ALBERT

Description: Abstract 2498 Background. MLL gene rearrangements are associated with unfavorable outcome in infant acute lymphoblastic leukemia (ALL) and have intermediate prognosis in infant acute myeloid leukemia (AML). Application of fluorescence in-situ hybridization (FISH) allows detecting not only conventional MLL rearrangements, but also concurrent 3'-deletion of MLL gene. However, detailed characteristics of infant leukemia carrying 3' MLL deletion remain unclear. Aim. To investigate molecular genetic features of MLL-rearranged infant acute leukemia with concurrent 3' MLL deletion. Methods. 64 patients (27 boys and 37 girls) aged from 1 day to 11 months (median 6.6 months) including 44 ALL patients, 18 AML patients, 1 patient with acute bilineage leukemia and 1 patient with acute undifferentiated leukemia were enrolled in the current study. Chromosome banding analysis was done according to standard procedure. FISH analysis using LSI MLL Dual Color, Break Apart Rearrangement Probe (Abbott Molecular, USA) was performed on at least 200 interphase nuclei and on all available metaphases. Presence of MLL rearrangements was detected by FISH, reverse-transcriptase PCR. In 29 cases long-distance inverse PCR was additionally performed. In case of MLL rearrangement presence standard FISH pattern was defined as simultaneous detection of 3 different fluorescent signals: 1 fused (orange) signal, 1 green signal derived from 3' part of MLL gene, 1 red signal from 5' end of MLL (1F1G1R). MLL rearrangements with concurrent 3' MLL deletion led to 1F1R FISH pattern formation due to lack of green signal. Results. FISH revealed MLL rearrangements in 73% of ALL cases that was higher than frequency of 11q23 translocations detected by conventional cytogenetics — 55%. In MLL-positive cases we found 38 patients (81%) with standard FISH pattern, 7 ones (15%) with concurrent 3'-deletion of MLL gene and 2 (4%) with complex MLL rearrangements. Among patients with 3' MLL deletions there were 1 case with 5' MLL duplication (1F2R) and 1 case with 5' MLL triplication (1F3R). Frequency of 3'-deletions were similar in ALL and AML patients (13% and 15%, respectively). We did not find more than one FISH pattern in bone marrow blast cells of each patient with 3' MLL deletion. In this cohort of patients all blast cells carried concurrent 3'-deletion of MLL gene. Moreover, percentage of blast cells carrying MLL rearrangements did not differ significantly between patients with standard FISH pattern (median 97%, range 22–100%) and 3'-deletion (median 83%, range 13–99%) (p=0.206). 3'-deletion of MLL was not associated with breakpoint position in MLL gene and type of translocation partner gene. MLL translocation partner genes detected in patients with 3' deletions were as follows AF4(n=2), MLLT3(n= 3), MLLT10(n=2). None of the patients with 3'-deletions had reciprocal fusion gene. Initial patients' characteristics (age, sex, WBC count, immunophenotype, CNS-status, type of MLL partner gene) and treatment response parameters (day 8 peripheral blood blast cell count, day 15 bone marrow status, day 36 remission achievement, minimal residual disease status at time point 4) did not differ significantly between 2 groups. Although cumulative incidence of relapse was lower in patients with 3'-deletion as compared to patients with standard FISH pattern (0.31±0.04 and 0.55±0.01, respectively), difference between these two groups was not statistically significant (p=0.359). Conclusion. In our work we characterized rare subgroup of infant MLL-rearranged acute leukemia carrying concurrent 3' MLL deletion. Our data provide additional information of molecular genetic features of acute leukemia in children younger than one year. Disclosures: No relevant conflicts of interest to declare.

Description: The efficacy of conventional and intensified chemotherapy in infant acute lymphoblastic leukemia (ALL) is limited worldwide particularly because of the high early relapses and treatment related mortality. We hypothesized that all-trans retinoid acid (ATRA) may participate in the differentiation of infant leukemic cells to normal progenitors with a consequent loss of malignant features and enhanced antiproliferative effects of chemotherapy. Our prospective multicenter non-randomized MLL-Baby/ALL-MB 2002 trial evaluated whether the novel recently developed ATRA based regimen, MLL-Baby is safe and more effective in the prevention of very early relapses comparing to ALL-MB 2002 - a well established protocol in Russia and Belarus. The trial was approved by Ethics Committees and parents’ informed consent was signed in all cases. The decision to receive MLL-Baby or ALL-MB 2002 was judged by the treating physician. The major difference between the 2 treatment approaches was the addition of ATRA in the MLL-Baby protocol. Patients were equally distributed of patients (pts.) between the two groups according to risk: only pts. with t(4;11) and/or MLL/AF-4 or without complete remission (CR) achieved on days 36/43 were subjects for the high risk group (HRG). The remaining pts were stratified to an intermediate risk group (IRG). Treatment schedules were also similar in both regimens except for CNS-disease prophylaxis: in MLL-Baby, cranial irradiation 12 Gy was retained only for HRG pts with initial CNS involvement who were older than 12 months and substituted by 5 additional intrathecal treatments, while all pts. allocated to ALL-MB 2002 1year of age underwent cranial irradiation 12 Gy, regardless of their initial CNS status and risk group. In MLL-Baby pts, the initial ATRA pulse in daily dose 25 mg/m2 was given after debulking of the main tumor from day 36 to day 43, followed by 12 in IRG and 16 in HRG 2-weeks of ATRA courses alternating with chemotherapy. Between September 2003 and November 2006, 40 pts. aged 1–12 months were enrolled onto MLL-Baby (n=19) and ALL-MB 2002 (n=21) protocols. Both groups were balanced for median age 8 (1–12) and 6 (2–12) months, p=0.47; initial WBC 115,5 (1,2–450) and 105,5 (2.6–350) per microliter, p=0.76; initial CNS disease 3 vs. 5, p=0.5; 11q23/MLL translocations 12 vs. 10 pts., including t(4;11) - 6 vs. 7 pts, p=0.74 and BI phenotype 9 and 4 cases correspondingly, p=0.37, respectively. No significant differences were observed between MLL-Baby and ALL-MB 2002 with respect to rates of induction deaths: 1 vs. 3 cases, CR rates 94.7% vs. 85.7%, deaths in CR 1 vs. 0; whereas the early relapse rate was higher with ALL-MB 2002 compared to MLL-Baby: RFS was 0.24±0.13 vs. 0.94±0.05 (p=0.02) with a median of follow-up 20 months (1–55). EFS differed significantly: 0.21±0.11 vs. 0.84±0.08 (p=0.03). Most relapses on ALL-MB 2002 (n=11) and MLL-Baby (n=1) developed very early: 7 of 11 pts. and 1 of 1 pt. respectively and were localized only to bone marrow in most cases: 6 of 11 pts. and 1 of 1 pt. correspondingly. Our data indicate that ATRA administration contributes positively towards early relapse-free outcome in infants with ALL. A prospective randomized clinical trial with longer follow-up is needed to confirm these results.

Description: Abstract 3422 Introduction. Currently there is no consensus in definition what level of BCR-ABL/ABL ratio increase predicts presence of kinase domain (KD) mutations. Several research groups use relatively low cut-off levels equal to 2.0- and 2.6-fold (S. Branford et al, Blood, 2004, R. Press et al Blood, 2009, respectively), that are close to the discrimination ability of real–time quantitative PCR (RQ-PCR) method. Alternatively, an NCCN guideline recommends beginning of mutation screening in case of 10-fold or greater elevation of BCR-ABL/ABL ratio. Aim. To define a threshold level of BCR-ABL/ABL increase that predicts presence of BCR-ABL mutations. Methods. Among 531 CML patients on imatinib (IM), both newly diagnosed and pre-treated with interferon-α, in 47 ones BCR-ABL mutation detection was performed. These were patients with suboptimal response or treatment failure according to the European LeukemiaNet criteria (M. Baccarani et al, 2009). Conventional cytogenetic analysis was performed every 6 months. Quantitative measurement of BCR-ABL/ABL transcripts ratio by RQ-PCR was done every 3–6 months. A major molecular response was defined as BCR-ABL/ABL transcripts level of 0.059% corresponded to 3 log reduction from the laboratory defined baseline level. Point mutations in the BCR-ABL KD were detected by reverse-transcriptase PCR and direct sequencing. Elevation of BCR-ABL/ABL was calculated by dividing of BCR-ABL/ABL value at the time point (TP) where mutation detection was performed to the BCR-ABL/ABL value at TP prior to mutation screening. Event-free survival (EFS) was defined as the time from IM beginning until any of the following events occurred: loss of complete hematological response, loss of major cytogenetic response, progression to AP/BC, death of any reason. Threshold level was defined by receiver operator characteristics (ROC) curve analysis. Positive and negative predictive values (PPV, NPV), sensitivity, specificity and overall correct prediction (OCP) were calculated. Results. 10 different point mutations of BCR-ABL gene were detected, including 3 ones in P-loop, 2 in IM-binding site, 3 in A-loop, and 2 mutations outside the KD. None of patients had 2 or more mutations simultaneously. Patients were divided into two groups: with (n=18) and without (n=29) BCR-ABL mutations. Groups did not differ in age, sex distribution, type of BCR-ABL transcript, frequency of cumulative achievement of CHR, CCyR, MMR and level of BCR-ABL/ABL increase (table 1). Median time between BCR-ABL/ABL measurement was similar in both groups: 6 months (range 1–12 months) (p=0.227). ROC curve analysis determined that increasing of BCR-ABL/ABL level in 5.5-fold corresponds to 92.9% of NPV. Area under curve was 68% (95% CI 50–95%) (p=0.022). Sensitivity, PPV and OCP were relatively low (40.6%, 40.6%, 56.5%, respectively) while specificity was high (92.9%). Conclusions. In our series 5.5-fold increase of BCR-ABL/ABL clearly predicts presence of BCR-ABL mutations and indicates the exact time for mutation detection performing in patients with suboptimal response and treatment failure. Nowadays, with availability of primary reference material for BCR-ABL quantification, approved by WHO (H. White at al, Hematologica, 2010) and successful harmonization of molecular monitoring of CML therapy (M. Mueller et al, Leukemia 2009) elevation level that corresponds with mutation presence could also be standardized. Application of international standardized threshold level would help to avoid unnecessary or late mutation tests. Disclosures: Ivanets: Novartis Pharma: Employment.

Description: Background Infant acute leukemia is characterized by high incidence of MLL gene rearrangements. Purpose To evaluate the distribution of MLL genomic DNA breakpoints and their relation to several diagnostic parameters among infant acute leukemia. Methods 72 infants with MLL-rearranged acute lymphoblastic leukemia (ALL) (n=52), acute myeloid leukemia (AML) (n=19) and mixed phenotype acute leukemia (n=1) were included in this study based on the availability of DNA material at diagnosis. In the observed group there were 28 boys (39%) and 44 girls (61%) with median age of 4.9 mo (range 0.03-11.9). Genomic DNA breakpoint detection in MLL gene and translocation partner genes (TPG) was performed by long-distance inverse PCR (LDI-PCR). Exon-intron numbering of MLL gene was done according to I. Nilson et al, 1996. Results Majority of ALL cases (n=28; 54%) was characterized by presence of MLL-AF4 fusion gene (FG), less frequently MLL-MLLT1 (n=12; 23%), MLL-MLLT3 (n=7; 13%) and others were found (Table 1). The most common breakpoint location within MLL gene in ALL patients was intron 11, detected in 25 cases (48%). The highest variability of MLL breakpoints was found in MLL-AF4-positive patients: only 11 of 28 (39%) had breakpoints in intron 11. The most stable pattern of MLL genomic DNA breakpoints was observed in MLL-MLLT1-positive patients: 8 of 12 (67%) had breakpoints in intron 11. In AML patients two the most prevalent FGs were MLL-MLLT3 (n=7, 37%) and MLL-MLLT10 (n=5, 26%). The remaining ones are listed in Table 1. The most frequent breakpoints location was intron 8 (8 out of 19, 42%). The most stable pattern was revealed for MLL-MLLT10 FG: MLL breakpoints in 4 of 5 (80%) cases were found in intron 9 (Table 1). ALL patients who had breakpoints in intron 11 were significantly younger (median 3.0 mo, range 0.03-11.6) than all others (median 5.6 mo, range 0.7-11.9) (p=0.025) and than patients with MLL breakpoints in intron 9 (median 6.6 mo, range 3.1-11.9) (p=0.017). For AML cases we did not find any relation between age and breakpoints locations. Distribution of MLL DNA breakpoints was similar in boys and girls and did not depend on type of TPG. Genetic recombinations involving MLL gene predominantly resulted in reciprocal chromosomal translocations (n=62; 86%). Beside them, 6 (11%) insertions were identified in all MLL-MLLT10-positive cases and MLL-SEPT6-positive one. In 11 (15%) patients we found breakpoints within the regions located from 0.7 Kb to 25.4 Kb 3' of the first exon of TPGs (MLLT1 n=9; EPS15 n=1; MYO1F n=1), however fusion transcripts at cDNA level were identified and sequenced in all these cases, indicating a spliced fusion mechanism. 3-way translocations were found in 5 patients and in 1 case we found combination of insertion with interstitial deletion of chromosome 11. The list of reciprocal genes involved in these 6 cases was as follows: CEP164, DNAH6, DCPA1, MCL1 as well as non-coding regions of 2q21.2 and 2p21. We also analyzed breakpoints in TPGs. Except above mentioned spliced fusion cases, the remaining 3 breakpoints in MLLT1 as well as 3 of 4 breakpoints in EPS15 and all breakpoints in MLLT11 were within intron 1 of corresponding genes. In AF4 the major breakpoint region included intron 3 (n=19), intron 4 (n=6) and intron 5 (n=2). We also revealed 2 rare breakpoints in intron 6 and 10. In MLLT3 the most frequent breakpoint location was intron 5 (n=12), additionally 2 cases in intron 5 were identified. In MLLT10 two separate breakpoint locations were found: intron 3 (n=1) and intron 8 (n=3) in combination with intron 9 (n=1). We estimated prognostic significance of MLL breakpoint locations in 31 cases of infant ALL treated by MLL-Baby protocol. 3-year cumulative incidence of relapse was remarkably higher in patients with breakpoints in intron 11 (n=18) in comparison to patients with breakpoint localized from intron 7 to exon 11, inclusively (n=13) (0.85±0.01 and 0.57±0.02, respectively), although difference between these two groups did not achieve statistical significance (p=0.261). Median follow-up time in the observed group was 30 months (range 6–42). Conclusion In the current study we estimated clinical and prognostic significance of MLL and TPG genomic DNA breakpoints in infant acute leukemia. Our data provide additional information of molecular genetic features of MLL-rearranged infant acute leukemia. Disclosures: No relevant conflicts of interest to declare.

Description: Acute leukemia (AL) in children less than 1 year old is the relatively rare disease with specific biological features and poor outcome. It is also characterized by high incidence of MLL gene rearrangements. Immunophenotype of infants’ leukemia varies due to presence or absence of MLL gene rearrangements. Aim of the study –description of immunophenotype in infant acute lymphoblastic and acute myeloid leukemia (ALL and AML respectively) due to presence of MLL gene rearrangements. Methods. Totally 540 cases of pediatric AL were studied. 113 patients (59 boys and 54 girls) aged from 5 days to 11 months were included in the study group. Their data was compared to 427 cases of acute leukemia in older children. Tumor cells immunophenotyping was performed by 6-8-color flow cytometry. Detection of various types of MLL-gene rearrangements was done by fluorescence in-situ hybridization, reverse-transcriptase polymerase chain reaction (PCR) and long-distance inverse PCR. Results. ALL was found less frequently in infants than in older children (68.1% and 86.9% respectively, p

Description: Background. Translocation t(7;12)(q36;p13) leading to MNX1 (HLXB9)-ETV6 fusion gene formation is recurrent chromosomal rearrangement, predominantly found in children under 24 months of age with acute myeloid leukemia (AML) and associated with dismal outcome. In the majority of cases t(7;12) is cryptic and can be detected by fluorescent in situ hybridization (FISH) only. Purpose. To evaluate the incidence of t(7;12)(q36;p13) and initial clinical parametres and treatment outcome of infant with AML carrying t(7;12) using novel 3-color FISH approach. Methods. 81 infants with de novo AML who was diagnosed between June 1999 and December 2014 were included in the current study. Median age in the observed group of patients was 6.9 months (range 0.3-11.7). Bone marrow morphology was done in all cases flow cytometry in 67 cases. FAB variant was available in 72 patients. Chromosomal banding analysis (CBA) were performed in all cases, while RT-PCR for the most common fusion gene transcripts (MLL rearrangements, RUNX1-RUNX1T1, PML-RARa, CBFB-MYH11, BCR-ABL1) were done in 52 cases, FISH for MLL rearrangements in 49 cases. All MLL-negative cases were screened for t(7;12) by novel 3-color FISH approach consisted of a break-apart probe composed of an orange labeled probe centromeric to the ETV6 gene in 12p13, a green labeled probe telomeric to ETV6 together witha probe combination made of two loci flanking the HLXB9 gene, both labeled in blue. All probes were applied simultaneously and constituted the 3-color probe set used as a novel approach in this study. All probes was synthesized on our demand by MetaSystems (Germany) and applied partly retrospectively, partly -from March 2012 - prospectively to available patients material. Written informed consent was obtained at all cases. Results. Among 81 included patients there were 80 cases of AML and 1 case of Biphenotypic acute leukaemia (BAL). Various 11q23/MLL rearrangements were revealed in 45 cases (55.6%); inv16 in 3 cases (3.7%), including 1 case of simultaneous detection of inv16 and t(7;12); t(1;22)(p13;q13) was found 5 cases (6.2%); complex karyotype in 5 cases (6.2%); t(7;12)(q36;p13) in 6 cases (7.4%); other cytogenetic aberrations and normal karyotype in 9 cases (11.1%) each. Translocations t(8;21) and t(15;17) were not detected. Median age of t(7;12)-positive patients was similar to t(7;12)-negative ones (7.0 vs 6.9 mo). All 6 patients with t(7;12) referred to AML high-risk group. Median WBC count was 29.7*109/L (range 15.7-210). Five of 6 patients had initial CNS disease, in all cases extramedullary organ involvement was observed. Three out of 6 t(7;12)-positive patients had immature FAB variants (one AML M0 and 2 AML M1), 2 patients had AML M5a and 1 BAL. Translocation t(7;12) was associated with immature immunophenotype. CD34-positive/CD117-positive cells were revealed in all 6 cases, that was significantly more common in comparison to t(7;12)-negative cases (p=0.004 and p=0.038, respectively). Interestingly, co-expression of CD7 antigen was detected in 5 out of 6 t(7;12)-positive cases and this phenomenon was observed in t(7;12)-positive group more frequent than in t(7;12)-negative ones (p=0.001). In 5 out of 6 cases t(7;12) was cryptic and was not found by CBA. In 5 patients extra copy of chromosome 19 was revealed, that could serve as predictor of presence of t(7;12). Application of 3-color FISH showed 2 types of breakpoint at chromosome 7: in 5 cases breakpoints localized at 7q36; 1 patient had interstitial deletion 7q11q36 and blue fluorescent signal was observed at 7q11. Hematological remission after first induction course was achieved only in one half of t(7;12)-positive patients. Relapses occurred in 3 patients. Hematopoietic stem cell transplantation (HSCT) was performed in 1st remission in 4 cases and 2nd remission in 1 case. EFS and OS were similar in t(7;12)-positive and t(7;12)-negative groups (0.33±0.16 vs 0.39±0.07 p=0.573 and 0.60±0.21 vs 0.45±0.08 p=0.571) with median of follow-up time 29 months. Conclusions. Our results provide additional clinical, immunological and cytogenetic data of t(7;12)-positive patients. Application of novel 3-color FISH approach revealed t(7;12)(q36;p13) in 7.4% infants with AML. Among MLL-negative patients it was the most common cytogenetic aberration (19.4%). Application of HSCT in both 1st and 2nd remission could overcome unfavorable influence of this translocation and led to appropriate OS. Disclosures No relevant conflicts of interest to declare.

Description: Abstract 2537 Background. MLL gene rearrangements are the most common genetic events in infant leukemia. Up to date more than 100 various MLL rearrangements were described. Purpose. To evaluate the distribution of MLL rearrangements among infants (aged from 1 to 365 days) with both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). Methods. 174 infants (117 ALL and 57 AML cases) were included in the current study. 11q23/MLL rearrangements were detected by chromosome banding analysis (CBA), fluorescence in-situ hybridization (FISH) and reverse-transcriptase PCR (RT-PCR). CBA was done according to standard procedure. FISH analysis using LSI MLL Dual Color, Break Apart Rearrangement Probe (Abbott Molecular, USA) was performed on at least 200 interphase nuclei and on all available metaphases. RT-PCR was performed as previously described (A. Borkhardt et al.,1994, N. Palisgaard et al., 1998, J. van Dongen et al., 1999). In 39 cases genomic DNA breakpoint was detected in MLL and translocation partner genes by long-distance inverse PCR (LDI-PCR). Exon-intron numbering of MLL gene was done according to I. Nilson et al, 1996. Results. 11q23/MLL rearrangements were revealed in 74 ALL patients (63.2%). Among this group MLL-AF4 was detected in the majority of cases (53.5%), less frequently were found MLL-MLLT1, MLL-MLLT3, MLL-MLLT10 and others (fig. 1a). Children with ALL under 6 months of age had significantly higher incidence of MLL rearrangements in comparison with older infants (84.0% vs. 47.8%, p

Description: Abstract 2547 Acute lymphoblastic leukemia (ALL) in children less than 1 year old is the relatively rare disease with specific biological features and poor outcome. It is also characterized by high incidence of MLL gene rearrangements. Immunophenotype of infants' leukemia varies due to presence or absence of MLL-rearrangements. Aim of the study. description of immunophenotype in infant acute lymphoblastic leukemia. Methods. Totally 421 cases of pediatric acute leukemia (AL) were studied. 81 patients (39 boys and 42 girls) aged from 5 days to 11 months were included in the study group. Their data was compared to 332 cases of acute leukemia in older children. Tumor cells immunophenotyping was performed by 6–8-color flow cytometry. Detection of various types of MLL-gene rearrangements was done by simultaneous application of chromosomal banding analysis, fluorescence in-situ hybridization, reverse-transcriptase polymerase chain reaction (PCR) and long-distance inverse PCR. Results. There were 54 (66.7%) ALL cases in the study group. ALL was found less frequently in infants than in older children (66.7% and 88.5% respectively, p

Description: Abstract 4700 Statement WT1 gene expression (GE) is widely used for monitoring of minimal residual disease (MRD) in acute myeloid leukemia (AML) patients. Predictive value of WT1 GE in MLL-positive AML is not clear. Comparison of WT1 GE and fusion genes (FG), detected at RNA and DNA levels is rarely done. Here we present comparison of MRD data, assessed by WT1 GE, FG transcripts and MLL fusions alleles (MFA). Materials and methods 27 samples from 5 MLL-positive AML patients (pts) were analyzed. Median age was 13 years (range 0.8-58 years). 5 samples were obtained at diagnosis, 21 samples during follow-up treatment, 1 at diagnosis of relapse. Initial diagnostics included cytomorphology, immunophenotyping of blast cells, cytogenetics. Presence of MLL rearrangements was detected by FISH, reverse-transcriptase PCR (RT-PCR) and confirmed by long-distance inverse PCR. Among 5 pts there were two MLL-MLLT4-positive cases, two MLL-MLLT10-positive. One patient carried MLL-MLLT3 fusion gene. Quantification of MFA in genomic DNA by patient-specific primers-probe combinations and detection of FG transcript kinetics in RNA/cDNA during treatment were performed by RQ-PCR as previously described (T. Burmeister et al, Leukemia 2006, 20; J. Gabert et al, Leukemia, 2003, 17, respectively). Due to high concordance rate (96%) between qualitative results obtained by FG transcript and MFA detection, these results were combined into one group named as standard methods (SM) of MRD monitoring. Sample was defined as positive if only one result obtained by SM was positive. Sample was defined as negative if both results assessed by FG transcript and MFA were negative. Quantification of WT1 was performed in bone marrow (BM) samples by real-time quantitative PCR (RQ-PCR) with normalization to ABL gene. Additionally, BM samples taken from 14 pts without hematological malignancies were investigated. WT1 threshold level (TL) calculation was based on ROC curve analysis. TL was defined as value with maximal sensitivity and specificity. Results ROC analysis of WT1 GE revealed an area under curve (AUC) of 0.890 (95% CI 0.800-0.990). TL was set at 32 with sensitivity of 62% and specificity of 100%. Value of TL was equal to upper level of WT1 normalized copy number (NCN) in BM of 14 pts without hematological malignancies (median 10, range 0-32 WT1 copies/104ABL copies). In AML pts it was detected 13 WT1-positive samples (48%). 21 samples (78%) were positive by SM. 6 samples (22%) were negative both by SM and WT1 GE. Discrepant results were found in 8 samples (30%) (table 1). These discrepant results were observed in follow-up samples only. Qualitative concordance between SM and WT1 GE was 70% in our series. Conclusions Based on the ROC curves analysis it was not found particular TL of WT1 NCN that clearly distinguishes MRD-negative pts from those with positive MRD, detected by SM. Applicability of WT1 NCN quantification for MRD monitoring in the assessed MLL-rearranged AML samples appears to be limited because of relatively high percentage of false-negative samples. Discrepant results could be explained by high variability of WT1 GE during antileukemic therapy, and presence of WT1 GE in normal BM. Thus WT1-negative results should be considered as truly MRD-negative with great caution and have to be confirmed by FG transcript and/or MFA quantifications. Disclosures: No relevant conflicts of interest to declare.

Description: Acute lymphoblastic leukemia (ALL) in infants (less than 1 year old) is a unique tumor with distinct biological features and poor outcome even when modern treatment schemes are used. Rearrangementsof MLL-gene, located in 11q23 region, are detected in approximately 75-80% of infants with ALL and lead to treatment resistance and high relapse rate. Nevertheless patients with germline MLL also demonstrate inferior outcome compared to ALL in older children. Thus additional risk factors implementation is one of the crucial points in infant ALL management. Minimal residual disease (MRD) measurement by multicolor flow cytometry (FCM) or various PCR technics is a well-standardized method of treatment response evaluation in childhood ALL, although in infants MRD data is not so widely applied. The aim of the study was to evaluate the relapse prediction feasibility in infant ALL by FCM MRD assessment during remission induction of MLL-Baby protocol. Methods. Totally 89 infants aged from 5 days to 11 months were enrolled in the present study. In 23 cases (25.8%) MLL gene was germline (MLL-g group), 33 patients (37.1%) had MLL-AF4 fusion while in remaining 33 cases (37.1%) other types of MLL-rearrangements were found. All patients were diagnosed as B-cell precursor ALL and all were treated by well established in Russia and Belarus MLL-Baby protocol, which is specially designed for infant ALL management. MRD was measured by 6-10-color FCM in bone marrow (BM) samples obtained at day 15 and at the end of remission induction (day 36). The availability of samples at at least one of these time-points was the only criteria for study group completion. In 43 patients with known types of MLL-rearrangements MRD was also assessed by fusion gene transcript (FGT) detection in RQ-PCR after first consolidation or first high risk block (for intermediate risk and high risk groups respectively). Relapse risk was investigated by cumulative incidence of relapse (CIR) estimation. Median of follow-up was 3 years 10 months. Results. Finally at day 15 MRD was studied in 71 cases. 17 patients (23.9%) were tested MRD-negative while remaining ones displayed various levels of MRD-positivity: 8 cases (11.3%) - from 0.01% to 0.1%; 14 (19.7%) - from 0.1% to 1%; 22 (31.0%) - from 1% to 10%; 10 (14.1%) - more than 10%. Proportion of MRD-positivity was lower in MLL-g group compared to MLL-rearranged (MLL-r) patients (58.8% and 81.5% respectively, p=0.06). Prognostic impact of day 15 MRD differed due to MLL-status. In MLL-r group significant differences between MRD(+) and MRD(-) patients were observed (n=10, CIR 0.28(0.18) and n=37, CIR 0.67(0.08) respectively, p=0.025). At the same time in MLL-g group these outcome differences were not significant (n=7, CIR 0 and n=9, CIR 0.22(0.14) correspondingly, p=0.197). Interestingly, in patients carrying MLL-AF4 fusion, known to be one of the most adverse types of MLL-rearrangements, day 15 MRD-negativity predicted low relapse incidence (n=5, CIR 0 and n=16, CIR 0.68(0.12) respectively, p=0.045). Thus day 15 MRD-negativity allows to detect low-risk MLL-r infants but it is not applicable in MLL-g group. It was previously shown that any detectable level of FGT after first consolidation or first high risk block predicts very poor outcome in MLL-r cases (G. Tsaur et al, ASH-2011). In current series RQ-PCR data in patients, FCM MRD(+) at day 15, distinguished groups of intermediate and very high relapse risk (n=17, CIR 0.51(0.13) and n=18, CIR 0.84(0.09) respectively, p=0.017). At day 36 FCM MRD was assessed in 82 infants. Among them 35 (42.7%) were tested negative while remaining 47 (57.3%) were MRD(+) at various levels. Prognostic value of day 36 FCM MRD data in MLL-r group was not significant: MRD(+) patients (n=23) had CIR of 0.71(0.08) while in MRD(-) cases (n=33) CIR was 0.49(0.12), p=0.153. Conversely, in MLL-g group low end-induction MRD (less than 0.1%) lead to excellent outcome compared to patients with higher MRD (n=14, CIR 0 and n=7, CIR 0.22(0.20) respectively, p=0.010). Conclusions. Thus FCM MRD data could distinguish infants with low risk of ALL relapse, but in MLL-r and MLL-g groups different time-points are prognosticaly significant. In MLL-g patients tandem application of FCM at early time-point and RQ-PCR later could help to define groups with low, intermediate and high relapse risk. MRD data could be added to MLL-Baby protocol risk group stratification, which is currently based on type of MLL-rearrangement. Disclosures No relevant conflicts of interest to declare.