Mab) rituximab displays significant activity, and, while causing prolonged normal B-cell depletion, spares T-cells. Recombinant immunotoxins, containing an Fv fragment of a Mab fused to truncated Pseudomonas exotoxin, have shown efficacy in HCL resistant to both purine analogs and rituximab. LMB-2 targets CD25 and can induce remission providing the HCL cells are CD25+. All HCL cells display CD22. Recombinant anti-CD22 immunotoxin BL22, targeting CD22, has shown significant efficacy in phase I and II testing, and avoids prolonged suppression of both normal B- and T-cells. An improved high-affinity version of BL22, termed HA22, is currently undergoing phase I testing.

Importance of minimal residual disease in hairy cell leukemia: monoclonal antibodies as a therapeutic strategy

With the use of nucleoside analogs as frontline therapy, the prognosis of hairy cell leukemia (HCL) has improved dramatically. Unfortunately, disease recurrence remains problematic. Eradication of minimal residual disease (MRD) persisting after therapy may further improve outcome. The evolution of available techniques used to assess MRD, and the potential incorporation of novel agents such as monoclonal antibodies (MoAbs) into the treatment armamentarium for HCL mandate that MRD analyses be performed concurrently with routine assessments of disease status. Herein, the available data regarding the prevalence and clinical relevance of MRD after therapy for HCL is reviewed.

Hairy cell leukemia

Hairy cell leukemia (HCL) is a chronic B-cell lymphoproliferative disorder characterized by pancytopenia and variable infiltration of the reticuloendothelial system with "hairy" lymphocytes. HCL is more common in men than women and has a median age of diagnosis of 52 yr. Typically, patients with HCL respond well to purine analog-based therapy. The purpose of this review will be to establish the current status of HCL with respect to its pathophysiology, diagnosis, management, and future directions.

2-CdA in the treatment of hairy cell leukemia: a review of long-term follow-up

Hairy cell leukemia is a rare, indolent, chronic lymphoproliferative disorder characterized by the proliferation of a malignant B-cell clone with irregular cytoplasmic projections. Treatment with purine analogs such as 2-chlorodeoxyadenosine (2-CdA) is associated with excellent remission rates and long-term survival. Although the majority of patients achieve a complete remission (CR), most have minimal residual disease detected by sensitive methods. Despite the long term disease-free survival, approximately 36% of patients relapse and many require further therapy. Repeat administration of 2-CdA is very effective in achieving a second CR. Recently, new agents such rituximab and BL22 were shown to be effective in the treatment of relapsed and refractory disease.

The role of rituximab in combination with pentostatin or cladribine for the treatment of recurrent/refractory hairy cell leukemia

BACKGROUND

The purine analogs pentostatin and cladribine have revolutionized the treatment of hairy cell leukemia (HCL) with overall responses in greater than 85% of patients and a median progression-free survival of up to 15 years. They continue to be effective at second- and even third-line therapy; however, alternative treatments are needed for patients who are or have become refractory to these agents or whose remissions are shorter with each course of therapy.

METHODS

The authors conducted a retrospective review of 8 patients who received pentostatin or cladribine combined concurrently (n = 6 patients) or sequentially (n = 2 patients) with rituximab at second-line therapy (n = 3 patients) and at subsequent lines of therapy (n = 5 patients). Results from a previously reported database of 219 patients with HCL (73 patients who received second-line therapy and 20 patients who received third-line therapy) were used as a historic control group against which to measure benefit.

RESULTS

All 8 patients responded to therapy, with 7 complete responses (CRs) (87.5%) and minimal toxicity. All patients who had CRs were negative for minimal residual disease (MRD). At a median follow-up of 29 months (range, 5-39 months) 1 patient developed recurrent disease, and the estimated 2-year recurrence rate was 20% (0% after second-line therapy and 25% after subsequent lines of therapy). In the historic control group, the CR rates were 70% after second-line therapy and 45% after third-line therapy, and the recurrence rates at 2 years were 15% and 33%, respectively.

CONCLUSIONS

The combination of purine analogs with rituximab was safe and effective for patients with recurrent and/or refractory HCL, and the current results suggested an added benefit compared with standard treatment.

Hairy cell leukemia: an elusive but treatable disease

Hairy cell leukemia (HCL) is a unique chronic lymphoproliferative disorder that can mimic or coexist with other clonal hematologic disorders and has been associated with autoimmune disorders. It should be entertained as an alternative diagnosis in patients with cytopenias being assigned the diagnosis of aplastic anemia, hypoplastic myelodysplastic syndrome, atypical chronic lymphocytic leukemia, B-prolymphocytic leukemia, or idiopathic myelofibrosis. Causative etiology or molecular defects remain unclear, although nonspecific chromosomal and molecular changes have been described. The typical presentation is that of a middle-aged man with an incidental finding of pancytopenia, splenomegaly, and inaspirable bone marrow. Treatment with a purine analogue, cladribine or pentostatin, results in extremely high, durable, overall, and complete response rates, although resistance and relapses do occur. A variant subtype exists and is frequently associated with a poor response. Because of its simplified dosing schedule, cladribine is commonly used as the initial therapy. Treatment of relapsed HCL is dictated by the duration of the preceding remission. Relapsed disease after a prolonged remission can often be successfully retreated with the same initial agent. Resistance in typical HCL is treated with the alternate purine analogue. New agents, such as rituximab and BL22, are actively being evaluated and show promising results in both HCL subtypes. This article uses two patients diagnosed with aplastic anemia and recently seen in consultation at our institution as a springboard to discuss the biology, pathogenesis, clinical presentation, diagnostic evaluation, and treatment options of HCL.

Monoclonal antibody therapy for hairy cell leukemia

The use of MoAb therapy for the treatment of HCL offers great promise and potential for improving progression-free survival. Rituximab has activity in the setting of previously treated HCL and the ability to eradicate MRD after 2-CdA given as frontline therapy. Alemtuzumab, epratuzumab, Hu-Max-CD20, and other candidate MoAb's should be studied in HCL. Appropriate pharmacologic investigation, use of antigen modulation, and assessments of soluble antigen levels should be considered with future clinical trial s of MoAb's in HCL to optimize therapeutic strategies.

Immunophenotyping and differential diagnosis of hairy cell leukemia

HCL and HCL-variant cells have a distinct immunophenotype that seems to correspond to that of a mature activated memory B cell. Although the two diseases have similarities in histology and membrane marker expression, such as the selected Ig heavy-chain expression and the reactivity with certain B-cell activation markers (eg, CD103), there are differences in their clinical course, morphology, and immunophenotype. Immunophenotyping is an essential tool for the diagnosis of these two disorders, for monitoring and assessing response to therapy, and for distinguishing them from other B-cell malignancies.

Hairy cell leukemia: towards a curative strategy

Although not all patients who have HCL require therapy at diagnosis, most eventually need treatment. Historically, splenectomy and interferon-alpha resulted in hematologic responses; however, responses tend to be short. The introduction of purine analogs dramatically changed the prognosis for most patients who hae HCL. It is now considered standard of care to use a purine analog, such as 2-CdA or 2'-DCF, as first-line therapy. This approach results in a high CR rate and prolong DFS. Although both agents yield the same rates of CR and survival, 2-CdA seems easier to administer and my be associated with less toxicity. Despite the excellent results with purine analogs, most patients have MRD detected by sensitive techniques; 30% to 40% of patients eventually relapse and most require further therapy. A repeat course of 2-CdA (or 2'-DCF) will result in CR in approximately 70% of patients. For patients who have relapsed or refractory disease, monoclonal antibody-based therapies are emerging options. Rituximab and BL22 are highly active in this setting. Until BL22 becomes widely available, rituximab is a reasonable choice for salvage therapy; however, the dosing schedule needs to be denied further. The roles of rituximab and BL22 as initial therapy for patients who have previously untreated HCL have not been investigated. Fig. 1 is a suggested algorithm for the treatment of HCL. With the introduction of effective new agents, further studies will determine whether the now achievable prolonged survival will translate into cure.

Hairy cell leukemia

Hairy cell leukemia is a rare B-cell neoplasm. When treated with either pentostatin or cladribine, complete and durable remissions can be secured and life expectancy for most patients is normal. A small minority of patients require alternative treatment with monoclonal antibodies or immunotoxins. Patients who attain a complete response to first-line treatment have the best prognosis.

Hairy Cell Leukemia: Diagnostic Pathology

The pathology of HCL has been reviewed with a focus on the diagnostic hematopathology of this rare, but fascinating, disease. The discrimination of HCL from other B-cell lymphoproliferations, particularly HCL-V and SMZL, has been emphasized. The unique responsiveness of HCL to 2-CdA and other chemotherapeutic agents makes this distinction critical. Fortunately, HCL has consistent cytologic, histologic, cytochemical, and immunologic features that make classification reliable and reproducible. Less straightforward is the differential diagnosis of SMZL and HCL-V, problematic because of the rarity of both disorders, lack of discriminating evidence-based criteria, and perhaps a biologic kinship between these two disorders that share many clinical and pathologic features. Fortunately, this is not a clinically critical distinction.

Minimal residual disease in hairy cell leukemia patients assessed by clone-specific polymerase chain reaction

Cladribine induces long-term complete remission in hairy cell leukemia (HCL) patients but does not clear minimal residual disease (MRD) according to high-sensitivity PCR assays. To quantify MRD in patients after anti-CD22 recombinant immunotoxin BL22 and other agents, we used a relative quantitative PCR (RQ-PCR) assay using a primer and probe, both patient specific for the immunoglobulin heavy chain rearrangement. Using this method, we were able to detect one Bonna 12 HCL cell in either 10(6) Jurkat cells or in 10(6) normal mononuclear cells. We studied 84 samples from 10 patients, taken before or after treatment with BL22 and other agents. Patient-specific RQ-PCR was much more sensitive than flow cytometry, which in turn was (as recently reported) more sensitive than PCR using consensus primers. RQ-PCR was positive in 62 of 62 (100%) flow-positive samples in 10 patients and in 20 of 22 (91%) flow-negative samples in six patients. The relative level of MRD as quantified by RQ-PCR correlated with disease status and remission. Thus, patient-specific RQ-PCR is the most sensitive test for MRD in HCL patients and could be used to determine maximal response in patients obtaining multiple cycles of nonmyelotoxic biological treatment for this disease.

Current treatment options in hairy cell leukemia and hairy cell leukemia variant

Hairy cell leukemia (HCL) is a chronic B-cell lymphoproliferative disorder characterized by splenomegaly, pancytopenia and circulating lymphocytes displaying prominent cytoplasmic projections. HCL has usually an indolent course and the patients with asymptomatic disease do not require therapy. Treatment of progressive symptomatic HCL includes a variety of pharmacological approaches such as interferon-alpha (IFN-alpha), pentostatin (DCF) and cladribine (2-CdA), which have significantly improved the disease prognosis. 2-CdA and DCF seem to induce a similar high response rate and a long overall survival. They are also active in relapsed patients. More recently high activity of anti-CD20 monoclonal antibody (rituximab) and anti-CD25 (LMB-2) and anti-CD22 (BL-22) immunotoxins have increased the number of therapeutic options for HCL. Splenectomy may be still indicated in patients with massive, symptomatic splenomegaly or results in severe cytopenia. IFN-alpha may have a place in patients with very severe cytopenia, in HCL in pregnancy and in patients who have failed prior therapy with purine nucleoside analogs. HCL variant (HCL-V) is a distinct clinico-pathological entity which seems to be resistant to IFN-alpha and purine nucleoside analogs - DCF and 2-CdA. However, preliminary observations suggest that monoclonal antibodies - rituximab and BL-22 immunotoxin are highly active in this disorder even refractory to 2-CdA. In this review current therapeutic strategies in HCL and HCL-V are presented.

Phase I Trial of Recombinant Immunotoxin RFB4(dsFv)-PE38 (BL22) in Patients With B-Cell Malignancies

Purpose

To conduct a phase I trial of recombinant immunotoxin BL22, an anti-CD22 Fv fragment fused to truncated Pseudomonas exotoxin.

Patients and Methods

Forty-six pretreated patients with CD22+ non-Hodgkin's lymphoma (NHL; n = 4), chronic lymphocytic leukemia (CLL; n = 11), and hairy cell leukemia (HCL; n = 31) received 265 cycles at 3 to 50 μg/Kg every other day × 3 doses.

Results

BL22 was active in HCL, with 19 complete remissions (CRs; 61%) and six partial responses (PRs; 19%) in 31 patients. Of 19 CRs, 11 were achieved after one cycle and eight after two to 14 cycles. All 25 responders benefited clinically with one cycle. The CR rate was 86% in patients enrolled at ≥ 40 μg/Kg every other day × 3, and 41% at lower doses (P = .011). The median duration for CR was 36 months (range, 5 to 66 months), and eight patients remain in CR at 45 months (range, 29 to 66 months). Lower but significant activity occurred in CLL. Neutralizing antibodies occurred in 11 (24%) of 46 patients (all HCL). A reversible hemolytic uremic syndrome requiring plasmapheresis was observed in one patient with NHL during cycle 1 and in four patients with HCL during cycle 2 or 3. The maximum-tolerated dose (MTD) evaluated at cycle 1 was 40 μg/Kg IV. QOD × 3. The most common toxicities at 30 to 50 μg/Kg every other day × 3 included hypoalbuminemia, transaminase elevations, fatigue, and edema.

Conclusion

BL22 was well tolerated and highly effective in HCL, even after one cycle. Phase II testing is underway to define the efficacy with one cycle and to study safety when additional cycles are needed for optimal response.

Long remissions in hairy cell leukemia with purine analogs

BACKGROUND

Both pentostatin and cladribine have efficacy in hairy cell leukemia (HCL), but it is not known which agent achieves better results.

METHODS

We reviewed a series of 219 patients with HCL, with median follow-up from diagnosis of 12.5 years (range 1.0 -34.6 yrs), treated with either pentostatin (n = 185) or cladribine (n = 34), to compare these agents and assess the potential for cure.

RESULTS

Overall response to pentostatin was 96% with a complete response (CR) in 81% and a median disease-free survival (DFS) of 15 years. Response to first-line cladribine was 100% with a CR in 82% and DFS of 11+ years. The relapse rates at 5 years and 10 years were 24% and 42%, respectively, with pentostatin, and 33% and 48% with cladribine. Survival at 10 years was respectively 96% and 100%. CR rates decreased with each sequential relapse through 69% to 45% (P < or = 0.001). Patients achieving CR after first-line treatment had a significantly longer DFS (P = 0.00007) than those achieving a partial response; a similar result was seen after second-line therapy (P = 0.00001). DFS also declined with sequential treatment (P = 0.00005).

CONCLUSION

We have shown equivalent efficacies for both agents in the treatment of HCL, with DFS showing no plateau. True cure in HCL remains elusive, but the addition of monoclonal antibodies may be beneficial. Our results suggest that achieving CR should remain the main goal of treatment.

Rituximab as treatment for minimal residual disease in hairy cell leukaemia

Purine analogues have dramatically improved the outcome of patients affected by hairy cell leukemia (HCL), although complete eradication of disease was achieved in few cases. The purpose of this study was to evaluate the role of Rituximab in eradicating minimal residual disease (MRD) in HCL patients after a pre-treatment with 2-chloro-deoxy-adenosine (2-CdA). Ten patients received four cycles of Rituximab after administration of Cladribrine. Before starting anti-CD20 antibody, two patients were in complete remission, six in partial remission and two showed no significant response to Cladribrine. All cases resulted IgH-positive. Median time from the last 2-CdA infusion was 5.7 months. Eight of 10 patients [four in partial remission (PR), two in complete remission (CR) and two unresponsive after 2-CdA] were evaluable for response. Two months after the end of anti-CD20 therapy, all evaluated patients presented a complete haematological remission. Moreover, Rituximab increased percentage of molecular remission up to 100% 1 yr after the end of treatment. Interestingly, in all cases but one, including those persistently polymerase chain reaction (PCR)-positive, semi-quantitative molecular analyses showed MRD levels lower than those found before Rituximab administration. Toxicity was very mild. The present results not only confirm the therapeutic effect of Rituximab, but also show its relevance in eradicating MRD in HCL.

Pathology of hairy-cell leukaemia

Hairy-cell leukaemia (HCL) is a low grade B-cell lymphoproliferative process that presents either with lymphocytosis or neutropenia/monocytopenia. It is a disease predominantly of bone marrow and spleen, although it can also involve other organs and sites. Recent advances including multi-parameter flow cytometry and the development of antibodies with high specificity for HCL have permitted precise distinction of typical HCL from other lymphoproliferative diseases that can morphologically mimic the appearance of HCL. Although there is a commonly held belief that HCL is associated with a significant increase in second neoplasms, several recent studies have not supported this notion. The development of extremely effective therapy for HCL results in a high incidence of complete remission. However, a significant percentage of patients continue to harbour minimal residual disease that can be revealed with immunohistochemical and flow cytometric studies.

Advances in the treatment of hairy-cell leukaemia

Hairy-cell leukaemia (HCL) is an uncommon B-cell chronic lymphoproliferative disorder that accounts for about 2% of all leukaemias. Although the disease is generally indolent in its natural course, the majority of patients require treatment for life-threatening infections due to pancytopenia or symptomatic splenomegaly. During the past 20 years, remarkable progress has been made in the treatment of HCL. Since the introduction of interferon-alpha, splenectomy, which was formerly the standard therapy, has been rarely used. With the purine analogues cladribine and pentostatin, response rates are even better than with interferon-alpha and long-lasting remissions can be achieved in most patients. Therefore, these agents are now considered the treatment of choice. Recently, immunotherapeutic approaches which use monoclonal antibodies have increased the number of therapeutic options for HCL and offer promising salvage strategies for patients who relapse or who are refractory to treatment with purine analogues. In this review the different treatment options available are discussed and recommendations for the clinical management of the HCL are summarised.

The diagnosis and treatment of hairy-cell leukaemia

The diagnosis of HCL is usually straightforward and is based on the identification of typical HCs in the blood and bone marrow. The suspected diagnosis is confirmed by a combination of TRAP cytochemistry, a distinctive immunophenotype and characteristic BM trephine appearances. Nucleoside treatment is highly effective in inducing prolonged remissions; relapsing patients can usually be successfully retreated with nucleoside. Monoclonal antibody therapy is a promising novel approach to the treatment of resistant disease.

Reference values for peripheral blood B-lymphocyte subpopulations: a basis for multiparametric immunophenotyping of abnormal lymphocytes

BACKGROUND AND OBJECTIVES

Immunophenotyping has become a useful tool for the differential diagnosis of chronic B-cell lymphoproliferative disorders. The aim of this work was to determine reference values of normal B-cell subpopulations.

MATERIAL AND METHODS

Blood samples from 38 healthy volunteers were analyzed by multidimensional flow cytometry, using a panel of directly conjugated antibodies. Results were expressed as percent of positive B cells and as median fluorescence intensity, an indirect assessment of the expression level.

RESULTS

CD20, CD22, CD24, CD40, CD79a, CD79b, FMC7, CD11a, CD18, CD44 were positive in the whole B cell population, whereas CD10, CD86, CD103, CD154 and FasL were almost absent from the B-lymphocyte population. 75% were IgD positive. The kappa/lambda ratio was 1.5. CD5, CD23, CD25, CD38, CD43, CD54, CD62L, CD80 and CD95 were positive in different B-cell subpopulations. The utility of all these markers in the differential diagnosis of chronic B-cell lymphoproliferative disorders is discussed.

CONCLUSION

In order to interpret a pathological immunophenotype, it is necessary to refer to quantitative and qualitative values of normal B-cell subpopulations.

Hairy cell leukemia

The standard therapy for hairy cell leukemia (HCL) is with the nucleoside analogs, 2"-deoxycoformycin (dCF) or 2-chlorodeoxyadenosine (CdA), which produce morphologic complete remissions (CRs) in the majority of patients, although residual hairy cells can frequently be detected by molecular or immunologic techniques. Relapses continue to occur over time, but most patients respond well to retreatment with the same agent. The longest follow-up is for patients treated with dCF, where the 5- and 10-year relapse-free survival rates are 80% to 85% and 67% to 76%, respectively. dCF is usually administered as 4 mg/m2 intravenously every second week until CR followed by two additional treatments for consolidation. CdA is administered as 0.09 mg/kg/d x 7, by continuous intravenous infusion, although it may be equally effective when given as daily boluses or subcutaneously. More recent studies have suggested that CdA, 0.15 mg/kg intravenously weekly x 6, produces equivalent response rates, while reducing the risk of febrile neutropenia (which occurs in approximately 50% of patients using the standard regimen). We have found this to be a very simple, safe, and effective regimen. Both dCF and CdA should be used with caution in the presence of renal or hepatic dysfunction, and both are contraindicated in the presence of active infection. Interferon-alfa (3 x 10(6) U subcutaneously three times per week for 12 months) produces inferior response rates but is less likely to cause febrile neutropenia. It can be considered for initial treatment for patients with active infection, patients at high risk of febrile neutropenia, and patients who cannot tolerate or are resistant to the nucleoside analogs. Splenectomy is now rarely performed in HCL, but it is required for splenic rupture and may be of value in "splenic" HCL or those with massive splenomegaly and hypersplenism. In preliminary studies, monoclonal antibodies directed against CD20 or CD25 also show activity in HCL, but their roles in this disease require further study.

Long term outcome of patients with hairy cell leukemia treated with pentostatin

BACKGROUND

With the introduction of new drugs such as interferon-alpha (IFN) and purine analogs, the management of hairy cell leukemia (HCL) patients has changed. However, pentostatin has been found to produce higher complete remission rates than IFN. The current study was undertaken to investigate response and long term follow-up in HCL patients treated with pentostatin.

METHODS

Between March 1989 and October 1996, 49 patients with HCL and 1 patient with a HCL variant were treated with pentostatin. Eighteen patients had received no prior therapy, 31 patients had received prior treatment with IFN, and 1 patient had received prior treatment with 2'-chlorodeoxyadenosine (2'CdA) and IFN. All patients except 1 were treated with a dose of 4 mg/m2 every 2 weeks. The median number of cycles was 12.

RESULTS

The overall response rate was 96% (48 of 50 patients); 22 patients (44%) achieved a complete response, 18 patients (36%) achieved a good partial response (defined as residual bone marrow infiltration < 5%), 8 patients (16%) achieved a partial response, and 2 patients died. For a median follow-up of 33 months off therapy, there were 5 recurrences between 12-66 months; 3 of these patients were treated further with and responded to 2'CdA and 2 died of disease progression at 12 and 40 months, respectively. In addition, 3 patients died of unrelated causes (1 of very early infection, 1 of toxic death and another of cardiac arrest) comprising an overall death rate of 14% (7 of 50 patients). The overall survival rate was 86% for a median follow-up of 38 months (range, 8-105 months). Major side effects were febrile episodes, herpes zoster, nausea/emesis, and pancytopenia.

CONCLUSIONS

This analysis confirms both the high remission rate and durable responses that may be achieved with pentostatin treatment in HCL patients. Although pentostatin is active, the risk of cytopenia and immunosuppression must be evaluated carefully.