Abstract: The ability to perform optimally under pressure is critical across many occupations, including the military, first responders, and competitive sport. Despite recognition that such performance depends on a range of cognitive factors, how common these factors are across performance domains remains unclear. The current study sought to integrate existing knowledge in the performance field in the form of a transdisciplinary expert consensus on the cognitive mechanisms that underlie performance under pressure. Methods International experts were recruited from four performance domains [(i) Defense; (ii) Competitive Sport; (iii) Civilian High-stakes; and (iv) Performance Neuroscience]. Experts rated constructs from the Research Domain Criteria (RDoC) framework (and several expert-suggested constructs) across successive rounds, until all constructs reached consensus for inclusion or were eliminated. Finally, included constructs were ranked for their relative importance. Results Sixty-eight experts completed the first Delphi round, with 94% of experts retained by the end of the Delphi process. The following 10 constructs reached consensus across all four panels (in order of overall ranking): (1) Attention; (2) Cognitive Control—Performance Monitoring; (3) Arousal and Regulatory Systems—Arousal; (4) Cognitive Control—Goal Selection, Updating, Representation, and Maintenance; (5) Cognitive Control—Response Selection and Inhibition/Suppression; (6) Working memory—Flexible Updating; (7) Working memory—Active Maintenance; (8) Perception and Understanding of Self—Self-knowledge; (9) Working memory—Interference Control, and (10) Expert-suggested—Shifting. Discussion Our results identify a set of transdisciplinary neuroscience-informed constructs, validated through expert consensus. This expert consensus is critical to standardizing cognitive assessment and informing mechanism-targeted interventions in the broader field of human performance optimization.

Abstract: In myeloid malignancies, presence of 'multi-hit' TP53 mutations is associated with lack of response to conventional therapy and dismal outcomes, particularly when found in combination with a complex karyotype. Therefore, it is crucial to understand the biological basis of TP53-mutant driven clonal evolution, suppression of antecedent clones and eventual disease transformation to inform the development of more effective therapies. Myeloproliferative neoplasms (MPN) represent an ideal tractable disease model to study this process, as progression to secondary acute myeloid leukemia (sAML) frequently occurs through the acquisition of TP53 missense mutations. To characterize tumor phylogenies, cellular hierarchies and molecular features of TP53-driven transformation, we performed single-cell multi-omic TARGET-seq analysis (PMID: 33377019 & 30765193) of 22116 hematopoietic stem and progenitor cells (HSPCs) from 35 donors and 40 timepoints (controls, MPN in chronic phase, pre-AML and TP53-mutated sAML; Figure1a). TARGET-seq uniquely enables single-cell mutation analysis with allelic resolution with parallel transcriptomic and cell-surface proteomic readouts. We invariably identified convergent clonal evolution leading to complete loss of TP53 wild-type alleles upon transformation, including parallel evolution of separate TP53 "multi-hit" subclones in the same patient (n=4/14) and JAK2-negative progression (n=2/14). Complex clonal evolution driven by chromosomal abnormalities (CAs) was present in all patients and TP53 multi-hit HSPCs without CAs were rarely observed. Subclones with recurrent CA such as monosomy 7 showed upregulation of RAS-associated transcription and preferentially expanded in xenograft models. Together, these data indicate that TP53 missense mutation, loss of TP53 wild-type allele and cytogenetic evolution are collectively required for leukemic stem cell (LSC) expansion. Integrated transcriptomic analysis of sAML samples (Figure1b) revealed three major populations: (1) a TP53-mutant cluster (Figure1c) characterized by an erythroid signature (e.g. KLF1, GATA1, GYPA; an unexpected finding as no cases showed diagnostic features of erythroid leukemia), (2) an LSC TP53-mutant cluster (Figure1d) and (3) a TP53-WT preleukemic cluster (Figure1e). The LSC cluster showed dysregulation of key stem cell regulators, from which we derived a novel 48-gene LSC score with prognostic impact in an independent AML cohort (HR=3.13; Figure1f). Importantly, this score was predictive of outcome irrespective of TP53 status for both de novo and sAML, demonstrating its broader potential clinical utility. TARGET-seq analysis uniquely allowed us to characterize rare TP53-WT preleukemic cells (preLSCs), which were almost exclusively confined to the immunophenotypic lineage-CD34+CD38-CD90+CD45RA- HSC compartment. PreLSC from sAML samples presented increased stemness, increased quiescence, aberrant inflammatory signaling and differentiation defects (Figure1g) as compared to HSCs from normal or MPN donors, both at the transcriptional and functional levels through in vitro long-term and short-term cultures. This indicates cell-extrinsic suppression of residual TP53-WT hematopoiesis. Longitudinal analysis of TP53-heterozygous mutant HSPCs at different stages of disease evolution (Figure1a) revealed that aberrant inflammatory signalling (e.g. BST2, IFITM1, IFITM3) in the genetic ancestors of TP53 "multi-hit" LSCs, but not the presence of TP53-mutations alone, was predictive of subsequent transformation. In a mouse model system, TP53-mutant cells challenged with sustained inflammatory stimuli acquired a mean 3-fold competitive advantage in WT: TP53 R172H/+chimeras. This indicates that pro-inflammatory cues from the tumour microenvironment promote fitness advantage of TP53-mutant cells whilst supressing antecedent clones. In summary, we present a comprehensive single-cell multi-omic analysis of the genetic, cellular and molecular landscape of TP53-mediated transformation, providing unique insights into the evolution of chronic hematological malignancies towards an aggressive acute leukemia (Figure1h). Since TP53 is the most commonly mutated gene in human cancer, we anticipate these findings will be of broader relevance to many other cancer types. Figure 1 Figure 1. Disclosures Kretzschmar: Vanadis Diagnostics, a PerkinElmer company.: Current Employment. Drummond: BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CTI: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Harrison: Geron: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Galacteo: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sierra Oncology: Honoraria; Constellation Pharmaceuticals: Research Funding; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte Corporation: Speakers Bureau; Promedior: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Mead: Abbvie: Consultancy, Honoraria; Celgene/BMS: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Speakers Bureau.

Abstract: Abstract 675 Background: Activation of the p53 pathway by inhibition of its negative regulator MDM2 has been proposed as a novel strategy for cancer therapy. We report the final results of the Phase 1 leukemia trial of RG7112, a small molecule antagonist of MDM2 which activates p53 by disrupting the p53-MDM2 interaction. Methods: The trial was designed as a multi-center, open-label Phase 1 MAD study of patients with relapsed/refractory leukemia treated with escalating doses of single agent RG7112 in two strata: A:AML, ALL, CML-BC; and B:CLL and S-CLL. RG7112 was administered orally daily for 10 days followed by 18 days of rest. Primary objectives were to determine MTD and DLT; secondary objectives to assess PK, PD and clinical responses. Enrollment is complete. 4 patients remain on study, and final data is being compiled. Peripheral blood was collected for PK and biomarkers pre-treatment, at multiple time points during the first 48 hours, and on d10. Bone marrow was collected pre-treatment, d10 and d28. Blood and marrow were purified by MACS sorting (CD19, 33 or 34 Ab). AmpliChip analysis of p53 mutational status (single nucleotide alterations exons 2–11) was performed. MIC-1 (macrophage inhibitory cytokine-1), a p53 transcriptional target, was analyzed in serum by ELISA as a pharmacodynamic marker of p53 activation. Baseline MDM2 mRNA levels, and changes from baseline, as a marker of p53 activation and feedback on MDM2, were measured by RT-PCR. A panel of 24 genes was assessed serially by TLDA (q-PCR). Results: 116 patients (84 AML,10 ALL, 2 CML, 20 CLL/sCLL) were treated with RG7112 doses ranging from 20 – 2430 (1215 BID) mg/m2/day × 10 days. The dose-exposure relationship (Cmax, AUC, and Ctrough) was approximately linear with a median half-life of 1–1.5 days. 43 patients with acute leukemia were dosed at the MTD of 1500 mg BID (flat dose) × 10 days. Major adverse events( 〉 20%) were nausea, diarrhea and vomiting. Other major ( 〉 10%) AEs were complications of leukemia (e.g. neutropenic fever). Clinical activity was noted during dose escalation (ASH 2011), including apoptosis in AML and CLL, CR in an AML patient (360mg/m2) stable for 6 cycles (10 months) and one patient with CLL/Richter's transformation with stable disease (40 mg/m2) for 〉 25 cycles. New data focuses on AML patients treated at MTD. This cohort received a median of 3 prior treatments, 16 were refractory to last treatment. 17 (40%) had evidence of hematologic improvement (greater than 50% drop in peripheral and/or BM blasts by d28). Of the 31 patients who completed cycle 1 dosing, 5 patients (16%) had a CR (2 CR, 2 CRi. 1 CR without recovery). Two CR patients have proceeded to allotransplant. All CR patients' blasts were p53wt. Of the 12 additional patients with single-agent hematologic activity, 3 had biochemical evidence of tumor lysis syndrome, 10 had p53status evaluable, and mutations were detected in 3: (exon 7 missense, exon 9 frameshift, intron 7 splice). p53 activation by RG7112 was demonstrated by MIC-1 induction in serum. MIC-1 levels were elevated at RG7112 plasma concentrations 〉 2 μg/mL or AUC24h 〉 50 μg · h/mL and were highly correlated (0.5629) with exposure to RG7112 (AUC24h) at steady state following a sigmoidal Emax model. Preliminary data review suggests a positive correlation between exposure to RG7112 and changes in MDM2 gene expression at day 2. In addition, q-PCR analysis demonstrated exposure-dependent induction of key p53 transcriptional targets including MDM2, p21, and PUMA. p53 protein increase by WB was demonstrated at the MTD in selected patients. These findings are consistent with the proposed mechanism of action of RG7112. Conclusions: We report evidence of single agent clinical activity in patients with leukemia treated with RG7112, including 6 AML patients with CR, 5 of 31 (16%) at the MTD, and additional patients with significant decreases in blasts. Concentration-related pharmacodynamic biomarker activity of the p53 pathway was demonstrated by increases in MIC-1 levels, and induction of p53 target genes including mdm2, p21 and PUMA. 4 patients remain on treatment and final results will be reported. We provide proof of mechanism and evidence for single-agent clinical activity of MDM2 antagonism in leukemia by demonstrating complete remission, lysis of leukemic blasts and activation of p53 pathway targets in leukemic cells from patients treated with RG7112. Clinical studies of RG7112 in combination are underway. Disclosures: Andreeff: Hoffmann-La Roche: Research Funding; Karyopharm Therapeutics: Unrestricted gift, Unrestricted gift Other. Yee:Roche: Membership on an entity's Board of Directors or advisory committees. Assouline:Roche: travel funding Other. Martinelli:Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Pfizer: Consultancy; Ariad: Consultancy. Drummond:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Geho:Roche: Employment. Blotner:Roche: Employment. Cheng:Roche: Employment. Vassilev:Roche: Employment. Ding:Roche: Employment. Zhi:Roche: Employment. Middleton:Roche: Employment. Nichols:Roche: Employment.

Abstract: Purpose: RG7112 is a small-molecule MDM2 antagonist. MDM2 is a negative regulator of the tumor suppressor p53 and frequently overexpressed in leukemias. Thus, a phase I study of RG7112 in patients with hematologic malignancies was conducted. Experimental Design: Primary study objectives included determination of the dose and safety profile of RG7112. Secondary objectives included evaluation of pharmacokinetics; pharmacodynamics, such as TP53-mutation status and MDM2 expression; and preliminary clinical activity. Patients were divided into two cohorts: Stratum A [relapsed/refractory acute myeloid leukemia (AML; except acute promyelocytic leukemia), acute lymphoblastic leukemia, and chronic myelogenous leukemia] and Stratum B (relapsed/refractory chronic lymphocytic leukemia/small cell lymphocytic leukemia; CLL/sCLL). Some Stratum A patients were treated at the MTD to assess clinical activity. Results: RG7112 was administered to 116 patients (96 patients in Stratum A and 20 patients in Stratum B). All patients experienced at least 1 adverse event, and 3 dose-limiting toxicities were reported. Pharmacokinetic analysis indicated that twice-daily dosing enhanced daily exposure. Antileukemia activity was observed in the 30 patients with AML assessed at the MTD, including 5 patients who met International Working Group (IWG) criteria for response. Exploratory analysis revealed TP53 mutations in 14% of Stratum A patients and in 40% of Stratum B patients. Two patients with TP53 mutations exhibited clinical activity. p53 target genes were induced only in TP53 wild-type leukemic cells. Baseline expression levels of MDM2 correlated positively with clinical response. Conclusions: RG7112 demonstrated clinical activity against relapsed/refractory AML and CLL/sCLL. MDM2 inhibition resulted in p53 stabilization and transcriptional activation of p53-target genes. We provide proof-of-concept that MDM2 inhibition restores p53 function and generates clinical responses in hematologic malignancies. Clin Cancer Res; 22(4); 868–76. ©2015 AACR.

Abstract: Introduction: Advanced systemic mastocytosis (AdvSM) comprises a heterogeneous group of clonal mast cell neoplasms, primarily driven by KIT D816V. Measures of AdvSM response, including the International Working-Group for Myeloproliferative Neoplasms Research and Treatment and European Competence Network on Mastocytosis (IWG-MRT-ECNM) criteria, are based on improvements in mast cell-related organ damage (C-findings), and further sub-classified by the extent of reduction in measures of mast cell disease (e.g. serum tryptase level, bone marrow mast cell burden). However, assessment of some C-findings lacks precision (such as splenomegaly and its resolution). Normalization of C-findings may not be an adequate surrogate for important clinical outcomes such as overall survival (OS). We evaluated whether pure pathologic response (PPR) criteria based on changes in bone marrow mast cells, serum tryptase, and complete blood count was more closely correlated with OS compared to the modified IWG-MRT-ECNM (mIWG-MRT-ECNM) criteria. Methods: As an exploratory post-hoc analysis of the phase 1 EXPLORER study of avapritinib in AdvSM, we evaluated responses lasting ≥12 weeks by both mIWG-MRT-ECNM and PPR criteria. At baseline, evaluability for mIWG-MRT-ECNM response required ≥1 evaluable C-findings; PPR required presence of bone marrow mast cell aggregates and/or serum tryptase ≥20 ng/mL. Per PPR, morphologic complete remission (mCR) is absence of bone marrow mast cell aggregates, serum tryptase & lt;20 ng/mL and full (or partial [mCRh]) hematologic recovery; morphologic partial remission (mPR) is ≥50% reduction in bone marrow mast cells and serum tryptase level. OS was analyzed by Kaplan-Meier method and was time from first dose to death. OS comparisons were by log-rank test, performed for best response and landmark analyses at various cycles. Results: As of the data cut-off of August 30, 2019, 80 patients enrolled including 62 with AdvSM (7 with aggressive SM [ASM], 44 SM with an associated hematologic neoplasm [SM-AHN] and 11 with mast cell leukemia [MCL]). Ten (16%) AdvSM patients (7 ASM, 3 SM-AHN) were not response evaluable (RE) per mIWG-MRT-ECNM criteria, due to a lack of an evaluable C-finding at baseline, and 4 additional AdvSM patients were recently enrolled and were not yet response evaluable. Of the 48 RE patients (3 ASM, 35 SM-AHN and 10 MCL) the best overall response rate (ORR) per mIWG-MRT-ECNM was 77% (8% CR, 19% CRh, 42% partial response [PR], and 8% clinical improvement [CI] ). Non-responders had stable disease (SD; 21%) or were not evaluable (NE) due to insufficient ( & lt;13 weeks) follow-up (2%). Responders (CR/CRh/PR/CI) had 18-month OS of 85% (CR/CRh, 100%; PR, 77%; CI, 75%; Figure 1A); non-responders had 18-month OS of 48% (SD, 53%; NE, 0%) (P=0.042). Per PPR criteria, the best ORR was similar at 79%; however, a greater proportion of patients were assessed as being in a complete remission (15% mCR, 27% mCRh and 38% mPR). Non-responders by PPR all had SD (21%). This demonstrates that elimination of measurable mast cell burden can be discordant with complete C-finding resolution. Responders (mCR/mCRh/mPR) by PPR had 18-month OS of 88% (mCR/mCRh: 100%; mPR: 72%; Figure 1B); non-responders (all SD) had 18-month OS of 21% (P=0.0001). Eventually, all 62 AdvSM patients will be evaluable by PPR criteria, including those 10 patients without mIWG evaluable C-findings at baseline; however, 5 patients had insufficient follow-up at the time of analysis. For the 57 AdvSM patients with sufficient follow up, the best ORR per PPR criteria was similar at 77% (14% mCR, 26% mCRh and 37% mPR). Overall, no patients had a best response of progressive disease based on mIWG or PPR criteria. Landmark analyses of PPR at the end of 6 cycles showed a trend in 18-month OS of mCR/mCRh & gt;mPR & gt;SD in patients with similar starting avapritinib doses of ≥200 mg daily (n=48 of 57 PPR-evaluable patients). Conclusions : In the phase I EXPLORER study, response assessment in AdvSM using PPR criteria increases the evaluable population, significantly correlates with OS, and should be explored as a potential primary endpoint for future trials. Disclosures Gotlib: Blueprint Medicines Corporation: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Chair of the Response Adjudication Committee and Research Funding, Research Funding; Deciphera: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: co-chair of the Study Steering Committee and Research Funding. Radia:Blueprint Medicines Corporation: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Education events. George:Blueprint Medicines Corporation: Consultancy, Other: I have received no funding for this research. ARUP Laboratories, owned by the University of Utah, has received funding; Allakos: Consultancy; Deciphera: Other: consultancy, but has received no financial compensation for the past 12 months; Celgene: Consultancy. Robinson:Blueprint Medicines Corporation: Research Funding. Drummond:Jazz: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Gilead: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicine Corporation: Research Funding. Bose:Incyte Corporation: Consultancy, Honoraria, Research Funding, Speakers Bureau; Kartos Therapeutics: Honoraria, Research Funding; Astellas Pharmaceuticals: Research Funding; NS Pharma: Research Funding; Pfizer, Inc.: Research Funding; Promedior, Inc.: Research Funding; Constellation Pharmaceuticals: Research Funding; Celgene Corporation: Honoraria, Research Funding; CTI BioPharma: Honoraria, Research Funding; Blueprint Medicines Corporation: Honoraria, Research Funding. Hexner:Samus Therapeutics: Research Funding; Novartis: Research Funding; American Board of Internal Medicine: Other: member of the hematology exam committee; Blueprint Medicines Corporation: Other: serves on a data safety monitoring committee, Research Funding. Winton:Blueprint Medicines Corporation: Research Funding; Samus Therapeutics: Research Funding; Incyte Corporation: Research Funding. Horny:Novartis: Consultancy; Blueprint Medicines Corporation: Consultancy. Tugnait:Blueprint Medicines Corporation: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Schmidt-Kittler:Blueprint Medicines Corporation: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Evans:Blueprint Medicines Corporation: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Lin:Blueprint Medicines Corporation: Current Employment, Current equity holder in publicly-traded company. Mar:Blueprint Medicines Corporation: Current Employment, Current equity holder in publicly-traded company. Deininger:Leukemia & Lymphoma Society: Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Other, Research Funding; Ariad: Consultancy, Honoraria, Other; Incyte: Consultancy, Honoraria, Other, Research Funding; Novartis: Consultancy, Other, Research Funding; Medscape: Consultancy; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Fusion Pharma: Consultancy; Blueprint Medicines Corporation: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: part of a study management committee, Research Funding; DisperSol: Consultancy; Galena: Consultancy, Honoraria, Other; Celgene: Research Funding; Gilead Sciences: Research Funding; SPARC: Research Funding; Sangamo: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Other, Research Funding. DeAngelo:Incyte Corporation: Consultancy; Glycomimetics: Research Funding; Forty-Seven: Consultancy; Amgen: Consultancy; Novartis: Consultancy, Research Funding; Pfizer: Consultancy; Abbvie: Research Funding; Jazz: Consultancy; Autolos: Consultancy; Shire: Consultancy; Takeda: Consultancy; Blueprint Medicines Corporation: Consultancy, Research Funding; Agios: Consultancy.

Abstract: Background: Aggressive Systemic Mastocytosis (ASM) and the related disorders, SM with associated hematologic non-mast cell disorder (SM-AHNMD) and mast cell leukemia (MCL), are mast cell (MC) neoplasms that cause debilitating allergy symptoms, markedly impair organ function and decrease life expectancy. Although the oncogenic KIT D816V mutant is recognized as an important driver in about 95% of advanced SM (ASM, SM-AHNMD, MCL), no currently approved therapy effectively targets KIT D816V. A phase 1 study (NCT02561988) was initiated in advanced SM to assess the safety, PK, and preliminary clinical activity of BLU-285, a potent, highly-selective oral inhibitor designed to target KIT D816V (IC50 = 0.27 nM). Methods: Adult patients (pts) with ASM, SM-AHNMD or MCL per WHO diagnostic criteria were given BLU-285 once daily on a 4-week cycle following a 3+3 escalation design. Adverse events (AEs) per CTCAE, PK and biomarkers including serum tryptase, D816V mutant allele fraction in blood and bone marrow and co-occurring mutations (Illumina TruSight panel) were assessed. Liver and spleen size were measured serially via CT or MRI. All cases will undergo central pathology review to confirm SM diagnosis and subtype. Results: At a 21-JUL-2016 cutoff, 6 pts (5 ASM; 1 SM-CMML) have been treated with BLU-285 in 2 cohorts at doses of 30 and 60 mg/day. All pts had confirmed D816V mutation in blood and bone marrow and all pts had ≥ 1 co-occurring mutation(s) in bone marrow (range 4-9, most frequently TET2 (5), DNMT3A (4) and GATA1 (4)). All pts had MC-related organ damage as evidenced by ≥ 1 C-finding (bone marrow dysfunction with ≥ 1 cytopenia; hepatomegaly with impaired liver function, ascites and/or portal hypertension; osteolytic skeletal lesions; splenomegaly with hypersplenism; malabsorption with weight loss). The median number of C-findings was 1.5 (range 1-3). 4 pts had urticaria pigmentosa. Concomitant medications for MC-related symptoms included anti-histamines (5), corticosteroids (2), leukotriene receptor antagonist (2) and/or cromolyn (1). 2 pts had received prior anti-neoplastic therapy with pegylated interferon (1) or midostaurin (1). Although early in dose escalation, marked improvements in disease symptoms and burden were seen in all pts across both dose levels. This included symptomatic relief of allergy symptoms with decreased use of corticosteroids (2), improved urticaria pigmentosa (3 of 4), and increased albumin (5)/weight gain (6), indicative of diminished malabsorption. Objective decreases in mast cell burden were also observed including decline in peripheral blood and bone marrow KIT D816V DNA levels (6), decreased splenomegaly (3), tryptase decline (5), and decreased bone marrow MCs (2 of 2) (1 pt had bone marrow aspirate MCs decline from 30% at baseline to 3%; 1 pt had bone marrow biopsy MCs decline from 80% to 20%, both at C3D1). Tryptase decline appears to be dose related, with 〉 50% decrease in 1/3 patients in the 30 mg cohort and 〉 50% decrease in 3/3 patients in the 60 mg cohort. Updated diagnostic, biomarker, bone marrow and response data will be presented at the time of the meeting. An MTD has not been determined and dose escalation continues. BLU-285 was well tolerated with most AEs being CTCAE grade 1 and no grade ≥ 4 events. Grade 2 AEs included fatigue, dizziness, headache, rash, shingles, anemia, elevated GGT and thrombocytopenia (1 patient each). Grade 3 alkaline phosphatase elevation was observed in 3 patients and grade 3 back pain in 1 patient. All pts remain on treatment, with duration of therapy ranging from 2-5 cycles. Initial PK data show that BLU-285 is rapidly absorbed (Tmax 2-4 h), and half-life is 〉 19 h supporting once daily dosing. Mean steady-state AUC and Cmax at the 30 mg dose level were 1,845 ng*h/mL and 89 ng/mL, which are below the maximally active exposure in KIT D816-mutant xenograft models. Conclusion: Currently approved therapies do not effectively target KIT D816V, a key genomic-driver in approximately 95% of SM. BLU-285, a potent, highly-selective inhibitor of this mutant has been well tolerated and demonstrates clinical activity early in dose escalation with objective decreases in MC burden and improvements in MC-related organ damage in advanced SM. These encouraging phase 1 data support selective targeting of KIT D816V and further clinical testing of BLU-285 in SM. Disclosures Drummond: BMS: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau; celgene: Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau; Roche: Honoraria, Speakers Bureau. DeAngelo:Novartis: Consultancy; Pfizer: Consultancy; Incyte: Consultancy; Amgen: Consultancy; Ariad: Consultancy; Baxter: Consultancy; Celgene: Consultancy. Deininger:Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Consultancy, Research Funding; Gilead: Research Funding; CTI BioPharma Corp.: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Bristol Myers Squibb: Consultancy, Research Funding; Ariad: Consultancy, Membership on an entity's Board of Directors or advisory committees. Radia:Novartis: Honoraria; Pfizer: Honoraria. Hexner:Blueprint medicines: Membership on an entity's Board of Directors or advisory committees; novartis: Research Funding. Shi:Blueprint Medicines: Employment, Equity Ownership. Alvarez-Diez:Blueprint Medicines: Employment, Equity Ownership. Evans:Blueprint Medicines: Employment, Equity Ownership. Healy:Blueprint Medicines: Employment, Equity Ownership. Wolf:Blueprint Medicines: Employment, Equity Ownership.

Abstract: Introduction: The KIT D816V oncogene is a key driver in 90-95% of patients with systemic mastocytosis (SM), a group of mast cell (MC) neoplasms including indolent SM (ISM), smoldering SM (SSM) and AdvSM. Debilitating symptoms related to MC proliferation and degranulation characterize ISM and SSM and are also prominent in AdvSM, which is further complicated by SM-related organ damage and decreased survival. Currently, there are no approved agents that selectively target KIT D816V, and there are limited tools to assess symptom improvement in SM. Avapritinib, a highly potent and selective inhibitor of the KIT D816V mutant, showed substantial clinical activity in AdvSM (83% overall response rate (ORR) per modified IWG-MRT-ECNM criteria) in the Phase 1 EXPLORER study [Deininger, et al, EHA, 2018]. We present results using a novel PRO questionnaire, the AdvSM-SAF, developed in accordance with FDA guidance, to assess changes in symptoms in the Part 2 dose expansion phase of EXPLORER. Methods: Patients (pts) received avapritinib at the recommended Phase 2 dose (300 mg once daily [QD]) in continuous 28-day (d) cycles. Pts completed the AdvSM-SAF and 2 additional PROs used in other cancers, the Patient Global Impression of Symptom Severity (PGIS) and the European Organization for Research and Treatment of Cancer Quality of Life (QLQ). PROs and KIT D816V mutant allele fraction (MAF) in blood were assessed serially as follows: AdvSM-SAF daily, from 7 d before first avapritinib dose, ie, baseline (BL: Cycle [C]1 Day [D] 1) and through C12, using an electronic diary; PGIS and QLQ at BL (C1D1) and on D1 of each cycle through C12; and KIT D816V mutant allele fraction (MAF) at BL and on D1 of C3, 7, 11, and then every 6 cycles. The AdvSM-SAF assesses severity of 8 symptoms (pruritus, flushing, spots, nausea, vomiting, diarrhea, abdominal pain, fatigue) on a 0-10 scale, and 2 items assess frequency of diarrhea and vomiting. Results are analyzed as a Total Symptom Score (TSS), combining all 8 severity items (maximum symptom score=80), and as a GI domain (combining 4 symptoms: nausea, vomiting, diarrhea, abdominal pain; maximum score 40) and Skin domain (combining 3 symptoms: pruritus, flushing, spots; maximum score 30). Analyses were based on 7 d average scores. AdvSM-SAF data were summarized at BL (C1D-7 to C1D-1), and over the 7-d interval prior to C3D1 and C7D1, and correlated with QLQ, PGIS and KIT D816V MAF. Results: As of 22 June 2018, 25 pts were treated in Part 2 of the study; 24 are ongoing, and enrollment and follow-up continues. The median duration of avapritinib treatment was 5.7 mo (range, 1.7+ to 10.3+ mo). AdvSM-SAF scores for 24 pts with data are shown the Table. Mean BL TSS, GI and Skin scores were 22.6, 9.1, and 7.1. The most severe BL symptom was fatigue (mean score of 6.4). Among 21 pts with scores at C3D1 and 12 pts with scores at C7D1, mean reductions from BL TSS, GI and Skin scores were 6.4, 3.9, and 1.5 points, and 11.1, 5.7, and 4.4 points, respectively, indicating further improvement with continued treatment. Symptom reductions were seen for all 8 items at C3D1. Further symptom improvement was observed for 6 of 8 items from C3D1 to C7D1. Reductions in AdvSM-SAF TSS, GI and Skin scores significantly correlated with improvement in QLQ Emotional (EF) and Cognitive functioning (CF) scales (p values for Pearson Correlation Coefficients 〈 0.0001, 〈 0.0001, and 0.04 with EF and 〈 0.0001, 0.0001, and 0.04 with CF, respectively). Among 18 pts with BL PGIS (mean 3.2, SD 1.15, range 1-5), improvement in PGIS was highly associated with improvement in GI score (p value 0.0004). Decreases in KIT D816V MAF correlated with reduction in TSS (p value 0.04). Conclusions: Avapritinib treatment resulted in meaningful symptom improvement as measured by the AdvSM-SAF in overall symptoms (TSS), GI and skin domains, and all individual symptoms, and improvement continued with longer duration of treatment. Reduction in AdvSM-SAF scores correlated with improvements in other PRO instruments, PGIS and QLQ, supporting the AdvSM-SAF as a useful new tool to assess symptoms in pts with AdvSM. Reduction in AdvSM-SAF scores also correlated with decreases in KIT D816V MAF, indicating that reductions in disease burden may correlate with reduced disease symptoms and improved quality of life. These data warrant further development of avapritinib in AdvSM, as well as in ISM and SSM where symptom burden and poor quality of life are the predominant disease manifestations. Disclosures Gotlib: Deciphera: Consultancy, Honoraria, Research Funding; Blueprint Medicines: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Promedior: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Kartos: Consultancy; Incyte: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Research Funding. Radia:Novartis: Speakers Bureau; Blueprint: Consultancy. DeAngelo:Glycomimetics: Research Funding; Shire: Honoraria; Pfizer Inc: Consultancy, Honoraria; Incyte: Consultancy, Honoraria; Amgen: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Honoraria; Takeda: Honoraria; ARIAD: Consultancy, Research Funding; BMS: Consultancy; Blueprint Medicines: Honoraria, Research Funding. Bose:CTI BioPharma: Research Funding; Celgene Corporation: Honoraria, Research Funding; Pfizer, Inc.: Research Funding; Blueprint Medicines Corporation: Research Funding; Incyte Corporation: Honoraria, Research Funding; Astellas Pharmaceuticals: Research Funding; Constellation Pharmaceuticals: Research Funding. Conlan:Blueprint Medicines: Employment. Oren:Blueprint Medicines: Employment. Shi:Blueprint Medicines: Employment. Deininger:Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Blueprint: Consultancy.