Cytogenetic Remission Research Articles

Interest of cytogenetic and FISH evaluation for prognosis evaluation in 198 patients with acute myeloid leukemia in first complete remission in a single institution

The prognostic interest of cytogenetic remission and fluorescent in situ hybridization (FISH) evaluation in patients with abnormal karyotype acute myeloid leukemia (AML) has been poorly studied. Among 198 patients that reached complete remission (CR), 24 did not reach cytogenetic remission (CyCR). CyCR had no prognosis impact, especially in patients with intermediate or unfavorable cytogenetic. Twenty of 52 evaluated patients in CyCR did not reach FISH CR. FISH CR was associated with better OS (p=0.004) and tended to be associated with better disease-free survival (DFS) (p=0.08). FISH evaluation may be a useful tool for prognosis evaluation and minimal residual disease (MRD) assessment in patients with abnormal cytogenetic AML.

Efficacy and safety analysis of interferon combined with imatinib in treating chronic myeloid leukemia

Imatinib has been recognized as the frontline therapy drug in chronic myeloid leukemia (CML), however, only limited patients could achieve complete molecular remission (CMR). Recent clinical and basic proofs indicated an improved treatment outcome by the combination of interferon and Imatinib. This study was purposed to evaluated systematically the efficacy and safety of interferon plus Imatinib in patients with CML. Data from relative clinical trials were from clinical trial of gov and Cochrane Collaboration. A comprehensive literature search was performed from data bases such as pubMed and EM. The results indicated that 7 clinical trials and 12 research papers met the criteria enrolled in study, included 697 cases in total. The combination group had higher complete cytogenetic remission (CCgR) rate than imatinib alone at 6 months (58% vs 42%; P = 0.0001) and 12 months (74% vs 68%; P = 0.004). The major molecular remission (MMR) rate was also higher in the combination group at 6 months (58% vs 34%; P = 0.0001) and 12 months (66% vs 47%; P < 0.0001). Furthermore, compared with single drug, the combination group had superior CMR rate at 6 months (13% vs 2%; P = 0.0002) and 12 months (14% vs 5%; P = 0.0009). The major adverse effects of combination therapy were rash, asthenia, edema and musculoskeletal events, and combination therapy was more prone to inducing neutropenia, thrombocytopenia and mild anemia. It is concluded that compared with Imatinib alone, the combination of interferon and Imatinib has better clinical efficacy in treating CML with earlier cytogenetic and molecular remission. It is also a safe therapy in spite of slightly weaker tolerance than single drug therapy.

A clinical and laboratory study of chronic myeloid leukemia with atypical BCR-ABL fusion gene subtypes

To explore the clinical and laboratory features of chronic myeloid leukemia (CML) with atypical e14a3 and e19a2 BCR-ABL fusion gene subtypes. We retrospectively analyzed a cohort of CML patients with Ph chromosome positive confirmed by cytogenetic and FISH but classical e13a3(b2a2), e14a2(b3a2)and e1a2 fusion transcripts negative identified by conventional real-time quantification RT-PCR (RQ-PCR). Further RQ-PCR was done with the forward primer and reverse primer designed to detect rare atypical BCR-ABL fusion genes including e14a3 and e19a2 transcripts. Direct sequencing analysis was performed on the PCR products and mutations in the BCR-ABL kinase domain were detected. The clinical data of patients were retrospectively analyzed. Six CML patients were found to carry t(9;22) abnormality and BCR-ABL rearrangement confirmed by FISH but classical BCR-ABL fusion genes negative detected by RQ-PCR. Further RQ-PCR and sequencing analysis confirmed the fusion of BCR exon 14 and ABL exon 3 in five CML patients (case 1-5) and the fusion of BCR exon 19 and ABL exon 2 in one CML patient (case 6). E255K and I293T IM-resistant mutations were detected in case 1 and 2, respectively. Among five cases with e14a3 transcripts, four were CML-CP, one CML-AP. Four patients were male and one was female. The median age was 48 years. The patient (case 6) with e19a2 transcripts was 40-year-old female with a diagnosis of CML-CP and PLT count was more than 1 000×10⁹/L. Imatinib (IM) therapy was administer in case 1, 2, 3, 4 and hematopoietic stem cell transplantation (HSCT) was undergone in case 5 after hydroxyurea (Hu) or interferon failure. Case 1 who had E255K IM resistant mutation, responded poorly to IM but obtained a complete cytogenetic remission (CCyR) after a substitution of dasatinib for IM. Case 2 and 3 achieved CCyR 6 months later after IM treatment and had been maintained well with IM despite I293T mutation in case 2. Case 4 attained CCyR 3 months later after IM treatment but relapsed and died soon. Case 5 was still in CCyR after HSCT. Case 6 with e19a2 transcripts got complete hematologic response after Hu treatment and CCyR was achieved soon after IM therapy. Incidence of CML with atypical transcripts is extremely low. They could benefit from tyrosine kinase inhibitors or HSCT. Rare and atypical BCR- ABL fusion gene subtypes could be missed by conventional RQ-PCR.

Association of genotypes and haplotypes of multi-drug transporter genes ABCB1 and ABCG2 with clinical response to imatinib mesylate in chronic myeloid leukemia patients

The introduction and success of imatinib mesylate (IM) has become a paradigm shift in chronic myeloid leukemia (CML) treatment. However, the high efficacy of IM has been hampered by the issue of clinical resistance that might due to pharmacogenetic variability. In the current study, the contribution of three common single nucleotide polymorphisms (SNPs) of ABCB1 (T1236C, G2677T/A and C3435T) and two SNPs of ABCG2 (G34A and C421A) genes in mediating resistance and/or good response among 215 CML patients on IM therapy were investigated. Among these patients, the frequency distribution of ABCG2 421 CC, CA and AA genotypes were significantly different between IM good response and resistant groups (P=0.01). Resistance was significantly associated with patients who had homozygous ABCB1 1236 CC genotype with OR 2.79 (95%CI: 1.217–6.374, P=0.01). For ABCB1 G2677T/A polymorphism, a better complete cytogenetic remission was observed for patients with variant TT/AT/AA genotype, compared to other genotype groups (OR=0.48, 95%CI: 0.239–0.957, P=0.03). Haplotype analysis revealed that ABCB1 haplotypes (C1236G2677C3435) was statistically linked to higher risk to IM resistance (25.8% vs. 17.4%, P=0.04), while ABCG2 diplotype A34A421 was significantly correlated with IM good response (9.1% vs. 3.9%, P=0.03). In addition, genotypic variant in ABCG2 421C>A was associated with a major molecular response (MMR) (OR=2.20, 95%CI: 1.273–3.811, P=0.004), whereas ABCB1 2677G>T/A variant was associated with a significantly lower molecular response (OR=0.49, 95%CI: 0.248–0.974, P=0.04). However, there was no significant correlation of these SNPs with IM intolerance and IM induced hepatotoxicity. Our results suggest the usefulness of genotyping of these single nucleotide polymorphisms in predicting IM response among CML patients.

Long term outcome of Ph+ CML patients achieving complete cytogenetic remission with interferon based therapy moving from interferon to imatinib era

Interferon α (IFNα) prolongs survival of CML patients achieving CCyR and potentially synergizes with TKIs. We report on the molecular status and long term outcome of 121 patients who were treated in Italy between 1986 and 2000 with IFNα based therapy and who obtained CCyR. After a median follow up of 16.5 years, 74 (61%) patients were switched to standard imatinib: 48 (65%) lost the CCyR on IFNα, and 36 (75%) are alive and in CCyR; 26 (35%) were switched to imatinib when they were still in CCyR on IFNα, and all 26 are alive and in CCyR. Forty-seven patients (39%) were never switched to imatinib: 24 (51%) continued and 23 (49%) discontinued IFNα, respectively, and 39/47 (83%) are alive and in CCyR. At last follow-up, the BCR-ABL transcripts level was available in 96/101 living patients (95%) The BCR-ABL:ABL ratio was between 0.1 and 0.01% (MR(3.0) ) in 17%, and less than 0.01% (MR(4.0) ) in 81% of patients. No patient was completely molecular negative (MR(4.5) or MR(5.0) ). The OS at 10 and 20 years is 92 and 84%, respectively. This study confirms that CCyR achieved with IFNα and maintained with or without imatinib or any other therapy significantly correlates with long term survival in CML patients who mostly have MR(4.0) . Complete molecular response (MR(4.5) or MR(5.0) ) seems to be unnecessary for such a long survival. This study further supports development of studies testing the clinical effect of the combinations of TKIs with IFNα.

TREATMENT RECOMMENDATIONS FOR CHRONIC MYELOID LEUKEMIA

The first treatment of chronic myeloid leukemia (CML) included spleen x-radiation and conventional drugs, mainly Busulfan and Hydroxyurea. This therapy improved the quality of life during the chronic phase of the disease, without preventing nor significantly delaying the progression towards advanced phases. The introduction of allogeneic stem cell transplantation (alloSCT) marked the first important breakthrough in the evolution of CML treatment, because about 50% of the eligible patients were cured. The second breakthrough was the introduction of human recombinant interferon-alfa, able to achieve a complete cytogenetic remission in 15% to 30% of patients, with a significant survival advantage over conventional chemotherapy. At the end of the last century, about 15 years ago, all these treatments were quickly replaced by a class of small molecules targeting the tyrosine kinases (TK), which were able to induce a major molecular remission in most of the patients, without remarkable side effects, and a very prolonged life-span. The first approved TK inhibitor (TKI) was Imatinib Mesylate (Glivec or Gleevec, Novartis). Rapidly, other TKIs were developed tested and commercialized, namely Dasatinib (Sprycel, Bristol-Myers Squibb), Nilotinib (Tasigna, Novartis), Bosutinib (Busulif, Pfizer) and Ponatinib (Iclusig, Ariad). Not all these compounds are available worldwide; some of them are approved only for second line treatment, and the high prices are a problem that can limit their use. A frequent update of treatment recommendations is necessary. The current treatment goals include not only the prevention of the transformation to the advanced phases and the prolongation of survival, but also a length of survival and of a quality of life comparable to that of non-leukemic individuals. In some patient the next ambitious step is to move towards a treatment-free remission. The CML therapy, the role of alloSCT and the promising experimental strategies are reviewed in the context of the new therapeutic goals.

Spontaneous hematological remission of acute myeloid leukemia.

Spontaneous remission (SR) of acute myeloid leukemia (AML) in adults is observed very rarely. To date, about 100 cases have been presented in the literature. To our best knowledge, we describe the first adult Polish patient suffering from acute myelomonocytic leukemia (48, XY, +13, +21/46, XY), in whom after supportive therapy, including non-irradiated, non-leukocyte depleted red cell transfusions and low-dose corticosteroid, we observed resolution of the disease without cytogenetic remission. We suggest a potential transfusion-associated graft versus-host-diseases (TA-GVHD) and graft-versus leukemia (GVL) reaction which might lead to spontaneous hematological remission. However, we did not observe clinical symptoms of such reactions apart from a short episode of non-infectious diarrhea. Additionally, steroids were administered but their role in inducing SR, in our opinion, seems less probable. This 77-year-old man remained in SR for 7 months, when repeated analysis showed AML recurrence. He died due to septic shock 2.5 months later. Additionally, we present a review of the literature.

Compassionate Use of Midostaurin in Myeloid and Lymphoid Neoplasia with FGFR1 Abnormality

Background: Patients with stem cell myeloproliferative disorders have a particularly poor prognosis and limited treatment options, i.e. mainly aggressive chemotherapy or allogeneic stem cell transplantation. In 2004, Chen et al. reported a patient presenting a t(8;13) (p11;q12) cytogenic anomaly who responded positively to treatment with PKC412 (midostaurin), an oral multi-targeted tyrosine kinase inhibitor. Here, we report a second case treated with the above-mentioned drug. Patient: A 71-year-old woman was diagnosed as having chronic myelogenous leukaemia with eosinophilia secondary to t(8;13) with FGFR1 involvement. Due to her age, an allogeneic stem cell transplantation was not possible. Treatment: A treatment combining aggressive chemotherapy and midostaurin was explored. The patient received one cycle of hyper-CVAD chemotherapy followed by maintenance therapy with midostaurin. A relapse occurred after six months, and she was treated with four more cycles of hyper-CVAD chemotherapy. The patient entered a complete clinical, haematological and cytogenetic remission. A maintenance therapy with midostaurin continued for four months until she developed a chemoresistant relapse followed by acute leukaemia. Conclusion: This is the second case of a t(8;13) myeloid and lymphoid neoplasm with FGFR1 abnormalities treated successfully with midostaurin. Midostaurin is administered orally, allows for outpatient care and in this case showed only occasional and minimal side effects. The combination of hyper-CVAD and midostaurin extended survival by 21 months without allogeneic transplantation. This case further supports the possibility of using midostaurin for the treatment of other diseases with FGFR1 dysregulations; however, specific clinical trials are needed to confirm this hypothesis.

Cytogenetic Response in Chronic Myeloid Leukaemia Patients Treated with Imatinib Mesylate Homolog-Drugs: 6 Year’s Transitional Study

Background: Treatment for Chronic Myeloid Leukaemia (CML) is mainly imatinib mesylate (IM) from original-brand, Glivec? or generic-type homologs, Imatib?. Materials and Methods: A collection of 149 CML patients was treated over a period of 6 years at Hiwa hospital. These patients were clustered into three groups: Group A was treated with Imatib for more than one year. All survivors of group A patients were switched to Glivec, classified as group B. Group C received only Glivec after June 2011. Imatib and Glivec are administered at doses 400-, 600- and 800-mg according to the CML stage. Results: Among group A patients, 68 (60%) were in complete haematological response (CHR), 32 (28.3%) developed acceleration and 13 (11.5%) patients were deceased. After switching to Glivec (group B), 69 (69%) patients remained in CHR, 10 (10%) patients weredeceased and 21 (21%) patients remained in acceleration. Of the 36 patients in group C, 33 (91.7%) were in CHR, 1 (2.8%) were in acceleration and 2 (5.5%) deceased. Those patients with CHR were tested randomly for BCR/ABL by FISH, and only 1/25 (4%) patients were found with complete cytogenetic response (CCyR) in group A, while 31/42 (73.8%) and 13/17 (76.5%) have CCyR in group B and C, respectively. Conclusions: Our results demonstrate a less cytogenetic response to treatment in patients of CML, who received the Imatib therapy, while a significant cytogenetic remission was found in patients with CHR after they switched to Glivec.

Dasatinib.

Dasatinib is an orally available short-acting dual ABL/SRC tyrosine kinase inhibitor (TKI). It potently inhibits BCR-ABL and SRC family kinases (SRC, LCK, YES, FYN), but also c-KIT, PDGFR-α and PDGFR-β, and ephrin receptor kinase. Dasatinib is an effective treatment for chronic myeloid leukemia (CML) and Philadelphia chromosome positive acute lymphoblastic leukemia (Ph+ ALL). Both diseases are characterized by a constitutively active tyrosine kinase; BCR-ABL. Dasatinib inhibits BCR-ABL with greater potency compared with other BCR-ABL inhibitors and is active in CML resistant or intolerant to imatinib. Dasatinib is approved for the treatment of CML (all phases) and for the treatment of Ph+ ALL, resistant or intolerant to prior imatinib treatment. Randomized trial data in CML show that first-line dasatinib provides superior responses compared with imatinib and enables patients to achieve early, deep responses, correlated with improved longer-term outcomes. A once-daily dose of 100mg in chronic phase CML results in high hematologic and molecular remission rates and prolongation of survival. In accelerated and blastic phase of CML, as well as in Ph+ ALL, complete hematologic and cytogenetic remissions frequently occur. Remissions however are very short. In these patients, once-daily 140mg is the recommended dose. The effect of dasatinib in other malignancies including solid tumors is subject of clinical studies. Regardless of many clinical trials in different tumor types and in different combinations of dasatinib with other agents, the role of dasatinib in the treatment of solid tumors has not yet been defined. Side effects of dasatinib are frequent but mostly moderate and manageable and include cytopenias and pleural effusions. The review presents the preclinical and clinical activity of dasatinib with a focus on clinical studies in CML.

Deep Molecular Response Is Reached by the Majority of Patients Treated With Imatinib, Predicts Survival, and Is Achieved More Quickly by Optimized High-Dose Imatinib: Results From the Randomized CML-Study IV

Deep molecular response (MR(4.5)) defines a subgroup of patients with chronic myeloid leukemia (CML) who may stay in unmaintained remission after treatment discontinuation. It is unclear how many patients achieve MR(4.5) under different treatment modalities and whether MR(4.5) predicts survival. Patients from the randomized CML-Study IV were analyzed for confirmed MR(4.5) which was defined as ≥ 4.5 log reduction of BCR-ABL on the international scale (IS) and determined by reverse transcriptase polymerase chain reaction in two consecutive analyses. Landmark analyses were performed to assess the impact of MR(4.5) on survival. Of 1,551 randomly assigned patients, 1,524 were assessable. After a median observation time of 67.5 months, 5-year overall survival (OS) was 90%, 5-year progression-free-survival was 87.5%, and 8-year OS was 86%. The cumulative incidence of MR(4.5) after 9 years was 70% (median, 4.9 years); confirmed MR(4.5) was 54%. MR(4.5) was reached more quickly with optimized high-dose imatinib than with imatinib 400 mg/day (P = .016). Independent of treatment approach, confirmed MR(4.5) at 4 years predicted significantly higher survival probabilities than 0.1% to 1% IS, which corresponds to complete cytogenetic remission (8-year OS, 92% v 83%; P = .047). High-dose imatinib and early major molecular remission predicted MR(4.5). No patient with confirmed MR(4.5) has experienced progression. MR(4.5) is a new molecular predictor of long-term outcome, is reached by a majority of patients treated with imatinib, and is achieved more quickly with optimized high-dose imatinib, which may provide an improved therapeutic basis for treatment discontinuation in CML.

Eosinophil Chimerism In The Differential Diagnosis Between DEK-CAN+ Acute Myeloid Leukemia Relapse and Chronic Graft Versus Host Disease

Eosinophilia is a rare recurrent finding in Acute Myeloid Leukemia (AML). The classical cases being: Core Binding Factor AMLs with chromosome 16 abnormalities, and AMLs with rearrangements of PDGFRA, PDGFRB and FGFR1. According to the 2008 WHO Classification, acute myeloid leukemia with t(6;9)(p23;q24) is a rare entity (0,7-1,8% of all AMLs) characterized by multilineage dysplasia, basophilia and unfavorable prognosis. The translocation leads to the development of the hybrid protein DEK-CAN. This cytogenetic alteration usually presents as a single abnormality, but can also be associated with complex karyotype. There are no descriptions of eosinophilia associated with DEK-CAN+ AML.We report the case of a 16-year old male patient that presented with generalized cutaneous pruritus and fever associated with peripheral blood eosinophilia (absolute count: 7.830/mm3) on August of 2010. We ruled out the most common causes of secondary eosinophilia, and then submitted the patient to a bone marrow aspiration that showed erythroid hyperplasia (58,8%), with dyserythropoiesis, eosinophilia (16,4%), dysgranulopoiesis, and 9,6% of blast cells, compatible with the diagnosis of AML-M6 according to the FAB classification. Cytogenetic study showed the presence of t(6;9) (p23;q34), FISH was negative for inv (16) and molecular studies showed FLT3 and NPM1 to be wild type. PDGFRb rearrangement was negative.The patient was treated with 2 cycles of cytarabin based chemotherapy, achieving hematological remission, but with sustained peripheral eosinophilia (absolute count: 920/mm3). Since the presence of t(6;9) is associated with dismal prognosis, the patient received a peripheral blood HLA matched related allogeneic stem cell transplantation (ASCT) in first remission.Four months after the ASCT, he presented with symptoms of sinusopathy and worsening of the peripheral blood eosinophilia (absolute count: 10.655/mm3). Bone marrow aspirate revealed blast count < 5% with 50,8% of eosinophils, and decreasing donor chimerism. Cytogenetic study revealed persistence of t(6;9) (p23;q24) associated to other abnormalities (including monosomy 5), revealing a complex karyotype. He was then submitted to a therapeutic trial with imatinib without response. Afterwards he received one cycle of cytarabine plus azacytidine with donor lymphocyte infusion during post chemotherapy aplasia. The patient recovered counts with 100% donor chimerism and shortly developed signs of chronic graft versus host disease (cGVHD) affecting eyes, skin and liver. Bone marrow evaluation revealed complete morphological and cytogenetic remission with normal eosinophil counts and 100% donor chimerism. He was then treated with prednisone and tacrolimus with good control of GVHD.Eleven months later, during tacolimus taper, the patients developed eosinophilia again. Bone marrow evaluation revealed morphologic and cytogenetic complete remission with 100% donor chimerism. Since eosinophilia had been a marker of AML activity in this patient, it became crucial to define whether this represented an impending relapse. We then performed eosinophil enrichment of peripheral blood eosinophils with Easysep (CD66b) beads, reaching a final sample with 80% of eosinophils (CD45high/CD16negative/CD13positive), and performed chimerism analysis in this sample. The results were compatible with 100% eosinophil donor chimerism, what ruled out the possibility of recipient neoplastic eosinophils. Tacrolimus tapering was stopped and two weeks later the patient developed worsening of cGVHD symptoms with sustained eosinophilia. Upon increasing the dose of tacrolimus, the eosinophilia resolved and we interpreted it to be secondary to cGVHD activity.Afterwards we designed a PCR reaction specific for DEK-CAN rearrangement and tested retrospectively all bone marrow samples RNA we had stored. While the test was positive in all previous episodes of eosinophilia, the testing of the last sample was negative, in agreement with the eosinophil chimerism finding. The patient is now in complete molecular remission 24 months after DLI with good cGVHD control.In conclusion, we have described a case of AML with DEK-CAN rearrangement secondary to t(6;9)(p23;q24) with eosinophilia. Additionally we have demonstrated how the study of eosinophil chimerism can be essential in the differential diagnosis between “neoplastic” and reactional eosinophilia. Disclosures:No relevant conflicts of interest to declare.

Alemtuzumab Is Safe and Associated With High Response Rates In Selected Patients With Myelodysplastic Syndrome

▪In a subgroup of patients with myelodysplastic syndrome (MDS) an immune mechanism is believed to cause bone marrow failure. In these individuals immunosuppressive treatment (IST) can restore marrow function. We previously reported a 68% response rate in a phase I/II study of alemtuzumab in 31 patients with low to int-2 risk MDS (Sloand etal JCO Dec 10, 2010:5166-5173). Patients were enrolled according to their predicted probability of response based on an algorithm that incorporated HLA-DR15 positivity, age and transfusion burden (Blood 2003 Oct 15; 102(8):3025-7). We now report updated efficacy data on our cohort of 40 patients and long term follow up data on responders. The first 37 patients received 10mg of alemtuzumab for 10 days intravenously. Alemtuzumab was administered subcutaneously in the subsequent 3 patients. Primary endpoints were changes in peripheral blood counts. Secondary endpoints included improvement in the transfusion requirements (in transfusion- dependent patients), duration of response, and late effects of treatment, relapse and survival. Thirty nine patients were evaluable. One patient discontinued treatment after one dose because of severe hypotension and was excluded from analysis. Median follow-up time was 25 months (3-64 months). Median age was 56 years (23-71 years). The overall response rate (ORR) was 64% (25/39) with 21% of patients having a complete response (8/39). Twenty of 29 (69%) int-1 patients; 4 of 7 (57 %) int-2 patients and 1 of 3 (33%) low risk patients responded following alemtuzumab treatment. Median time to response was 3 months with median duration of response 9 months (range 1-69 months). Eight of 11 patients who relapsed regained their response with addition of cyclosporine and one patient was lost to follow up. The median duration of response in patients rescued with cyclosporine is 37 months (1-42 months). The median duration of response to immunosuppressive treatment (alemtuzumab +/- cyclosporine) is 22.2 months (range 3-69 months). All responding patients who were previously transfusion dependent became transfusion independent after alemtuzumab treatment. One of three patients who received subcutaneous alemtuzumab administration responded. The median survival for all patients was 34 months (range 1-72 months) (figure 1a) with median survival of 36 months (6-72 months) in responding group compared to 16 months (1-56 months) in non-responding group (p<0.001) (figure 1b). Five of twelve patients with abnormal cytogenetics at the start of treatment had a complete cytogenetic remission at one year. One patient with monosomy 7 and another with del 13 were in cytogenetic remission for 4.5 years and 4 years respectively. Decline in their blood counts correlated with re-emergence of initial clone. Three patients with del 13, 5q- and del 5 continue to remain in cytogenetic remission at 4, 2 and 1 years respectively. The absolute neutrophil count at baseline was significantly associated with overall survival on univariate analysis. On multivariate analysis, factors significantly associated with overall survival were male sex, bone marrow hypocellularity/normocellularity, prior immunosuppressive treatment, baseline absolute neutrophil count and platelet count. All patients became lymphopenic after alemtuzumab administration and most patients continued to be lymphopenic at 3 years. Baseline absolute lymphocyte count, ratio of CD4/CD8 cell count, absolute CD4 and NK cell counts and kinetics of lymphocyte recovery were not predictive for response. Alemtuzumab was generally well tolerated with most patients having manageable infusion reactions with the first dose. Sixteen of the 39 patients became transiently positive for EBV DNA and 6 of 29 CMV seropositive patients had reactivation but no patient developed clinically significant viral disease. Alemtuzumab is well tolerated and is effective in a subset of patients with MDS. Long term responses with cytogenetic remissions are possible. Patients who relapse can be rescued with cyclosporine. Immunosuppresion should be considered in patients likely to respond based on a simple algorithm and alemtuzumab is an alternative to ATG based regimens. [Display omitted] [Display omitted] Disclosures:Off Label Use: Alemtuzumab use as immunosuppresive agent in myelodysplastic syndrome.

Monitoring By Chromosome Banding Analysis (CBA) and FISH Of Circulating CD34+ Cells In Low-Risk MDS Patients Treated In The Le-Mon-5 Study With Lenalidomide Monotherapy Reveals 82% Cytogenetic Responders With Different Response – , Evolutionary -, and Remission Patterns and No Increased Karyotype Evolution (KE)

IntroductionBesides a more reliable and frequent measurement of cytogenetic response, it was our aim to find out whether lenalidomide treatment in patients with IPSS low- or intermediate I-risk MDS can foster karyotype evolution (KE) and thus increase the risk of leukemic transformation. Thus, it is an important goal of the Le-Mon-5 study to examine the cytogenetic course under treatment with lenalidomide. In this study, only lower risk MDS patients with an isolated del(5q) are included. MethodsWe performed a rigid initial pretreatment screening of bone marrow (bm) aspirates by chromosome banding (CBA) as well as FISH-analysis to ensure an isolated del(5q). For initial screening as well as frequent cytogenetic follow-up every two to three months (FISH analysis of immunomagnetically enriched CD34+ peripheral blood cells (PBC) = CD34+ pb FISH), we used panels of 8 to 13 FISH probes covering the most common aberrations in MDS (Braulke et al. Leuk Res, 2010, 2013). Using this method we intended a reliable surveillance of cytogenetic changes occurring during therapy. Complete cytogenetic remission (CCyR) was defined as: no metaphases with del(5q) and abnormal FISH result below the laboratory threshold (5% EGR1-loss in CD34+ PBC) and partial cytogenetic remission (PCyR) was defined as: >50% reduction of clone size, also including cases with a CCyR at only one time point and those with either only CBA-CCyR or FISH-CCyR. ResultsFrom the initially screened 145 MDS patients, 84 could be included in the study according to the study inclusion criteria. Currently, follow-up data (at least 2 different time points) are available for 67 patients. An ongoing (>1 time point) CCyR was observed in 22 (33%) patients after a median follow-up of 18 (6-33) months. Thirty-three patients (49%) had a PCyR. Considering only CD34+ pb FISH results 31 (46%) patients showed a complete molecular-cytogenetic remission.A cytogenetic response was observed after a median of 6 (2-12) months after initiation of therapy for a median duration of 10 (2-25) months. In twelve patients (18%) the size of the del(5q) clone did not change. The median del(5q)-clone size at start of therapy was 60% in responders. After 10 cycles maximum clone size reduction was achieved (n=26) (median: 2.6%; range: 0% - 33.6%), after 24 months of observation clone size in responders (n=22) still was reduced to a median of 10.8% (range: 0.5% -76%) (Figure 1). [Display omitted] In 10 of 67 patients (15%) a KE occurred in the del(5q) clone after a median time of 18 months (6-42). This is not increased compared to the rate of spontaneous KE (13%) in a representative MDS cohort (n=729) studied recently by our group by banding analysis (Cevik et al. DGHO 2013, accepted for oral presentation). Remarkably, in one patient a KE with loss of a p53 allele and a 20q- deletion resolved after the 8th cycle of lenalidomide and after the 10th cycle a complete cytogenetic remission was achieved (Figure 2). In two additional cases, the del(5q) clone was completely eliminated, however a new cell clone with independent abnormalities (t(3;3)(q21;q26), second case: inv(11)(p15q23)del(11)(q13q22)) emerged under lenalidomide. There is a growing body of evidence that these clones were preexistent initially but below the cytogenetic detection level and were possibly suppressed by the del(5q) clone until its cytogenetic remission. [Display omitted] ConclusionsOur interim results show that:•A cytogenetic response to lenalidomide can be achieved in >80% of pts. with isolated del(5q) and lower-risk MDS•CBA can be complemented reasonable by CD34+ pB FISH, which allows a reliable monitoring of response and KE•Cytogenetic response to lenalidomide is durable (median 10 months as yet)•KE is not increased in this patient group under treatment with lenalidomide•In one case with KE and acquisition of additional p53 allelic loss and 20q-deletion continuation of lenalidomide finally lead to a CCyR Disclosures:Platzbecker:Celgene: Honoraria. Nolte:Celgene: Honoraria, Research Funding. Giagounidis:Celgene: Honoraria. Götze:Celgene Corp: Honoraria. Schlenk:Celgene: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Chugai: Research Funding; Amgen: Research Funding; Novartis: Research Funding; Ambit: Honoraria. Bug:Celgene: Honoraria, Research Funding. Germing:Celgene: Honoraria. Haase:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

TP53 Mutations Detected By Next-Generation Deep-Sequencing In Patients With Myelodysplastic Syndrome and Isolated Deletion (5q): Results From a German Multicenter Trial

BackgroundBeside cytogenetic aberrations, additional gene mutations are powerful predictors of outcome in myeloid diseases. Moreover, myelodysplastic syndromes with isolated deletion (5q) (MDS del(5q)) have been regarded as one of the most favorable entities among MDS. However, a substantial proportion of MDS del(5q) patients experience transformation into AML soon after diagnosis (Germing et al. Leukemia. 2012;26:1286-1292). Mutations of TP53 gene have early been recognized as an unfavorable prognostic biomarker in MDS in general and recent data suggest a role of TP53 mutations in the transformation of MDS del(5q) into AML. Lenalidomid (Len) is now approved in the US as well as in Europe for the treatment of MDS del(5q) it is of particular interest whether Lenalidomide can alter the course of pretreatment TP53 mutated MDS del(5q). MethodsThe Le-Mon-5 trial investigated the safety and efficacy of Len in patients with MDS and isolated deletion (5q). All patients gave their written informed consent to the clinical trial and to additional molecular genetic analyses. Bone marrow aspirates were performed at screening prior treatment initiation and during follow-up every 6 months. Only freshly extracted, high-quality DNA from ficollized mononuclear cells was used for next-generation deep-sequencing analysis. For generation of PCR amplicon libraries TP53 oligonucleotide primer plate assays were used and technically validated within the IRON-II (Interlaboratory Robustness Of Next generation sequencing) research study network. Amplicon deep-sequencing of TP53 (exons 4-11) was performed on a Roche 454 GS Junior system. Mean coverage of sequenced exons was about 800-fold allowing an approximate detection sensitivity of 2% mutational burden. ResultsCentral cytological, histological and cytogenetic review was performed in all patients establishing the diagnosis of MDS with isolated deletion (5q). A total of 68 patients (male: n=9) were analyzed with a median age of 71 years (range 41-88 years). TP53 mutations prior to treatment initiation with Len were found in 7 patients (10%). Mean mutation frequency was 38%. Notably, we did not find mutation frequencies lower than 15%. Of 4 evaluable patients, three patients became transfusion independent within 4 months of Len treatment. Of 2 patients we had follow-up samples available. Both patients showed no difference with regard to the mutation frequency after a follow-up of 4 and 17 months on Len treatment (27% and 51%, respectively). Noteworthy, one the two patients achieved a complete cytogenetic remission despite maintaining his TP53 mutation frequency. ConclusionUsing freshly extracted DNA we achieved high-quality NGS results with a high mean coverage of the relevant coding region of TP53. However, prevalence of TP53 mutations in our patient cohort was lower as compared to previously published data and we did not find low-level allele burdens as published by other groups, which might be due to the different sample sources used. Transfusion independence as well as cytogenetic remissions can be achieved in patients with TP53 mutations who are treated with Lenalidomide. Disclosures:Platzbecker:Celgene: Honoraria. Giagounidis:Celgene: Consultancy, Honoraria. Götze:Celgene Corp.: Honoraria. Haase:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Kohlmann:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Bug:Celgene: Honoraria, Research Funding. Hofmann:Celgene: Research Funding. Germing:Celgene: Honoraria, Research Funding. Nolte:Celgene: Honoraria, Research Funding.

Elderly CML Patients On Early Applied High Dose Imatinib Achieve Molecular Remissions As Fast As Younger Patients In Contrast To Patients On Standard Dose Imatinib: A Subanalysis Of The German CML-Study IV

IntroductionThe outcome of elderly patients with chronic myeloid leukemia (CML) treated with imatinib has been studied in several trials. However, there are no reports on the effects of different imatinib dosages in older vs. younger CML patients. MethodsTo evaluate the efficacy of imatinib in the elderly, we analyzed data from the German CML-Study IV, a randomized 5-arm trial designed to optimize imatinib therapy alone or in combination. There was no upper age limit for inclusion. Patients with BCR-ABL positive CML in chronic phase randomized to imatinib 400 mg/d (IM400) or imatinib 800 mg/d (IM800) were compared, stratified according to median age at diagnosis in western populations ≥ 65 years vs. < 65 years, regarding effectively administered imatinib dose, time to hematologic, cytogenetic and molecular remissions, adverse events (AEs), rates of progression to accelerated phase (AP) and blast crisis (BC), survival, and causes of death. The full 800 mg dose was given after a 6 weeks run-in period with imatinib 400 mg/d to avoid excessive cytopenias. The dose could then be reduced according to tolerability for maximum patients' compliance. ResultsFrom July 2002 through March 2012, 1,551 patients were randomized, 828 of these to IM400 or IM800. Median age of these patients was 52 years (IM400: 53 years; IM800: 51 years). 784 patients were evaluable for follow-up (IM400: 382; IM800: 402). 193 patients were ≥ 65 years, 591 < 65 years. 110 patients (29%) on IM400 and 83 (21%) on IM800 were ≥ 65 years. Median observation time on IM400 was 63.0 months in the elderly and 67.6 months in the younger group, on IM800 50.9 months in the elderly and 50.1 months in the younger group. The median dose per day was lower for elderly patients on IM800 (421 mg/d for patients ≥ 65 years vs. 556 mg/d for patients < 65 years), with the highest median dose in the first year (466mg/d for patients ≥ 65 years vs. 630mg/d for patients < 65 years). The median dose for patients on IM400 was 400 mg/d for both age groups. There was no difference between age groups in achieving a complete hematologic remission or a complete cytogenetic remission, neither if IM400 and IM800 were combined, nor in an analysis according to treatment groups. Elderly patients on IM400 achieved major molecular remission (MMR) and deep molecular remission (MR4) significantly later than younger patients (18.1 vs. 15.9 months, p=0.013; 54.4 vs. 33.3 months, p=0.012, respectively) whereas no difference was detected for patients on IM800 (11.9 vs. 10.5 months; 24.2 vs. 26.1 months, respectively). Imatinib was well tolerated in elderly patients with only few WHO grade 3-4 AEs being more frequent in the elderly than in younger patients (dermatologic AEs on IM400: 5.4 vs. 0.4%; infections on IM800: 8.3 vs. 2.5%). There were no significant differences between age groups in probabilities of progression to AP or BC neither if IM400 and IM800 were combined, nor in an analysis according to treatment groups. Five-year age-adjusted relative survival for elderly patients was comparable to that of younger patients. ConclusionWe could demonstrate that elderly patients achieved molecular remissions significantly later when treated with standard dose imatinib but not when treated with higher imatinib dosages. As the safety profile of IM800 in senior patients was favorable too we conclude, that the optimal dose for elderly patients could be higher than 400 mg/d. Disclosures:Müller:Ariad: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Hochhaus:Pfizer: Consultancy; ARIAD: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding, Travel Other. Hehlmann:BMS: Consultancy, Research Funding; Novartis: Research Funding. Saussele:BMS: Honoraria, Research Funding, Travel, Travel Other; Pfizer: Honoraria; Novartis: Honoraria, Research Funding, Travel Other.

Effective Targeting Of Chronic Myeloid Leukemia Initiating Activity With The Combination Of Arsenic Trioxide and Interferon Alpha

Imatinib is the standard of care in the treatment of Chronic Myeloid Leukemia (CML) patients. However, imatinib is not curative since most patients who discontinue therapy will relapse, stressing the need for novel therapies that target leukemia initiating cells (LIC). Arsenic trioxide induces complete remission in patients with acute promyelocytic leukemia (APL). We previously demonstrated that, through full degradation of PML-RARA, the combination of arsenic and retinoic acid eradicates APL LICs and cures the disease. Interferon alpha (IFN) induces hematologic and cytogenetic remissions and interestingly, improved outcome was reported with the combination of interferon and imatinib. We investigated the effects of arsenic and IFN on human CML cell lines or primary cells and the bone marrow retroviral transduction/transplantation murine CML model. In vitro, the combination of arsenic and IFN inhibited proliferation and activated apoptosis. Importantly, arsenic and IFN synergistically reduced the clonogenic activity of primary bone marrow cells derived from CML patients. Moreover, in a murine transplantation model of CML, we show that arsenic/IFN prolonged survival of primary leukemic mice and sharply diminished transplantation of CML cells in secondary recipients, pointing to exhaustion of CML LICs. Our results also suggest that IFN/arsenic may clear LICs independently from oncoprotein catabolism. Interestingly, arsenic/IFN effect on CML LIC activity was significantly superior to that of imatinib.These studies plea for a clinical exploration of this combination, knowing that IFN and arsenic have both shown clinical activity in CML, alone or in combination with imatinib. Disclosures:No relevant conflicts of interest to declare.

A Phase I Study Of Azacitidine After Donor Lymphocyte Infusion For Relapsed Acute Myeloid Leukemia Post Allogeneic Stem Cell Transplantation

BackgroundDisease relapse remains a significant cause of morbidity and mortality for patients with acute myeloid leukemia (AML) following allogeneic stem cell transplantation (alloSCT). In the event of relapse, remissions may be re-established with salvage chemotherapy, but are rarely durable. Reinfusion of additional donor lymphocytes (DLI) from the same donor without prophylactic immunosuppression has been used to potentially augment the graft vs leukemia (GVL) effect, and shown to prolong survival in the post alloSCT relapse setting (Schmid et al, JCO 2007). However, DLI is also associated with an increased incidence of acute graft versus host disease (aGVHD). Regulatory T cells (Tregs) are characterized by increased FoxP3 gene expression and have been correlated with a reduced incidence and severity of GVHD. Using a mouse model, Choi et al (Blood, 2010) observed that administration of azacitidine post stem cell infusion resulted in increases in both FoxP3 expression and Treg numbers, and reduced the incidence and severity of GVHD without hindering neutrophil engraftment. Based on these findings, we conducted a study of azacitidine following salvage chemotherapy and subsequent DLI for AML patients with post alloSCT relapse, with the goal of reducing the incidence and severity of aGVHD. Objectives(i) To establish the MTD of azacitidine administered after salvage chemotherapy and DLI in patients with relapsed AML after alloSCT and (ii) to determine the response rate, the rate of aGVHD, and overall survival of this regimen. Patient/MethodsPatients with relapsed AML after allogeneic stem cell transplant undergoing salvage chemotherapy followed by DLI were eligible for enrollment. Patients with prior exposure to azacitidine were not excluded. Salvage chemotherapy was determined by the treating physician. Six to twenty-one days following the completion of chemotherapy, a DLI was administered consisting of > 1x106 CD3+ cells/kg. Azacitidine was administered on Days 4, 6, 8 and 10 post-DLI. G-CSF was administered daily beginning Day +11 post-DLI until neutrophil recovery. Dose escalation was done using a 3+3 design with two azacitidine dose levels, 45mg/m2 and 75mg/m2. Dose-limiting toxicity (DLT) was defined as treatment-related grade 3-5 non-hematologic toxicities or bone marrow suppression lasting past Day +32 in the absence of persistent AML. ResultsEight patients were enrolled from June 2012-July 2013. The median age was 54.5 years (range 31-68) and five were female. Four of eight patients received stem cells from sibling donors. The median time post alloSCT until salvage chemotherapy was 109 days (range 56-1102). Pre-DLI chemotherapy consisted of: FLAG-Ida (3), FLAG (1), MEC (1), 7+3 (1), CLAM (1), or Azacitidine (1). Three patients were treated in the 45mg/m2 dose level and 5 patients were treated in the 75mg/m2dose level; no DLTs or grade 3-5 treatment related toxicities were observed. Five patients experienced aGVHD, all of which was grade I or II and easily controlled. The median duration of time to neutrophil recovery was 17 days post DLI (range 6-34) and 24 days from last day of salvage chemotherapy (range 16-41), similar to historical controls. Six patients achieved responses, including two cytogenetic complete remissions, one hematologic complete remission, and three complete remissions with incomplete blood count recovery; two patients failed to achieve remission. At the time of abstract submission, the median follow-up for all patients was 102 days (range 31-308). Four responders have subsequently relapsed and three patients have expired from refractory disease. ConclusionAdministration of azacitidine post salvage chemotherapy and DLI is well tolerated and does not hinder neutrophil recovery. The recommended dose for further studies is 75mg/m2. Disclosures:Off Label Use: vidaza for GVHD prophylaxis. Abboud:Novartis: Honoraria; Ariad: Honoraria; Alexion: Honoraria; Teva: Speakers Bureau. Schroeder:sanofi-aventis: Research Funding; celgene: Research Funding. Stockerl-Goldstein:Celgene : Speakers Bureau; Millennium: Speakers Bureau. Vij:celgene: Honoraria, Research Funding. Westervelt:celgene: Honoraria, Research Funding.

A Distinct Immunophenotypic Profile Of Del(5q) MDS Allows For Fast Monitoring Of Response To Treatment With Lenalidomide Or Azacitidine

IntroductionPatients with MDS harboring a del(5q) often display characteristic morphological features in the bone marrow. For the first time we have recently demonstrated a strong association of the presence of a cytogenetic abnormality - del(5q) - with a specific 5-parameter immunophenotypic profile measured by flow cytometry (FCM). The aim of this prospective study was to test, if this FCM profile could also be applied for monitoring response to treatment with disease-modifying drugs like lenalidomide and azacitidine. Patients and methodsOverall, 137 FCM investigations were performed in 52 well-characterized patients with MDS and a del(5q) (IPSS low/int-1: n=30, int-2/high: n=22) including 34 patients with isolated del(5q): 53 measurements before treatment and 84 during treatment (lenalidomide=47 and/or azacitidine=35; chemotherapy and/or allogeneic transplantation=6). Nineteen of 41 thereupon evaluated patients showed a concomitant TP53 mutation. An 8-color/5-tube FCM diagnostic procedure (lyse-stain-wash) was performed on a FACS-Canto II cytometer. Thus, the typical del(5q) FCM profile includes the following 5 parameters: percentage of myeloid progenitors (myPC > 2%) = 3 points, CD45 MFI ratio (lymphocytes : myPC ≤ 7.0) = 10 points, SSC ratio (granulocytes : lymphocytes < 6.0) = 2 points, CD71 (≤ 20%) on granulocytes = 1.5 points, and female gender = 1.5 points. The weighting of these parameters has been done using a logistic regression model. ResultsIn 48/53 (92%, mean score=16.5±2.0) of the FCM measurements before therapy del(5q) was predictable with the 5-parameter FCM score. In the few FCM inconclusive cases the mutational analysis showed a TP53 mutation. Remarkably, in all 18 cases being in cytogenetic complete remission (CCR) in response to therapy the disappearance of del(5q) by conventional cytogenetic analyses was accompanied by the disappearance of the del(5q) FCM profile (specificity=100%; mean score=13.0±1.0). On the other hand, in patients without CCR during treatment the presence of del(5q) could be predicted by the FCM-score (≥ 15) with a sensitivity of 65% (43/66; mean score=15.5±3.0). Of note, in most of those inconclusive measurements (85%) a mutation of the TP53 gene and/or a deletion of chromosome (17p) could be detected suggesting a modification of the immunophenotype mediated by these molecular changes. Interestingly, the complexity of karyotypic abnormalities appeared to play a minor role in modifying the immunophenotype because in two-thirds of the FCM inconclusive cases del(5q) was present as a single abnormality. ConclusionThe proposed 5-parameter del(5q) FCM profile can serve as a surrogate for the presence of a del(5q) and could therefore be used as a rapid tool for response monitoring during treatment with disease-modifying drugs. The role of TP53 mutations in modifying the FCM-profile in this context should be the purpose of further investigations. Disclosures:No relevant conflicts of interest to declare.

MDR1 Gene Expression Predicts Response and Progression-Free Survival Of Ph+ CML Patients On Second-Line Nilotinib Therapy After Imatinib Failure - 4-Year Follow-Up

IntroductionThe activity of the drug efflux transporter protein MDR1 reduces the intracellular concentration of nilotinib and thereby impairs its efficacy. Nilotinib has been shown to be efficacious in imatinib-resistant patients. In the face of competing second-generation tyrosine-kinase inhibitors (TKI), early identification of favorable responders is crucially important. We have reported the unexpected positive prognostic impact of high MDR1 gene expression at time of imatinib resistance for subsequent 2nd line nilotinib treatment. Here, we present (i) a 48-month follow-up of our clinical data and (ii) additional functional analyses studied in an established in vitro, transposon-based vector system with stable siRNA mediated knockdown of MDR1. AimWe sought to assess (i) whether high MDR1 expression remains associated with improved cumulative rates of major molecular remission (MMR), complete cytogenetic remission (CCyR) and patients' outcome (progression-free survival, PFS) after 48 months and (ii) the impact of MDR1 expression on nilotinib in vitro sensitivity. Methods(i) We analyzed 83 patients resistant to imatinib frontline treatment in chronic phase CML treated with nilotinib 400 mg bid within the CAMN107A2101 trial. MDR1 and BCR-ABL mRNA expression levels were determined by qRT-PCR using LightCycler™ technology, normalized against beta-glucuronidase (GUS) and standardized according to the international scale (IS). Log-rank tests were performed to compare PFS and the cumulative incidences (CI) of MMR and CCyR at 48 months. (ii) MDR1high overexpressing (K562-DoxH1) and MDR1low knockdown (K562-DoxMM) cell lines were used for in vitro testing (Rumpold et al., Exp Hematol 2005). Results(i) (a) At 24 and 48 months, patients with MDR1/GUS ratios ≥2.0 attained MMR in 39% and 41%, CCyR in 58% (at both time points), and PFS rates of 75% and 67%, whereas patients with initial MDR1/GUS ratios <2.0 had significantly worse response and PFS rates, i.e. MMR in 13% and 16% (p=0.014), CCyR in 35% and 39% (p=0.044), and PFS of 50% and 46% (p=0.032). (b) BCR-ABL tumor burden prior to nilotinib revealed a significant impact on molecular response rates. BCR-ABLIS <28% separated best concerning cumulative incidences of MMR by 24 and 48 months (41% vs 21% and 48% vs 21%, p=0.009). (c) Nilotinib in vitro sensitivity of BCR-ABL kinase domain mutations at time of imatinib resistance was associated with improved PFS under nilotinib therapy: patients without any mutation showed PFS rates of 71% and 63% at 24 and 48 months, whereas those with either sensitive mutations, intermediately sensitive mutations or mutations with unknown IC50attained PFS rates of 67% and 61%; patients with mutations resistant to nilotinib achieved PFS rates of 23% at both time points (p=0.01). (ii) Even though MDR1high K562 cells are less sensitive than MDR1low expressing cells, nilotinib (applying doses from 0.01 µM up to 0.5 µM) was still able to significantly impede proliferation of both MDR1high and MDR1low, whereas imatinib-mediated growth inhibition was only seen in MDR1low, but not in MDR1highcells. Conclusion(i) At the time of imatinib-resistance, a high MDR1 gene expression predicts favorable MMR, CCyR, and PFS on consecutive 2nd line nilotinib treatment. As shown earlier, single nucleotide polymorphisms (SNPs) within MDR1 (1236CT/TT and 2677GT/TT) were significantly associated with higher MDR1 expression. (Agrawal et al., ASH 2010) (ii) Our functional data support our clinical observation that nilotinib remains efficacious in MDR1 overexpressing cells, whereas even dose-escalated imatinib does not reverse resistance. High MDR1 gene expression might select patients whose mode of resistance is essentially determined by increased efflux activity of MDR1 and not by other pathways of resistance that cannot be overcome by nilotinib. Altogether, our data might be used for the clinical risk stratification in case of imatinib resistance before switching to nilotinib and are undergoing prospective validation within the ENEST1st study. Disclosures:Saussele:Novartis: Honoraria, Research Funding, Travel Other; BMS: Honoraria, Research Funding, Travel, Travel Other; Pfizer: Honoraria. Purkayasatha:Novartis: Employment. Woodman:Novartis: Employment. Hehlmann:BMS: Consultancy, Research Funding; Novartis: Research Funding. Hochhaus:Novartis: Consultancy, Honoraria, Research Funding, Travel Other; BMS: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria; Ariad: Consultancy, Honoraria. Müller:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Ariad: Consultancy, Honoraria, Research Funding.