Terminal-deoxynucleotidyl transferase (TdT): serial observations on patients with leukemia

Terminal-deoxynucleotidyl transferase (TdT) bone marrow determinations were performed on 67 patients with leukemia using the indirect immunofluorescence technique. A total of 103 smears were evaluated on 32 patients with acute lymphoblastic leukemia. With some exceptions, TdT levels were elevated at onset, declined during induction except in resistant cases, decreased during remission on chemotherapy, showed slight elevation during remission off chemotherapy, and rose during relapse in those cases previously positive. The most important finding was that patients in remission may have elevated TdT levels. Those were usually less than 10%. A total of 124 bone marrow smears were evaluated on 29 patients with acute myeloid leukemia. In general, values in all categories were below 1%, with a few elevated between 1% to 10%. Six patients with chronic myelogenous leukemia in blast crisis had 13 bone marrow smears evaluated. Five were in myeloblastic crisis and had values of less than 1%; 1 was lymphoblastic which had 50% positive cells at onset. In our experience, TdT determinations are of value in lymphoblastic leukemia in diagnosis, in predicting response to therapy, and in detecting early relapse.     

Prognostic significance of terminal transferase activity in childhood acute lymphoblastic leukemia: a prospective analysis of 164 patients

Whether the level of terminal deoxynucleotidyl transferase (TdT) activity in mononuclear cells from bone marrow and peripheral blood has prognostic significance has been analyzed prospectively in 164 children with T and non-T, non-B marked acute lymphoblastic leukemia (ALL). TdT was measured at diagnosis to assess its value as a predictor of duration of remission and length of survival. It was measured repeatedly during remission to assess whether it could predict relapse. Ninety-seven percent of the children achieved a complete remission of their disease, and 40% relapsed during the study. The level of TdT activity in blasts at diagnosis varied 1000-fold from patient to patient. There was no statistically significant relationship between TdT activity in cells at diagnosis and the achievement of complete remission, the duration of remission, or length of survival. TdT activity was significantly increased in the bone marrow of 65% of patients at the time of marrow morphological relapse, but was rarely increased in marrow from patients with isolated testicular or central nervous system relapse. Wide fluctuations in TdT activity were characteristically seen in mononuclear cells from the marrow and peripheral blood of patients with ALL at all stages of their disease. An isolated high value of TdT activity in the bone marrow or peripheral blood cannot be taken as evidence of impending relapse. Quantitative measurements of TdT activity alone on mononuclear cells from bone marrow and peripheral blood are helpful in differential diagnosis, but cannot guide therapy of children with ALL.     

Detection of minimal residual disease in B-lineage acute lymphoblastic leukaemia by quantitative flow cytometry

The clinical significance of detecting minimal residual disease (MRD) in B-lineage acute lymphoblastic leukaemia (ALL) was evaluated by quantitative flow cytometry using a combination of TdT with CD10 and CD19. 53 patients with B-cell precursor ALL were followed during and after completion of treatment (median follow-up 23 months). Nine patients relapsed and MRD had been detected in six of them, 5–15 weeks before relapse despite morphological complete remission. 43 patients remain in clinical remission and in none of these was MRD detected. Disease-free survival based on the detection of MRD by flow cytometry showed a statistically significant difference between both groups ( P  < 0.0001). The absence of MRD correlates with a low relapse rate, whereas the presence of MRD predicted early relapse. This study has shown that flow cytometry can improve the morphologic assessment of bone marrow (BM) remission status in B-lineage ALL. The finding of < 5% blasts in BM aspirates did not correlate with 'true' remission in a proportion of cases as residual leukaemic blasts were detected by flow cytometry in nine samples from six patients. On the other hand, the presence of > 5% blasts assessed by morphology was not necessarily a feature of relapse in five patients as these cells were shown to have a phenotype identical to normal TdT-negative B-cell precursors. Quantitative flow cytometry was more informative than conventional morphology to assess remission status and showed a strong correlation with clinical outcome. This methodology is useful to define MRD in the majority of patients with B-lineage ALL and should be tested in prospective clinical trials.     

Terminal Deoxynucleotidyl Transferase Expression in Acute Non-lymphoid Leukaemia: an Analysis by Immunofluorescence

S ummary . Indirect immunofluorescence for terminal transferase enzyme (TdT) was used to study the blasts of 64 patients with acute non-lymphoid leukaemia (ANLL). In 32 patients no TdT positive cells were seen. In 19 cases a small subpopulation of cells expressing TdT was detected; these constituted up to 5% of total nucleated cells, and it was not clear whether these TdT positive cells were part of the leukaemic process or represented residual normal bone marrow lymphoid cells.
The remaining 13 patients had TdT positive cells accounting for 7–90% of the total. In two of these cases TdT was expressed on blasts with myeloid features, representing an aberrant expression of TdT by myeloid cells; in contrast, in three cases mixed populations of TdT positive lymphoid blasts and TdT negative myeloid blasts were observed. In the remaining cases it was not possible to determine whether the TdT positive cells had definite lymphoid or myeloid features. Cytogenetic analysis showed no evidence of the Philadelphia chromosome. Response to treatment was assessed in 11 of the 13 patients. Only one patient remitted with the initial choice of therapy (DAT); four failed to respond to initial regimes of vineristine and prednisone (V & P) while the other five patients did not respond to myelotoxic combinations (DAT). Only one patient subsequently entered complete remission on second line therapy (V & P). This group of patients with TdT⁺ ANLL had a particularly bad prognosis, and appeared to differ from cases of TdT positive acute undifferentiated leukaemia, which often respond to V & P therapy.     

Flow-cytometric detection of minimal residual disease with atypical antigen combinations in patients with de novo acute myeloid leukemia

 The immunophenotypic features in adult de novo acute myeloid leukemia (AML) patients at diagnosis using flow cytometry double marker analysis and the detection of minimal residual disease with atypical leukemia-associated antigen combinations during remission were investigated. Fifty adult patients with de novo AML at diagnosis were studied. Bone marrow samples from 21 patients with AML were analyzed upon achievement of complete remission and during continuous complete remission. Ten bone marrow samples of normal donors were also studied. CD34/CD13, CD34/CD33, CD33/CD7, CD33/CD10, CD33/CD19 and CD33/TdT are the leukemia-associated antigen combinations used for the detection of minimal residual disease. The outcome of 19 patients has been evaluated. Of these 19 patients, 10 were found to be in immunophenotypic remission (median follow-up after the study: 837 days, range 620–1343 days). Only one patient in this group has relapsed so far. In the other nine patients residual disease was detected. Seven of these patients developed systemic relapse following a median follow-up time of 86 days after the study (range 34–273 days), one received allogeneic bone marrow transplantation 70 days after the study, and another has been in complete remission and off chemotherapy for 36 months. The presence of cells with atypical antigen combinations identified at diagnosis in certain patients is valuable for monitoring the disease in remission. The persistence of such a population in remission has indicated the impending relapse in this study. Received: 11 October 1999 / Accepted: 11 February 2000     

Cellular phenotypes of normal and leukemic hemopoietic cells determined by analysis with selected antibody combinations

Individual leukemic cells and the corresponding rare normal cell types in nonleukemic bone marrow were analyzed with various combinations of antisera (labeled with different fluorochromes: TRITC and FITC). Double staining for membrane Ia-like molecules (TRITC) and nuclear terminal transferase (FITC) was a very useful combination that distinguished common non-T, non-B ALL (Ia+,TdT+) and thymic ALL (Ia-,TdT+) from the rare cases of B ALL (Ia+,TdT-) and from AML (frequently Ia+, TdT-; in some cases Ia-, TdT-). Additional antisera (such as anti-ALL, anti- HuTLA, anti-immunoglobulin reagents, etc.) confirmed the diagnosis and further characterized the leukemic blasts. Ia+,TdT+ cells could be observed in low numbers in normal and nonleukemic regenerating marrow and were probably normal precursor cells; this reagent combinations was, therefore, not useful for monitoring residual non-T, non-B ALL blasts in treated patients. Other marker combinations detecting pre-B ALL blasts (double staining for cytoplasmic IgM and nuclear TdT) and Thy-ALL blasts (HuTLA+,TdT+) were, however, virtually leukemia specific in the bone marrow and could be used to effectively monitor residual leukemic cells throughout the disease. These combined single-cell assays are not only economical and informative but are also important for assessing the heterogeneity of leukemia and for standardizing new mouse or rat monoclonal antibodies for diagnosis.     

Terminal-deoxynucleotidyl-transferase immunofluorescence on bone marrow smears: Serial studies on 28 patients

Terminal-deoxynucleotidyl-transferase (TdT) activity determinations, using the indirect immunofluorescence technique, were performed on 28 consecutive leukemia patients. Fifteen patients with acute lymphoblastic leukemia had 38 bone marrow smears examined. TdT-positive cells were a good indicator of disease activity in acute lymphoblastic leukemia in that numbers were increased at the time of diagnosis, normal during remission, and increased during relapse. Ten patients with acute myeloid leukemias had 42 smears studied. The number of TdT-positive cells did not reflect the activity of the disease, except for two patients with acute myelomonocytic leukemia in which TdT-positive cells were mildly increased during relapse. Three patients with chronic myelogenous leukemia had eight smears studied. The number of positive cells seemed meaningful only in following the course of lymphoid blast crisis. It would therefore appear that TdT determinations seem to be of value in lymphoblastic leukemia, but of limited value in myeloid leukemias.     

Immunophenotypic transformation from acute undifferentiated leukemia to Burkitt's-like acute lymphoblastic leukemia

Progression of more differentiated to less differentiated malignant phenotypes has been described infrequently during the natural evolution or at relapse of treated hematopoietic malignancies. This report describes an unusual instance of immunophenotypic transformation from an immunologically undifferentiated acute leukemia to a leukemia that at relapse possessed morphologic and immunologic markers characteristic of a Burkitt's-like acute lymphoblastic leukemia. A 26-year-old man initially presented with pancytopenia and a bone marrow diffusely replaced with blast cells morphologically most consistent with a French-American-British L2 subclassification. The surface immunophenotype of the blasts at diagnosis showed HLA-DR surface antigen but no myeloid, lymphoid, or immunoglobulin determinants. Despite successful induction and ongoing consolidation chemotherapy, the patient had a relapse five months after diagnosis; blast cells at relapse demonstrated marked cytoplasmic vacuolation consistent with a Burkitt's-like L3 acute lymphoblastic transformation. Immunophenotypic analysis revealed the presence of restricted immunoglobulin determinants (mu heavy chain and kappa light chain), as well as two separate B lineage surface determinants (BA-1 and B-1). Immunophenotypic transformations may reflect the presence of either a multiclonal or multipotent leukemic population; documentation of the frequency of such transformations and genomic analysis of the transformed subpopulations may be helpful in furthering the understanding of molecular mechanisms involved in leukemogenesis.     

Interferon therapy for Ph1 positive CML patients relapsing after T cell-depleted allogeneic bone marrow transplantation

Eighteen chronic myeloid leukemia patients with hematological (four patients) or only cytogenetic (14 patients) relapse occurring after T cell-depleted allogeneic bone marrow transplantation (BMT) have been treated with alpha 2b interferon (IFN) at a starting dose of 5 x 10(6) i.u./m2 subcutaneously three times a week. All four patients with hematological relapse achieved long-lasting hematological remission without reduction of bone marrow Ph1 positive cells. When IFN was started the median percentage of bone marrow Ph1-positive metaphases was 50% (range 9-100) for the 14 patients with cytogenetic relapse. Twelve (85.7%) of these patients are alive with a median follow-up of 25 months (range 20-37 months) from cytogenetic relapse and 33 months (range 27-49 months) from BMT. Six (43%) of the 14 patients progressed to hematological relapse and eight patients (57%) are still in hematological remission with two patients achieving complete cytogenetic remission confirmed at molecular level by disappearance of the M-BCR rearranged band. IFN therapy may be a good alternative to conventional chemotherapy for transplanted CML patients with hematological relapse and the treatment of choice for patients with a persistent cytogenetic relapse occurring after T cell-depleted BMT.     

Gemtuzumab ozogamicin-induced long-term remission in a woman with acute myelomonocytic leukemia and bone marrow relapse following allogeneic transplantation

A 56-year-old woman with acute myelomonocytic leukemia underwent myeloablative allogeneic hematopoietic stem cell transplantation (allo-SCT) from a matched unrelated donor in her first complete remission (CR). Veno-occlusive disease (VOD) prophylaxis consisted of low-dose heparin and ursodeoxycholic acid. Graft-versus-host disease (GVHD) prophylaxis comprised tacrolimus and short-term methotrexate. On day 14, VOD developed, but gradually resolved with supportive therapy. On day 58, she showed grade II acute GVHD, but this resolved spontaneously. On day 140, she developed hematological relapse with 40.2% marrow infiltration of CD33-positive blasts. Following the discontinuation of tacrolimus, gemtuzumab ozogamicin (GO) was administered. After GO administration, the patient exhibited mild VOD and severe pancytopenia with a sustained high fever for 6 weeks without evident infection. Bone marrow examination revealed severe hypoplastic marrow with 1.3% blasts 4 weeks after GO administration. Although transfusion-dependent pancytopenia persisted for 8 months after GO administration, bone marrow examination revealed the recovery of normal hematopoietic cells with 0.8% blasts. The patient has remained in CR with incomplete blood count recovery for 7 years following GO administration. Although the standard treatment for acute myeloid leukemia relapse after allo-SCT still remains to be established, GO may be a promising option.     

Measurement of terminal deoxynucleotidyl transferase mRNA in clinical samples: a new parameter in analysis of leukemia cells

A 1750 base pair cDNA to human terminal deoxynucleotidyl transferase (TdT) has been cloned. This cDNA detects a dominant 2200 base pair messenger RNA species in normal and leukemic cells synthesizing the enzyme. A quantitative dot blot assay was utilized to survey a number of clinical samples from patients with TdT positive and negative leukemias as well as cells from normal volunteers. A linear relationship was detected between the amount of TdT mRNA and the amount of enzyme activity in bone marrow cells. The assay is sensitive enough to detect normal TdT levels in bone marrow, and distinguish these levels from the lack of such mRNA in peripheral blood and bone marrow of patients with myeloid leukemia. Elevated levels of mRNA were found in two cases of patients in clinical remission. The prognostic significance of these observations must await further study.     

Terminal deoxynucleotidyl transferase-containing cells in peripheral blood: implications for the surveillance of patients with lymphoblastic leukemia or lymphoma in remission

An indirect immunofluorescence assay was used to quantitate TdT- containing (TdT+) cells in the mononuclear leukocyte fraction of peripheral blood from normal subjects and patients with acute lymphoblastic leukemia (ALL) and lymphoblastic lymphoma (LL). In normal children (10) and adults (10), 0.036% +/- 0.014% (mean +/- SD) and 0.030% +/- 0.015% TdT+ cells were found. In peripheral bloods from 10 children receiving chemotherapy for tumors other than ALL or LL, 0.040% +/- 0.039% TdT+ cells were found. Serial determinations were performed on 15 patients with ALL or LL who were in clinical remission. Eight of these patients remained in continuous remission and always had fewer than 0.11% TdT+ cells in their peripheral blood. Three patients who developed systemic relapse were found to have progressively rising numbers of TdT+ cells in their peripheral blood prior to clinical evidence of relapse. All 3 of these patients had greater than 0.1% TdT+ cells in their peripheral blood from 3 to 8 wk prior to clinical relapse. In 3 other patients, localized extramedullary relapse developed, but no trend was found on serial TdT determinations. Thus, the indirect immunofluorescence assay for TdT detects a small population of cells in normal peripheral blood. In patients with ALL, progressive increases above this normal level were associated with subsequent bone marrow relapse.     

Prospective long-term minimal residual disease monitoring using RQ-PCR in RUNX1-RUNX1T1-positive acute myeloid leukemia: results of the French CBF-2006 trial

In t(8;21)(q22;q22) acute myeloid leukemia, the prognostic value of early minimal residual disease assessed with real-time quantitative polymerase chain reaction is the most important prognostic factor, but how long-term minimal residual disease monitoring may contribute to drive individual patient decisions remains poorly investigated. In the multicenter CBF-2006 study, a prospective monitoring of peripheral blood and bone marrow samples was performed every 3 months and every year, respectively, for 2 years following intensive chemotherapy in 94 patients in first complete remission. A complete molecular remission was defined as a (RUNX1-RUNX1T1/ABL1)×100 ≤ 0.001%. After the completion of consolidation therapy, a bone marrow complete molecular remission was observed in 30% of the patients, but was not predictive of subsequent relapse. Indeed, 8 patients (9%) presented a positive bone marrow minimal residual disease for up to 2 years of follow-up while still remaining in complete remission. Conversely, a peripheral blood complete molecular remission was statistically associated with a lower risk of relapse whatever the time-point considered after the completion of consolidation therapy. During the 2-year follow-up, the persistence of peripheral blood complete molecular remission was associated with a lower risk of relapse (4-year cumulative incidence, 8.2%), while molecular relapse confirmed on a subsequent peripheral blood sample predicted hematological relapse (4-year cumulative incidence, 86.9%) within a median time interval of 3.9 months. In t(8;21)(q22;q22) acute myeloid leukemia, minimal residual disease monitoring on peripheral blood every 3 months allows for the prediction of hematological relapse, and to identify patients who could potentially benefit from intervention therapy.     

Predictors of response to reinduction chemotherapy for patients with acute myeloid leukemia who do not achieve complete remission with frontline induction chemotherapy

Eighty-one patients with acute myeloid leukemia who had persistent leukemia following standard induction therapy with cytarabine plus daunorubicin (7+3 regimen) underwent reinduction therapy with a combination of mitoxantrone, etoposide, and high-dose cytarabine (HiDAC). Patients achieving complete remission (CR) then received consolidation therapy with HiDAC plus mitoxantrone. Patients with matched sibling donors were referred for allogeneic bone marrow transplantation (BMT) in CR-1. The overall response rate to reinduction was 53%. The major adverse predictors of CR on multivariate analysis were poor risk cytogenetics, a higher % bone marrow blasts prior to reinduction therapy and increased age. The median relapse-free survival (RFS) was 9 months and the estimated 2-year RFS was 30%. No significant predictors of RFS or overall survival (OS) were found among the patients achieving CR. Patients undergoing allogeneic BMT in CR-1 after double induction had a 50% 2-year OS. Patients relapsing after achieving CR with double induction had a poor outcome with a 4% 1-year OS. The results indicate that patients with poor risk cytogenetics or marrow blast percentage >or= 60% following 7+3 induction have a low probability of achieving CR with reinduction and should be considered for novel approaches to improve CR rates. Patients achieving CR are at high risk of relapse and should be considered for allogeneic BMT or novel strategies to attempt to reduce relapse rates.     

Clinical activity of azacitidine in patients who relapse after allogeneic stem cell transplantation for acute myeloid leukemia

Disease relapse is the most common cause of treatment failure after allogeneic stem cell transplantation for acute myeloid leukemia and myelodysplastic syndromes, yet treatment options for such patients remain extremely limited. Azacitidine is an important new therapy in high-risk myelodysplastic syndromes and acute myeloid leukemia but its role in patients who relapse post allograft has not been defined. We studied the tolerability and activity of azacitidine in 181 patients who relapsed after an allograft for acute myeloid leukemia (n=116) or myelodysplastic syndromes (n=65). Sixty-nine patients received additional donor lymphocyte infusions. Forty-six of 157 (25%) assessable patients responded to azacitidine therapy: 24 (15%) achieved a complete remission and 22 a partial remission. Response rates were higher in patients transplanted in complete remission (P=0.04) and those transplanted for myelodysplastic syndromes (P=0.023). In patients who achieved a complete remission, the 2-year overall survival was 48% versus 12% for the whole population. Overall survival was determined by time to relapse post transplant more than six months (P=0.001) and percentage of blasts in the bone marrow at time of relapse (P=0.01). The concurrent administration of donor lymphocyte infusion did not improve either response rates or overall survival in patients treated with azacitidine. An azacitidine relapse prognostic score was developed which predicted 2-year overall survival ranging from 3%–37% (P=0.00001). We conclude that azacitidine represents an important new therapy in selected patients with acute myeloid leukemia/myelodysplastic syndromes who relapse after allogeneic stem cell transplantation. Prospective studies to confirm optimal treatment options in this challenging patient population are required.     

The early reduction of leukemic blasts in bone marrow on day 6 of induction treatment is predictive for complete remission rate and survival in adult acute myeloid leukemia; the results of multicenter, prospective Polish Adult Leukemia Group study

The aim of this study was to prospectively evaluate the impact of early bone marrow response on complete remission (CR) rate and long-term outcome in adults with acute myeloid leukemia. Bone marrow cytology was assessed on day 6 of induction treatment in 164 patients, revealing the presence of ≥5% blasts in 61 cases. In this subgroup the CR rate was significantly lower compared to the remaining patients (P < 0.00001) resulting in decrease of the overall survival (P = 0.002). Persistence of ≥5% blasts in bone marrow on day 6 of induction is an easily available surrogate marker to be used for treatment decisions.     

Early allogeneic blood stem cell transplantation after modified conditioning therapy during marrow aplasia: stable remission in high-risk acute myeloid leukemia

Two patients with high-risk acute myeloid leukemia (AML) whose bone marrow aspirates showed more than 25% blasts between 2 and 4 weeks after the first induction chemotherapy immediately received modified conditioning therapy with intravenous busulfan at 50% of the usual dose and fludarabine, before hematologic recovery occurred. Unmanipulated G-CSF mobilized peripheral blood stem cells from an HLA-identical sibling donor were transfused and haematopoietic recovery was achieved in both recipients. Both of them are in continuing hematological remission with full donor chimerism 12 and 22 months after transplantation. Early treatment intensification with allogeneic cell therapy during marrow aplasia might cure high-risk AML patients who are unlikely to achieve remission with conventional chemotherapy protocols.     

Allogeneic marrow transplantation for myeloproliferative disorders other than chronic myelogenous leukemia: Review of forty cases

The role of allogeneic marrow transplantation as treatment of myeloproliferative disorders other than chronic myelogenous leukemia is not yet determined. At our center, 1 patient with primary myelofibrosis, 1 with mastocytosis, and 4 with myeloid metaplasia have been transplanted using HLA-identical sibling donors. All patients engrafted with full donor chimerism, and morphologic and cytogenetic manifestations of disease in the marrow resolved posttransplant. Three patients died; two with relapse and one from infection. The other three patients are alive in remission at 24+, 28+, and 32+ months posttransplant. Including these cases, a total of 40 patients transplanted for myeloproliferative disorders have been reported. The most common indications for transplantation were cytopenias, increasing blasts in marrow or blood, uncontrolled counts on conventional therapy, poor prognosis cytogenetics, organ dysfunction, and consolidation after induction therapy for blast transformation. Using the outcome data published for these patients, the actuarial estimate of 3-year survival is 55% (95% C.I., 44–76%) with a median reported follow-up of survivors of 21 months (range, 4–158 months). For patients with myeloproliferative disorders and evidence of accelerated disease, HLA-identical marrow transplantation is well tolerated and can result in an extended disease-free survival. Am. J. Hematol. 57:24–28, 1998. © 1998 Wiley-Liss, Inc.     

Terminal deoxynucleotidyl transferase in acute leukemias by direct immunofluorescence

TdT (terminal deoxynucleotidyl transferase) can be detected by radio enzymatic assay, biochemical assay in cell extracts, serum or plasma, and intracellularly in the smear by indirect immunofluorescent methods. The IgG fraction of anti-TdT serum is conjugated with fluoresceinisothiocyanate and used directly on the cytospin smears of methanol fixed bone marrow/blood smears. The mice thymocytes and peripheral mononuclear cells of healthy donors were used as positive and negative controls, respectively, for TdT. 64% of our cases of ALL were found to be TdT+. The lymphoblasts of L1 morphology (FAB classification) were more frequently positive for TdT as compared to blasts with L2 morphology. 71% of our cALLa positive blasts in acute lymphoblastic leukemias were TdT+ve as compared to 58% of T-ALL blasts. 75% of PAS positive ALL cases were positive for TdT as well. Only 57% of the cases when acid phosphatase showed unipolar positivity (T type) were positive for TdT. 12% of cases with acute myeloid leukemia (6/47) were TdT+ve and 33% of CML in blastic crisis had TdT+ve blasts. Biochemical assay and IF assay for TdT were in good correlation in our study.     

Trisomy 13: a new recurring chromosome abnormality in acute leukemia.

A new recurring chromosome abnormality was identified in 8 of 621 consecutive successfully karyotyped adults with de novo acute leukemia. These eight patients had trisomy 13 as the sole cytogenetic abnormality. On central morphologic review, five cases were classified as subtypes of acute myeloid leukemia, one as acute mixed lymphoid and myeloid leukemia, one as acute lymphoid leukemia, and one as acute undifferentiated leukemia. Blasts of all eight cases expressed one or more myeloid differentiation antigens. Three also expressed T-lineage-associated antigens; however, none of these had rearrangement of the T-cell receptor beta, gamma, or delta genes. Four of six cases tested were TdT positive. All eight patients with trisomy 13 were treated with intensive induction chemotherapy; only three entered a short-lived complete remission. Survival of patients with trisomy 13 ranged from 0.5 to 14.7 months, and was significantly shorter than that of the remaining patients (median 9.5 v 16.2 months, P = .007). We conclude that trisomy 13 is a rare, recurring clonal chromosome abnormality in acute leukemia associated with a poor prognosis. Malignant transformation of an immature hematopoietic precursor cell is suggested by the expression of antigens characteristic of both the myeloid and lymphoid lineage, the high incidence of TdT positivity, and the morphologic heterogeneity in these leukemias.