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Indian Journal of Cancer, Vol. 46, No. 2, April-June, 2009, pp. 160-168 Original Article Clinico-hematological profile in biphenotypic acute leukemia Gujral S, Polampalli S, Badrinath Y, Kumar A, Subramanian PG, Raje G, Amare P, Arora B, Banavali SD, Nair CN Hematopathology Laboratory, Tata Memorial Hospital (TMH), Mumbai Code Number: cn09031 Abstract 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. Keywords: Biphenotypic leukemia, cytogenetics, immunophenotyping Introduction Biphenotypic Acute Leukemia (BAL) is defined as a biologically different group of leukemia arising from a precursor stem cell and co-expressing more than one lineage specific marker. [1],[2] It has been previously classified as mixed or hybrid leukemia, myeloid antigen positive acute lymphoblastic leukemia (MY + ALL) or lymphoid antigen positive acute myeloid leukemia (LY + AML). [1],[2],[3],[4] The World Health Organization (WHO) recommends the European Group for the Immunological Characterization of Acute Leukemias (EGIL) classification, for a diagnosis of BAL [1],[2],[4] [Table - 1]. Another popular criteria for diagnosis of BAL is the Saint Jude′s criteria [5] [Table - 2]. BAL is defined when the score is greater than two for myeloid and one for lymphoid lineages. -Anti MPO is a cytoplasmic marker specific for myeloid, -CD79a (cytoplasmic and membrane), CD22 (cytoplasmic and membrane), and cytoIgM are specific for B- lymphoid, while CD3 (cytoplasmic and membrane) is specific for T-cells Incidence of BAL has been reported to vary from 1 to 8%. [6],[7] This wide variation may be attributed to a number of reasons including lack of consistent diagnostic criteria, use of a limited panel of antibodies by different laboratories, avoiding cytoplasmic markers in the primary panel, and the failure to recognize the lack of lineage specificity of some of the antibodies used. There is limited data available regarding the clinico-hematological profile, treatment protocols, and treatment outcome in patients with BAL. There is no agreement as to whether induction therapy should be directed against a lymphoid and/or myeloid drugs or whether this should be followed by hematopoietic stem cell transplantation. The aim of this retrospective study was to study the incidence of BAL, correlate different subtypes of BAL with age, sex, morphology, and cytogenetic findings, to correlate the clinico-hematological data with the treatment response. We also attempted to compare both St Jude′s and the EGIL′s criteria for their diagnostic and clinical relevance. Materials and Methods Diagnosis of BAL was based on the previously described scoring system, adopted and proposed by the EGIL criteria. [1] This scoring system aims at distinguishing the bona fide BAL from those with aberrant expression of a marker from another lineage (Ly + AML or My + ALL). EGIL′s scoring system is based on a scoring system with various markers assigned with a score of 2, 1, or 0.5, depending on their specificity for myeloid or lymphoid lineage. Those cases having a score greater than 2 for at least two lineages (myeloid, T-cell, B-cell) were labeled as BAL. St Jude′s is another criteria for the diagnosis of BAL, based on the expression of two lineage specific markers, that is, expression of anti myeloperoxidase for myeloid lineage, cytoCD3 for T lineage, and cytoCD79a and cytoCD22 for B lineage. Our laboratory received 2689 new cases of acute leukemia (AL) from August 2003 to July 2006. The cases were diagnosed based on the WHO classification, [4],[8] including clinical details, morphology, cytochemistry, immunophenotyping, and molecular genetics, including Fluorescent in-situ hybridization (FISH) and polymerase chain reaction (PCR) studies. We included those cases that fulfilled the EGIL′s scoring system criteria for the diagnosis of BAL, as per the recommendation of WHO classification. [4] For the morphologic examination, all the bone marrow (BM) aspirates / peripheral blood smears (PBS) included were air dried and subsequently stained with Wright′s stain. Cytochemical stains included myeloperoxidase and alpha naphthyl acetate esterase (ANAE). [9] Cytochemical MPO was done in all cases. ANAE was done only in those selected cases where the blasts had morphology of monoblasts and cytochemical MPO was negative or weakly positive. Bone marrow aspirates collected in the hospital operation theater were immediately transported to the flow cytometry (FCM) laboratory. The lyse and wash technique was performed to prepare the cells. For nuclear and cytoplasmic markers, the cells were fixed with 2% formaldehyde (Qualigen, India) for 15 minutes and permeabilized with 0.2% saponin reagent (Sigma) followed by addition of the respective antibodies. Cells were incubated in the dark for 30 minutes at room temperature and washed with phosphate buffered saline. Three color FCM immunophenotyping was performed on FACS Calibur (Becton-Dickenson, San Jose, California) by collecting 10000 ungated list mode events, selecting an appropriate blast gate on the combination of forward and side scatter, and analyzing cells with the most appropriate blast gate. Tumor cells were stained with various combinations of fluorochrome-like fluorescein isothiocyanate (FITC), phycoerythrin (PE), and phycoerythrin-cyanine 5 (PECY5) labeled monoclonal antibodies (BD Pharmingen). The typical combinations in the primary minimal panel were three colors with forward scatter channel / side scatter channel (FSC / SSC) and included CD4PE, CD8FITC, and CD19PE-CY5; CD10PE, CD117PECY5, and CD3FITC; Anti HLADRFITC, CD33PE, and CD56PECY5; CD7 FITC, CD14PE, and CD34PECY5; and CD2FITC, CD13PE, and CD45PECY5. CD45 conjugates were available with FITC and PECY5. Additional markers in the secondary panel were performed (in 8% cases only) in the following circumstances: (i) The primary minimal panel did not yield sufficient marker expression for unequivocal lineage assignment, (ii) When two or more lineage associated markers of two or more lineage were positive in the primary minimal panel to rule out BAL, (iii) for subtyping of AML, and (iv) in some cases as per choice of the reporting hematopathologist. Additional markers were not done in following circumstances: (i) When only one marker CD13 alone or CD33 alone were seen in a leukemia, expressing CD10, CD19, and HLADR with or without CD34, (ii) Where CD7 and CD4 or CD19 alone were expressed in a leukemia with expression of two or more markers of myeloid associated antigens like CD13, CD33, and CD117 with HLADR expression, (iii) When CD10 alone, CD13 alone or CD33 alone was expressed along with T cell markers, and (iv) When CD4 / CD8 dual negativity or CD4 / CD8 dual positivity was seen along with CD7 expression and HLADR negativity, along with lack of expression of other primary minimal B-cell and myeloid markers (in cases of TALL). List of additional antibodies in the secondary panel included Lambda PE, Kappa FITC, AntiTdtPE (terminal deoxynucleotidyl transferase), cytoCD3PE, cytoCD22PE, AntiMPOFITC, CytoCD79aPE, and CD16PECY5. CD41FITC, CD61PE, and Anti Glycophorin PE were done in those cases where there was a strong morphological suspicion of AMLM7 and AMLM6, respectively, or else when the rest of the markers did not reach a conclusive diagnosis. Anti T cell receptor (TCR) alpha beta Fluorescein isothiocyanate (FITC) and Anti TCR gamma delta PE were done in few cases. Tdt was done in only those situations where difference was between reactive and malignant T-cell populations, mainly in fluids, and in few cases of TALL. Surface antigens were performed before processing the cells for cytoplasmic and nuclear antigens. Metaphase-interphase FISH was performed in the cancer cytogenetics laboratory using dual color translocation probes of LSI AML / ETO, PML / RARA, BCR / ABL, TEL / AML ES, LSIMLL, and CBF-B, RARA dual color break apart probes (Vysis Inc.). FISH methodology was followed as mentioned elsewhere, AML / ETO, [10] PML / RARA, [11] BCR / ABL, [12] MLL, [13] and RT-PCR was carried out in the molecular genetics laboratory, to detect the fusion transcripts, using specific primers for BCR-ABL, AML1-ETO, CBFb -MYH1 (Inv16) in AML, and PML-RARA t(15;17), PLZF-RARA, t(11;17), and NPM, t(5;17) in APML, using an optimal thermal cycler (Perkin Elmer / Techne) at the baseline and follow-up. PCR methodology was followed as described in the literature, for AML1-ETO, [14] CBFb -MYH1 , [15] PML-RARA and variants, [16] and BCRABL. [17] FISH data was available in all cases of BAL and was correlated with the morphological and immunophenotypic impressions. Molecular data (PCR) was however available in few selected cases only. Results A total of 2689 cases of AL, based on morphologic criteria were reviewed between August 1, 2003, and July 31, 2006, using morphology, cytochemistry, immunophenotyping, and molecular tests including FISH and RT-PCR. There were 21 males and 11 females (M: F - 2:1). Age ranged from 2 - 60 years (median age 24 years). Twenty patients (62%) were adults (th ≥18 years), and 12 (38%) pediatrics (< 18 years). B-Myeloid and T-Myeloid subtypes had equal distribution in adults and children, whereas, B-T subtype was common in children [Table - 3]. Hepatosplenomegaly was observed in 12, and lymphadenopathy in nine cases. Baseline investigations revealed hyperleucocytosis (total white cell count of more than 10.5 x 10 9 /L) in 15 patients, low hemoglobin in 14 (range - 3 to 11 g/dL), and low platelet count in 14 patients (range - 14 x 10 9 /L to 120 x 10 9 /L). Serum lactate dehydrogenase (LDH) was raised in seven, serum alkaline phosphatase in six, and liver enzymes in eight cases. Out of these 32 cases (1.2%), 29 were primary ( de novo ), and three were secondary BAL. Two cases of secondary BAL, which were initially diagnosed as Common ALL antigen positive ALL (CALLA positive ALL), relapsed as T-Myeloid BAL and B-Myeloid BAL each. Another case of Hodgkin′s Lymphoma (post chemotherapy) relapsed as T-Myeloid BAL. Sixteen cases revealed a polymorphous blast population varying in small-to-intermediate to large size. The blasts contained scanty-to-moderate cytoplasm and blue cytoplasm, and occasional blasts showed granules. Some blasts also showed two to three prominent nucleoli. One case showed myeloblasts having a moderate amount of cytoplasm, with prominent nucleoli and Auer rods. Another 16 cases revealed a monomorphic population of blasts with FAB ALL-L1 or L2 morphology. Six of these cases revealed blasts with hand mirror morphology. Cytochemical myeloperoxidase (MPO) was positive in four and nonspecific esterase (NSE) in two cases only. A polymorphous population of blasts was seen in 16 cases (T-Myeloid - 10 cases, B-Myeloid - six cases). Another 15 cases had monomorphic blast population (FAB - L1/L2 morphology), more common in B-Myeloid BAL (eight cases) [Table - 4]. FCM revealed a heterogeneous population of blasts on the scatter plots on SSC / FSC. Two cases revealed two distinct populations (? two clones) of blasts, which could be easily separated on FSC/SSC plots, based on the size of the blasts. However the immunophenotypic characters were similar in both cases. Out of 32 cases of BAL, 14 (44%) had B-Myeloid phenotype, 13 (40%) had T-Myeloid phenotype, three (10%) had B-T phenotype, and two (6%) had Trilineage phenotype. All cases showed co-expression of markers from at least two different lineages. Thus the myeloid component was seen in 29 cases (90%), in combination with B and T lymphoids in that order. Only 29 of these 32 cases fulfilled St Jude′s criteria of BAL. These three cases were of T-Myeloid BAL, which expressed cyCD3, CD3, CD7, CD4, and CD8 for T lineage and CD13, CD33, and CD117 for myeloid lineage without Anti-MPO expression. According to EGIL′s criteria both the lineages had more than two points to fulfill the criteria for BAL, however, according to St Jude′s criteria, only cCD3 (T lineage specific marker) was expressed, and not Anti-MPO (myeloid lineage specific marker). Therefore these three cases of BAL will be labeled as T-ALL with aberrant myeloid expression, based on St Jude′s criteria. HLA-DR was expressed in 22 (69%) cases (15 adults and seven children) and CD34 was expressed in 24 cases (75%) (17 adults, seven children). There was no correlation of expression of these markers with different subtypes of BAL. In addition there were another 577 cases of AL, which revealed aberrant expression of markers falling short of being labeled as BAL. Out of 577 cases with aberrant expression, there were, AML with CD7 (20% cases), AML with CD19 (11%), B-cell ALL with CD13 (6%), B-cell ALL with CD7 (1%), T-cell ALL with CD10 (44%), and T-cell ALL with CD13 (11%). FISH analysis was done for BCR-ABL fusion, MLL, and TEL/AML1 gene rearrangements. Seven patients showed BCR-ABL fusion positivity (22%). Among primary BAL, seven cases revealed BCR-ABL gene rearrangement. These cases may also be labeled as chronic myelogenous (or myeloid) leukemia (CML) blast crisis with biphenotypic expression. One had MLL gene rearrangement (3%) and one showed TEL/AML1 (3%). Conventional karyotyping was done in a few cases only. One case revealed trisomy 21, 22 (3%) and another one showed hyperdiploidy (3%). All cases with BCR-ABL gene rearrangement, MLL gene rearrangement, TEL/AMLI, and Trisomy 21, 22 were adults and showed B-Myeloid type of BAL. One case of Triphenotypic acute leukemia revealed hyperdiploidy. Only 15 patients (10 adults and five children) took chemotherapy [Table - 5]. ALL type of treatment regimen, taht is, MCP 841 protocol [18],[19],[20] was given to five pediatric patients and BFM 90 protocol [21],[22],[23] was given to two adults . Standard AML induction chemotherapy, that is, daunarubicin and cytarabin, [24],[25] was given to four patient (two adults and two children), while two patients received palliative treatment. Two Philadelphia (Ph) chromosome (BCR-ABL) positive patients were treated with Imatinib Mesylate. [26],[27],[28] None of the patients underwent stem cell transplantation. Morphological complete remission (CR) (< 5% blasts in the bone marrow aspiration smear) was achieved in eight patients (five children, three adults). Six achieved CR at the end of one month of induction, while two achieved late CR (at the end of two months of induction). Median time to CR was 35 days. Correlation was done between CR and other parameters such as treatment protocol, age, HLA-DR, CD34, CD56 expression and different types of BAL. CR was achieved in five children and three adults. Out of these eight patients, six patients received ALL therapy (five pediatric patients with MCP 841 and one adult with BFM 90 protocol). One patient who received AML therapy achieved late CR at the end of two months. Out of the two adults, who were treated with imatinib, one patient achieved CR, while the CR status was not known in the other patient. CR was achieved more commonly in children. All five pediatric BAL achieved CR and four of these were associated with HLA-DR and CD34 negativity (also seen in two out of 10 adults). CR was achieved in all the three cases of B-T subtypes (100%), two out of four cases of T-Myeloid, and three out of six cases of B-Myeloid. Thus B-T subtype had a good response in comparison to other subtypes. Two cases of T-Myeloid BAL, which were labeled as T-ALL with aberrant myeloid expression (due to absence of Anti-MPO expression) by St Jude′s criteria and treated as ALL, also responded well to treatment [Table - 5]. Seven out of eight patients who achieved CR at the end of the induction period are alive at a median follow up of two years, without any relapse, while one patient was lost to follow-up. Patients who did not achieve CR opted for palliative or supportive treatment. One patient expired during treatment and the remaining seven were lost to follow-up [Table - 5]. Discussion Biphenotypic Acute Leukemia has been defined by the EGIL group and has been recommended by the WHO classification of hematolymphoid neoplasm. Biphenotypic Acute Leukemia is divided into four subtypes based on a scoring system; B-Myeloid, T-Myeloid, B and T-Lymphoid, and Trilineage leukemia. Saint Jude′s criteria for a work up of these neoplasms have been defined by Campana et al. The latter define true mixed-lineage leukemia, giving more credence to cytoplasmic expression of highly lineage-specific markers (e.g., cCD22/cCD79a, cCD3, and anti-MPO). Both these criteria have their own limitations. Selection of the diagnostic criteria may vary from laboratory to laboratory. There is a paucity of published reports of incidence and subtypes of BAL based on the WHO classification from India. There are few studies on the biological behavior and clinico-hematological correlation of BAL. [6],[29],[30] The overall incidence of BAL in our study was 1.2% with male to female ratio being 2:1. It was more common in adults (62%) than children (38%). There were three cases of secondary BAL initially diagnosed as CALLA positive ALL (two cases) and Hodgkin′s lymphoma (one case). Secondary BAL had been reported, evolving from relapsed cases of CALLA positive ALL, [6] AML, [31] T-cell lymphoblastic lymphoma [32] and breast cancer. [33] There seemed to be a lineage switch among the population of tumor cells during the process of leukemic conversion and the heterogeneous stem cells had a potential to differentiate stochastically into any lineage at the primitive stage of normal hematopoiesis. [34],[35] Phenotypic interconversion between myeloid and lymphoid lineage, observed in our report may partially reflect this stochastic model. Three cases of T-Myeloid BAL, which were initially diagnosed as T-ALL with aberrant myeloid expression by St Jude′s criteria (due to absence of Anti-MPO, a lineage specific marker for myeloid) when reviewed, fulfilled the criteria of EGIL for the diagnosis of T-Myeloid (expressed CD13, CD33, CD117, CD3, CD7, and cytoCD3). There were two cases of Trilineage leukemia in our study. Expression of all three lineage specific antigens in the leukemic blasts is extremely rare and there are few single case reports in the literature. [36],[37] Most cases express early hematopoietic markers such as CD34 and HLA-DR, suggesting an early precursor stem cell origin. Absence of these markers was associated with a better treatment outcome in children (four out of five cases). However four patients (three adults, one pediatric) achieved CR despite HLA-DR and CD34 being positive. Seven patients who did not achieve CR showed expression of HLA-DR and CD34. Two other studies have shown similar findings, where expression of CD34 was associated with a poor treatment outcome. [6],[7],[29],[30] The morphology of the blasts in BAL is not consistent. The cells may display myeloid differentiation features such as azurophilic granules or Auer rods, or have lymphoid / undifferentiated morphology. In some cases, there appear to be polymorphous or two blast populations, one larger population resembling myeloid blasts and another with smaller lymphoid appearing blasts. Sixteen of our cases revealed mixed type of polymorphous population of blasts, while another 16 cases revealed a monomorphic population of blasts consisting of FAB - ALL L1 and L2 type of blasts (one case had myeloblasts with Auer rods). The polymorphous mixed type was commonly associated with the T-Myeloid type of BAL, while the monomorphic morphology (FAB - ALL-L1 / L2) was associated with B Myeloid BAL. There are not enough studies in literature to support our findings, however, occasional studies have shown that myeloid morphology is seen more commonly in Ly + AML, and lymphoid morphology in mixed B and T Lymphoid BAL. [30],[38] FISH data revealed BCR-ABL fusion in seven cases, MLL gene and TEL/AML 1 in one case each. Conventional karyotyping could be done in few selected cases only where one case showed trisomy [21],[22] and another case had hyperdiploidy. There is no single chromosomal abnormality that is unique to BAL. However, the present and few other studies have shown that structural abnormalities are common and there is a high incidence of (Philadelphia) Ph positivity and rearrangements involving 11q2. [37],[39],[40] Studies have also shown that Ph positivity and MLL gene rearrangement is an important risk factor for the survival of these patients and has a bad prognosis. [6],[30],[40] In our study out of the two Ph positive patients treated with the imatinib mesylate drug, only one patient achieved remission. This patient continues to be in remission without any relapse with a follow up of 28 months. Clinical trials have shown that approximately 60% of the patients treated with imatinib alone achieve a remission or clearance of peripheral blasts with 19% CR. However these responses were short lived with median time to progression and overall survival of only two to four months. [26],[27],[28] But recent trials have shown that administration of imatinib in addition to induction and consolidation chemotherapy for newly diagnosed Ph positive ALL enhances efficacy and prevents the development of secondary resistance. [41],[42],[43] Clinical significance has not been determined and there are no uniform treatment protocols of BAL. There is no consensus as to whether induction therapy should be with lymphoid and/or myeloid drugs and whether this should be followed by hematopoietic stem cell transplantation. Treatment protocols vary depending upon the choice of the treating oncologist. In the present study, three cases with B-Myeloid, and one case with Trilineage BAL received AML induction therapy, and two cases, one each of B-Myeloid and T-Myeloid received palliative therapy. However, three cases of B-T Lymphoid, three cases of T-Myeloid, and one case of B-Myeloid received ALL kind of treatment (MCP 841 in pediatric and BFM 90 in adult patients). Another two cases received imatinib mesylate. All five pediatric cases and one adult who received ALL kind of treatment achieved CR. While only one out of four patients who received AML treatment achieved CR. Thus children had better treatment outcome than adults, which was statistically significant, as reported in literature. [6],[38] Seven out of eight patients who achieved CR are still alive with a median follow up of two years and have not relapsed. Also HLA-DR and CD34 negativity seen in children who achieved CR can be associated with an important prognostic factor for deciding a better treatment outcome. B-T BAL was seen only in children and had a better treatment outcome than other subtypes of BAL. Since B and T were both of lymphoid lineages, this subtype responded well to the ALL kind of treatment regimen (MCP841). However, two cases of T-Myeloid BAL, which were diagnosed as T-ALL with aberrant myeloid expression by St Jude′s criteria, and treated as ALL, achieved CR, and continue to be in remission. As per EGIL′s scoring system both these cases should have been diagnosed as T-Myeloid BAL, which usually has a bad prognosis. Thus lineage specific cytoplasmic markers (St Jude′s criteria) may be the single most important criteria for the diagnosis of BAL. For validation of this observation, larger studies on AL with aberrant expression have to be studied, applying both the criteria, to see the clinical behavior and treatment response in these patients. There were a few drawbacks of this study. We did three color immunophenotyping with FSC/SSC gating and CD45 gating was done in two cases only. Our approach for immunophenotyping was semi-directed; a primary minimal panel followed by additional antibodies, as and when required. Cytoplasmic markers were done as additional markers in those suspected cases where a definite lineage assignment could not be given on the primary panel. We did not have markers (CD24, CD1A, CD65, CD15, and CD64) as recommended in the EGIL criteria for a complete workup, for diagnosis of BAL. This may be a cause of lower percentages of BAL. Other markers like Tdt, TCR alpha beta, and TCR gamma delta could be done in a few cases only. We did 14 - 20 antibodies per case (mean = 16) for immunophenotyping, a number much less than many other laboratories. [44] Seven cases revealed BCR-ABL gene rearrangement. These cases may be labeled as chronic myeloid leukemia in blast crisis (with biphenotypic expression). Moreover molecular studies (PCR) were not done in all cases, to differentiate between CML blast crisis (p210) from Ph positive ALL (p180). Chemotherapy and tyrosine kinase inhibitors are the mainstay of the treatment; hence it is extremely important to know the BCR-ABL status, so as to institute correct treatment. Though we followed both these criteria for diagnosis of BAL, we prefer and recommend St Jude′s criteria, as it is easy to follow and needs lesser number of antibodies (thus is cost effective). Many laboratories avoid doing cytoplasmic markers, citing technical difficulties; however, it is desirable to do cytoplasmic markers in the primary panel itself, so as not to miss any BAL. Limited by a small number of patients, important conclusions can still be drawn from this study. Immunophenotyping has definite prognostic implications in patients with BAL and pediatric BAL and T-B lymphoid BAL have better prognosis than other BAL subtypes. A comprehensive panel of reagents (antibodies) is required including cytoplasmic markers to make a correct diagnosis of BAL. 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 CML in blast crisis, with biphenotypic expression, and treated accordingly. Minimal antibody panel done by laboratories may further lead to under diagnosis of BAL. Though national guidelines [45] recommend at least ten antibodies, mainly CD13, CD33, CD117, CD10, CD19, HLADR, CD7, CD5 (or CD2), CD45, and CD34 as a primary minimal panel for a case of AL, additional antibodies may be extremely important so as not to miss BAL. Moreover, it is recommended to do intracytoplasmic markers in the primary panel itself, so as not to miss any cases of BAL. BAL may not be a very aggressive subtype, [46] as seen in few of our subtypes of BAL, including B-T BAL, pediatric BAL, and BCR-ABL positive BAL. References
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