Specific features of stem cell (CD34+) subvariant of acute lymphoblast cell leukemia in children

The authors have examined 134 children with acute lymphoblast cell leukemia (ALCL) who were treated at the Research Institute of Pediatric Oncology and Hematology, Russian Cancer Research Center, in January 1990 to November 1999, and followed up till March 1, 1999. The mean duration of follow-ups was 57.46 +/- 2.87 months. The minimum follow-up was 4 months. The immunophenotypical features of stem cell immunological subvariant of ALCL identified from the presence of 10% or 15% of CD34+ lymphoblast cells were similar in the leukemia clone. There is evidence for the isolation of the least mature, stem-cell immunological subvariant of ALCL in children. The immunophenotypic features of stem-cell ALCL in children were as follows: the expression of myeloid antigens (linear and different marker leukemias) and the higher rates of involvement of B-cell leukemias. The clinical and hematological features of stem-cell versus CD34-negative ALCL in children were the low levels of leukocytes (p = 0.009) and blast cells (p = 0.018) in the peripheral blood at diagnosis. At the same time, stem-cell ALCL showed a poorer prognosis. Moreover, blast cell CD34 antigen expression deteriorated prognosis for pre-pre-B (common) immunological variant of ALCL (p = 0.035). Intensified ALCL treatment programmes improved relapseless survival of patients with stem-cell ALCL (p = 0.0042).     

Plasma soluble interleukin-2 receptor (sIL-2R) levels in patients with acute leukemia

The plasma soluble interleukin-2 receptor (sIL-2R) level was higher in 137 patients with acute leukemia (1,489 +/- 1,798 U/ml, including 98 cases of acute myeloid leukemia (AML), 1,063 +/- 1,414 U/ml, and 39 cases of acute lymphoblastic leukemia (ALL), 2,561 +/- 2,194 U/ml), compared to 49 normal control subjects, 421 +/- 151 U/ml). The ALL patients showed elevated plasma sIL-2R levels more frequently than the AML patients (92.3% vs 44.9%). No patient with either hypoplastic AML or AML with multilineage dysplasia and only 1 of 13 patients with acute promyelocytic leukemia (APL) had an elevated plasma sIL-2R level. All the My+ ALL patients (15 cases) showed elevated plasma sIL-2R levels. Plasma sIL-2R levels were significantly lower after chemotherapy in the ALL patients, but were not significantly lower in the AML patients. IL-2R was expressed on the leukemic cells in 36 (53.7%) of 67 AML and in 9 (21.4%) of 42 ALL cases. None of the AML M3, M4, M5, M6, or M7 subgroups showed IL-2R expression. The My+ ALL patients (42.9%, 6/14) showed IL-2R expression more frequently than the other ALL subgroups (10.7%, 3/28) (p = 0.025). The plasma sIL-2R level was correlated with the proportion of leukemic cells expressing IL-2R in acute leukemia. However, there were many cases, particularly ALL cases, who had elevated plasma sIL-2R levels without IL-2R expression on their leukemic cells. These results suggest that the plasma sIL-2R level is a valuable marker for monitoring ALL after chemotherapy, particularly in My+ ALL cases, and that the T cell immune reaction to leukemia appears to be much higher in ALL patients than in AML patients.     

Electron microscopic studies on the occurrence of activated neutrophils in peripheral blood of children with acute leukemias

Peripheral blood (PB) cells are examined to assess cellular maturity and the degree of bone marrow abnormality in children with acute leukemias. During the ultrastructural assessments of PB cells in these children, we noted a frequent occurrence of activated neutrophils. This phenomenon had not been reported previously. We here report for the first time the identification of activated neutrophils in PB of children with acute leukemias. To examine the impact of activated neutrophils, we compared two groups of children including 18 with acute lymphoblastic leukemia (ALL) and 7 with acute myelogenous leukemia (AML) by an ultrastructural leukocyte count method. Many cases (50%) showed more than 30% activated neutrophils per total neutrophil count in PB. Activated neutrophils were elongated or amoeboid-shaped cells ranging from 13-18 microns in greater diameter with a decreased number of granules in the cytoplasm. A significantly higher rate of activated neutrophils was observed in ALL as compared with AML (median: 42.97% vs. 10.64%). Non-leukemic hospitalized (n =3) and healthy (n = 3) control cases showed a median rate of 3.32% activated neutrophils in PB. These findings reveal that a significantly high rate of activated neutrophils occurs in PB of children with ALL which may be exploited in the diagnostic assessment of children with acute leukemias.     

Impact of cellular CD71 (transferrin receptor 1) expression in Egyptian acute leukemia: correlation with clinicopathologic features

Cellular transferrin receptor 1 (CD71) has been identified as a proliferation marker. Inferior outcome with higher expression was observed in many solid tumors. This study objected to assess the expression of CD71 in patients with acute leukemia and to address its prognostic significance and relations to clinicopathologic features. The study included 34 acute myeloid leukemia (AML) and 64 acute lymphoblastic leukemia (ALL) newly diagnosed cases from Mansoura Oncology Center. CD71 was analyzed on blast cells by flow cytometry. CD71 expression was significantly elevated in both AML and ALL. Antigen expression apparently increased in T-ALL, while in AML there was a trend toward a gradual increase of antigen expression in relation to maturation evidence of myeloid subtypes. CD71 expression correlated positively with total leukocyte count in ALL cases and negatively with platelet count in AML cases. In ALL, higher CD71 expression was associated with higher relapse rate and was an independent prognostic factor of overall survival (HR 1.8; 95 % CI 1.2–4.1). In conclusion, CD71 is overexpressed in acute leukemia; it predicts adverse clinical outcome in ALL. In addition, CD71 antagonism could be a possible therapeutic target in acute leukemia.     

获得性21三体恶性血液病的临床和细胞遗传学特征

目的 分析21三体恶性血液病患者的临床及细胞遗传学特点.方法 采用骨髓直接法和(或)培养法制备染色体标本,采用R显带技术进行核型分析,并进行临床随访.结果 共发现25例患者存在21三体,其中急性髓系白血病(acute myeloid leukemia,AML)13例,占同期进行染色体检查的AML患者总数的1.5%,包括M5h6例;急性淋巴细胞(acute lymphoblastic leukemia,ALL)8例,占同期进行染色体检查的ALL患者总数的2.2%,其它类型4例.25例中13例为单纯获得性21三体,其余病例均合并其它异常.随访的19例患者的中位生存期为9个月.结论 单纯21三体在AML中以M5b多见,伴21三体异常的恶性血液病预后还存在争议.     

Low incidence of TEL/AML1 fusion and TEL deletion in Korean childhood acute leukemia by extra-signal fluorescence in situ hybridization

TEL/AML1 fusion in acute leukemia results from cryptic translocation of chromosome 12 and 21, the presence of which suggests a favorable prognosis. The incidence of TEL/AML1 fusion in B-lineage ALL is approximately 25%, but the incidence in Korea has not yet been reported. To investigate the incidence of TEL/AML1 fusion and TEL deletion, bone marrow specimens from 77 Korean children with newly diagnosed acute leukemia were analyzed by FISH. We applied extra-signal FISH to discriminate a true TEL/AML1 fusion from a false-positive fusion signal. To determine the cut-off value of the TEL/AML1 fusion signal, 20 normal bone marrow specimens and 28 normal peripheral blood specimens were also analyzed. The frequency of patients with TEL/AML1 fusion was 13.3% (4 cases) among 30 B-lineage ALL and 9.5% among 42 ALL. One TEL/AML1 fusion-positive patient was also found among 4 acute biphenotypic leukemias. TEL/AML1 fusion was not found in any samples from patients with T-lineage ALL or AML. The incidence of TEL deletion was 6.7% (2 cases) among 30 B-lineage ALL and 4.8% among 42 ALL. The incidences of TEL/AML1 fusion and TEL deletion in Korean children with acute leukemia appear to be lower than those in other countries, suggesting a racial difference.     

Blood stem cell transplantation in pediatric oncology]

Large-dose chemotherapy (LDCT) with auto- and allogenic transplantation of blood stem cells (BSC) in pediatric oncology remains so far the last hope for many patients. The number of such procedures made in Europe increases by 10% every year. At the same time many issues of the place and role of transplantation in pediatric oncology remains unclear. Based on 240 sessions of cytopheresis, the author show that BSC can be sampled from severe pretreated patients despite the drug therapy regimen. The efficacy of G-KSF and GM-KSF used to stimulate BSC secretion is similar. After LDCT with BSC autotransplantation, the relapse-free survival rates in patients with Ewing's sarcoma and acute myeloblast-cell leukemia were 55.4 and 44.4%, respectively (in the first and second remissions). Consolidation as LDCT with BSC autotransplantation without cleansing the material from malignant cells is not a sufficient therapeutical measurement in disseminated neuroblastoma. Whether partial compatible related BSC transplantation can be possible made after non-myeloablative preparation regimens is shown.     

The proportion of abnormal karyotypes in acute leukemia samples related to method of preparation

Bone marrow and peripheral blood were studied from 200 patients with acute leukemia [109 with acute myeloid leukemia (AML), 91 with acute lymphoblastic leukemia (ALL)] who had samples cultured for varying times and who had a mixture of chromosomally abnormal and normal cells. The mean percentage of abnormal metaphase cells increased with culture time. The peak was reached at 48 hours and declined slightly after 72 hours in culture for ALL patients. The mean percentage of abnormal cells increased up to 72 hours in culture for AML patients. In 68 patients (31 AML and 37 ALL), cytogenetic data were available from samples processed with both direct preparations and culture methods. The percentage of abnormal cells increased after culture in 49 patients (23 AML and 26 ALL), while it decreased or remained at the same level in 19 patients. For AML patients, the mean percentage of abnormal cells was significantly different between direct (38%) and cultured preparations (63%), (p less than 0.001). Seven of 9 patients with AML who showed a greater than 50% increase in abnormal cells after culture had either a t(8;21), t(15;17), or abnormalities involving 11q23. The two patients who showed a significant decrease in abnormal cells both had a translocation involving 11q13. Compared with ALL, more AML patients showed greater than 80% abnormal bone marrow metaphase cells at diagnosis or at relapse.     

Utility of white blood cell suspect flags and histogram pattern in the detection of acute leukemia by Advia-60 automated hematology analyzer

Blood samples from patients with acute leukemia, when analyzed with automated hematology counters, tend to introduce inaccuracies in the automated differential count and can cause diagnostic confusion without providing definite clues to the presence of abnormal cells. We designed this study to assess the utility of white blood cell (WBC) flags and histogram pattern generated by Advia-60 automated hematology analyzer in the recognition and categorization of acute leukemia. Data printouts of 31 newly diagnosed cases of acute leukemia, 22 with acute myeloid leukemia (AML) and 9 with acute lymphoblastic leukemia (ALL) were reviewed. All cases of AML and ALL generated the WBC suspect blastflag M2 associated with two of the non blast suspectflags G1 and G2. Among the cases of AML, 95.5% of the WBC histogram patterns were definitive of the presence of abnormal cells and were indicative of the myeloid nature of cells. Only 44.4% of the histograms in the cases of ALL could be definitive of the presence of abnormal cells and 33.3% were indicative of their lymphoid nature. Significantly, 55.5% of the histograms in ALL were normal. The false positives for both AML and ALL were 10.5% when only WBC flagging was considered and were reduced to 0.05% when the flags were combined with histogram patterns for interpretation. Combined flagging and histogram recognition can be of aid in identifying cases of acute leukemia and the morphologist can then assess these samples further. This ensures that cases of acute leukemia, especially in high output laboratories, are not inadvertently missed.     

MLL-CBP fusion transcript in a therapy-related acute myeloid leukemia with the t(11;16)(q23;p13) which developed in an acute lymphoblastic leukemia patient with Fanconi anemia

We describe a boy with Fanconi anemia (FA) who developed acute lymphoblastic leukemia (ALL) (FAB-LI) followed by acute myeloid leukemia (AML) (FAB-M5) at relapse. The patient was diagnosed with early pre-B-cell ALL without preceding aplastic anemia and was treated with ALL-oriented chemotherapy which included doxorubicin (a total dose of 140 mg/m(2) administered), which is a topoisomerase II inhibitor. Complete remission was obtained, but after 38 weeks AML developed. The karyotype of ALL cells at diagnosis showed 46,XY, and that of AML cells at relapse was 46,XY, t(11;16)(q23;p13). An MLL gene rearrangement and MLL-CBP chimeric mRNA were found in AML, but not in ALL. A diagnosis of FA was confirmed by an increased number of chromosomal breaks and rearrangements in peripheral blood lymphocytes cultured with mitogen in the presence of mitomycin C. We conclude that this FA patient developed ALL followed by a therapy-related t(11;16)-AML resulting in an MLL-CBP fusion. Further examination of such patients would shed light on leukemogenesis in FA patients. Genes Chromosomes Cancer 27:264-269, 2000.     

Second Hematopoietic Stem Cell Transplantation for Post-Transplantation Relapsed Acute Leukemia in Children: A Retrospective EBMT-PDWP Study

Outcome data were collected from the European Society for Blood and Marrow Transplantation registry on 373 children from 120 centers with relapsed leukemia (214 with acute lymphoblastic leukemia [ALL] and 159 with acute myelogenous leukemia [AML]) who underwent second allogeneic hematopoietic stem cell transplantation (HSCT) between 2004 and 2013. Overall survival (OS) was 38% at 2 years and 29% at 5 years, and leukemia-free survival (LFS) was 30% at 2 years and 25% at 5 years. Median follow-up after second HSCT was 36.4 months in the ALL group and 50.2 months in the AML group. In the ALL group, OS was 43% at 2 years and 33% at 5 years, and LFS was 34% at 2 years and 31% at 5 years. In the AML group, OS was 32% at 2 years and 24% at 5 years, and LFS was 24% at 2 years and 17% at 5 years. The 2-year nonrelapse mortality (NRM) rate was 22% in the ALL group and 18% in the AML group. Favorable prognostic factors (P?<?.05) for OS and LFS included >12 months between transplantations and chronic graft-versus-host disease after the first HSCT (in both groups), complete response before the second HSCT (ALL group only), and age >12 years (AML group only). Findings were more consistent over time in the ALL group, with no significant differences between 2-year and 5-year rates of relapse, NRM, and LFS. Children with relapsed acute leukemias have a substantial likelihood of long-term survival following second HSCT. Given the many novel targeted and immunomodulation therapies currently under development, it is important to identify specific patient subpopulations that may benefit from a second HSCT compared with those better suited to new approaches.     

Myeloperoxidase gene expression in acute leukemias

Since myeloperoxidase (MPO) is considered to be a critical marker of differentiating acute myelogenous leukemia (AML) from acute lymphocytic leukemia (ALL), the analysis of MPO gene expression may provide further insight into the leukemia classification and the lineage fidelity of leukemia cells. By Northern blot hybridization using full-length MPO cDNA as a probe, approximately 66% of AML cells (3/4 M1 cases, 2/4 M2 cases, 15/15 M3 cases, 11/15 M4 cases, and 2/12 M5 cases) were found to express MPO mRNAs, whereas none of 18 ALL cases did. MPO mRNA was detectable when AML cells contained at least 10% peroxidase-positive cells. APL (M3) cells expressed high levels of mRNA in accordance with heavy staining for peroxidase.     

Implication of Early Lymphocyte Recovery after Allogeneic Hematopoietic Stem Cell Transplantation in Children with Leukemia

Purpose

The repopulating lymphocytes after allogeneic hematopoietic stem cell transplantation have an important role not only on the prevention of serious infections in the early transplantation period, but also on the killing of residual leukemic cells by graft-versus-leukemia effect. The aim of this study was to analyze the impact of lymphocyte recovery after allogeneic stem cell transplantation in children with hematologic malignancies.

Materials and Methods

We evaluated 69 children transplanted for acute lymphoblastic leukemia (ALL) (n=34), acute myeloid leukemia (AML) (n=26), chronic leukemia (n=7) and juvenile myelomonocytic leukemia (n=2) between 1996 and 2008 at the Chonnam National University Hospital, Korea. The patients were grouped based on absolute lymphocyte counts (ALC) <500/µL or ≥500/µL at D+21 and D+30 after transplant.

Results

Patients with a High ALC at D+21 and D+30 had a faster neutrophil and platelet engraftment. The High at D+30 group had a better 5 year overall survival (71% vs. 53%, p=0.043) and event-free survival (72% vs. 53%, p=0.065) than the Low at D+30 group. The incidence of grade II-IV acute and chronic graft-versus-host disease (GVHD), and relapse rate did not differ by the ALC counts. However, the Low at D+30 group had a significantly increased risk for transplant-related mortality (p=0.019). The univariate analysis showed that the factors associated with decreased survival were a Low ALC at D+30, patients with high risk ALL, and grade II-IV aGVHD in patients with ALL and AML.

Conclusion

Early posttransplant serial lymphocyte measurement would be a simple but useful method for predicting transplant outcomes.     

Detection of terminal deoxynucleotidyl transferase in acute leukemias using monoclonal antibodies directed against native and denatured sites

Monoclonal antibodies (MoAb) directed against human terminal deoxynucleotidyl transferase (TdT) have been developed recently. The authors evaluated the reactivity of two TdT MoAb, one directed against a native site and the other against a denatured site, in bone marrow samples from patients with acute lymphoblastic leukemia (ALL) and acute myelogenous leukemia (AML). Results were correlated with the immunophenotype and compared with those obtained with an anti-TdT polyclonal antibody (PoAb). The authors found that 39 of the 45 children (87%) with ALL were positive with the anti-TdT PoAb, while only 25 of 45 (56%) were positive using MoAb. In the 41 of 45 cases of ALL for which marker studies were available, there was no relationship between immunophenotype and reactivity with the PoAb or either MoAb. Five cases of AML were studied and two were positive using the PoAb, but none showed staining with the MoAb. The authors' findings demonstrate that, although MoAb may be used to detect TdT in acute leukemia, the two MoAb used do not correlate with immunophenotype and are less sensitive than the PoAb. However, the MoAb appears to demonstrate more specificity for ALL than the PoAb, since it was not reactive in PoAb+ AML.     

Allogeneic bone marrow transplantation after hyperfractionated total-body irradiation and cyclophosphamide in children with acute leukemia

Ninety-seven children with either acute lymphoblastic leukemia (ALL) or acute myelogenous leukemia (AML) received HLA-identical bone marrow transplants from sibling donors, after preparation with 1320 cGy of hyperfractionated total-body irradiation and high-dose cyclophosphamide. Kaplan-Meier product-limit estimates (means +/- SE) of disease-free survival at five years among patients with ALL in second remission, third remission, and fourth remission or relapse were 64 +/- 9, 42 +/- 14, and 23 +/- 11 percent, respectively, with probabilities of relapse of 13 +/- 7, 25 +/- 13, and 64 +/- 16 percent. Among patients with AML in first remission, second remission, and third remission or relapse, five-year disease-free survival estimates were 66 +/- 10, 75 +/- 15, and 33 +/- 19 percent, with respective relapse probabilities of 0, 13 +/- 12, and 67 +/- 19 percent. The most frequent cause of death in patients in early remission (ALL in second or third remission or AML in first or second remission) was bacterial sepsis, fungal sepsis, or both, most often in the presence of acute or chronic graft-versus-host disease. Among patients with ALL who received transplants while in second remission, the duration of the initial remission had no effect on the probability of relapse after transplantation. The only pretransplantation factor that significantly affected outcome was the disease status at the time of transplantation; patients in early remission had better disease-free survival. We conclude that transplantation after preparation with hyperfractionated total-body irradiation and cyclophosphamide is an effective mode of therapy in children with refractory forms of acute leukemia.     

Combination assay of IAP and ADA in hematologic malignancies

We measured the levels of adenosine deaminase (ADA) and immunosuppressive acid protein (IAP) in 10 patients with acute myeloid leukemia (AML), 5 with acute lymphoblastic leukemia (ALL), 8 with chronic myeloid leukemia (CML), 7 with myelodysplastic syndrome (MDS), 5 with malignant lymphoma (ML), 3 with multiple myeloma (MM) and one with adult T cell leukemia. On admission, the level of IAP was abnormally high in all cases of AML and ALL 50% of CML cases, 71.4% of MDS cases, 60% of ML cases and none of MM cases. ADA was elevated in all cases of ALL, 77.8% of AML and CML cases, 57.1% of MDS cases, 60% of ML cases and 33.3% of MM cases. In 7 patients with AML, the level of IAP returned to normal when they achieved complete remission. On the other hand, the level of ADA had already returned to normal even during induction therapy. ADA showed a positive correlation with the absolute number of peripheral blasts and lactic dehydrogenase both in AML and ALL. These results suggest that ADA indicates the activity of leukemia and IAP indicates the immunocompetence of the host.     

Immunoalkaline phosphatase labeling of terminal transferase in hematologic samples

Early studies of terminal transferase (TdT) expression in acute leukemia indicated that this enzyme is only found in acute leukemia of lymphoblastic type (ALL). More recently, however, several reports have suggested that TdT-positive blast cells may be found in a substantial number of cases of acute myeloid leukemia (AML). In this study, a sensitive immunoalkaline phosphatase procedure (the APAAP technic) has been used to stain normal and neoplastic blood and bone marrow samples for TdT with the use of both polyclonal and monoclonal anti-TdT antibodies. As expected, most cases of ALL studied (63 of 65) were TdT-positive. In addition, however, blast cells in 22 out of 59 (37%) cases of AML were stained by anti-TdT antibodies. Both nuclear and cytoplasmic localization were seen in each type of acute leukemia. These findings, together with previous immunocytochemical and biochemical studies, suggest that a substantial number of cases of AML express TdT (usually in a minority of blast cells) and that the frequency with which these cases are detected is directly related to the sensitivity of the staining technic used.     

Extramedullary Relapse of Acute Leukemia after Allogeneic Hematopoietic Stem Cell Transplantation: Different Characteristics between Acute Myelogenous Leukemia and Acute Lymphoblastic Leukemia

Extramedullary relapse (EMR) of acute leukemia (AL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a contributor to post-transplantation mortality and remains poorly understood, especially the different characteristics of EMR in patients with acute myelogenous leukemia (AML) and those with acute lymphoblastic leukemia (ALL). To investigate the incidence, risk factors, and clinical outcomes of EMR for AML and ALL, we performed a retrospective analysis of 362 patients with AL who underwent allo-HSCT at the First affiliated Hospital of Soochow University between January 2001 and March 2012. Compared with patients with AML, those with ALL had a higher incidence of EMR (12.9% versus 4.6%; P = .009). The most common site of EMR was the central nervous system, especially in the ALL group. Multivariate analyses identified the leading risk factors for EMR in the patients with AML as advanced disease status at HSCT, hyperleukocytosis at diagnosis, history of extramedullary leukemia before HSCT, and a total body irradiation–based conditioning regimen, and the top risk factors for EMR in the patients with ALL as hyperleukocytosis at diagnosis, adverse cytogenetics, and transfusion of peripheral blood stem cells. The prognosis for EMR of AL is poor, and treatment options are very limited; however, the estimated 3-year overall survival (OS) was significantly lower in patients with AML compared with those with ALL (0 versus 18.5%; P = .000). The characteristics of post–allo-HSCT EMR differed between the patients with AML and those with ALL, possibly suggesting different pathogenetic mechanisms for EMR of AML and EMR of ALL after allo-HSCT; further investigation is needed.     

Anti-CD10 immunoperoxidase staining of paraffin-embedded acute leukemias: comparison with flow cytometric immunophenotyping

CD10 is common in B-precursor acute lymphoblastic leukemia (ALL) but is rare in acute myeloid leukemia (AML). However, until recently, analysis for CD10 has generally required fresh or frozen tissue. 56C6 is a monoclonal antibody that is now commercially available for the detection of CD10 in routinely processed paraffin-embedded tissue. Immunoperoxidase stains for CD10 on paraffin-embedded bone marrow core biopsy specimens (B5-fixed, decalcified) and marrow aspirate clots (formalin-fixed) were compared with flow cytometric immunophenotyping for CD10 on fresh cell suspensions in 20 cases of AML and in 30 cases of ALL. CD10 detection by immunohistochemistry agreed with CD10 by flow cytometry in 98% (49 of 50) of acute leukemias. The results matched in 100% (20 of 20) of AML. Five percent (1 of 20) of AMLs expressed CD10. Two of the AMLs with monocytoid differentiation were interpreted as negative for CD10 by flow cytometry, although these had nonspecific dim immunofluorescence for multiple markers, including CD10, and these cases were negative by immunohistochemistry. CD10 detection by immunohistochemistry agreed with CD10 by flow cytometry in 97% (29 of 30) of ALL. Eighty-four percent (21 of 25) of B-precursor ALL and 40% (2/5) of T-lineage ALL expressed CD10 by immunohistochemistry. In 1 case of B-precursor ALL, CD10 was dimly positive in 24% of the blasts by flow cytometry but negative by immunohistochemistry. We conclude that immunohistochemical staining of paraffin-embedded tissue, either B5- or formalin-fixed, is an effective method for the detection of CD10 in acute leukemia. This technique is useful in distinguishing AML from ALL.