Sproat, Lisa

Background Venetoclax + hypomethylating agent (Ven-HMA) therapy has demonstrated improved outcomes in elderly/unfit patients with newly-diagnosed acute myeloid leukemia (ND-AML) (N Engl J Med 2020;383). However, ~50% of patients who respond to Ven-HMA, eventually relapse (Am J Hematol 2024;99). In the current study we examined the prognostic contribution of gene mutations, karyotype, measurable residual disease (MRD) status and clinical risk factors for relapse in patients with ND-AML treated with Ven-HMA therapy. Methods Our study population of ND-AML was retrospectively recruited from Mayo Clinic (MN, AZ, FL), after institutional review board approval and based on documentation of complete remission with/without count recovery (CR/CRi) following Ven-HMA therapy. Relapse-free survival was determined from the time of remission to relapse or last follow-up. Survival analysis was censored for transplant. The 2022 European LeukemiaNet (ELN) criteria was used to assign cytogenetic risk and classify treatment response (Blood 2022;140). Standard statistical analyses were performed using JMP Pro (Version 17.0.0). Results 247 ND-AML patients treated with Ven-HMA (median age 73 years, 62% male, 64% de novo) who achieved CR (n=153), or CRi (n=94) were included. MRD by multiparameter flow cytometry (sensitivity 0.01%) performed at the time of CR/CRi, was negative in 117 (70%) of 166 informative cases. ELN cytogenetic risk categories at diagnosis included favorable 2%, intermediate 69%, or adverse 29%. Mutations involved TET2 21%, SRSF2 21%, TP53 19%, ASXL1 18%, DNMT3A 18%, NPM1 17%, IDH2 15%, RUNX1 15%, K/NRAS 12%, IDH1 8%, FLT3-ITD 7%, and DDX41 in 6% of informative cases. Relapse was documented in a total of 99 (40%) patients who achieved CR (39%) or CRi (41%) after a median remission duration of 6 months (1-31). Patients that relapsed within the first-year vs those that did not, were more likely to be males (75% vs 55%), MRD positive (44% vs 24%), and harbor TP53 mutations (23% vs 16%). Univariate analysis for RFS identified male gender (12 vs 29 months; p=0.02), secondary AML (10 vs 21 months; p<0.01), adverse karyotype (9 vs 22 months; p<0.01), TP53 mutations (6 vs 18 months, p<0.01) and MRD positive remission (13 months vs not reached; p<0.01) as risk factors for relapse; on the other hand, IDH2 mutations (not reached vs 15 months; p<0.01) were associated with a lower risk of relapse. Multivariable analysis confirmed male gender (HR 2.2), TP53 mutations (HR 3.0) and MRD positive remission (HR 1.7) as unfavorable predictors of relapse. Subsequently, in a three-tiered relapse prediction model, RFS was significantly inferior in the presence of three risk factors (male gender, TP53 mutations, MRD positive remission) (n=10, median 4 months), vs two (n=34, median 10 months) vs ≤ 1 risk factor (n=122, median 31 months) (p<0.01); 1-year cumulative incidence of relapse was 100%, 56%, and 26% in the presence of three, two and ≤ 1 risk factors, respectively. 50 of 99 (65%) patients received salvage therapy which included cladribine-cytarabine-Ven (n=19), intensive induction chemotherapy (n=9), FLT3 inhibitors (n=5), Ven-HMA-FLT3 inhibitor (n=1), IDH1/2 inhibitors (n=5), glasdegib-cytarabine (n=4), gemtuzumab (n=3), lenalidomide (n=1), or investigational therapies (n=3); in addition, Ven-HMA was resumed in 14 patients in whom treatment had been discontinued for a median of 5 months (2-12). Overall, 20 (31%) of patients achieved second CR/CRi and response rates were similar with intensive vs less intensive therapy (CR/CRi; 44% vs 29%; p=0.37). Median follow up after relapse was 3.4 months (1-66), during which 73 (74%) deaths, and 4 (5%) ASCT were recorded. Median transplant-censored survival was 4.2 months (1-year; 22%), and inferior in patients with adverse karyotype (median 4.6 vs 3.4 months; p=0.02), and TP53 mutations (3.6 vs 4.4; p=0.11); on the other hand, male gender (3.5 vs 6.8 months; p=0.51), MRD positive remission (4.6 vs 4.2; p=0.56), and IDH2 mutations (6.7 vs 4.2; p=0.28), did not influence post-relapse survival. Conclusions The current study identifies male gender, TP53 mutations, and MRD status as powerful predictors of relapse and proposes a relapse prediction model for ND-AML patients receiving Ven-HMA therapy. Furthermore, relapse following Ven-HMA was associated with uniformly poor outcomes, regardless of salvage treatment strategy.

Background TP53-mutant (mt) myelodysplastic syndromes (MDS) are high-risk (HR) neoplasms, with high rates of AML progression and suboptimal response to hypomethylating agents (HMA). Given the lack of effective therapies for HR-MDS, azacitidine (AZA) was combined with venetoclax (VEN) in a phase Ib MDS study demonstrating safety and early efficacy (Garcia et al. ASH abstract 2023). We retrospectively sought to explore clinical outcomes comparing VEN + HMA, to HMA alone in TP53mt HR-MDS. Methods Among 221 TP53mt MDS pts treated at the Mayo Clinic between January 2007 and April 2024, we reviewed outcomes of pts who received HMA alone (n=98) or HMA+VEN combination (n=34) as their first-line chemotherapy regimen. MDS diagnosis was based on the 5th edition of WHO classification of hematolymphoid tumors (Khoury et al. Leukemia 2022). Responses were assessed according to the International Working Group 2006, MDS response criteria (Cheson et al Blood 2006). Results Baseline characteristics and response The median age (years [yrs]) was 65 (R,37-80) and 70 (range [R], 19-87) yrs in the HMA + VEN and HMA alone groups (gps) (p= 0.42), respectively. The median bone marrow (BM) blast % (9.5 [R, 0-18] vs 5 [R, 0-16], p= 0.01) and TP53 variant allele frequency (VAF) (42 [R, 6-96] vs 37 [R, 2-94], p= 0.03) were significantly higher in HMA + VEN compared to HMA gps, respectively. However, proportion of pts with biallelic (BA)/multihitTP53mt (85% vs 79%, p= 0.61) and complex cytogenetics (CG) (85% vs 81%, p= 0.85) were not different between HMA + VEN and HMA alone gps. The distribution of pts with frequently occurring myeloid co-mutations (ASXL1, TET2, DNMT3A, RAS, BCOR and splicing factor) were not significantly (NS) different between the two gps. IPSS-M scores were assessed in 108 (83%) pts; HR/very HR-MDS as per IPSS-M were NS different between HMA + VEN and HMA gps (100% vs 91%, p= 0.12). While the overall response rate (ORR) (76% vs 49%, p= 0.01) and marrow complete remission (mCR) rates (21% vs 7%, p= 0.05) were higher with HMA+VEN compared to HMA, CR rates were similar (17% vs 12%, p= 0.47). Higher proportion of pts were bridged to allogeneic stem cell transplantation (allo-HCT) (41% vs 20%, p= 0.02), while AML progression rates (29% vs 31%, p= >0.99) were comparable between HMA + VEN and HMA gps, respectively. The non-relapse mortality (NRM) at day 60 (3% vs 3%, p=0.96) and day 90 (3% vs 4%, p=0.75) were comparable between HMA + VEN and HMA gps, respectively. RFS and OS The median follow-up from the time of initiation of HMA or HMA + VEN was 9.7 months (mo) (R, 0.3-90.6). The median RFS (8.47 vs 9.90 mo, p= 0.83) and OS (16.33 vs 14.20 mo, p= 0.66) from the time of initiation of therapy were comparable between the two gps. Similarly, among transplanted pts, there was no OS difference between HMA (21.7 mo) and HMA + VEN (18.43 mo) gps, respectively (p= 0.72). Comparable results for OS and RFS were obtained in both gps after censoring pts at the time of allo-HCT. Multivariable analysis for RFS and OS We conducted multivariable analysis (MVA) for RFS and OS using baseline variables that were significant/ trended towards significance (p<0.1), on univariate analysis (UVA) censored at the time of allo-HCT. Achieving ORR (HR; 0.30, 95% CI: 0.14-0.62, p= 0.001) retained significance for better RFS in MVA. Interestingly CR (HR; 1.74, 95% CI; 0.63-4.77, p= 0.28), BA TP53mt (HR; 1.27, 95% CI; 0.13-11.72, p= 0.83) and complex CG (HR; 1.52, 95% CI 0.16-14.03, p= 0.70) did not retain significance for RFS in MVA. In MVA for OS, achievement of ORR (HR; 0.56, 95% CI; 0.30-1.05, p=0.07) and CR (HR; 0.32, 95% CI; 0.09-1.11, p=0.071) trended towards favorable OS. BA TP53mt status (p= 0.42) and complex CG (p= 0.19) did not significantly impact OS in UVA. Conclusion We conclude that while HMA+VEN combination therapy in comparison to HMA monotherapy led to improved response rates, with higher percentage of pts being bridged to allo-HCT, this was not associated with reduced risk of AML transformation, or improved RFS/OS. We eagerly await results from the prospective randomized trial of VEN + AZA in treatment-naïve HR-MDS (VERONA).

Abstract Venetoclax + hypomethylating agent (Ven‐HMA) is currently the standard frontline therapy for older/unfit patients with newly diagnosed acute myeloid leukemia (ND‐AML). Our objective in the current retrospective study of 301 adult patients (median age 73 years; 62% de novo) with ND‐AML was to identify molecular predictors of treatment response to Ven‐HMA and survival; European LeukemiaNet (ELN) genetic risk assignment was favorable 15%, intermediate 16%, and adverse 69%. Complete remission, with (CR) or without (CRi), count recovery, was documented in 182 (60%) patients. In multivariable analysis, inclusive of mutations only, “favorable” predictors of CR/CRi were NPM1 (86% vs. 56%), IDH2 (80% vs. 58%), and DDX41 (100% vs. 58%) and “unfavorable” TP53 (40% vs. 67%), FLT3‐ ITD (36% vs. 63%), and RUNX1 (44% vs. 64%) mutations; significance was sustained for each mutation after adjustment for age, karyotype, and therapy‐related qualification. CR/CRi rates ranged from 36%, in the presence of unfavorable and absence of favorable mutation, to 91%, in the presence of favorable and absence of unfavorable mutation. At median follow‐up of 8.5 months, 174 deaths and 41 allogeneic stem cell transplants (ASCT) were recorded. In multivariable analysis, risk factors for inferior survival included failure to achieve CR/CRi (HR 3.4, 95% CI 2.5–4.8), adverse karyotype (1.6, 1.1–2.6), TP53 mutation (1.6, 1.0–2.4), and absence of IDH2 mutation (2.2, 1.0–4.7); these risk factors were subsequently applied to construct an HR‐weighted risk model that performed better than the ELN genetic risk model (AIC 1661 vs. 1750): low ( n = 130; median survival 28.9 months), intermediate ( n = 105; median 9.6 months), and high ( n = 66; median 3.1 months; p < .001); survival in each risk category was significantly upgraded by ASCT. The current study identifies genotype signatures for predicting response and proposes a 3‐tiered, CR/CRi‐based, and genetics‐enhanced survival model for AML patients receiving upfront therapy with Ven‐HMA.

Background: Venetoclax (Ven) in combination with hypomethylating agent (HMA) is the preferred treatment for elderly/unfit patients with newly-diagnosed acute myeloid leukemia (AML). Current prognostication for AML is based on European LeukemiaNet (ELN) genetic risk stratification which has limited applicability in patients treated with Ven-HMA ( Blood, 2022). Accordingly, our primary objective was to determine predictors of treatment response and survival outcomes in treatment-naïve AML patients receiving Ven-HMA. Methods: Our study population was recruited from Mayo Clinic (MN, FL, AZ), after institutional review board approval and based on documentation of newly-diagnosed AML treated with Ven-HMA outside of clinical trials between November 2018 and April 2023. Cytogenetic and molecular studies were performed by conventional karyotype, and next-generation sequencing, respectively. Response was assessed according to the 2022 ELN criteria Results: Patient characteristics A total of 301 newly-diagnosed AML patients (median age 73 years, 66% male, 62% de novo) received a median of 3 cycles (range 1-48) of azacitidine 75 mg/m2 days 1-7 ( n=100) or decitabine 20 mg/m2 days 1-5 ( n=201) with Ven. ELN 2022 cytogenetic risk included favorable (1%, n=4), intermediate (61%, n=184) or adverse (38%, n=113). Mutations involved TP53 in 77/301 (25%), ASXL1 in 54/279 (19%), RUNX1 in 54/296 (18%), NPM1 in 44/299 (15%), DNMT3A in 40/296 (13%), K/NRAS in 41/296 (14%), IDH1 in 20/301 (6%), IDH2 in 30/301 (10%), FLT3-ITD in 25/301 (8%) and DDX41 in 9/247 (4%) of informative cases. Predictors of response Complete remission, with (CR) or without (CRi), count recovery, was documented in 182 (60%) patients, including CR in 36% and measurable residual disease (MRD) negative by flow cytometry in 77% of 105 informative cases that achieved CR/CRi. Median time to CR/CRi was 1.4 months. In univariate analysis, CR/CRi was more likely to occur in the presence of NPM1 mutation, (86% vs. 56%; p &lt; .01), IDH2 mutation, (80% vs. 58%; p = .02), DNMT3A mutation, (78% vs. 57%; p = .01), or DDX41 mutation, (100% vs. 58%; p &lt;.01), and in the absence of adverse karyotype, (71% vs. 42%; p &lt; .01), TP53 mutation, (67% vs. 40%; p &lt;.01), FLT3-ITD mutation, (63% vs. 36%; p = .01), or RUNX1 mutation, (64% vs. 44%; p = .01); in multivariable analysis, adverse karyotype, ( p &lt; .01), FLT3-ITD ( p &lt; .01), RUNX1 ( p &lt; .01), NPM1 ( p = .03), IDH2 ( p = .04), and DDX41, ( p = .01) mutations remained significant. Predictors of survival After a median follow-up of 8.5 months (range 0.5-56), 13.2 months for living patients, 174 (58%) deaths, 73 relapses (40% of those achieving CR/CRi), and 41 (14%; including 35 in CR/CRi) allogeneic hematopoietic stem cell tranplants (AHSCT) were documented. In univariate analysis of pre-treatment variables, thrombocytopenia &lt; 100 x 10 9/l, (HR 1.5, 95% CI 1.03-2.2; p = .03), adverse karyotype, (HR 2.8, 95% CI 2.1-3.8; p &lt; .01) TP53 mutation, (HR 2.5, 95% CI 1.8-3.5; p &lt; .01), or absence of IDH2 mutation, (HR 3.5, 95% CI 1.7-7.6; p &lt; .01) predicted inferior survival. Failure to achieve CR/CRi (HR 4.5, 95% CI 3.3-6.1; p &lt; .01) was also associated with inferior survival and in multivariable analysis, failure to achieve CR/CRi, (HR 3.4, 95% CI 2.5-4.8; p&lt; .01), presence of adverse karyotype, (HR 1.6, 95% CI 1.1-2.6; p = .02), TP53 mutation, (HR 1.6, 95% CI 1.002-2.4; p = .04), and absence of IDH2 mutation (HR 2.2, 95% CI 1.004-4.7; p = .04) were identified as risk factors for survival. Subsequent HR-weighted scoring resulted in three-tiered risk stratification: low (0-1 point; n= 130), intermediate (2-3 points; n= 105), and high (4-5 points; n= 66), with respective median survival (3-year rate) of 28.9 (48%), 9.6 (6%), and 3.1 (0%) months ( p &lt; .01) (Figure). AHSCT had an independent favorable impact on survival (HR 0.3, 95% CI 0.1-0.6; p &lt; .01), most apparent in low ( p =0.04), and intermediate ( p &lt;.01), as opposed to high ( p = .06) risk. Conclusions: In the current single institutional series of Ven-HMA treated newly-diagnosed AML, response to Ven-HMA was the foremost predictor of survival. Additional risk factors for survival included adverse karyotype, presence of TP53 and absence of IDH2 mutations. These observations allowed for a three-tiered genetics-enhanced survival model with CR/CRi as a backbone, and also confirmed survival advantage from AHSCT, regardless of risk category.

Introduction Atrial fibrillation/flutter (Afib) contributes independently to the hematopoietic cell transplant comorbidity index (HCTCI) and is a known complication of allogeneic hematopoietic transplantation (AlloHCT) which has been linked to inferior outcomes, particularly in older patients. An electrocardiogram (ECG)-based artificial intelligence (AI) algorithm to predict Afib and cardiac contractile dysfunction risk has been validated (Lancet 394:861, 2019). We hypothesized that assessment of pre-transplant Afib risk using the AI algorithm may predict future development of Afib and help identify patients at higher risk for this complication. Methods 191 consecutive MDS patients undergoing AlloHCT with curative intent using myeloablative (28.3%) or reduced intensity conditioning (62.3%) in the Mayo Clinic Comprehensive Cancer Center (Rochester, Jacksonville, Phoenix) between November 2015 and January 2022 were included in this retrospective analysis. Primary outcome was Afib within 100 days and 365 days of transplantation, and we also assessed the outcomes of Death and Relapse. Revised IPSS (IPSS-R) and HCTCI scores were included for all patients. Elevated Afib risk score using the AI algorithm was calculated from pre-transplant ECG, performed during vital organ testing at AlloHCT clearance. In addition to left ventricular (LV) ejection fraction (EF) we evaluated detailed echocardiographic (Echo) parameters including LV volume and mass indices, left atrial volume index (LAVI), maximum trans mitral flow velocities during LV filling (E velocity) and during the diastolic phase due to atrial contraction (A velocity), the velocity of the annulus away from the apex during the protodiastolic phase (e' velocity), E/A and E/e' ratios, the presence of valvular disease, and right ventricular systolic pressure (RVSP). We performed an analysis using a Cox proportional hazards regression models (adjusting for age and sex) to evaluate associations with Afib risk, Relapse, and Overall Survival. Results The median age was 64 years (18-75), 58.6% were male, 6.9% non-white race, and 3.7% Hispanic/Latino ethnicity. Most patients had an HCTCI score of 0-3 (76.3%). GVHD prophylaxis was predominantly with calcineurin inhibitor-based regimes plus/minus methotrexate or mycophenolate mofetil (83.8%). 5.2% of patients had a history of Afib before transplant. Non-relapse mortality was 7.9% at 100 days, and 18.3% at 365 days. N=25 patients (13.1%) developed Afib within 100 days, and n=28 (14.7%) within 1-year after AlloHCT. On multivariable analysis, Age [Hazard Ratio (HR) 2.83, 95% Confidence Interval (CI) 1.36-5.89, p=0.0055] and Echo parameters [including LAVI (HR 2.10, CI 1.23-3.58, p=0.0067), E velocity (HR 3.28, CI 1.29-8.80, p=0.013), E/A ratio (HR 3.74, CI 1.75-7.97, p=0.0006), E/e ' ratio (HR 1.81, CI 1.07-3.07, p=0.026) and RVSP (HR 1.68, CI 1.04-2.70, p=0.032)] were significantly associated with Afib risk; elevated AI risk score was significant in the univariate model (HR 2.74, CI 1.15-6.53, p=0.023) but was borderline in the multivariate model (HR 2.34, CI 0.98-5.60, p=0.056) ( Table 1). Based on previous observations we evaluated the association of AI and Echo parameters with Relapse and Death after AlloHCT ( Table 1). Age (HR 1.32, CI 1.01-1.71, p=0.041) and IPSS-R (HR 1.20, CI 1.08-1.33, p=0.0009) were significantly associated with Death after AlloHCT, while HCTCI (HR 1.10, CI 1.00-1.22, p=0.052) and higher LV EF (HR 0.63, CI 0.38-1.06, p=0.084) were borderline. For Relapse, only IPSS-R (HR 1.52, CI 1.31-1.75, p=1.22E-08) was significant, while increase Echo E velocity was of borderline significance (HR 0.45, CI 0.20-1.02, p=0.057). Conclusions Afib is a common post-AlloHCT complication and is more frequent with increasing Age. Echo parameters (specifically E/A ratio) predict significantly higher Afib risk, while the baseline ECG AI algorithm was of borderline significance. The selection of patients with lower HCTCI scores, and the low background prevalence of Afib in this cohort (i.e., selection of patients with lower baseline cardiac morbidity) are possible explanations for non-significance of the AI algorithm. As anticipated Age and IPSS-R are the greatest predictors of Death after AlloHCT, although the suggestion of an association with baseline Echo parameters highlights the importance of identifying those who may benefit from preemptive Cardiology intervention.

AbstractBackgroundMyeloid neoplasms (myelodysplastic syndrome [MDS], myelofibrosis, and chronic myelomonocytic [CMML]) are aggressive hematological malignancies for which, despite recent approvals, novel therapies are needed to improve clinical outcomes. The hedgehog (HH) pathway is one of the main pathways for cancer stem cells survival and several HH inhibitors (HHi) are approved in clinical practice.MethodsSonidegib (SON), an oral HHi, was tested in this phase 1/1b trial in combination with azacitidine (AZA, 75 mg/m2 days ×7) in patients with newly diagnosed and relapsed/refractory (r/r) chronic MN or acute myeloid leukemia (AML).ResultsSixty‐two patients (28 [45%] newly diagnosed) were treated in this study, including 10 patients in the dose‐finding component and 52 patients in phase 1b. SON 200 mg oral daily on days 1–28 each cycle was deemed the recommended dose for phase 1b. Out of 21 rrAML patients, two achieved response (one complete response/one morphologic leukemia‐free state) with no responses seen in seven r/r MDS/CMML patients. In newly diagnosed AML/MDS, response was seen in six (three had complete remission, two had morphological leukemia‐free status) of 27 patients. Median overall survival was 26.4 and 4.7 months for newly diagnosed MDS and AML, respectively. Safety was satisfactory with common (>20%) side effects including fatigue, constipation, nausea, cough, insomnia, and diarrhea. Only 7% of patients died in the study, and none of the deaths were deemed related to treatment.ConclusionsOur study shows that AZA + SON are a safe combination in a patient with MN. Similar to other hedgehog inhibitors, this combination yielded limited response rate in patients with myeloid neoplasms.

Abstract DDX41 mutations (germline and somatic) are associated with late onset myelodysplastic syndromes/acute myeloid leukemia (MDS/AML). Myeloid neoplasms (MN) with germline predisposition was identified as a distinct category in the 2016 WHO classification revision, including MN with germline DDX41 mutation. We retrospectively analyzed the molecular findings and clinical characteristics of thirty-three DDX41-mutated (mDDX41) patients at our institution. We identified 14 distinct pathogenic DDX41 variants in 32 patients and 8 DDX41 variants of unknown significance (VUS) in 9 patients. Five (16%) patients had a second DDX41 somatic mutation p.R525H and 13 (40%) had at least one additional oncogenic co-mutation in other genes. The median age at the time of diagnosis was 66 years, with male predominance (72%) and the majority of patients had normal cytogenetics (91%). Two-year overall survival (OS) was 86% and 6 (21%) MDS/AML patients with relatively preserved hematopoietic function were observed without further intervention. In comparison to AML patients with prognostically more favorable subtypes [t(8;21), n=27 and inv(16), n=40], mDDX41 patients in our cohort showed similarly favorable OS. Our study highlights that mDDX41-MN patients often have an indolent course and mDDX41-AML has comparable OS to favorable-risk AML.

Abstract Background: Adult relapsed/refractory acute lymphoblastic leukemia/lymphoma (rALL) carries a very poor prognosis with limited options for effective salvage therapy. To date, there has been only a single retrospective report on the use of clofarabine in adult rALL demonstrating CR rate of 31% in this setting (Barba P et al. 2012). Aim: To evaluate the efficacy and toxicity of clofarabine based therapy in a relatively large cohort of adult rALL patients. Method: After IRB approval, a retrospective single institution study of all patients (pts) diagnosed with rALL treated with a clofarabine based regimen at Mayo Clinic between 2000 - 2014 was performed. Categorical variables were analyzed using Pearson's chi-squared test while continuous variables were analyzed using the Wilcoxon / Kruskal-Wallis test with P < 0.05 considered statistically significant. Survival estimates were calculated using Kaplan-Meier method and means were compared using log ranks. Results: Presenting features: We identified a total of 22 pts with a diagnosis of rALL who received clofarabine based therapy. 20 patients were evaluable and 2 were excluded (one received clofarabine as salvage for positive MRD and the other as systemic maintenance with CNS directed therapy for an isolated CNS relapse). Among evaluable pts, median age at time of Clofarabine based chemotherapy was 39 years (range 19-65) and 50% were males. Thirteen had B-ALL while 7 had T-ALL. Median leukocyte count was 6 x109 (0.2-28.7), hemoglobin 9.8 g/dL (7-12.9), platelet 65 x109 (12-493), peripheral blood blast 4% (0-88) and bone marrow blasts 80% (0-95) while five pts had extramedullary disease. Median number of prior regimens was 2 (1-7).. 8 (40%) pts were post allogeneic transplant Treatment and Response: 10 pts (50%) received clofarabine monotherapy, 7(35%) clofarabine and cytarabine, and 3 (15%) had clofarabine, etoposide and cyclophosphamide. Overall response rate (CR/CRi + PR) was 35%. Five (25%) achieved CR/CRi, and 2 achieved PR. Among those who achieved CR, 4 out 5 proceeded to further therapy; 2 to allogeneic stem cell transplant and two additional patients received donor lymphocyte infusion (DLI). One pt with PR also proceeded to allogeneic stem cell transplant. In comparative analysis, there were more males 6 (86%) vs 1(14%) in the responding arm (P = 0.014), otherwise the number of regimens prior to clofarabine, type of clofarabine regimen, transplant status, T vs B cell ALL, did not impact response. Median overall survival was 2.4 months (1.3-2.9) in non-responders vs. 12.8 months (3-27.4) in responders (P =0.0007) (Figure 1). All pts who proceeded to transplant or DLI relapsed with a median time to relapse of 6.4 (4.8-13.7) months. Toxicity: Rash/Hand Foot syndrome was observed in 3 pts (19%), Grade III-IV liver toxicity occurred in 4 (26%) with no permanent sequela. Opportunistic infection occurred in 3 pt (17%). Conclusion: Clofarabine based chemotherapy was a well-tolerated salvage regimen in heavily pretreated patients and was an effective bridge to definitive therapy in a significant proportion of cases. Prospective evaluation of these findings is warranted. Figure 1. Figure 1. Disclosures Al-Kali: Celgene: Research Funding.