E865 PATTERN OF CNS RELAPSE IN ACUTE LYMPHOBLASTIC LEUKEMIA BCR-ABL POSITIVE, THE IMPORTANCE OF CHARACTERIZATION OF ABL1 MUTATIONS IN CEREBROSPINAL FLUID R Sanchez 1 , R Ayala 2 , RA Alonso 3 , J Ribera 4 , O García 4 , S Mercadal 5 , P Montesinos 6 , R Martino 7 , P Barba 8 , J González-Campos 9 , M Barrios 10 , E Lavilla 11 , C Gil 12 , T Bernal 13 , L Escoda 14 , E Abella 15 , ML Amigo 16 , MJ Moreno 17 , P Bravo 18 , R Guàrdia 19 , JM Hernández-Rivas 20 , A García-Guiñón 21 , S Piernas 22 , JM Ribera 4 , J Martínez-López 2,* 1 Biología Molecular Hematología, 2 Fundación Hospital Universitario 12 de Octubre, 3 Hematología, Hospital Universitario 12 de Octubre, Madrid, 4 ICO- Hospital Germans Trias i Pujol. Institut de Recerca contra la Leucèmia Josep Carreras, 5 ICO- Hospital Duran i Reynals (Bellvitge), Barcelona, 6 Hospital La Fe, Valencia, 7 Hospital Sant Pau, 8 Hospital Vall d’Hebron, Barcelona, 9 Hospital Virgen del Rocío, Sevilla, 10 Hospital Carlos Haya, Málaga, 11 Hospital Lucus Augusti, Lugo, 12 Hospital General Universitario de Alicante, Alicante, 13 Hospital Central de Asturias, Oviedo, 14 Hospital Joan XXIII, Tarragona, 15 Hospital del Mar, Barcelona, 16 Hospital Meseguer, Murcia, 17 Hospital Virgen de la Victoria, Málaga, 18 Hospital Fuenlabrada, Fuenlabrada (Madrid), 19 ICO-Hospital Josep Trueta, Girona, 20 Hospital Universitario de Salamanca, Salamanca, 21 Hospital Arnau de Vilanova, Lleida, 22 Hospital Parc Taulí, Sabadell (Barcelona), Spain Background: He incidence of central nervous system (CNS) relapse among patients with BCR/ABL-positive acute lymphoblastic leukemia (ALL) is 8-17%. Although tyrosine-kinase inhibitors (TKI), especially imatinib, are included in the first-line treatment in these patients, their concentration in CNS is too low to effectively prevent CNS relapse, making CNS prophylaxis mandatory. Aims: To study the frequency, predictors and evolution of BCR-ABL positive ALL patients with CNS relapse in two consecutive clinical trials of the PETHE- MA group using imatinib and chemotherapy. As secondary objective we pro- posed the introduction of a new method for the study of variants of uncertain significance (VUS) in kinase domain of the BCR-ABL from cDNA of cere- brospinal fluid (CSF) blasts, in order to adapt the TKI used in relapse according to the clonal evolution from bone marrow (BM) to CSF cells. Methods: It has been reviewed data of CNS relapse of patients included in two consecutive clinical PETHEMA trials (PETHEMA-LAL-PH-2008 and PETHEMA-LAL-OPH-2007), for treatment of BCR-ABL- Ph+ ALL patients. In two patients with combined BM and CSF we analyzed the BCR-ABL mutations at diagnosis and at relapse in both sites. Kinase domain of cDNA was amplified in two steps by nested PCR in the samples of BM at diagnosis and BM or CSF at relapse, covering the whole kinase domain from residues Gly227 to Gly514. Further enzymatic fragmentation of the domain yielded ~200 bp of small frag- ments. Ion Torrent ultra deep-sequencing of the resulting fragments allowed us to evaluate the variants of the chimeric protein. Results: A total of 138 ALL BCR/ABL positive patients were analyzed and 128 reached complete remission, 30 of them have relapsed (13 [43%] involving CNS [isolated or combined], 16 [53%] BM and 1 in unknown site). The overall survival probability at 2 years was 69% for the “CNS Relapse” group (IC95%: 44-94%; p=0.067) and 44% for the “Not CNS Relapse” group (IC95%: 20-68%; p=0.067, Figure 1a). In a multivariable analysis any clinical variable was asso- ciated with CNS relapse probability. In two of the CNS and BM relapsed patients we have performed massive sequencing experiments of ABL1 Kinase domain mutational status. In the first patient ultra-deep NGS of BM samples at diag- nosis and at relapse did not show VUS or pathogenic variants, but the CSF study at relapse confirmed the variant c.1159 T>A, p.L387M. The same study in the second patient also found the same pathogenic variant only in CSF blast cells (Figure 1b), whereas, the VUS c.733 A>G, p.K245E was found only in the BM sample at diagnosis. Figure 1. Summary/Conclusions: In BCR-ABL ALL patients treated with imatinib and chemotherapy CNS relapse was a significant feature, despite CNS prophylaxis, In our series we did not find any clinical variable predicting CNS relapse. We have found the pathogenic variant p.L387M in CSF blasts of two patients with combined CNS and BM recurrence, this variant not being found in BM samples at diagnosis or at relapse. These mutations were sensitive to other TKIs with better penetration to CSF. Based on these results, a mutational study of the kinase domain of the BCR-ABL in blast cells obtained from CSF, should also be integrated in the mutation study of these patients in order to select the TKI according to the clonal evolution from BM to CSF cells. E866 PROGNOSTIC IMPACT OF COPY NUMBER ALTERATIONS IN A SERIES OF PEDIATRIC PATIENTS WITH DE NOVO B-CELL PRECURSOR ACUTE LYMPHOBLASTIC LEUKEMIA IN A SINGLE CENTER M Trabazo Del Castillo 1,* , S Rives 2,3 , N Vega-Garcia 1 , R Malatesta 1 , C Estella 1 , A Català 2,3 , M Torrebadell 1,3 , R Berrueco 2,3 , A Ruiz-LLobet 2 , L Calvente 1 , A Alonso-Saladrigues 1 , M Mesegué 1 , M Solsona 1 , M Camós 1,3 1 Hematology Laboratory, 2 Pediatric Hematology. Department of Hematology and Oncology, Hospital Sant Joan de Déu, University of Barcelona, Esplugues de Llobregat, 3 Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain Background: Gene copy number alterations (CNAs) have been recently pro- posed as variables for risk stratification in acute lymphoblastic leukemia (ALL). However, their use in clinical practice is controversial, as their prognostic impact could depend on the applied therapeutical protocol and the interaction with other clinical and biological variables. Aims: To analyze the prognostic impact of CNAs in a series of pediatric patients with B-cell precursor ALL (pre-B ALL) treated in a single center. Methods: Pediatric patients (0-18 years) with pre-B ALL, diagnosed between 1999 and 2015 and homogeneously treated according to consecutive protocols of the Spanish Hematology and Oncology Pediatric Society (SEHOP) Cooperative Group (SHOP-99, SHOP-2005, SEHOP-PETHEMA 2013). CNAs were studied by MLPA technique with SALSA-P335 kit (MRC-Holland) and Coffalyser software. Results: We included 55 patients with a median age of 4.7 years (range 1.1- 14.9), 56% males. Only one patient had central nervous system infiltration. Median WBC count was 8.4x10 9 /L (range 1.1-296.9). All cytogenetic subtypes were represented. We observed the presence of CNAs in 29 patients (53%), including 17 (31%) cases with one CNA, 8 (15%) patients with 2 CNAs and 4 (7.5%) patients with ≥3 CNAs. The most frequent CNAs were deletions of CDKN2A/B, observed in 12 patients (22%), followed by ETV6 deletions in 11 cases (20%) and IKZF1 deletions in 9 cases (16%); also, we observed deletions of PAX5 in 7 cases (13%), of BTG1 in 4 patients (7%), of RB1 in 2 cases (4%), JAK2 deletions in one case and CRLF2 alterations (PAR region) in one case. IKZF1 deletions were more frequently observed in BCR-ABL1 rearranged cases and in patients with B-other subtype (cases with absence of main cytogenetic categories), and ETV6 deletions predominated in cases with ETV6-RUNX1 rearrangement. Among those patients with more than one CNA, IKZF1 was the gene most frequently involved (IKZF1plus, 7 cases). The presence of CNAs was significantly correlated to older age (p=0.006), hyperleukocytosis >20x10 9 /L (p=0.018) and high levels of minimal residual disease (MRD>10%) at day 15 of induction, assessed by flow cytometry (p=0.012). A higher number of CNAs (≥2) was found in boys (p=0.026). Noticeably, the patient with CNS infiltration har- bored 3 CNAs. IKZF1 deletions were associated with high hyperleukocytosis (>100x10 9 /L, p=0.001), older age (p=0.001), high NCI risk (p=0.008) and high MRD levels at day 15 (p<0.0001). We found the same associations for IKZF1plus. CDKN2A/B deletions showed a trend to high WBC count (>100x10 9 /L, p=0.051) and presence of MRD at the end of induction (MRD>0.01%, p=0.082). We found no significant associations for ETV6 or PAX5 deletions. After a median follow up 2.6 years (0.3-11.9) all patients are alive and 3 patients relapsed, with an event free survival (EFS) at 5 years of 87±7%. The presence of ≥2 CNAs correlated to worse EFS (64±16% vs 100%, p=0.043). Summary/Conclusions: in our series, the presence of CNAs, mainly IKZF1 deletions, were associated with poor prognostic factors like older age, high WBC count and high levels of MRD at early timepoints. We are currently expanding our series to confirm our results. GRANTS: PI12/2417, PN I+D+I, ISCIII (SGE, FIS), CIBERER, Fundación AECC, Fundación Sandra Ibarra, Fundación Cris contra el cáncer & “Força Miquel”, “Candela” & “Mua” projects. E867 COMBINED BLINATUMOMAB + DASATINIB/IBRUTINIB THERAPY OF RELAPSED ACUTE LYMPHOBLASTIC LEUKEMIA PATIENTS- ANTILEUKEMIC EFFECT ON THE T-HELPER AND T-REGULATORY CELLS REDUCTION BACKGROUND A Sokolov * , E Parovichnikova, V Troitskaya, I Galtseva, M Firsova, J Davidova, N Kapranov, V Savchenko National Research Center for Hematology of the Ministry of Healthcare of the Russian Federation, Moscow, Russian Federation Background: Blinatumomab, bispecific anti-CD3/CD19 monoclonal antibody, 354 | haematologica | 2016; 101(s1) 21 st Congress of the European Hematology Association