ALBERT

Description: Introduction and objectives. Flow-cytometry based automated blood cell counters measure the volume (V), conductivity (C) and light scatter (S) of cells and make available these values for each subpopulation of white blood cells. Although differences in V, C and S among several lymphoproliferative disorders, reactive lymphocytes and normal lymphocytes have been described, the ability to use this this information to detect lymphoproliferative disorders has not been defined. Methods. We registered VCS data of all consecutive cases of lymphocytosis (lymphocytes 〉 3.5x10e9/l) detected in routine laboratory testing during 50 non-consecutive days. Lymphocytes were evaluated morphologically, immunophenotypically and by conventional cytogenetics if necessary and the patients were evaluated clinically to document diagnosis adequately. Discriminant analisys modelling was used to assess the ability to predict diagnosis of VCS data. Results. 202 cases of lymphocytosis were detected in 120 males and 82 females, mean age 53 years (SD 16). Patients were considered to have normal lymphocytes (N=102, 50%), to present a reactive lymphocytosis (N=43, 21%, 20 of them HIV infected patients) or achieved a final diagnosis of lymphoproliferative disorder (N=57, 28%, 43 of them CLL). The mean volume of CLL lymphocytes was significantly lower than that of normal and reactive lymphocytes (p=0.009) and so was light scatter (p=0.018). When mean VCS values and their standard deviations were included in a discriminant analysis model, a unique function adequately classified 166/189 cases (87%) as CLL versus reactive or normal. Sensitivity and specificity were 73% and 92% respectively and false positive and false negative cases were 26% and 8% respectively. Inclusion of a second discriminant function did not improve significantly the predictive power of the model. Conclusion, VCS data from flow-cytometry based automated blood cell counters can be used to differentiate CLL from normal or reactive lymphocytes by simple discriminant analysis classification.

Description: Abstract 4897 Objective. To study the frequency, type and prognostic significance of clonal chromosomal abnormalities following SCT in patients with AML and MDS. Patients and methods. One hundred thirty patients were studied between 2000 and 2010. Karyotypes were analysed by G-banded chromosomes obtained from 24 hours bone marrow cultures, and were described according to ISCN 2009. Results. Clonal abnormalities were observed in 36/130 patients (28%) with a median follow-up was 11 months (range 3–131). Initial diagnosis (OMS 2008): AML with maduration (8 patients), acute erythroid leukaemia (4), acute monocytic leukaemia (3), AML with multilineage dysplasia (3), AML with myelodysplasia-related changes (3), AML with inv(16)(p13q22) (2), acute monoblastic leukaemia (2), AML with minimal differentation (2), AML without maduration (1), acute myelomonocytic leukaemia (1), refractory anaemia with excess blasts (4), chronic myelomonocytic leukaemia (2) and refractory cytopenia with multilineage dysplasia (1). Treatment before SCT: idarubicin, cytarabine, etoposide and mitoxantrone (25), idarubicin, cytarabine and etoposide (6), idarubicin, cytarabine, etoposide and gemtuzumab (2), FLAG-ida (2) and azacitidine (1). SCT type: autologous (23 patients), allogeneic of reduced intensity (7), allogenic (4), umbilical cord blood (1) and syngeneic transplant (1). Conditioning regimen: TBI and cyclophosphamide (24 cases), fludarabine and busulfan (7), busulfan and cyclophosphamide (4) and thymoglobulin, thiotepa, fludarabine and busulfan (1). The median time between SCT and the appearance of clonal abnormalities was 6.5 months (range 2–51). At the time of clonal abnormality detection, 32 patients were in cytological and/or clinical relapse and 4 in cytological remission. In 15 cases the initial clone reappeared, 2 showed the initial abnormalities with an acquired abnormality and 19 presented de novo clonal abnormalities (53%). The most frequent clonal chromosomal abnormalities observed were: complex karyotype (22%), estructural abnormalities with afection of chromosomes 1, 4, 6, 7, 10, 11, 12, 16 and 17 (22%), +21 (5%) and +11 (3%). The median survival from the appearance of clonal abnormalities was 2.5 months (range 1–100). There were no differences when we compared the survival of patients with de novo clonal abnormalities with that of patients with initial abnormalities (including those with acquired abnormality). Furtheremore there were no differences when we compared the median survival of relapsed patients with normal Karyotype with that of patients with clonal chromosomal abnormalities following SCT (2.5 months [range 1–25] and 2.5 months [range 1–100] respectively). At the time of the analysis only 1 patients are alive and in complete remission (100 months). Conclusions. 1. The appearance of clonal abnormalities following SCT in patients with AML and MDS is frequent and the majority of cases are detected at the time of relapse. Half of cases presented de novo clonal abnormalities and the majority were not related with prior irradiation exposition, alkylating agents neither topoisomerase II inhibitors. The prognosis of patients with acquired clonal abnormalities after SCT is poor. Disclosures: No relevant conflicts of interest to declare.

Description: Introduction Monoclonal B-Cell Lymphocytosis (MBL) is a frequent condition characterized by a clonal B-cell population detected in the blood or bone marrow, in otherwise asymptomatic individuals.A small proportion of patients with MBL need clinical attention. Its prevalence is around 3-5% in healthy adults over age 40 and rises with age. The largest studies of MBL features are focused on healthy population, therefore additional data regarding the population referred to hospital are necessary. Genotype and immunophenotype data are well described in the literature so far, but a comprehensive framework of the condition is still required. Data of features not well described heretofore like bone marrow pattern of infiltration would help in the differential diagnosis. The aim of this work was to analyze the clinical and laboratory findings of MBL reclassified from CLL or other B-cell lymphoproliferative disorders (LPD) with peripheral involvement, referred to a centre. Patients and methods Three hundred seventy-one LPD patients with peripheral blood involvement diagnosed between years 2000 and 2009 in a single centre were revised to reclassify them according to the World Health Organization consensus cut-off of 5x109/L circulating B cells. From those reclassified as MBL, blood count, biochemistry, immunophenotype, cytogenetics, bone marrow trepine biopsy and results of CT screening were registered, as well as treatment and outcome data. Only those patients who were followed in our centre were included. Results Seventy-three LPD (20%) were reclassified as MBL, with a median age of 72 years (range: 42-94) and a 52% of males. Proportions of CLL-like LPD, CD5 negative non CLL-like and CD5 positive non CLL-like switched from 65%, 21% and 14% to 84%, 7% and 9% after the reclassification. In only seven out of 41 patients the bone marrow was not infiltrated, while the majority had an interstitial and a mixed nodular and interstitial infiltration (44% and 36%, respectively). Only 2 out of 49 patients had a concomitant infection with hepatitis C virus. Fifty-nine % of patients had a FISH alteration, predominantly chromosome 13 deletion. Thirty-seven out of 69 patients (54%) fulfilled criteria of LPD progression, with 10 patients (15%) requiring treatment (7 out of them because of progression of CLL). The mean (SD) B-lymphocyte count at diagnosis of patients with LPD progression was 3.58x10^9/L (0.9x10^9/L) versus 3.03x10^9/L (1.1x10^9/L) in those who did not progress, p=0.023. The 12-year progression free survival of the whole series was 38% (CI 95% 23-53) with a median of 4.08 years (range: 2.3-5.8). The 12-year overall survival was 54% (29-79), with a median follow-up of 7.73 years (1.7 – 12.9). Conclusions An important proportion of LPD with peripheral involvement can be reclassified to MBL, with a higher prevalence of CLL-like LPD than the global set of patients. The pattern of bone marrow infiltration was predominantly interstitial, followed by a mixed pattern of infiltration. A high percentage of patients in this series evolved to LPD, but a small subset required specific treatment. The patients with LPD progression had a significantly higher B-lymphocyte count than those who did not. Disclosures: No relevant conflicts of interest to declare.

Description: Background: ETP-ALL was included as a provisional identity in the 2016 WHO classification of ALL. This subtype was first identified by Coustan-Smith et al. in 2009. However, this immunophenotype-based classification does not fully enclose all ETP-ALL cases identified by gene expression profile (GEP). Although early studies in small series of ETP-ALL suggested a very poor outcome for ETP ALL more recent and larger series have showed improvement in outcome treating children with a contemporary protocol based on chemotherapy schedules, or after allogeneic stem cell transplantation (allo-SCT) in adults. Aim: To investigate the clinical and biological features of ETP-ALL cases in the Spanish cohort of adult T-cell ALL (T-ALL) patients and to assess the potential impact of high-risk therapy on their outcome. Method: One hundred eighty-five adults with T-ALL treated according to two consecutive MRD-oriented high-risk adult PETHEMA protocols -ALL-HR-2003 (NCT00853008) and ALL-HR-11 (NCT01540812; still ongoing)- were included in this study. The EGIL criteria were used to define the immunologic subtype of T-ALL after central review of immunophenotype reports, and the criteria proposed by Zuurbier et al. (Zuurbier L. et al. Haematologica 2014; 99:94-102) were used to define ETP-ALL. These later criteria consist of a combination of immunophenotypic markers (absence of CD1a-/CD4-/CD8-, cut-off 25%), that resemble those published by Coustan-Smith, with the advantage that include most ETP-ALL cases, as identified by GEP, avoiding the use of partial expression of CD5 marker to immuno-classify these patients. Results: Thirty-four out of 167 evaluable patients (20%) with T-ALL showed an ETP-ALL immunophenotype. Patients with ETP-ALL were older (mean 39 [SD 12] vs. 33 [12] yr; p=0.011), showed more frequently lymph node involvement (79% vs. 56%; p=0.021) and lower WBC counts at diagnosis (mean, 72 [155] vs. 97 [112] x109/L; p=0.004). At genetic level, ETP-ALL patients were associated with the absence of deletions in CDKN2A/B gene cluster (91% vs. 26%; p10% BM blasts on day+14) vs. 37% of non-ETP (p

Description: Relapsed/refractory T-cell acute lymphoblastic leukemia (T-ALL) has a dismal outcome, and no effective targeted immunotherapies for T-ALL exist. The extension of chimeric antigen receptor (CAR) T cells (CARTs) to T-ALL remains challenging because the shared expression of target antigens between CARTs and T-ALL blasts leads to CART fratricide. CD1a is exclusively expressed in cortical T-ALL (coT-ALL), a major subset of T-ALL, and retained at relapse. This article reports that the expression of CD1a is mainly restricted to developing cortical thymocytes, and neither CD34+ progenitors nor T cells express CD1a during ontogeny, confining the risk of on-target/off-tumor toxicity. We thus developed and preclinically validated a CD1a-specific CAR with robust and specific cytotoxicity in vitro and antileukemic activity in vivo in xenograft models of coT-ALL, using both cell lines and coT-ALL patient–derived primary blasts. CD1a-CARTs are fratricide resistant, persist long term in vivo (retaining antileukemic activity in re-challenge experiments), and respond to viral antigens. Our data support the therapeutic and safe use of fratricide-resistant CD1a-CARTs for relapsed/refractory coT-ALL.

Description: Background & Objective: Acute Lymphoblastic Leukemia (ALL) is an aggressive neoplasia characterized by a high genetic heterogeneity both at diagnosis and at relapse. Due to the high incidence of relapse in adults and the dismal prognosis beyond recurrence, diagnosis and relapse samples of adult ALL patients were carefully analyzed in order to identify genetic alterations related with drug resistance and disease progression. Patients & Methods: Paired diagnosis-relapse bone marrow samples from 5 adult B-cell precursor ALL (B-ALL) patients were analyzed (Ph+ ALL [n=2], normal karyotype [n=1], t(1;19)(q23;p13) [n=1] and t(8;13)(p21-22;q12) [n=1]). Copy Number Alterations (CNA) were studied with Multiplex Ligation-dependent Probe Amplification (MLPA, kits P-335 and P-202 from MRC-Holland, Amsterdam, Netherlands) and Affymetrix CytoScan HD arrays (Affymetrix, Santa Clara, USA). In the array analyses, only the CNA that encompassed at least 25 markers were considered significant. Results: Regarding karyotype, 2 patients (1 Ph+ and 1 t(1;19) at diagnosis) showed the same chromosomal translocations within a complex karyotype at relapse. On the contrary, the other Ph+ patient showed a normal karyotype at relapse, while 2 patients did not experience any karyotypic change. Regarding immunophenotype, 3/5 patients showed changes on antigen expression from diagnosis to relapse such as expression of markers of immaturity (CD34, TdT positivity and CD38 negativity), loss of lymphoid markers (CD20 and CD22) and/or acquisition of myeloid markers (CD33 and CD66c). Concerning CNA, all relapse samples were genetically related to the diagnosis clone (common clonal origin). All relapsed populations lost CNA detected at diagnosis and/or acquired new CNA but retained some of the CNA showed at diagnosis revealing clonal evolution from ancestral clones. CNA in B-ALL key genes involved in lymphoid development (IKZF1, PAX5, EBF1,VPREB1 and BLNK), proliferation (CDKN2A/B, RB1, CRLF2, C-MYC and ERG), apoptosis (BTG1, TP53 and ATM), hematopoiesis transcription factors (ETV6 and MLL) and histone modifications (KDM6A) were detected, among others. Losses in 9p were the most recurrent event both at diagnosis and at relapse. CDKN2A/B deletions were observed in all relapse samples (3/5 in homozygosis) while PAX5 deletions were present in 4/5 relapsed cases. Interestingly, all relapse samples showed CNA favoring the activation and/or the transcription of proteins involved in the Akt/C-MYC signaling pathway. Another common feature (4/5 patients) were CNA affecting genes involved in drug transport such as several ABC transporter genes and genes related to drug resistance such as PRKDC and RUNX1T1 (in 3/4 of the cases, the CNA appeared exclusively at relapse or were already present at diagnosis and increased their frequency at relapse). CNA in genes that may confer stem cell characteristics (EGR1 and USP16) were another recurrent event at relapse (3/5 samples, 2 of them were not present at diagnosis). CNA affecting the X/Y PAR1 region (CRLF2, CSF2RA and IL3RA) or VPREB1 at 22q11.22 were detected in 3/5 relapse samples, respectively. An important apoptosis cluster at 11q21q24.2 (BIRC2/3, CASP1/4/5/12, hsa-miR-34b/c, ATM and BTG4) was lost in 2/5 relapse samples (one of them was not detected at diagnosis and the other increased its frequency at relapse). Finally, ETV6 deletion (12p13.2) and duplication of Xq26.2q28 (containing ABCD1, BCAP31 and genes coding for several cancer/testis antigens) were observed in 2 relapse samples. Conclusions: SNP arrays analysis of paired B-cell precursor ALL samples at diagnosis and at relapse allows the identification of genetic alterations potentially related with ALL progression. The systematic analysis of relapse samples could contribute to the identification of specific genetic targets with potential therapeutic impact for each patient (personalized medicine). Disclosures Martínez-López: Novartis: Honoraria, Speakers Bureau. Sole:Celgene: Membership on an entity's Board of Directors or advisory committees.

Description: Objectives: To analyze MRD in 65 patients (pts) with good prognosis AML: 30 t(8;21) and 35 inv(16), using both FC and RT-PCR, and to investigate the prognostic value of MRD in the pts outcome. Methods: MRD was monitored in CR pts (n=55) by FC in 101 follow-up samples obtained after various cycles of treatment, as follows: 40 post-induction (ind), 30 post-intensification (int) and 31 at the end of treatment (ttm), and by RT-PCR in 76 samples: 31, 23 and 22, respectively. In 35 pts the two techniques were applied at the same time of the ttm. MRD by FC was assessed using fixed combinations of three monoclonal antibodies. AML1/ETO and CBFb/MYH11 were analyzed following the BIOMED protocol. Results: Twenty-seven percent (n=15) of CR pts relapsed: 6 with t(8;21) and 9 with inv(16). The mean MRD by FC was 1.1% after ind, 0.2% after int and 0.1% at the end of ttm. At the end of ttm, the MRD detected by FC in relapsed and not relapsed pts were significativaly different: 0.3% vs 0.08% (p=0.002). By RT-PCR, the mean of fusion transcript copies/ablx104 differed between relapsed and nonrelapsed pts: 2385 vs 122 (p=0.001) after ind, 56 vs 7.6 after int (p=0.0001) and 75 vs 3.3 (p=0.0001) at the end of ttm. Relapses were more commonly observed in those pts with FC MRD level 〉0.1% at the end of ttm than in pts with ≤0.1%: 50% vs 12% (p=ns); likewise, using RT-PCR, a cutoff level of 〉10 copies at the end of ttm correlated with high risk of relapse: 80% of pts with RT-PCR 〉10 relapsed compared to 12% of pts with levels 0.1 (p=0.1) and the leukemia free survival (LFS) was 78% and 44%, respectively (p=0.05). For pts with RT-PCR ≤10 at the end of ttm, the OS was 100% and for pts with RT-PCR 〉10 it was 30% (p=0.007) and the LFS was 87% and 20%, respectively (p=0.001). MRD was identified after ind in 55% of relapsed pts and at the end of ttm in 83% of relapsed pts. Only 1 pt (1/13) with FC MRD

Description: Introduction In the last years genome wide profilings have identified recurrent Copy Number Alterations (CNA) in genes potentially involved in the pathogenesis of Acute Lymphoblastic Leukemia (ALL). These studies have identified deletions in B-cell development genes (IKZF1, EBF1, PAX5, TCF3, etc.), cell cycle regulation genes (CDKN2A/B, RB1, TP53, etc.), glucocorticoid resistance genes (BTG1, CREBBP) and growth factor receptors genes (CRLF2, CSF2RA, IL3RA) among others. Some of these CNA (i.e. IKZF1, CDKN2A, CRLF2) have been reported to have prognostic significance in several pediatric series but there are very few data regarding their impact in B-lineage adult ALL. Our aim was to analyze the frequency and prognostic significance of CNA in a series of 125 B-lineage adult ALL patients treated according to risk-adapted protocols from the Spanish PETHEMA Group. Methods Bone marrow or peripheral blood (with significant blast burden) samples from 125 B-lineage adult ALL patients enrolled in risk-adapted protocols from the PETHEMA Group were analyzed at diagnosis. MLPA assays (MRC-Holland) were performed for the following genes: IKZF1, IKZF2, IKZF3, EBF1, CDKN2A/B, PAX5, ETV6, BTG1, RB1, hsa-miR-31, X/Y PAR1 region genes (CRLF2, CSF2RA, IL3RA) and 14q32.33 region genes (IGH D, MTA1, KIAA0284). Fragment analysis was made by Genescan in an ABI-3130 sequencer (Applied Biosystems). Data normalization provided a value indicative of the presence or absence of CNA: 0-0.20 homozygous deletion, 0.21-0.70 heterozygous deletion, 0.71-1.30 normal, 1.31-1.70 heterozygous duplication and 1.71-2.20 homozygous duplication. Results The median age [range] was 40 [15-74] years, 71 (57%) males, median WBC count 12.11 x109/L [0.4-388]. Immunophenotype: pro-B 14 (11%), common 71 (58%), pre-B 26 (21%), mature-B 10 (8%), unavailable 2 (2%). Cytogenetics: normal 16 (13%), hyperdiploid 6 (5%), hypodiploid 2 (2%), t(9:22) 20 (16%), t(1;19) 8 (6%), 11q23/MLL 11 (9%), 8q24/C-MYC 7 (5%), complex 1 (1%), iAMP21 2 (2%), other translocations or deletions 31 (25%), no growth 20 (16%). CNA frequencies of the 125 patients are shown in the table. IKZF1 deletions were significantly associated with EBF1 deletions, high WBC count and Philadelphia (Ph) chromosome. In the IKZF1 deleted cohort whole gene deletions were as frequent as Ik6 isoforms (28% each). A high codeletion rate was detected in genes located in 9p (CDKN2A/B with PAX5, CDKN2A/B with hsa-miR-31 and PAX5 with hsa-miR-31). CDKN2A/B also showed concomitant deletions with ETV6 while PAX5 showed codeletions with BTG1. CDKN2A/B and PAX5 deleted patients had higher WBC counts than non-deleted individuals. Clinical follow-up data was available for 123 patients of the whole series and for the 105 patients of the Ph-negative cohort. Multivariate analysis showed that advanced age, BTG1 deletions and EBF1 deletions were negative prognostic factors for achieving Complete Remission (CR) and WBC count and IKZF1 deletions significantly reduced CR duration in both cohorts. Interestingly, there were significant differences in relapse rates between whole and partial gene IKZF1 deletions. IKZF1 haploinsufficient patients had a probability of CR duration at 3 years of 83% ± 30% vs. 6% ± 12% of partial gene deletion carriers. Advanced age and IKZF1 deletions were predictors for overall survival in the Ph-negative cohort and age〉30 years, IKZF1 deletions and hsa-miR-31 deletions were associated with poor prognosis in the whole series. Conclusions In B-lineage adult ALL, deletions of IKZF1, EBF1, BTG1 or hsa-miR-31 are markers with prognostic significance in addition to age and WBC count. Patients with partial IKZF1 gene deletions have a significantly higher probability of relapse than those with whole gene loss. These genetic abnormalities could help to better define prognostic subgroups in adult patients with B-lineage ALL. Supported by the grants PI10/01417 and RD12-0036-0029 from Instituto Carlos III and a grant from the Spanish Society of Hematology and Hemotherapy (2012). Disclosures: No relevant conflicts of interest to declare.

Description: Background. Several studies have reported cases of Ph-positive CML treated with imatinib developing chromosomal abnormalities in Ph-negative cells. Trisomy 8 is the most frequent of these abnormalities, but monosomy 7 has also been detected. The association of these cytogenetic alterations with severe myelodysplasia has been scarcely reported. We present 2 cases of monosomy 7 with severe myelodysplasia arising during imatinib treatment of Ph-positive CML, one evolving as a transient clonal abnormality, and the other with a fatal evolution to AML. Case 1. A 55 year-old man was diagnosed with Ph-positive chronic phase CML in July 2000. He started treatment with IFN-α without cytogenetic response, and in October 2002 he began imatinib-mesylate (400 mg/day). After 6 months on imatinib he developed anemia and neutropenia, with severe dysplastic features on peripheral blood. Dysplastic features in the 3 series with 70% of ring syderoblasts were observed in the bone marrow. The ultrastructural study showed numerous erythroblasts with iron-loaded mitochondria and some “ring forms”. The cytogenetic study was: 46,XY,t(9;22)(q34;q11)[4]/ 45,XY,-7[12]/46,XY[6]. The dose of imatinib was reduced (300 mg/day). Three months later, peripheral blood cell counts were normal, the myelogram showed mild dyserythropoiesis without ring syderoblasts and the cytogenetic study was: 46,XY,t(9;22)(q34;q11)[7]/47,XY,+8[15]. Monosomy 7 was not detected by FISH. From January 2004 he has been treated with imatinib (300 mg/day) and IFN-α and the karyotype is: 46,XY,t(9;22)(q34;q11)[15]/ 46,XY[6]. Monosomy 7 and trisomy 8 have not been detected. Case 2. A 47 year-old man was diagnosed with Ph-positive chronic phase CML in October 2001. He was initially treated with hydroxyurea and in February 2002 a peripheral blood allogeneic stem cell transplant from a HLA-identical sibling, conditioned with busulfan and cyclophosphamide, was performed. Seven months later Ph chromosome was detected in 100% of metaphases and the patient was treated with 2 donor lymphocyte infusions without response. Imatinib at a dose of 400 mg/day plus G-CSF was started. After 14 months on imatinib, a complete cytogenetic response was obtained and 9 months later, molecular response was achieved too. Three months later (March, 2005), pancytopenia was detected. In the bone marrow, severe dysplasia in the 3 series with predominance of erythroid precursors and 41% of ring syderoblasts, were observed. The cytogenetic study showed a complex karyotype harboring monosomy 7: 45,XY,-7[9]/45,X,add(Y)(q12),-7[4]/46,XY,-7,+21[2]/46,XY[5]. Imatinib was stopped and 2 months later the patient was diagnosed with refractory anemia with excess of blasts. He rapidly progressed to AML and has been treated with idarubicine, cytarabine and etoposide as induction therapy without response. Monosomy 7 (2 cases) and trisomy 8 (case 1) were not retrospectively detected by FISH, prior to the introduction of imatinib. Conclusions. Severe myelodysplasia with monosomy 7 can develop in Ph-negative metaphases of patients with CML treated with imatinib. Although in some cases these alterations are transient, in others the evolution can be fatal to AML. Imatinib may play a role in the appearence of these clonal abnormalities.

Description: Objective. To study the incidence, type and prognostic significance of clonal chromosomal abnormalities following SCT in patients with AML. Patients and methods. From February 2000 to March 2008, 74 patients were studied. Karyotypes were analysed by G-banded chromosomes obtained from 24 hours bone marrow cultures, and were described according to ISCN 2005. Results. Clonal abnormalities were observed in 17/74 patients (23%). Median follow-up was 11 months (range 5–47). Initial diagnosis: AML2 (6 cases), AML5a (3), AML6 (3), AML with inv(16)(p13;q22) (1), AML with multilineage dysplasia (1), AML5b (1), AML1 (1) and AML0 (1). Treatment before SCT: idarubicin, cytarabine and etoposide (16), FLAG-ida (1). All patients presented a normal karyotype at the time of SCT. SCT type: autologous (12 patients), allogeneic (3), allogeneic of reduced intensity (2). Conditioning regimen: TBI and cyclophosphamide (14 cases), busulfan and cyclophosphamide (1), fludarabine and busulfan (2). The median time between SCT and the appearance of clonal abnormalities was 8 months (range 3–36). At the time of clonal abnormality detection, 16 patients were in cytological and/or clinical relapse and 1 in complete remission. In 4 cases the initial clone reappeared, 1 showed the initial abnormalities with an acquired abnormality and 12 presented de novo clonal abnormalities. The median survival from the appearance of clonal abnormalities was 2 months (range 1–40). At the time of the analysis all patients had died. Conclusions. The appearance of clonal abnormalities following SCT in patients with AML is frequent. Time between SCT and the appearance of clonal abnormalities is short. The majority of patients presented de novo clonal abnormalities with cytological and/or clinical relapse and poor prognosis.