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Background: Despite recently approved novel targeted therapies, most patients with high-risk acute myeloid leukemia (AML) still require allogeneic hematopoietic cell transplantation (HCT) to achieve long-term survival. However, older patients with relapsed/refractory (R/R) AML are often unable to undergo HCT due to the toxicity of myeloablative pre-conditioning. Since higher doses of chemotherapy and radiation are associated with prolonged myelosuppression or infectious complications, targeted radiotherapy with Iomab-B, employed in the SIERRA trial, was designed to minimize toxicities in a patient population unable to tolerate standard high-dose myeloablative HCT pre-conditioning. We hypothesize that Iomab-B, which spares non-hematologic organs such as the GI tract, exhibits a favorable toxicity profile with respect to mucositis, febrile neutropenia (FN), and sepsis. Methods: The SIERRA trial is a prospective trial for patients ≥55 years of age with R/R AML (≥5% blasts) and 8/8 HLA-matched related or unrelated donors. Patients were randomized (1:1) to Iomab-B or Conventional Care (CC). Those in the Iomab-B group received a dosimetric infusion of Iomab-B followed by nuclear imaging to determine the personalized therapeutic dose to be delivered to the bone marrow and to other sites of disease. Therapeutic dose calculations, utilizing the Olinda software (Version 2.1, Hermes Medical) to determine the delivery of a maximum of 24 Gray (Gy) dose to the liver, were performed based on the imaging results. HCT is performed 12-14 days following the infusion of a therapeutic dose of Iomab-B, and a non-myeloablative conditioning backbone of fludarabine (30 mg/m2 x 3) and low-dose Total Body Irradiation (TBI 2 Gy x 1 dose). CC patients received the investigator's choice of salvage therapy. Safety data was evaluated from randomization and up to 100 days after HCT in the patients randomized to the Iomab-B group. We specifically evaluated AE variables of mucositis (Gr 2-4), FN (Gr3,4) and sepsis. An analysis was performed with both total activity of Iomab-B as well as with the radiation dose delivered to the bone marrow, stomach wall, small and large intestinal walls. For each of the 3 AEs of interest, a multivariate analysis was performed, allowing each of the predictor variables to be included in the model. Results: A total of 106 patients were randomized at the time of analysis. For those randomized to Iomab-B, data is available for 45 patients that received a therapeutic dose of Iomab-B and HCT. The median dose of Iomab-B administered was 603 mCi (range 313-1027 mCi) and the median radiation dose delivered to the marrow in the Iomab-B group was 14.7 Gy (range 4.6 - 32 Gy). All patients (median age 64) treated with a therapeutic dose of Iomab-B achieved neutrophil engraftment after a median of 14 days post-HCT (range 9-22), despite presenting with a median 26% marrow blasts prior to initiation of therapy. Rates of mucositis, FN, and sepsis are shown in Table 1. No correlation between AEs (FN, mucositis, sepsis) and administered Iomab-B activity (p=0.08), nor with dose delivered to GI tract (p=0.09) was observed. Furthermore, these AEs were not related to the dose of radiation received by the small intestine (median 2.7 Gy range 1.1-6.8 Gy) large intestine (median 2.6 Gy range 0.9-6.5 Gy), nor an average of all 4 GI sites (median 2.8 Gy range 1.6-6.8 Gy). Conclusions: Unlike cases involving treatment with cytotoxic chemotherapy and external beam radiation where mucositis, infections and sepsis increase along with the administered dose, targeted myeloablative conditioning with Iomab-B resulted in low incidences of severe mucositis, FN, and sepsis. These AEs do not appear to be related to the total dose of Iomab-B administered nor to the specific radiation dose delivered to the bone marrow. Furthermore, a low dose of radiation (2.8 Gy) was received by the GI tract compared to the larger dose of radiation (14.7 Gy) delivered to the marrow. Taken together, these results represent potentially significant improvements in the safe delivery of myeloablative therapy with high-dose targeted radioimmunotherapy, prior to HCT in older patients with R/R AML. This SIERRA trial is currently enrolling patients (www.sierratrial.com or clinicaltrials.gov NCT02665065). Disclosures Gyurkocza: Actinium: Research Funding. Nath:Actinium: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Daiichi Sankyo: Consultancy, Honoraria. Stiff:Kite, a Gilead Company: Research Funding; Gamida Cell: Research Funding; Atara: Research Funding; Unum: Research Funding; Delta-Fly: Research Funding; Macrogenics: Research Funding; Amgen: Research Funding. Hari:Amgen: Consultancy; GSK: Consultancy; Janssen: Consultancy; BMS: Consultancy; Takeda: Consultancy; Incyte Corporation: Consultancy. Al-Kadhimi:Actinium Pharmaceuticals Inc.: Research Funding; Genzyme: Research Funding; Bluebird Bio: Current equity holder in publicly-traded company; Gilead Science: Current equity holder in publicly-traded company; Moderna: Current equity holder in publicly-traded company; Novavax: Current equity holder in publicly-traded company. Abboud:Ryvu: Research Funding; Actinium Pharmaceuticals Inc.: Research Funding; Pfizer: Research Funding; Johnson & Johnson: Current equity holder in publicly-traded company; BMS: Current equity holder in publicly-traded company; Abbott Labs: Current equity holder in publicly-traded company; AbbVie Inc: Current equity holder in publicly-traded company; AlloVir: Research Funding; Forty Seven Inc: Research Funding. Magalhaes-Silverman:Kadmon Holdings: Research Funding; Actinium Pharmaceuticals: Research Funding; Incyte: Research Funding. Foran:Xencor: Research Funding; Trillium: Research Funding; Takeda: Research Funding; Kura Oncology: Research Funding; Aptose: Research Funding; Aprea: Research Funding; Actinium: Research Funding; Boehringer Ingelheim: Research Funding; Abbvie: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Revolution Medicine: Consultancy; Agios: Honoraria, Research Funding; H3Biosciences: Research Funding. Schuster:Amgen, Abbvie, Gilead, Takeda, Celgene, Pharmacyclics, Astellas, Verastem, Merck, Novartis, Takeda, Genentech,, Seattle Genetics: Other: Personal Fees; Karyopharm: Membership on an entity's Board of Directors or advisory committees. Kebriaei:Pfizer: Other: Served on advisory board; Kite: Other: Served on advisory board; Amgen: Other: Research Support; Ziopharm: Other: Research Support; Novartis: Other: Served on advisory board; Jazz: Consultancy. Levy:Karyopharm,Takeda, BMS: Consultancy, Honoraria, Speakers Bureau. Giralt:KITE: Consultancy; NOVARTIS: Consultancy, Honoraria, Research Funding; OMEROS: Consultancy, Honoraria; ACTINUUM: Consultancy, Research Funding; MILTENYI: Consultancy, Research Funding; TAKEDA: Research Funding; CELGENE: Consultancy, Honoraria, Research Funding; JAZZ: Consultancy, Honoraria; AMGEN: Consultancy, Research Funding. Liang:Actinium Pharmaceuticals: Current Employment. Berger:Actinium Pharmaceuticals Inc.: Current Employment, Current equity holder in publicly-traded company. Reddy:Actinium Pharmaceuticals Inc.: Current Employment, Current equity holder in publicly-traded company.

Crystal-storing histiocytosis (CSH) is an uncommon condition in which histiocytes accumulate a crystalline matter within their cytoplasm. Generally, those crystals are composed of either monoclonal or polyclonal immunoglobulin chains, which have a strong association with an underlying lymphoproliferative or plasma cell disorder (LP-PCD). Rarely, CSH has been reported as local or generalized manifestation of a variety of benign disorders. These cases are associated with crystals composed of nonimmunoglobulin substances. We are reporting an exceptional case of a local colonic CSH with Charcot–Leyden crystals. This patient underwent a screening colonoscopy that detected some polyps. The biopsy reported tubular adenomas, with a markedly dense, transmural inflammatory infiltrates, which were predominantly composed of eosinophils and crystal-storing histiocytes containing Charcot–Leyden crystals. The patient had a negative workup for LP-PCD and autoimmune conditions, including a normal skeletal survey and bone marrow aspirate/biopsy. The only positive laboratory workup was an elevated absolute eosinophil count and a positive IgG anti-Strongyloides antibody. Giving those findings, this parasitic infection is the most likely etiology of the CSH in our patient. Although there was an initial negative evaluation for LP-PCD, close monitoring of patients with either immunoglobulin or nonimmunoglobulin CSH is recommended.

AbstractDonor cell leukemia is a very rare cause of relapse after allogeneic hematopoietic cell transplantation (alloHCT). Herein, we describe an unprecedented case of donor cell‐derived chronic myelomonocytic leukemia (CMML) presenting seven years after a 51‐year‐old man received a matched‐related alloHCT from his 59‐year‐old brother for T‐cell acute lymphoblastic leukemia.

7523 Background: tALL is a recently appreciated but poorly defined clinical entity. We define tALL as any prior exposure to cytotoxic chemotherapy and/or radiation for another malignancy, and we report a comparative analysis of characteristics, cytogenetics and outcomes for this subset among a modern unselected ALL cohort from the Mayo Clinic Cancer Center (MCCC). Methods: We performed a systematic search in the 3-site MCCC registry and included all patients (pts) diagnosed and received at least 1 cycle of ALL-directed therapy and/or underwent allogeneic transplantation (AlloHCT) between 2008-2018. Comparisons of characteristics between tALL and dnALL were made using a Wilcoxon rank sum test (continuous variables) and Fisher’s exact test (categorical variables). Time-to-event variables were compared using unadjusted Cox proportional hazards regression models. Results: 431 ALL pts were identified during the study period, including n = 69 (16%) classified as tALL. Median follow-up from diagnosis was 2.3 years (range 0-18 years). The most common prior malignancies among tALL pts were Breast (24.6%), Lymphoma (15.9%), Myeloid (15.9%), GU/GYN (14.5%) and Myeloma (11.6%). In comparison to dnALL, pts with tALL were significantly older (63.2 vs 45.2 years, P < 0.001), more often female (65.2% vs 39.8%, P < 0.001), less frequently Hispanic (3.5% vs 13.1%, P = 0.042); more often of B-lineage (92.8% vs 81.8%, P = 0.022). On review of cytogenetics, tALL pts more often had hypodiploidy/near triploidy (Ho/Tr) (21.7% vs 4.1%, P < 0.001), more often had monosomal (MDS-like) (33.3% vs 12.4%, P = 0.0047) and complex karyotype (38% vs 17.3%, P = 0.0069). Importantly, incidence of BCR/ABL-positive (Ph+) ALL was not significantly different. Latency period between exposure to prior cancer therapy and development of tALL was significantly longer for Ph+ compared to Ph-negative ALL (median 9 vs. 4 years, P = 0.007). Patients with tALL had a 3-year OS after diagnosis of 37% [vs 59.7% for dnALL (HR death 1.86, 95% CI 1.31-2.65, P < 0.001)]. However, the two groups did not differ significantly regarding occurrence of AlloHCT (HR = 0.91, 95% CI 0.63-1.31, P = 0.61) or post-AlloHCT survival (HR = 1.29, 95% CI 0.75-2.23, P = 0.35). Conclusions: Therapy-related ALL represents an important & unique clinical entity with poor prognosis & adverse cytogenetic features. Ph+ tALL has a longer latency and similar frequency in both tALL and dnALL. AlloHCT appears to be an appropriate treatment strategy, possibly abrogating the poor prognosis of tALL.

7021 Background: Case-control studies (CCS) have identified germline variants (GVs) & genes associated with AML risk and/or outcome. However, whether these genes also harbor somatic mutations (SMs) in AML and whether these SMs are associated with clinical phenotypes and outcome is unknown. We systemically interrogated PubMed (terms "AML genetic polymorphisms"), yielding 612 reports (1981-2018), from which we identified unique variants/single nucleotide polymorphisms (SNPs) in 100 genes associated with AML risk and/or outcome in CCS. To determine the prevalence and relevance of SMs in these genes in an unselected AML population, we performed an analysis using WES of cases in the highly-annotated MCAEC (Finn, Ca Epidemiol 2015). Methods: We performed WES using remnant cytogenetic pellets from AML diagnosis in 98 MCAEC patients with available samples, sequenced at a depth of ~100 million paired-end 100bp reads using Agilent SureSelectXT Human All Exon V5 + UTRs target enrichment kit. Sequencing reads were aligned to human reference genome, and SMs including non-synonymous (NS) and truncating single nucleotide variants (SNVs) and small INDELs were identified and filtered using Exome Sequencing Project, 1000 genome, HapMap, & Mayo Clinic (MC) internal Biobank GV database. Copy number aberrations (CNAs) were identified & filtered using public CN polymorphism databases. For this analysis we evaluated the prevalence of somatic SNVs, INDELs, & CNAs in the 100 nominated genetic risk genes in collaboration with MC Cancer Center to determine their association with clinical phenotype and outcome. Results: Of the 100 unique genes, there were 40 with SM in our dataset, with 126 total mutations. Most were mutated in a very small number of patients, allowing insufficient statistical power to perform association analyses. However, an NS mutation in CYP2B6 (c.785A > G, p.Lys262Arg) had a minor allele frequency of 12.0%; this variant has been reported in association with breast cancer risk, but not with AML. Conclusions: We studied SM’s in AML genetic risk genes using WES of tumor samples. While representing a smaller sample size, this suggests their contribution to AML development may be limited in a broader clinical population. These results & prevalence of the novel CYP2B6 rs2279343 variant in AML must be confirmed in larger cohorts.

7104 Background: The use of MRD to predict outcome in AML is controversial. We sought to determine concordance between FC and BM biopsy morphology on day 14 (D14BM) and CR bone marrow (CRBM) specimens and whether MRD detected by FC predicted for inferior outcomes. Methods: We performed a retrospective analysis of adult AML patients treated between 2005 and 2010 with standard induction chemotherapy. Based upon BM morphology and FC, patients were designated as BM+FC+, BM+FC-, BM-FC+, or BM-FC-. Outcomes assessed included induction failure, RFS and OS. Results were adjusted for age at diagnosis, NCCN risk classification, and secondary AML status. Results: Of 287 evaluable patients, 74 had D14 BM and FC results and 98 had CR BM and FC results. Using BM morphology as the gold standard, discordance rates for the presence and absence of disease for the D14 BM by FC were 29% and 23% respectively. Multivariate analysis revealed that patients categorized as BM-FC+ at D14 were more likely to experience induction failure (HR 8.62, CI 0.36-208) and had lower RFS and OS (HR 1.47, 1.95 CI 0.40-5.41, 0.52-7.36 respectively). Analysis of the CR BM samples showed similar results. Conclusions: In this retrospective study there was a high discordance rate between FC and BM morphology on D14 BM and CR BM. While there was a trend toward inferior patient outcomes when disease was detected by FC but not morphology, this was not statistically significant. Limitations of our study include the retrospective nature of the analysis, paucity of patient samples that had a FC evaluation, lack of data to see if positive FC at D14 or CR changed clinician therapy choices and interpretation bias by pathologists as a result of access to FC results during BM morphology interpretation. Larger prospective studies are needed to evaluate whether MRD detected by FC as early as D14 during AML therapy affects clinical outcomes.

7046 Background: In CML-CP there is perceived complexity in risk stratification at diagnosis, and in testing for BCR-ABL kinase domain mutation (KD mut, including T315I) at relapse. We sought to understand AHOP practices in the context of NCCN and European LeukemiaNet guidelines. Methods: Between 2010 and 2012, we studied time dependent practice preferences of n=1,335 AHOP’s using a proprietary, live, case-based market research tool. A core case scenario and variations based on available diagnostic & treatment options were constructed. Preference data were acquired using blinded audience response technology. All responses for each scenario were obtained contemporaneously prior to any display of summary respondent selections. All sources of research support were double blinded. AHOP's were presented with a scenario of 59-year old CML-CP patient, then indicated preferred management from up to 9 relevant available/emerging diagnostic or therapeutic options following relapse after 1st-line imatinib. Results: The majority of AHOP’s in 2012 either did not calculate (52%), or were unfamiliar (21%) with Sokal or Hasford risk stratification score. Diagnostic preferences following relapse from 2010-12 are noted in Table (distribution over time, p<0.0001). If T315I was then detected in scenario, we noted marked differences in subsequent treatment preference in 2012 vs. 2011, respectively: decreased AlloBMT (16% vs. 32%); & increased 2nd-line dasatinib (26% vs. 14%) or bosutinib (12% vs. 8%) vs. nilotinib (8% vs. 20%) despite lack of efficacy for each in T315I. Preference increased slightly for ponatinib (16% vs. 14%), but not for omacetaxine (2% vs. 6%). Conclusions: Most AHOP’s do not apply risk stratification. Increasing preference for KD mut panel testing at relapse conforms to guidelines, although not all AHOP’s test. Heterogeneity in T315I treatment suggests uncertainty or unfamiliarity with newer agents, and evidence-based efforts are needed to improve awareness. [Table: see text]

7047 Background: In addition to secondary AML (sAML), important lifestyle and environmental exposures associated with increased risk of AML development have been identified in recent case-control studies including obesity (BMI>30kg/m2), smoking, regular acetaminophen use, and rural/farm habitat. The association of these exposures with AML cytogenetic risk groups is unknown. We therefore evaluated relevant exposures in a cohort of 301 AML patients with confirmed central cytogenetics analysis diagnosed and treated at Mayo Clinic FL and AZ since 1995. Methods: Documented patient exposures were extracted from central electronic medical records, including: prior chemotherapy/radiation or hematologic malignancy, occupation, select medications, “toxins” (esp. benzene) and solid organ transplantation (SOT). Standard cytogenetic risk categories (including intermediate abnormal) were applied. The association of epidemiologic exposures with cytogenetic risk was evaluated on multivariable analysis using logistic regression models. Results: sAML was significantly associated with cytogenetic risk groups, as was prior SOT, healthcare occupation, farm habitat and toxin exposures [see Odds Ratios (OR), Table). In contrast, prior radiation for epithelial malignancies, smoking and BMI were not independently associated with specific cytogenetic risk categories. Conclusions: Specific epidemiologic exposures are significantly associated with AML cytogenetic risk categories suggesting a unique clinical phenotype. This supports a link to leukemogenesis and requires validation in a controlled prospective therapeutic study. [Table: see text]