Correction: Clinical impact of measurable residual disease monitoring by ultradeep next generation sequencing in NPM1 mutated acute myeloid leukemia.

[This corrects the article DOI: 10.18632/oncotarget.26400.].

Clinical impact of measurable residual disease monitoring by ultradeep next generation sequencing in NPM1 mutated acute myeloid leukemia.

Detection of measurable residual disease (MRD) by mutation specific techniques has prognostic relevance in NPM1 mutated AML (NPM1 mut AML). However, the clinical utility of next generation sequencing (NGS) to detect MRD in AML remains unproven. We analysed the clinical significance of monitoring MRD using ultradeep NGS (NGS-MRD) and flow cytometry (FCM-MRD) in 137 samples obtained from 83 patients of NPM1 mut AML at the end of induction (PI) and consolidation (PC). We could monitor 12 different types of NPM1 mutations at a sensitivity of 0.001% using NGS-MRD. We demonstrated a significant correlation between NGS-MRD and real time quantitative PCR (RQ-PCR). Based upon a one log reduction between PI and PC time points we could classify patients as NGS-MRD positive (<1log reduction) or negative (>1log reduction). NGS-MRD, FCM-MRD as well as DNMT3A mutations were predictive of inferior overall survival (OS) and relapse free survival (RFS). On a multivariate analysis NGS-MRD emerged as an independent, most important prognostic factor predictive of inferior OS (hazard ratio, 3.64; 95% confidence interval [CI] 1.58 to 8.37) and RFS (hazard ratio, 4.8; 95% CI:2.24 to 10.28). We establish that DNA based NPM1 NGS MRD is a highly useful test for prediction of relapse and survival in NPM1 mut AML.

CD19 negative precursor B acute lymphoblastic leukemia (B-ALL)-Immunophenotypic challenges in diagnosis and monitoring: A study of three cases.

BACKGROUND: CD19 is a B-cell specific marker, expressed on all stages of B-lymphocytes including plasma cells. It is widely used in the flow cytometric immunophenotyping (FCI) of B-cell and plasma cell malignancies. The analysis approach of FCI for the diagnosis and monitoring of B-cell acute lymphoblastic leukemia (B-ALL) is totally based on the CD19-based primary gating strategy and it would be challenging to study B-ALL without CD19 expression. Since CD19 negative B-ALL are extremely rare, we report three cases of B-ALL with negative expression of CD19 and discussed its implication in the diagnosis, residual disease monitoring and future targeted therapy. METHODS: Peripheral blood (PB) and bone marrow (BM) samples from three cases suspicious of acute leukemia were studied for morphology, cytochemistry, immunophenotyping and cytogenetics. FCI was performed using a comprehensive six to eight-color multiparametric assay. The cytogenetic studies for standard recurrent genetic translocations were performed by FISH & Karyotyping. RESULTS: The three cases studied were diagnosed as B-ALL based on the expression of CD10, CD20, CD22, CD34, and CD79a by leukemic blasts. CD19 was studied using two different clones (i.e. J3-119 & HIB-19) and found to be severely down regulated in all three cases. There were no significant differentiating features in morphology. Cytogenetic studies were negative for recurrent translocations. CONCLUSION: We report three cases of extremely rare CD19 negative B-ALL. Lack of awareness of negative CD19 expression in B-ALL can leads to incorrect immunophenotypic diagnosis and monitoring of B-ALL, especially in laboratories using limited markers. © 2016 International Clinical Cytometry Society.

Leukemic phase of anaplastic lymphoma kinase positive, anaplastic large cell lymphoma.

Anaplastic large cell lymphoma (ALCL) is a distinct type of CD30+ T/null-cell non-Hodgkin's lymphoma that frequently involves nodal and extranodal sites. The presence of leukemic phase in ALCL is extremely rare and occurs exclusively with ALK1-positive ALCL. We describe two patients with ALK1-positive ALCL who developed a leukemic phase with rapid progression of the disease. Immunophenotypic pattern assessed on peripheral blood by flow cytometry revealed CD45, CD30, and CD25 positivity in both cases but NPM-ALK1 was expressed in only one case. Both patients developed leukemic phase as a terminal event of the disease and we share the immunophenotypic features of both cases.

Immunophenotyping of mature T/NK cell neoplasm presenting as leukemia.

INTRODUCTION: Mature T/NK cell lymphomas (MTNKL) presenting as leukemia are rare and show considerable overlapping of clinical, morphological and immunophenotypic features. AIM: Critical analysis of the morphology and immunophenotypic profile of MTNKL. MATERIALS AND METHODS: We reviewed 380 consecutive cases of mature lymphoid neoplasm that presented as leukemia and were diagnosed on morphology and immunophenotyping of bone marrow and/or peripheral blood samples. RESULTS: Peripheral blood and bone marrow involvement was seen in all cases. MTNKL constituted 4% (nine cases) of all mature lymphoid neoplasms presenting as leukemia. It included four cases of T-large granular leukemia (T-LGL), two of T-cell prolymphocytic leukemia small cell variant (T-PLL), two of adult T-cell leukemia/lymphoma (ATLL) and one of primary cutaneous gamma delta T-cell lymphoma (PCGDTCL). T-LGL revealed CD4-/CD8+ phenotype in three, and CD4+/CD8+ phenotype in one case. CD56 was absent in all the cases of T-LGL. One case of T- PLL small cell variant showed CD4+/CD8- phenotype, while the other revealed CD4-/CD8+ phenotype. Both cases of ATLL showed CD4+/CD8+/CD25+ phenotype. The single case of PCGDTCL showed CD4-/CD8- phenotype pattern. CD3 and CD5 were expressed in all MTNKL. CD7 was absent in three cases of T-LGL. TCRalpha/beta was performed in three cases of T-LGL and was positive in all. TCRalpha/beta was also seen in both the cases of T-PLL small variant. However, TCRalpha/beta was seen in the single case of PCGDTCL. CONCLUSION: Mature nodal T/NK cell neoplasms are rare and MTNKL presenting as leukemia are even rarer. There is an overlap between the immunophenotypic profiles of different MTNKL subtypes and elaborate T/NK cell panels are required for their evaluation.

Comparison of platelet counts by CellDyn Sapphire (Abbot Diagnostics), LH750 (Beckman Coulter), ReaPanThrombo immunoplatelet method (ReaMetrix), and the international flow reference method, in thrombocytopenic blood samples.

BACKGROUND: We compared the international flow reference method (IRM) platelet counts with those obtained from CellDyn Sapphire (impedance and optical counts), LH750 (impedance counts), and the flowcytometry based ReaPanThrombo Immunoplatelet method (ReaMetrix). We further evaluated the degree of agreement of above methods with the IRM at the transfusion thresholds of 10 x 10(9) l(-1) and 20 x 10(9) l(-1). METHODS: A total of 104 thrombocytopenic blood samples with platelet count of <50 x 10(9) l(-1) were selected for the study. All samples were tested in parallel by various methods within 6 h of blood collection. RESULTS: For bias estimation, a Bland-Altman analysis was done by taking the IRM as the standard method. The bias for CDS-I counts was +6.505 x 10(9) l(-1) (95% LA -2.110 to +15.122), for CDS-O counts the bias was -3.779 x 10(9) l(-1) (95% LA -8.950 to +1.392), for LH750 the bias was +0.111 x 10(9) l(-1) (95% LA -5.862 to +6.084) and that for ReaMetrix was -1.602 x 10(9) l(-1) (95% LA -7.400 to +4.194). The LH750 had the least average bias and it overestimated platelet counts marginally. The ReaMetrix method showed the highest degree of agreement with the IRM, at both the threshold points with a K value of 0.960 (threshold < or = 10 x 10(9) l(-1)) and 0.923 (threshold < or = 20 x 10(9) l(-1)). CONCLUSIONS: Impedance platelet counts from LH750 were more accurate than optical methods in thrombocytopenic patients. ReaMetrix immunoplatelet counts show the maximum degree of agreement with the IRM at clinically relevant transfusion thresholds. We conclude that as current platelet transfusion thresholds are based on results of automated hematology analyzer methods, the true thresholds may be determined using the IRM and CD41/61 based single-platform immunoplatelet methods.

Immunophenotyping of mature B-cell non Hodgkin lymphoma involving bone marrow and peripheral blood: critical analysis and insights gained at a tertiary care cancer hospital.

We evaluated the diagnostic utility of flow cytometry immunophenotyping in bone marrow aspirates and peripheral blood, in the assessment of mature B-cell non-Hodgkin lymphoma (MBNHL). We analyzed 356 cases of MBNHL received for immunophenotyping over a 4 year period. All cases were reviewed, correlated with biopsy specimen (lymph node and splenectomy). Discrepant cases were re-evaluated. Common subtypes included chronic lymphocytic leukemia (CLL) (243 cases, 68.5%), follicular lymphoma (30 cases, 8.5%), mantle cell lymphoma (20 cases, 5.5%), splenic marginal zone lymphoma (18 cases, 5%), hairy cell leukemia (18 cases, 5%). CD5+/CD23+ had a high positive predictive value (PPV) for diagnosing CLL whereas CD5+/CD23- had a high negative predictive value (NPV) for diagnosing mantle-cell lymphoma (MCL). Limited panel of 9 antibodies mainly CD19, CD5, CD23, CD10, FMC7, kappa, lambda, CD3 and CD20 help diagnose more than 92% of cases of MBNHL. Minimal diagnostic panels become important in countries with limited resources.

Intracytoplasmic antigen study by flow cytometry in hematolymphoid neoplasm.

Flow cytometric detection of intracellular antigens has become a standard method in establishing proper leukemic cell lineage affiliation. It has a non-debatable contribution to the diagnosis of hematolymphoid neoplasm as well as in minimal residual disease. Combination of analysis of fluorescence labeling and light scatter properties of cells allows rapid and better determination of target cell antigens. Regarding the detection of intracellular antigens, standardization of the procedure remains, however, a real challenge. Detection of intracellular antigens by flow cytometry (FCM) requires effective fixation and permeabilization of the cell membrane. In the available literature, some reports describe methodologies to achieve satisfactory results for detection of either cytoplasmic or nuclear antigens; however, no methodological consensus has yet been achieved among the laboratories. This article is an attempt to describe different approaches to detect intracellular molecules by FCM.

Clinico-hematological profile in biphenotypic acute leukemia.

BACKGROUND: We present a clinico-hematological profile and treatment outcome of Biphenotypic Acute Leukemia (BAL). AIM: Study incidence and subtypes of BAL, correlate with age, morphology, and cytogenetic findings and correlate the clinico-hematological data with the treatment response. St Jude's and the EGIL's criteria have been compared for their diagnostic and clinical relevance. MATERIAL AND METHODS: Diagnosis was based on WHO classification, including clinical details, morphology, cytochemistry, immunophenotyping, and molecular genetics. We included those cases, which fulfilled the European Group for the Immunological Characterization of Acute Leukemia's (EGIL's) scoring system criteria for the diagnosis of BAL, as per recommendation of the WHO classification. RESULTS: There were 32 patients diagnosed with BAL, based on EGIL's criteria. Incidence of BAL was 1.2%. B-Myeloid (14 cases) followed by T-Myeloid BAL (13 cases) were the commonest subtypes. Polymorphous population of blasts (16 cases) was commonly associated with T-Myeloid BAL (10 cases). BCR ABL fusion positivity was a common cytogenetic abnormality (seven cases). Fifteen patients received chemotherapy; eight achieved complete remission (CR) at the end of the induction period. CONCLUSIONS: Pediatric BAL and T-B lymphoid BAL have a better prognosis. A comprehensive panel of reagents is required, including cytoplasmic markers; to diagnose BAL. St Jude's criteria is a simple, easy, and cost-effective method to diagnose BAL. The outcome-related prognostic factors include age, HLA-DR, CD34 negativity, and subtype of BAL. BCR-ABL expression is an important prognostic factor, as these cases will be labeled as Chronic myeloid leukemia (CML) in blast crisis with biphenotypic expression and treated accordingly.

Immunophenotypic profile of acute leukemia: critical analysis and insights gained at a tertiary care center in India.

BACKGROUND: To analyze the spectrum of various types and subtypes of acute leukemia. METHODS: Two thousand five hundred and eleven consecutive new referral cases of acute leukemia (AL) were evaluated based on WHO classification. RESULTS: It included 1,471 cases (58%) of acute lymphoblastic leukemia (ALL), 964 cases (38%) of acute myeloid leukemia (AML), 45 cases (1.8%) of chronic myelogenous leukemia in blast crisis (CMLBC), 37 cases (1.5%) of biphenotypic acute leukemia (BAL), 1 case of Triphenotypic AL, and 2 cases of acute undifferentiated leukemia (AUL). Common subtypes of ALL were B-cell ALL (76%), which comprised of intermediate stage/CALLA positive (73%), early precursor/proBALL (3%). T-cell ALL constituted 24% (351 cases) of ALL. Common subtypes of AML included AMLM2 (27%), AMLM5 (15%), AMLM0 (12%), AMLM1 (12%), APML (11%), and AML t(8;21) (9%). CMLBC was commonly of myeloid blast crisis subtype (40 cases). CONCLUSION: B-cell ALL was the commonest subtype in children and AML in adults. Overall incidence of AML in adults was low (53% only). CD13 was most sensitive and CD117 most specific for determining myeloid lineage. A minimal primary panel of nine antibodies consisting of three myeloid markers (CD13, CD33, and CD117), B-cell lymphoid marker (CD19), T-cell marker (CD7), with CD45, CD10, CD34, and HLADR could assign lineage to 92% of AL. Cytogenetics findings lead to a change in the diagnostic subtype of myeloid malignancy in 38 (1.5%) cases.

RUNX1 aberrations in ETV6/RUNX1-positive and ETV6/RUNX1-negative patients: its hemato-pathological and prognostic significance in a large cohort (619 cases) of ALL.

A large-cohort study (619) of acute lymphoblastic leukemia (ALL) revealed an ETV6/RUNX1 (previously known as TEL/AML1) incidence of 18% in pediatric B-cell precussor ALL, indicating no geographical heterogeinity. Association of CD34-negative phenotype, peak incidence in the 3- to 7-year age group, and a comparatively low frequency of ETV6 homologue loss in ETV6/RUNX1-positive cases were distinct findings in this series. Additional genetic changes, such as ETV6 loss, extra RUNX1, ETV6/RUNX1 duplication, and MLL aberrations in the ETV6/RUNX1-positive group, supported the hypothesis of the ETV6/RUNX1 leukemogenic model that these secondary changes are necessary for leukemogenesis rather than progression of disease. This study disclosed RUNX1 alterations in the ETV6/RUNX1-negative group of BCP-ALL that encourages the investigation of RUNX1 at a large scale with longer follow-up, which will focus on the prognostic importance and the underlying biology of disease.

Report of proceedings of the national meeting on "Guidelines for Immunophenotyping of Hematolymphoid Neoplasms by Flow Cytometry".

BACKGROUND: Immunophenotyping of hematolymphoid neoplasms is being done in many laboratories in India. The first national meeting on "Guidelines for Immunophenotyping of Hematolymphoid Neoplasms by Flow Cytometry" was held on 14 March 2008 in Mumbai, India. AIM: To achieve uniformity in the laboratory practice regarding antibody panel selection in diagnosing hematolymphoid neoplasms. SETTINGS AND DESIGN: Members of the Inter-Laboratory Comparison Program (ILCP) group in Mumbai prepared a draft regarding immunophenotypic panel selection for acute leukemias (ALs) and chronic lymphoproliferative disorders (CLPDs), which was further circulated among national and international cytometrists, hematopathologists, and oncologists for their written inputs, suggestions, proposed modifications; as well as their indications, if any, of the recommendations not being acceptable. Practice-based questionnaire was circulated among all the participants. RESULTS: Consensus was attained, and the panel recommended the use of a minimal screening panel, followed by a secondary directed panel. The aim of the minimal screening panel would be to provide a diagnosis of all commonly occurring hematolymphoid neoplasms without the need of additional antibodies in most cases. CONCLUSION: Thus we could attain a consensus for our guidelines in selecting panels for ALs and CLPDs. The guideline is an attempt to formulate a minimal panel for immunophenotyping of hematolymphoid neoplasms. Laboratories are encouraged to add additional antibodies to the above panel to increase the sensitivity; however, they should refrain from immunophenotyping with fewer antibodies. This national guideline hopefully brings about uniformity and comparability in reporting of leukemia and lymphoma and bridges the divide between low-cost reporting and an accurate diagnosis.

Betulinic acid induces apoptosis in human chronic myelogenous leukemia (CML) cell line K-562 without altering the levels of Bcr-Abl.

Betulinic acid (BA), a plant derived triterpenoid, isolated from various sources shows cytotoxicity in cell lines of melanoma, neuroectodermal and malignant brain tumors. Chronic myelogenous leukemia (CML) is characterized by Philadelphia chromosome (Bcr-Abl), a molecular abnormality leading to the intrinsic tyrosine kinase activity that provides growth and survival advantage to the cells. Present study describes the cytotoxicity of BA on human CML cell line K-562, positive for Bcr-Abl. The decrease in the viability of K-562 cells treated with BA at different concentrations and time intervals was assessed using MTT assay. Cell death induced by BA was determined to be apoptotic as measured by FACS analysis of PI stained nuclei, PS externalization by Annexin-V fluorescence and characteristic DNA fragmentation. DiOC6(3) fluorescent probe determined alterations in the mitochondrial membrane potential (MMP). RT-PCR confirmed the expression levels of Bcr-Abl in controls and K-562 cells treated with BA. The rapid loss of MMP of K-562 cells upon treatment with BA shows the direct activation of apoptosis at the level of mitochondria, overcoming the resistance of the high levels of expression of Bcr-Abl.

Protection of Ewing's sarcoma family tumor (ESFT) cell line SK-N-MC from betulinic acid induced apoptosis by alpha-DL-tocopherol.

Betulinic acid (BA) is known to induce apoptosis in melanoma neuroectodermal and malignant brain cancer cell lines. Present report describes the role of antioxidants on the BA-induced toxicity to human cell line SK-N-MC. Hydrophilic antioxidants viz., L-ascorbic acid (VitC) and N-acetyl-L-cysteine (l-NAC) had no protective effect on BA-induced apoptosis at the maximal concentrations tested. The lipophilic antioxidant, alpha-DL-tocopherol (VitE) showed a concentration and a time dependent effect on the protection of SK-N-MC cells from BA-induced apoptosis. The apoptotic parameters were analyzed using FACS analysis of propidium iodide (PI) stained nuclei, PS externalization using Annexin-V assay and changes in mitochondrial membrane potential. Generation of superoxide radical was monitored by the fluorescent dye hydroethidium (HE). Cells showed Annexin-V positivity and an increase in the propidium iodide (PI) uptake in the early hours of treatment with BA, which was concomitant with the loss of mitochondrial membrane potential. Addition of alpha-DL-tocopherol to the cell cultures 1-h prior to the treatment with BA abolished all the effects of BA-induced apoptosis. These observations suggest that BA initiates events at membrane level leading to induction of apoptosis. The observed ineffectiveness of hydrophilic antioxidants and substantial protection by lipophilic antioxidants indicate involvement of membrane-associated damages that form the basis of BA-induced cytotoxicity.

Haematologic and immunophenotypic profile of acute myeloid leukemia: an experience of Tata Memorial Hospital.

OBJECTIVES: To study the hematologic and immunophenotypic profile of 260 cases of acute myeloid leukemia at diagnosis. MATERIAL AND METHODS: This is a retrospective analysis of 260 cases of AML diagnosed at our institution between 1998 and 2000. Diagnosis was based on peripheral blood and bone marrow examination for morphology cytochemistry and immunophenotypic studies. SPSS software package, version 10, was used for statistical analysis. RESULTS: Seventy-six percent of our cases were adults. The age of the patients ranged from one year to 78 years with a median age of 27.2 years. There were 187 males and 73 females. The commonest FAB subtype, in both children and adults, was AML-M2. The highest WBC counts were seen in AML-M1 and the lowest in AML-M3 (10-97 x 10(9)/L, mean 53.8 x 10(9)/L). The mean values and range for hemoglobin was 6.8 gm/l (1.8 gm/l to 9.2 gm/l), platelet count 63.3 x 10(9)/L (32-83 x 10(9)/L), peripheral blood blasts 41.4% (5 to 77%) and bone marrow blasts 57.6% (34-96%). Myeloperoxidase positivity was highest in the M1, M2 and M3 subtypes. CD13 and CD33 were the most useful markers in the diagnosis of AML. CD14 and CD36 were most often seen in monocytic (38%) and myelomonocytic (44%) leukemias. Lymphoid antigen expression was seen in 15% of cases. CD7 expression was the commonest (11%). CONCLUSION: AML accounted for 39.8% of all acute leukemias at this institution. The most common subtype was AML-M2. Myeloperoxidase stain was a useful tool in the diagnosis of myeloid leukemias. CD13 and CD33 were the most diagnostic myeloid markers.

Leukemia in infants.

OBJECTIVE: Acute Leukemia is rare in infants. It is characterized by non-specific symptomatology requiring a high index of suspicion on the part of a pediatrician for referral and diagnosis. It has peculiar biological features, unresponsiveness to treatment and poor prognosis. METHODS: Eighteen infants with acute leukemia were seen during 1994 to 2001 and were analyzed on the basis of clinical and laboratory data. There were 13 cases of Acute Lymphoblastic Leukemia (ALL), 4 cases of Acute Myeloid Leukemia (AML) and one case remained unclassifiable, as the surface markers could not be done. Morphologically 9/13 cases of ALL were of FAB L1 type and remaining of L2 subtype, and 2/4 cases of AML were of FAB M1 type and remaining of M2 subtype. RESULT: Clinical data was available completely only in 11 cases. Hyperleucocytosis was present in 4 cases, organomegaly in 8 cases and lympadenopathy in 5 cases. One patient presented with a chloroma in the retrorbital region although there was no parenchymal involvement of the brain. Immunophenotyping could be done in 13 cases, where 7 cases were diagnosed as CALLA positive-ALL (HLADR+, CD19+, CD10+), 2 cases as Early Pre-B ALL (HLADR+, CD19+, CD10 negative), one as T ALL (cCD3+, CD2+, CD7+) and 3 cases as AML (CD13+, CD33+, HLADR+). None of our patients received treatment.

Production & evaluation of a monoclonal antibody against human myeloperoxidase.

We describe the production of a mouse monoclonal antibody (H2E1) against human myeloperoxidase antigen. After production and characterisation, this antibody was compared with commercially available monoclonal antibodies, cytochemical myeloperoxidase and previously produced polyclonal antibody. Reaction with various cell lines proved that this monoclonal antibody was specific for myeloid lineage. This monoclonal showed positivity in 81.8 per cent of acute myeloid leukaemias whereas the polyclonal antibody was 100 per cent positive. We found that the polyclonal antibody was more sensitive as compared to the monoclonal. This is probably due to the lack of recognition of individual epitopes on the antigen. We recommend the use of antibodies which have different epitope recognition as most specific for myeloperoxidase.

Calla positive acute lymphoblastic leukemia after etoposide-based therapy for Ewing's sarcoma.

This is an unusual and interesting case report concerning a 10 year old boy with an initial diagnosis of Ewing's sarcoma of the right tibia. He was successfully treated with a chemotherapy regimen consisting of vincristine, cyclophosphamide (cumulative dose 7200 mg/m2), doxorubicin, etoposide (cumulative dose 2700 mg/m2) and cisplatin and local radiotherapy to the tibia. After an interval of 37 months he developed CALLA positive acute lymphoblastic leukemia with 11q23 chromosomal abnormality. The possible roles of etoposide and cyclophosphamide are discussed.

Evaluating efficiency of bone marrow harvest and its manipulation--role of CD 34 positivity.

We evaluated harvested marrow cells for total nucleated cells (27.49 x 10(9)), absolute 'lymphocyte' count (6.29 x 10(9)) and CD 34 positive cells (3.57 x 10(9)). The same parameters were studied after in vitro manipulation to remove RBCs and plasma. Reinfused WBCs contained 12.87 x 10(9) nucleated cells, 4.25 x 10(9) absolute 'lymphocyutes' and 3.34 x 10(9) CD 34 positive cells. The corresponding figures for loss during in vitro manipulation (tubing, RBCs and plasma) are 14.62 (53.18%), 2.04 (32.43%) and 0.23 x 10(9) (6.44%) cells respectively. Therefore CD 34 positivity may be a better indicator of total yield, loss during manipulation and reinfusion of hemopoietic progenitor cells in bone marrow transplantation.

Hairy cell leukemia--an unusual presentation.

Hairy cell leukemia is a chronic lymphoproliferative disorder affecting middle-aged adults, with the median age of 50-55 years. The majority of the patients present with cytopenia. A high count is usually a feature of the hairy cell leukemia variant. We report a case of a 23-year-old male who presented with fever and cough of 15 days duration. His peripheral blood count was 63 x 10(9)/l. His peripheral blood and bone marrow smear showed hairy cells which were positive for tartarate-resistant acid phosphatase stain. Surface markers and electron microscopic study on peripheral blood ruled out hairy cell leukemia variant as a differential diagnosis.