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Mast cell leukemia (MCL) is the leukemic form of SM with at least 20% mostly immature mast cells on bone marrow aspirate. MCL may develop de novo, in the absence of a prior SM, or it may represent a progression from a previous SM. MCL may be sub-divided into the more frequent, aggressive acute form with signs of organ damage (C-findings) and the chronic form lacking C-findings and presenting a more stable course, although over time, progression to acute MCL is common. The 2022 WHO subtype of MCL with an associated hematological neoplasm was renamed MCL with an associated myeloid neoplasm in the 2022 International Consensus Classification (ICC). The relevance of the distinction between the leukemic and aleukemic forms based on the percentage of circulating mast cells is a matter of debate. The current knowledge on MCL is restricted mainly to single reports or case series with a limited number of larger studies. Our aim is to provide a comprehensive overview of this rare disease in terms of clinical manifestations, morphology, phenotype, molecular characteristics, differential diagnosis, outcome and treatment. A general overview on mastocytosis is also included.

Decitabine, a DNA hypomethylating agent, was approved for use in adults with acute myeloid leukemia (AML) not eligible for standard chemotherapy and is now widely accepted as standard treatment. Although a number of clinical trials demonstrated its benefits in elderly AML patients, older adults and patients with frequent comorbidities are typically under-represented in such settings. Thus, the aim of the present study is to evaluate, in a real-world setting, the effectiveness and toxicity of decitabine administered as a single agent in unselected previously untreated elderly AML patients not eligible for intensive chemotherapy. In nine hematological departments of the Apulian Hematological Network (REP), we enrolled 199 patients (median age: 75.4 years; range: 61–91) with de novo (n = 94) or secondary/therapy-related (n = 105) AML treated with decitabine 20 mg/m2 for five days every 4 weeks. Hazard ratios (HR) and their 95% confidence intervals (CI) were estimated using multivariate Cox regression. The average number of cycles administered per patient was 6.3 (SD: 6.0; median: 5 cycles). Complete response was achieved by 31 patients (15.6%) and partial response by 57 (28.6%), for a total of 88 responders overall (44.2%). After a median follow-up of 33.6 months, median OS was 8.7 months (95% CI: 7.4–10.3), and the 6-month, 1-year, and 3-year OS rates were 62.7%, 37.0%, and 7.1%, respectively. Mortality was increased in AML patients with ≥3 comorbidities (HR = 2.45; 95% CI: 1.18–5.08) vs. no comorbidities and in those with adverse karyotype (HR = 1.58; 95% CI: 1.05–2.38) vs. favourable or intermediate profile. Infection was the main registered adverse event (46.0%). In conclusion, this REP real-life study demonstrates, after a follow-up of almost 3 years, how decitabine administered to AML patients not suitable for intensive chemotherapy is effective and well tolerated, even in a population of truly elderly patients with frequent comorbidities.

Chronic myeloid leukemia (CML) patients in sustained “deep molecular response” may stop TKI treatment without disease recurrence; however, half of them lose molecular response shortly after TKI withdrawing. Well-defined eligibility criteria to predict a safe discontinuation up-front are still missing. Relapse is probably due to residual quiescent TKI-resistant leukemic stem cells (LSCs) supposedly transcriptionally low/silent and not easily detectable by BCR-ABL1 qRT-PCR. Bone marrow Ph+ CML CD34+/CD38− LSCs were found to specifically co-express CD26 (dipeptidylpeptidase-IV). We explored feasibility of detecting and quantifying CD26+ LSCs by flow cytometry in peripheral blood (PB). Over 400 CML patients (at diagnosis and during/after therapy) entered this cross-sectional study in which CD26 expression was evaluated by a standardized multiparametric flow cytometry analysis on PB CD45+/CD34+/CD38− stem cell population. All 120 CP-CML patients at diagnosis showed measurable PB CD26+ LSCs (median 19.20/μL, range 0.27–698.6). PB CD26+ LSCs were also detectable in 169/236 (71.6%) CP-CML patients in first-line TKI treatment (median 0.014 cells/μL; range 0.0012–0.66) and in 74/112 (66%), additional patients studied on treatment-free remission (TFR) (median 0.015/μL; range 0.006–0.76). Notably, no correlation between BCR-ABL/ABLIS ratio and number of residual LSCs was found both in patients on or off TKIs. This is the first evidence that “circulating” CML LSCs persist in the majority of CML patients in molecular response while on TKI treatment and even after TKI discontinuation. Prospective studies evaluating the dynamics of PB CD26+ LSCs during TKI treatment and the role of a “stem cell response” threshold to achieve and maintain TFR are ongoing.

Therapy with Tyrosine Kinase Inhibitors (TKIs) changed the fate of Philadelphia-positive Chronic Myeloid Leukemia (CML). At present, the therapeutic strategy aims to improve the management of the disease and the quality of life of the patients. In July 2015, we started a prospective multicentric randomized trial with the aim to validate the policy of the intermittent de-escalation treatment and to explore the impact of this strategy on the Quality of Life. To this purpose, CML patients older than 60 years in stable (≥2 years) MR3.0 or MR4.0 molecular response were randomized to receive a FIXED intermittent TKIs regimen (one month ON and one month OFF), as previously published (Russo D, Blood 2013; Russo D, BCJ 2015), versus a PROGRESSIVE intermittent TKIs regimen (one month ON and one month OFF for the 1st year; one month ON and two months OFF for the 2nd year; one month ON and three months OFF from the 3rd year) (OPTkIMA study, ClinicalTrials.gov: NCT02326311). Molecular monitoring was performed according to the 2015 ELN guidelines, every 3 months by RT-PCR on peripheral blood (Baccarani M,Blood 2013). In case of MR3.0 (MMR) loss, checked in two monthly consecutive RT-PCR analysis, patients were planned to exit the study and to resume TKIs daily. This first interim report have been focused on the patients who, by intention to treat, have completed the first year of the study for an historical comparison with the previous INTERIM trial (Russo D, Blood 2013; Russo D, BCJ 2015). During the first year, both the patients randomized in the FIXED and in the PROGRESSIVE arms were given the TKIs treatment one month ON and one month OFF. Up to June 2018, 177 patients have been enrolled by 26 Italian Hematological Centers (first patient randomized in July 2015) and 121/177 patients (68%) completed the first year of OPTkIMA study. The median age was 71 years (range 60-89) and 64% of the patients were belonging to the Sokal intermediate/high risk goup. 96/121 (79%), 14/121 (12%) and 11/121 (9%) patients were receiving imatinib (IMA), nilotinib (NILO) and dasatinib (DAS), at the time of enrollment. Overall, 59/121 (49%) and 62/121 (51%) patients have been randomized in the FIXED and PROGRESSIVE arm, respectively. 41/62 patients (66%) randomly assigned to the PROGRESSIVE arm have entered the second year of therapy. 34/121 patients (28%) went out of the study during the first year. The reasons for protocol discontinuation were: informed consent withdrawn (2 cases), second cancer (4 cases), loss of MR3.0 (28 cases). (Table 1). Among the 28 patients who lost the MMR, 17 and 11 were in MR4.0 and MR3.0, respectively, when they were enrolled into the study. Thus the probability of loosing the MR3.0 while on OPTkIMA was 21,7% at one year (Figure 1). All the 28 patients resumed TKIs continuously and all obtained at least the MR3.0 response, within 6 months and are currently included in the study follow up. The intermittent treatment was well tolerated, with 4 serious adverse events (1 appendicitis, 1 atrial fibrillation, 1 cardiac failure, 1 hip fracture) and 3 adverse events (1 diarrohea, 1 pruritus and 1 fever), none of which have been considered treatement-related. None of the patients experienced the TKI withdrawn syndrome. According to this first interim report, we found that a policy of intermittent TKIs administration in elderly patients is safe and well tolerated. Analysis of patient-reported QoL outcomes is ongoing and will further add information on the overall treatment effectivness of the new PROGRESSIVE intermittent TKI administration. After the 1st year, 28/121 patients (23%) lost MR3.0 and all of them re-gained the major molecular response within 6 months from resumption of continuous treatment. The probability of MR3.0 loss while on OPTkIMA at 1 year was 21,7% and this is quite comparable with the 20% MR3.0 loss observed in the previous INTERIM trial (Russo D, Blood 2013; Russo D, BCJ 2015). Disclosures Efficace: Bristol Meyers Squibb: Consultancy; Seattle Genetics: Consultancy; Lundbeck: Research Funding; TEVA: Research Funding; AMGEN: Research Funding; Incyte: Consultancy; Amgen: Consultancy; TEVA: Consultancy; Orsenix: Consultancy. Abruzzese:Novartis: Consultancy; BMS: Consultancy; Pfizer: Consultancy; Ariad: Consultancy. Bonifacio:Incyte: Consultancy; Pfizer: Consultancy; Amgen: Consultancy; Novartis: Research Funding; Bristol Myers Squibb: Consultancy. Castagnetti:Incyte: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Bristol Meyers Squibb: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Giai:Novartis: Consultancy; Pfizer: Consultancy.

Chronic myeloid leukemia (CML) patients in sustained “deep molecular response” may stop TKI treatment without disease recurrence; however, half of them lose molecular response shortly after TKI withdrawing. Well-defined eligibility criteria to predict a safe discontinuation up-front are still missing. Relapse is probably due to residual quiescent TKI-resistant leukemic stem cells (LSCs) supposedly transcriptionally low/silent and not easily detectable by BCR-ABL1 qRT-PCR. Bone marrow Ph+ CML CD34+/CD38− LSCs were found to specifically co-express CD26 (dipeptidylpeptidase-IV). We explored feasibility of detecting and quantifying CD26+ LSCs by flow cytometry in peripheral blood (PB). Over 400 CML patients (at diagnosis and during/after therapy) entered this cross-sectional study in which CD26 expression was evaluated by a standardized multiparametric flow cytometry analysis on PB CD45+/CD34+/CD38− stem cell population. All 120 CP-CML patients at diagnosis showed measurable PB CD26+ LSCs (median 19.20/μL, range 0.27–698.6). PB CD26+ LSCs were also detectable in 169/236 (71.6%) CP-CML patients in first-line TKI treatment (median 0.014 cells/μL; range 0.0012–0.66) and in 74/112 (66%), additional patients studied on treatment-free remission (TFR) (median 0.015/μL; range 0.006–0.76). Notably, no correlation between BCR-ABL/ABLIS ratio and number of residual LSCs was found both in patients on or off TKIs. This is the first evidence that “circulating” CML LSCs persist in the majority of CML patients in molecular response while on TKI treatment and even after TKI discontinuation. Prospective studies evaluating the dynamics of PB CD26+ LSCs during TKI treatment and the role of a “stem cell response” threshold to achieve and maintain TFR are ongoing.

First-line nilotinib in chronic myeloid leukemia is more effective than imatinib to achieve early and deep molecular responses, despite poor tolerability or failure observed in one-third of patients. The toxicity and efficacy of tyrosine kinase inhibitors might depend on the activity of transmembrane transporters. However, the impact of transporters genes polymorphisms in nilotinib setting is still debated. We investigated the possible correlation between single nucleotide polymorphisms of hOCT1 (rs683369 [c.480C>G]) and ABCB1 (rs1128503 [c.1236C>T], rs2032582 [c.2677G>T/A], rs1045642 [c.3435C>T]) and nilotinib efficacy and toxicity in a cohort of 78 patients affected by chronic myeloid leukemia in the context of current clinical practice. The early molecular response was achieved by 81% of patients while 64% of them attained deep molecular response (median time, 26 months). The 36-month event-free survival was 86%, whereas 58% of patients experienced toxicities. Interestingly, hOCT1 and ABCB1 polymorphisms alone or in combination did not influence event-free survival or the adverse events rate. Therefore, in contrast to data obtained in patients treated with imatinib, hOCT1 and ABCB1 polymorphisms do not impact on nilotinib efficacy or toxicity. This could be relevant in the choice of the first-line therapy: patients with polymorphisms that negatively condition imatinib efficacy might thus receive nilotinib as first-line therapy.

BACKGROUND: Compared with imatinib, nilotinib is a potent breakpoint cluster region/v-abl Abelson murine leukemia viral oncogene (bcr-abl) kinase inhibitor, and it induces higher rate and rapid complete cytogenetic response (CCyR), yet no clinical data are available regarding its efficacy against chronic myeloid leukemia (CML) stem cells. Earlier studies demonstrated that clusters of differentiation 34–positive, Philadelphia chromosome–positive (CD34+Ph+) cells are detectable in about 45% of patients with CML, despite being on long-term imatinib therapy and having achieved sustained CCyR. METHODS: CD34+ cells from bone marrow of de novo CML patients in the chronic phase (n = 24) treated with nilotinib (median duration of therapy, 22 months) were isolated and scored for BCR-ABL by fluorescent in situ hybridization (FISH) analysis. Similar analysis was also performed in 5 de novo CML chronic phase patients who achieved CCyR within 3 months of nilotinib therapy. RESULTS: FISH evaluation of a median of 100 CD34+ nuclei per patient revealed that only 1 of 20 (5%) evaluable patients showed residual Ph+ progenitor cells. In this patient, just 1 of 140 (0.7%) CD34+ interphase nuclei was found to be positive for BCR-ABL. Surprisingly, no CD34+Ph+ cells were found even in those 5 patients evaluated after 3 months of nilotinib treatment. CONCLUSIONS: This study assessed for the first time the persistence of CD34+Ph+ cells during nilotinib first-line treatment. Preliminary results showed that in patients in CCyR, even after short-term nilotinib therapy, residual leukemic progenitors are very rarely detected compared with imatinib-treated CCyR patients. It is yet to be determined if these findings will have an impact in the path to a cure of CML with tyrosine kinase inhibitors. Cancer 2012. © 2012 American Cancer Society.

// Monica Bocchia 1 , Sara Galimberti 2 , Lara Aprile 1 , Anna Sicuranza 1 , Antonella Gozzini 3 , Francesca Santilli 4 , Elisabetta Abruzzese 5 , Claudia Barate 2 , Barbara Scappini 3 , Giulia Fontanelli 2 , Monika Malgorzata Trawinska 5 , Marzia Defina 1 , Alessandro Gozzetti 1 , Alberto Bosi 3 , Mario Petrini 2 and Luca Puccetti 1 1 Department of Hematology, University of Siena, Azienda Ospedaliera Universitaria Senese, Siena, Italy 2 Department of Clinical and Experimental Medicine, U.O. Hematology, University of Pisa, Pisa, Italy 3 Functional Unit of Hematology, University of Florence, Florence, Italy 4 Department of Medicine and Aging, University of Chieti, Chieti, Italy 5 Hematology Unit, S. Eugenio Hospital, Tor Vergata University, Rome, Italy Correspondence: Monica Bocchia, email: // Keywords : PAOD, TKI, CML, inflammation, atherothrombotic risk Received : March15, 2016 Accepted : July 18, 2016 Published : August 05, 2016 Abstract Several reports described an increased risk of cardiovascular (CV) events, mainly atherothrombotic, in Chronic Myeloid Leukemia (CML) patients receiving nilotinib. However, the underlying mechanism remains elusive. The objective of the current cross-sectional retrospective study is to address a potential correlation between Tyrosine Kinase Inhibitors (TKIs) treatment and CV events. One hundred and 10 chronic phase CML patients in complete cytogenetic response during nilotinib or imatinib, were screened for CV events and evaluated for: traditional CV risk factors, pro/anti-inflammatory biochemical parameters and detrimental ORL1 gene polymorphisms (encoding for altered oxidized LDL receptor-1). Multivariate analysis of the whole cohort showed that the cluster of co-existing nilotinib treatment, dyslipidaemia and G allele of LOX-1 polymorphism was the only significant finding associated with CV events. Furthermore, multivariate analysis according to TKI treatment confirmed IVS4-14 G/G LOX-1 polymorphism as the strongest predictive factor for a higher incidence of CV events in nilotinib patients. Biochemical assessment showed an unbalanced pro-inflammatory cytokines network in nilotinib vs imatinib patients. Surprisingly, pre-existing traditional CV risk factors were not always predictive of CV events. We believe that in nilotinib patients an induced “inflammatory/oxidative status”, together with a genetic pro-atherothrombotic predisposition, may favour the increased incidence of CV events. Prospective studies focused on this issue are ongoing.

Introduction Recently there have been some reports of Peripheral Arterial Occlusive Disease (PAOD) in chronic myeloid leukemia (CML) patients treated with second generation Tyrosine Kinase inhibitor (TKI) nilotinib. PAOD is mainly caused by atherosclerosis, which is a multifactorial disease of the vessels involving lipid accumulation, thrombogenic components, cell death and inflammatory responses in the arterial wall. With the intent to elucidate a potential correlation between TKIs treatment and mechanisms underlining PAOD or other atherotrombotic events, we investigated a previously described (and confirmed in different settings) genetic and biochemical trait associated with vascular events, in a series of CML patients treated in with TKIs. Patients and Methods Seventy-five CML patients referring to three Italian Hematology Centers (Siena, Pisa and Firenze), of which 39 treated with imatinib and 36 with nilotinib (median treatment time 10 years, range 3-13ys and 3 years, range 2-6ys, respectively), all in complete cytogenetic response and with various degree of molecular response, entered the study. During a routine follow-up visit the patients were evaluated for: classical risk factors (Diabetes Mellitus, Dyslipidemia, Arterial Hypertension, Body Mass Index, Cigarette Smoking, Familiarity); sCD40L level and Endogenous Thrombin Potential (ETP) as markers of platelets and coagulation activation; oxidized LDL (oxLDL) level as early stage atherogenesis promoter; IL6, IL10, TNFα cytokines network as indicator of pro/anti-inflammatory balance; 3'UTR polymorphism of OLR1, encoding for the oxidized LDL receptor 1 (LOX-1), as independent genetic predisposition for atherotrombotic events. In addition the patients were screened for PAOD a/o other atherotrombotic episodes. Results The distribution of classical risk factors was homogeneous in the two groups of patients. On the contrary we noted significant differences in several biochemical parameters evaluated (Table 1). Evaluation of events (i.e. PAOD, Acute Coronary Syndrome and Cerebral Ischemia) showed a statistically significant difference in the two groups with 9/36 (25%) atherotrombotic events occurring in the nilotinib group and 3/39 (7.6%) events occurring in the imatinib group (p=0.019). Multivariate analysis showed that the most strictly related factors to the increased risk of events in this series of CML patients were: nilotinib treatment, oxLDL level (O.R.3.8 95% C.I. 1.8-6.9, p< 0.001, β 1.61), IL10 level (O.R.3.3 95% C.I. 1.9-5.1, p< 0.001, β 1.55) and the presence of an intermediate or high risk OLR1 variant allele (O.R.3.1 C.I. 1.6-4.8, p< 0.001, β 1.59). Discussion These preliminary data suggest that an unbalance of pro/anti-inflammatory cytokines network observed in nilotinib treated patients, together with genetic pro-atherothrombotic predisposition conferred by LOX-1, may have a role in the increased incidence of vascular events. The pro-inflammatory condition could be responsible of the pro-atherotrombotic activation, mainly by enhanced lipid peroxidation, as confirmed by altered sCD40L, ETP and oxLDL levels, despite the use of anti-atherothrombotic drugs. The link between pro-inflammatory stimuli and lipid peroxidation is a well established trigger of accelerated atherogenesis in the general population. As such, in a condition of potential increased lipid peroxidation as described in carriers of detrimental SNPs of LOX-1, the enhanced inflammatory milieu observed during nilotinib treatment could be an additional factor of accelerate atherothrombosis. Further studies are needed to both elucidate the mechanism underlining nilotinib-induced pro-inflammatory status and confirm LOX-1 mutations as a useful genetic tool to identify nilotinib-treated patients at potential increased atherothrombotic risk. Disclosures: Galimberti: Novartis and Bristol Mayer Squibb: Honoraria. Gozzini:Novartis and Bristol Mayer Squibb: Honoraria. Baratè:Novartis and Bristol Mayer Squibb: Honoraria. Scappini:Novartis and Bristol Mayer Squibb: Honoraria. Bosi:Novartis and Bristol Mayer Squibb: Honoraria. Petrini:Novartis and Bristol Mayer Squibb: Honoraria. Bocchia:Novartis and Bristol Mayer Squibb: Honoraria.

Introduction: In chronic myeloid leukemia (CML), tyrosine Kinase Inhibitors (TKIs) treatment is a potentially life-time therapy for the majority of patients (pts), as few of them, only after achieving a deep and stable molecular response, may discontinue TKIs without recurrence of disease. Available data suggest that relapse after TKIs discontinuation is due to the persistence of leukemic stem cells (LSCs) intrinsically resistant to TKIs. Survival of CML LSCs may be the consequence of activation of several pathways BCR-ABL1 independent. qRT-PCR, the most sensitive assay to monitor disease status in CML pts, may be inappropriate to quantify residual quiescent CML LSCs that are transcriptionally silent. Therefore, the possibility to easily quantify LSCs during TKIs treatment is a great opportunity to better understand the behavior of residual LSCs and potentially to identify those pts candidates to safely discontinue TKIs. Recently, Valent et al described that CD34+/CD38-/Lin- CML LSCs specifically co-express dipeptidylpeptidase IV (CD26) and that CD26 is a potential biomarker for the quantification and isolation of CML LSCs, in bone marrow samples of CML patients. Furthermore, Culen et al. quantified CD26+ LSCs bone marrow compartment in 31 CML patients at diagnosis and their number appears to correlate with response to TKIs treatment. In the present study we wanted to explore the feasibility, rate and potential implication of detecting CD26+ LSCs in peripheral blood (PB) from CML pts during TKI treatment. Methods: CML pts during first line treatment with any approved TKIs, referring to several Italian Hematology Centers, entered this non interventional cross sectional study after signing a proper informed consent. During a routine follow up visit, in which pts were checked for molecular response by standard PB qRT-PCR BCR-ABL1 analysis, additional 3 mls of PB were collected in EDTA and sent within 24 hours to Siena Hematology Lab to detect CD34+/CD38-/CD26+ LSCs by multicolor flow cytometry. After red blood cells lysis, cells were incubated with anti CD45 (BD Biosciences), CD34 (581), CD38 (HIT2), CD26 (M-A261) (BD Pharmigen). After washing, acquisition and analysis were performed by FACSCanto II (BD Biosciences, NR Nannini) using DIVA 8 software (BD, Biosciences). CD45+ cells acquired for each sample ranged from 500,000 to 1,000,000. Isotype controls were included in each staining. In 5 pts a FISH analysis of PB sorted CML LSCs population was also performed. Results: to validate our assay we first performed a FISH analysis of both PB sorted CD34+/CD38-/CD26+ and CD34+/CD38-/CD26- in 5 CML patients at 3-6 months after starting treatment, confirming Ph+ cells only in the CD26+ fraction. Afterward, we checked for circulating CML LSCs a total of 202 CML pts in first line treatment with TKIs for a median of 39 months (range 1-175). Type of TKI, length of treatment, molecular response and quantification of LSCs are summarized in Table 1. PB CML LSCs were detectable in 146/202 (72.3%) pts with a median number of CD26+ of 0,0165 cells/µL (range 0,0018-0,66). Kendall rank correlation coefficient used to analyze the relation between the measurable variables showed no correlation between BCR-ABL/ABLIS ratio (median 0,004 range 0-61) and number of residual LSCs (r 0.118 p=0.097). In 56/202 (27.7%) pts CD26+ LSCs were undetectable, yet we found no correlation with the concomitant degree of molecular response. Conclusions: this study represents the first attempt to measure in a large cohort of CML patients residual circulating LSCs during TKIs treatment. In our hands PB LSCs flow-cytometry assay appeared feasible, specific and sensitive and thus suitable for routine monitoring. As expected, the majority of CML patients, even in deep molecular response, still harbor residual LSCs and the number of PB CD26+ did not correlate with the number of BCR-ABL1 copies. This evidence suggests that the molecular response refers to transcriptionally active CML progenitor cells and not to quiescent, TKIs resistant, CML LSCs. Prospective studies evaluating the behavior of PB CML LSCs during different TKIs treatment, as well as studies monitoring PB CD26+ in CML pts that discontinued TKIs treatment are ongoing. Our goal is to rule out the impact, if any, of a "stem cell response" in addition to the standard molecular response in the management of CML patients mainly to identify those pts candidates for a safe TKI discontinuation. Disclosures Bocchia: Janssen: Honoraria; Novartis: Honoraria; Bristol-Myers Squibb: Honoraria. Aprile:Novartis: Honoraria. Castagnetti:Pfizer: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; ARIAD Pharmaceuticals: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Tiribelli:Ariad Pharmaceuticals: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Speakers Bureau. Breccia:Novartis: Consultancy, Honoraria; Bristol Myers Squibb: Honoraria; Celgene: Honoraria; Ariad: Honoraria; Pfizer: Honoraria. Rosti:Roche: Honoraria, Research Funding, Speakers Bureau; Incyte: Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau.

A 63-year-old woman with chronic myeloid leukemia (CML) received treatment with interferon (IFN)-α for 6 years. After achieving a complete cytogenetic response that was repetitively documented, IFN-α treatment was stopped. Despite maintenance of a complete cytogenetic response, a progressive rise of the BCR-ABL1 transcript was detected and loss of major molecular response occurred about 2 years after stopping IFN-α therapy. Disease remained at molecular level.Peripheral blood quantitative real-time PCR every 3 months and periodical bone marrow aspirate were performed to monitor disease.Chronic-phase, Philadelphia-positive CML that was still detectable after complete cytogenic response 2 years after cessation of IFN-α therapy.The patient was treated with a target immune approach receiving a therapeutic vaccine that consisted of an immunogenic 25-mer b2a2 breakpoint-derived peptide (CMLb2a2-25) with binding properties for several HLA-DR molecules. After nine boosts of vaccine the patient developed an adequate b2a2-25 peptide-specific CD4(+) T-cell response and BCR-ABL1 transcript started to decline in peripheral blood. No hematological or extrahematological effects were documented during therapy. At the last evaluation, 39 months since vaccinations commenced, the patient is in complete molecular response with an undetectable level of BCR-ABL1 transcript both in peripheral blood and in bone marrow and she continues to receive boosts of vaccine every 3 months as the only treatment.

Abstract 648 Introduction: Imatinib (IM) 400mg daily is the standard treatment for chronic myeloid leukemia (CML) patients and a complete cytogenetic response (CCyR) is achieved in the majority of patients within one year of treatment. In addition, a considerable number of patients reach a major molecular response (i.e BCR-ABL/ABL ratio Results: Current interim analysis shows that vaccinations (a total of over 400 shots) were very well tolerated, with CMLVAX100-GMCSF toxicity consisting exclusively of some redness and itching at the site of injection and with only 4/43 patients (9%) experiencing a mild fever. Regarding immune response induced by vaccination, 29/43 patients (67%) showed a significant in vitro b3a2-peptide-specific CD4+ T cell proliferation. With respect to MRD response, we observed a reduction of at least 50% of pre-vaccine BCR-ABL/ABL values after 6 months of treatment (i.e. after 9 vaccinations) in 22/43 (51%) patients and the reduction was confirmed in 14/29 (48%) patients who reached the 9th month evaluation (i.e. after 10 vaccinations); 14/43(32%) patients had at least one documented undetectable transcript during this time period. In 2/43 patients we observed a significant raise of BCR-ABL transcript level, after 3 and 18 months from starting vaccinations with subsequent loss of CCyR. Conclusions: CMLVAX100 vaccine appears to induce a reduction of long lasting molecular MRD surviving IM in about half of vaccinated CML patients, thus confirming preliminary results. If this BCR-ABL-specific immune control of MRD will have a substantial impact on the rate of BCR-ABL mutations, disease evolution and ultimately survival needs longer observation time to be determined. Disclosures: Baccarani: Novartis Pharma: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Mayer Squibb: Consultancy, Honoraria, Research Funding, Speakers Bureau.