ALBERT

Description: Introduction: Venetoclax (VEN) based therapy has become a standard of care in front line and relapsed-refractory (R/R) CLL based on favorable efficacy and toxicity. Whereas prospective data regarding activity of therapies following ibrutinib (IBR) or idelalisib (IDE) are available in the settings of progression (VEN, non-covalent BTKi) and intolerance (acalabrutinib), how best to manage patients (pts) who discontinue (dc) VEN remains a key unanswered question. With the increased use of VEN in early lines of therapy (LOT; CLL 14, MURANO), the activity of BTK inhibitors (BTKi) and cellular therapies following VEN becomes a critical issue. No prospective study has addressed this question, and currently reported VEN clinical trials have limited information about subsequent treatments. While recent data describe VEN resistance mechanisms (Guieze 2018, Blombery 2019), the impact of VEN resistance on efficacy of post VEN therapies is unknown. To address this gap, we conducted an international study to identify a large cohort of pts who dc VEN and have been subsequently treated. Methods: We conducted an IRB approved multicenter (31 US, EU, South American sites, in partnership with UK CLL Forum and CORE registry), retrospective cohort study of CLL pts who dc VEN for any reason. We examined demographics, dc reasons, responses, survival, adverse events (AEs) and activity of post VEN therapies. Primary endpoints were overall response rate (ORR) and progression free survival (PFS) for the post VEN treatments stratified by treatment type (BTKi, PI3Ki and cellular therapy: CAR-T or alloHSCT). ORR was defined by iwCLL criteria and PFS was defined from VEN dc to disease progression (PD), death, or last follow up for next treatment. Pts were further stratified by BTKi (resistant / intolerant) and PI3Ki exposure prior to VEN. PFS-2 was defined as time from VEN start to tumor progression on IBR or death from any cause. Results: 326 CLL pts who dc VEN in the front line (4%) and R/R settings (96%) were identified. The cohort was 69% male, 87% white, median (med) age 66 (38-91) at VEN start, 27% treated with VEN based combinations (n=88, med 6 cycles anti-CD20 abs). Pre VEN prognostic features: 82% IGHV unmutated (n tested=166), 47% del17p (n=306), 45% TP53 mut (n=217), 39% complex karyotype (n=273), 23% BTK mut (n=79), 18% NOTCH1 mut (n=103), 10% PLCγ2 mut (n=74). Pts received med 3 therapies (0-11) prior to VEN; 40% were BTKi naïve (n=130), 60% were BTKi exposed (196) and 81% were IDE naïve (n=263). Most common reasons for VEN dc were PD (38%), AE (20%), Richter's transformation (RT, 14%), 8% pt preference, and HSCT 5%. Of 326 pts who dc VEN, 188 (58%) were treated with a subsequent LOT, 61 are alive and untreated and 77 died prior to a subsequent LOT. Post VEN sequencing analyses focused on BTKi, PI3Ki and cellular therapy (CAR-T or alloHSCT) activities following VEN dc (Table1). ORR to BTKi was 84% (n=44) vs. 54% (n=30, p

Description: Introduction: Venetoclax (Ven) is approved for relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL) as monotherapy (Ven mono) or in combination (Ven paired) with rituximab based on clinical trials with selected patients (pts) and limited ibrutinib exposure. Whether Ven paired is superior to Ven mono, patterns of care, and outcomes following Ven discontinuation are unknown. Further, better delineation of adverse events (AEs) when Ven is used outside of clinical trials is needed. To address these gaps, we conducted a multicenter, international study in partnership with CLL Collaborative Study of Real World Evidence (CORE) and UK CLL Study Forum examining the clinical experience of 348 Ven treated CLL pts, representing the largest series of Ven treated pts reported to date. Methods: We conducted a retrospective cohort analysis of CLL pts treated with Ven across 24 US and 42 UK academic and community centers. We examined demographics, baseline disease characteristics, dosing, AEs, TLS risk and outcomes, response rates, outcomes (overall survival (OS) and progression free survival (PFS)), and tx sequencing. TLS events were defined by Howard criteria. PFS and OS were estimated by the Kaplan Meier method. Comparisons of outcomes used the Log Rank test. Univariate and multivariate analyses were performed with COX regression. All other comparisons were descriptive. Results: Of these 348 CLL pts, 94% were R/R, median age 67 years (range:37-91), 69% male, 85% white, and 73% Rai stage ≥2. 19% received Ven on clinical trial. 79% had Ven mono; Ven was paired most commonly with anti-CD20 (n=51) and ibrutinib (n=10). Pts received a median of 3 tx (range 0-15) before Ven; 78% received ibrutinib, 29% received PI3Ki, 20% had ≥2 prior kinase inhibitors, and 68% had chemoimmunotherapy. Median time from most recent tx to Ven start was 1.1 months (range 0-62). Pre-Ven prognostic markers included 43% del17p, 34% TP53 mutated, 24% del11q, 38% complex karyotype (≥ 3 abnormalities), and 84% IGHV unmutated (Table 1). TLS risk was low in 38%, intermediate in 34% and high in 28%. During ramp up, TLS was observed in 10% (22 lab, 9 clinical TLS events, 3 missing data). Following dose escalation, 70% achieved a stable Ven dose of 400 mg, 33% required ≥ 1 dose interruption and 27% required ≥ 1 dose reduction. AEs included grade 3 neutropenia 39%, grade 3 thrombocytopenia 29%, infections 25%, grade ≥ 2 diarrhea 7.8%, and neutropenic fever 7.7%. AEs were similar whether treated on or off clinical trial. The ORR to Ven mono, Ven paired was 81% (34% CR), 86% (29% CR). With a median follow-up of 14.2 months, median PFS and OS were not reached (12 month PFS 74%, OS 82%). Figure 1 depicts PFS stratified by Ven mono vs. paired, clinical trial vs. clinical practice, del17p status, and complex karyotype. Pts who discontinued Ven due to AEs had better OS compared with those who discontinued due to progression or Richter Transformation (RT) (Median OS 47 vs. 15.1 vs. 8.6 months, respectively). In multivariate analyses, complex karyotype was the only independent predictor of PFS (HR 2.8, p

Description: Background: Solid tumor patients are at a heightened risk for developing therapy-related myeloid neoplasms (tMN). Recent studies show evidence of somatic mutations in leukemia-associated genes in normal healthy individuals, referred to as clonal hematopoiesis (CH). We and others have shown that clonal hematopoiesis (CH) is also frequent in cancer patients. A detailed characterization of the relationship between exposure to specific oncologic regimens, the molecular features of CH presentation and how these relate to tMN risk is warranted to inform treatment decisions, early detection and prevention strategies. Methods: To determine the relationship between CH and oncologic therapy, we performed a systematic interrogation of CH in a cohort of 17,478 solid tumor patients with clinical, outcome and molecular profiling by MSK-IMPACT. MSK-IMPACT is a targeted panel of cancer-associated mutations used to screen tumor samples against a blood control sample. Mutation detection was performed on blood derived sequencing data (median coverage at 600x) using the matched tumor as a comparator and accounted for background sequencing error rates. Results: Overall, 40% of the 17,478 patients were treatment naïve prior to IMPACT testing, 37% had received chemotherapy alone, 17% had received radiation therapy and 18% had received both. CH was identified in 4013 (23%) of patients, median VAF was 4% (range=1-80%). The vast majority (76%) had a single mutation whereas 9% had two and 5% had three or more. The number of mutations correlated with clone size (p-value=

Description: Background: Despite recent advances in the therapeutic armamentarium for AML, outcomes remain dismal for patients (pts) with relapsed/refractory (R/R) AML. Response rates with high dose cytarabine (HiDAC) salvage chemotherapy are approximately 20%. Multiple immune aberrations in AML lead to immune suppression, exhaustion, and senescence. Programmed Death-1 (PD-1), a co-inhibitory receptor (IR) on immune cells, suppresses immune activation and is exploited by leukemic cells to evade immune surveillance. PD-1 and other IRs are up-regulated during disease progression. We hypothesized that pembrolizumab, a monoclonal antibody targeting PD-1, after HiDAC would stimulate a T-cell mediated anti-leukemic immune response. Methods: Eligibility for this study included R/R AML 18-70 years, ECOG PS 0-1 and adequate organ function. Treatment consisted of HiDAC (60 years: 1.5 gm/m2 IV Q12hours days 1-5) followed by pembrolizumab 200 mg IV on day 14. The primary objective of this study was to estimate the overall complete remission (CR + CRi) rate. Secondary objectives included assessment of safety, durability of CR, overall survival (OS) and biomarker correlates of response. Overall responders were eligible to receive maintenance phase pembrolizumab 200 mg IV Q3weeks for up to 2 years until progression. Allogeneic stem cell transplant (alloSCT) was permissible before or after maintenance phase. Results: Thirty-seven pts were enrolled and evaluable (Table 1). Sixteen (43%) pts had refractory disease and 16 (43%) pts had relapsed AML with CR1 duration 3: n=1), AST elevation (32%; Grade 〉3: n=1), fatigue (27%), alkaline phosphatase elevation (24%), and maculopapular rash (19%; Grade 〉3: n=2). Grade 〉3 immune-related adverse events (iRAE) were rare (maculopapular rash: n=2, AST/ALT increase: n=2, right upper quadrant pain with lymphocytic infiltrate in liver: n=1) and self-limiting. Five (14%) pts required steroid administration for grade 2 hyperbilirubinemia (n=1), grade 3 ALT elevation (n=1), grade 3 AST elevation with liver biopsy revealing no evidence of iRAE (n=1), grade 3 bilirubin subsequently deemed to be a delayed hemolytic transfusion reaction (n=1), and grade 3 systolic dysfunction without evidence of myocarditis by endomyocardial biopsy or cardiac MRI (n=1). Sixty-day mortality was 3% (1/37) due to progressive AML. Median time to full neutrophil (〉1x109/L) and platelet (〉100x109/L) recovery was 32 and 31 days, respectively. The overall response (ORR: CR+CRi+PR+MLFS) and composite CR (CR+CRi) rates were 46% [29%,63%] and 38% [22%,55%], respectively, meeting the primary endpoint of the study. Notably, 13/28 (46%) pts receiving HiDAC + pembrolizumab as their first salvage regimen achieved CR/CRi. Two pts refractory to HiDAC (administered within past 6 months) achieved CR including one pt who was refractory to HiDAC salvage 1 month prior to enrollment and ultimately achieved CR without evidence of minimal residual disease. Nine (24%) pts received an alloSCT. There were no instances of Grade 〉3 acute GVHD or veno-occlusive disease post-alloSCT. Nine (24%) pts received maintenance phase pembrolizumab (median # of cycles = 3; range: 1-12) for CR (n=8) or PR (n=1). Seven out of 9 pts relapsed/progressed after maintenance phase. Median follow-up among survivors, and median OS, event-free survival and disease-free survival was 7.8 months, 8.9 months [6.0,13.1], 6.9 months [4.2,11.5], and 5.7 months [1.9,7.3], respectively. Conclusions: Pembrolizumab can be safely administered after HiDAC salvage in R/R AML. Severe iRAE's were uncommon despite administration after cytotoxic chemotherapy. The addition of pembrolizumab to HiDAC led to an encouraging overall CR rate meeting the primary endpoint of the study. Immunogenomic biomarker analyses consisting of B cell receptor amplicon sequencing, RNA-seq of blasts and CD8+ T cells, CD8+ T cell receptor repertoire, whole exome sequencing and flow cytometry analyses are ongoing to determine predictors of response. These results warrant further investigation of IR blockade and other immunomodulatory therapeutic strategies after intensive cytotoxic chemotherapy in AML. Disclosures Zeidner: Takeda: Research Funding; Merck: Research Funding; AsystBio Laboratories: Consultancy; Pfizer: Honoraria; Tolero: Honoraria, Research Funding; Daiichi Sankyo: Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Agios: Honoraria; AbbVie: Honoraria. Vincent:Pharmacyclics: Research Funding; Merck: Research Funding. Foster:Bellicum Pharmaceuticals: Research Funding; Macrogenics: Research Funding; Celgene: Research Funding; Daiichi Sankyo: Consultancy. Coombs:Dedham Group: Consultancy; Covance: Consultancy; Cowen & Co.: Consultancy; Octopharma: Honoraria; H3 Biomedicine: Honoraria; Loxo: Honoraria; Pharmacyclics: Honoraria; Medscape: Honoraria. Webster:Pfizer: Consultancy; Amgen: Consultancy; Genentech: Research Funding. DeZern:Astex Pharmaceuticals, Inc.: Consultancy; Celgene: Consultancy. Smith:Jazz: Consultancy; Pfizer: Consultancy; Novartis: Consultancy; Agios: Consultancy. Levis:Amgen: Consultancy, Honoraria; Astellas: Consultancy, Research Funding; FUJIFILM: Consultancy, Research Funding; Menarini: Consultancy, Honoraria; Novartis: Consultancy, Research Funding; Daiichi Sankyo Inc: Consultancy, Honoraria; Agios: Consultancy, Honoraria. Luznik:Merck: Research Funding, Speakers Bureau; Genentech: Research Funding; AbbVie: Consultancy; WindMiL Therapeutics: Patents & Royalties: Patent holder. Serody:Merck: Research Funding; GlaxoSmithKline: Research Funding. Gojo:Amphivena: Research Funding; Amgen Inc: Consultancy, Honoraria, Research Funding; Juno: Research Funding; Merck: Research Funding; Jazz: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria. OffLabel Disclosure: Pembrolizumab is investigational for AML.

Description: The incidence of chronic lymphocytic leukemia (CLL) is significantly lower in African Americans than whites, but overall survival is inferior. The biologic basis for these observations remains unexplored. We hypothesized that germline genetic predispositions differ between African Americans and whites with CLL and yield inferior clinical outcomes among African Americans. We examined a discovery cohort of 42 African American CLL patients ascertained at Duke University and found that the risk allele frequency of most single nucleotide polymorphisms known to confer risk of development for CLL is significantly lower among African Americans than whites. We then confirmed our results in a distinct cohort of 68 African American patients ascertained by the CLL Research Consortium. These results provide the first evidence supporting differential genetic risk for CLL between African Americans compared with whites. A fuller understanding of differential genetic risk may improve prognostication and therapeutic decision making for all CLL patients.

Description: Background: CD8+ T-cells in AML pts co-express multiple inhibitory receptors (IRs), including PD1, and IR expression increases with disease progression (Knaus et al, JCI Insight 2018). AZA upregulates pathways related to immunity and immune evasion in tumor cells, including PD-L1, (Wrangle et al, Oncotarget 2013) providing rationale for exploring AZA/Pembro combination in AML. Aims: To assess safety and response to AZA/Pembro after minimum 2 cycles of therapy in relapsed/refractory (R/R) (Cohort 1) and newly diagnosed (dx) older AML (Cohort 2). Methods: Cohort 1: Pts must have failed prior AML therapy. The first 6 pts (run in phase) received AZA 75 mg/m2 Days (D) 1-7 with Pembro 200 mg beginning on D8 and every (q)3 weeks (wks) thereafter. AZA cycles were repeated q4wks. No pts experienced dose limiting toxicity after minimum 3 cycles observation. After safety was established with the dosing schedule, patients with prior allogeneic stem cell transplant (alloSCT) were included and Cohort 2 started enrollment. Cohort 2: Pts ≥65 years (yrs) with newly dx AML and not candidates, or unwilling to receive, intensive chemotherapy. Other eligibility criteria (Cohort 1 and 2): ECOG PS 0-2 (changed to PS 0-1), adequate organ function, and no autoimmune processes requiring systemic immunosuppression. Results: Efficacy: Cohort 1 : 37 R/R pts have been enrolled. Baseline characteristics are summarized in Table 1A. 29 (78%) pts completed at least 2 cycles and are evaluable for response: 4 achieved complete remission (CR)/CR with incomplete hematologic recovery (CRi) (2/2) (14%) (Table 1B), 1 partial remission (PR) (4%), 4 hematologic improvement (HI) (14%), and 7 stable disease (SD) for at least 6 cycles (24%). The median # of cycles to response was 4 (range, 2-6). The 4- and 8-week mortality were 8% [all with rapidly progressive disease (PD): 2 received AZA for 3 and 5 days only] and 13%, respectively. With a median follow-up of 14.9 months (mos), the median overall survival (OS) for the whole cohort, responders + SD, and CR/CRi/PR is 10.8 mos (40% 1-yr), 13.9 mos (51% 1-yr), and 17.2 mos (75% 1-yr). The median event-free survival (EFS) is 6 mos, for all responders + SD 8.7 mos versus 2.6 mos for others (P

Description: Background: Recent genomic studies have identified somatic mutations in leukemia genes in asymptomatic individuals without known hematologic disease. These mutations lead to clonal expansion of hematopoietic cells, in the absence of clinically overt hematologic transformation. This entity is thought to be analogous to other precursor conditions such as monoclonal gammopathy of undetermined significance (MGUS) and monoclonal B-cell lymphocytosis (MBL); consistent with this notion, a subset of patients with clonal hematopoiesis can subsequently develop myeloid malignancies, including myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). However, the incidence of clonal hematopoiesis in patients with solid tumors has not been extensively studied. Moreover, most genomic profiling platforms used to identify somatic mutations in epithelial tumors use blood as the matched normal control, which may lead to the identification of clonal hematopoiesis in a subset of cancer patients. We therefore sought to assess for clonal hematopoiesis in patients with solid tumors seen at Memorial Sloan Kettering Cancer Center (MSKCC) who were profiled using paired tumor/blood sequencing which is primarily designed to identify tumor-specific mutations. Methods: The study population included patients at MSKCC who were consented on protocol NCT01775072, “Tumor genomic profiling in patients evaluated for targeted cancer therapy.” All patients had tumor and blood genomic profiling sequenced using the MSK-IMPACT hybridization capture-based next-generation sequencing assay, which encompasses all protein-coding exons of 410 cancer-associated genes. For assessment of the incidence and distribution of blood mutations, 3,964 patients consented were evaluated. Patients with known active hematologic malignancies at time of sequencing were excluded from analyses. For comparisons regarding clinical correlations, 2,146 patients were included for whom detailed chart review has been performed. We investigated for the presence of “hotspot” mutations, collected from COSMIC database (v71), in matched blood DNA. Mutations were scored as present in the normal blood if they were detected in more than 8 reads with a variant allele frequency (VAF) greater than 2% which was at least twice the VAF seen in tumor. For cases where at least one mutation exceeded these thresholds, we reduced the VAF threshold in blood to 1% to detect secondary events. Mutations where VAF in the normal blood and the tumor sample were both greater than 30% were excluded as likely germline events. Results: Clonal hematopoiesis was identified in 108/3,964 solid tumor patients who had paired tumor/blood sequencing (2.7% of all patients); 7 patients had 2 unique mutations. DNMT3A mutations were most frequent, occurring in 34% of patients with clonal hematopoiesis (Figure 1). 107/115 mutations (93%) were in known leukemia-associated genes. We collected and analyzed detailed clinical parameters for 2,146 patients, including 42 patients (2.0%) with clonal hematopoiesis. The mean age at the time of testing was 62.1 years in patients with clonal hematopoiesis and 57.2 years in patients without evidence of clonal hematopoiesis (p = 0.015). When comparing baseline blood parameters, there were no statistically significant differences between the two groups. 62% of patients with clonal hematopoiesis had previous radiation therapy compared to 45% of patients without clonal mutations in their blood (p = 0.046). There was no statistically significant difference in the proportion of patients who had received previous chemotherapy (71% of patients in each group). On prospective follow up of patients with clonal hematopoiesis, no patients have progressed to develop overt MDS or AML, though median follow up was limited (median 11.7 months, range 5.5-16.7 months). Conclusions: Clonal hematopoiesis in solid tumor patients without known hematologic disease is common and is associated with increasing age and prior radiation therapy. In our cohort, no patients with clonal hematopoiesis progressed to overt MDS or AML though follow up is limited. Ongoing prospective observation of these patients is imperative to determine the clinical impact of these mutations after ongoing exposure to cytotoxic therapy. Further data including updated clinical and genomic correlates will be presented. Reference: Cheng DT et al. J Mol Diagn 2015 May; 17(3): 251-64. Figure 1. Figure 1. Disclosures Hyman: Chugai Pharma: Consultancy; Biotherapeutics: Consultancy; Atara: Consultancy, Honoraria. Levine:Loxo Oncology: Membership on an entity's Board of Directors or advisory committees; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees; Foundation Medicine: Consultancy.

Description: Background: Acute myeloid leukemia (AML) is an aggressive malignancy with poor prognosis, especially in the elderly for whom hypomethylating agent therapy may be the only standard treatment option. Data from The Cancer Genome Atlas Research Network indicates 44% of patients with de novo AML carry mutations in genes that regulate DNA modifications, such as IDH1/2, DNMT3A, and TET2. Small retrospective series have reported differential response to hypomethylating agents (HMAs) in patients with mutations in the DNA modification pathway. For example, Itzykson et al. reported an increased response rate with azacitidine in MDS and AML patients with TET2 mutations compared with those without (82% vs 45%, p = 0.007). Next, Metzeler et al. reported an increase in CR rate with decitabine therapy in patients with DNMT3A mutations as compared with those without (75% vs 34% CR, p = 0.05). Emadi et al. noted a higher response rate in AML patients with IDH1/2 mutations compared to those without (71% vs 23%, p = 0.01) in patients receiving either decitabine or azacitidine. In contrast, Dinardo et al. did not find an association between responses to HMAs in patients with IDH1/2 and DNMT3A mutations in a retrospective analysis of 68 elderly AML patients. Recent evidence demonstrates that WT1 mutations lead to loss of TET2 function, suggesting thatAML pts with WT1 mutations may also be sensitive to HMAs. These findings suggest that mutations in the TET/IDH/WT1/DNMT3A pathway might confer increased sensitivity to HMAs. We aimed to determine if there was an association between response and mutations in the DNA methylation pathway in AML patients treated with HMAs at our institution. Methods: This is a single institution, retrospective study. Of a cohort of 288 molecularly characterized AML patients, 76 patients were treated with HMAs; either alone (n= 59) or in combination with another agent (n= 17). In our cohort, 39 patients were treated with HMA in the frontline setting and 37 were treated in the relapsed/refractory setting. DNA was obtained from peripheral blood or bone marrow aspiration samples. Testing was performed using a targeted enrichment NGS assay designed with the RainDance DeepSeq system, covering clinically relevant regions in 30 genes known to be mutated in myeloid malignancies. Samples were subjected to microdroplet emulsion PCR and sequenced on an Illumina MiSeq to an average depth of at least 500X. 51.3% of patients had mutational profiling at time of diagnosis, and the remainder had mutational profiling at time of relapse/refractory disease. Genes affecting DNA modification pathway (DNMT3A, IDH1/2, TET2, WT1) were analyzed as a composite (present/absent). Results: Among patients receiving HMA for AML, the mean age was 67.1 years and 68% of patients were male. Using the NCCN cytogenetic/molecular risk categories, 7/76 had "better" risk, 35/76 had "intermediate" risk, 28/76 had "poor" risk and 6/76 patients' risk status could not be determined. Four of the 76 patients had incomplete molecular data available and were excluded from analysis; therefore, the final cohort under study was 72 patients. 34/39 of the frontline HMA patients were evaluable for response and 32/37 of the relapsed/refractory patients were evaluable for response. Among the 34 patients treated with HMAs in the frontline setting, 16 had mutations affecting DNA methylation and 18 patients did not. The CR rate (CR + CRi) in patients with DNA pathway mutations was 8/18 (44%) vs. 3/16 (19%) in patients without mutations (p = 0.15). Among the patients treated with HMAs in the relapsed/refractory setting, responses were rare with only 3 patients (9.4%) achieving CR. Responses were too few to demonstrate statistical relationships. Conclusions: We noted a trend toward an improved CR rate in patients with DNA modification mutations. However, the difference was not statistically significant in this small study cohort. Given the rarity of mutations and size of published cohorts, including ours, it has been difficult to demonstrate statistically significant associations between mutations and response to HMAs. A meta-analysis of existing data may overcome barriers of small numbers in individual studies, though retrospective nature of studies and publication bias may influence these results. A prospective trial with comprehensive molecular profiling of all patients is warranted to determine true associations. Disclosures Levine: Foundation Medicine: Consultancy; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees; Loxo Oncology: Membership on an entity's Board of Directors or advisory committees.

Description: Background: Despite therapeutic advances, AML remains a disease in which the majority of patients relapse after attaining remission. The presence of bone marrow MRD is associated with impending AML relapse. Prediction and prevention of relapse could improve outcomes, but most current MRD tests either require bone marrow aspirate or detect individualized molecular genetic features present in a minority of AML. Furthermore, bone marrow MRD assessments are impractical if performed frequently enough to detect most early relapses. We developed and tested a novel microfluidic chip device (MCD) that can quantitate cell numbers using automated methods and explored its ability to detect low levels of peripheral blood leukemic cells with aberrant immunophenotypes. Methods: The MCD contains sinusoidal capture channels that were coated with antibodies with specificity towards one of the commonly expressed markers found on immature myeloid cells--CD33, CD34 and CD117 (capture antigens). Initial spiking experiments used fluorescently labeled leukemia cell lines HL60 (CD33+), KG1 (CD34+), Kasumi1 (CD117+) spiked into a 5000 cell/mL suspension. Cell suspensions were passed through MCDs coated with a capture antigen known to be expressed on the tested cell line. These experiments established an efficient capture using a flow rate of 1mL/sec. Then, AML patients with an aberrant immunophenotype were enrolled in a pilot study either at the start of induction chemotherapy or prior to allogeneic stem cell transplant (SCT). For patients receiving induction chemotherapy, whole blood samples were obtained monthly starting at the time of remission assessment, or monthly starting prior to SCT. Buffered whole blood was passed through MCDs coated with a capture antigen known to be expressed on patient myeloblasts. The captured cells were then released, eluted, centrifuged and plated on a glass slide. Plated cell pellets were then labeled with fluorescent antibodies targeting surface proteins known to be aberrantly (either by lineage infidelity or asynchronous expression) expressed on the patients' AML blasts. Automated fluorescence microscopy was used to identify and quantify captured cells with the known aberrant immunophenotype of the AML blasts. Descriptive statistics described serial cell counts in patients maintaining remission and relapsing patients. Results: Of 31 patients who have been enrolled in the study to date, 13 had at least 3 post-remission MCD analyses. Of these patients, 6 had either morphologic relapse or persistent/rising marrow MRD. In these patients, there was a trend towards higher initial aberrant immunophenotype cell counts, with mean initial count = 59 (95% CI 1, 108), compared to other patients with mean initial count = 15 (95% CI 5, 25). Of 5 patients who relapsed with MCD data within 1 month prior to relapse, the mean absolute rise prior to relapse above minimum MCD cell count was 54 (95% CI 2, 105), in comparison to non-relapsing patients with mean rise of 9 (95% CI 3, 15). From the initial 16 patients, 10 underwent induction therapy (the other 6 were enrolled prior to SCT). In these 10 patients there was a non-significant association between peripheral blood aberrant immunophenotype cells and remission status following induction. A total of 8 patients underwent allogeneic SCT. Two of these patients had known bone marrow MRD at the time of SCT and had a statistically significant greater number of aberrant immunophenotypic cells pre-SCT (48 and 60) compared to the 6 MRD negative patients (median = 12, range 9, 42). Conclusions: A novel MCD assay can reliably capture and detect low numbers of AML blasts from peripheral blood using immunofluorescent imaging and automated cell counts to quantify leukemia cells with aberrant immunophenotypes. Because this method uses peripheral blood, frequent sampling is feasible and of minimal risk to patients. An ongoing clinical trial will further explore the associations between MCD-based cell enumeration and clinical endpoints in AML patients that were suggested in the pilot phase of this study. Because the MCD releases trace populations of viable cells, additional experiments, such as primary cell culturing and single cell sequencing, are possible. Figure Disclosures Foster: Bellicum Pharmaceuticals, Inc: Research Funding; Daiichi Sankyo: Consultancy; MacroGenics: Research Funding; Celgene: Research Funding. Fedoriw:Alexion Pharmaceuticals: Consultancy, Speakers Bureau. Zeidner:Celgene: Consultancy, Honoraria, Research Funding; AsystBio Laboratories: Consultancy; Merck: Research Funding; Covance: Consultancy; Pfizer: Honoraria; Agios: Honoraria; Daiichi Sankyo: Honoraria; Tolero: Honoraria, Research Funding. Coombs:Covance: Consultancy; Octopharma: Honoraria; Medscape: Honoraria; Cowen & Co.: Consultancy; Loxo: Honoraria; H3 Biomedicine: Honoraria; Dedham Group: Consultancy; Pharmacyclics: Honoraria; Abbvie: Consultancy. Mirkin:BioFluidica: Employment. Zomorrodi:BioFluidica: Employment. Toughiri:BioFluidica: Employment. Bartakova:BioFluidica: Employment. Carson:BioFluidica: Employment. Muller:BioFluidica: Employment.