Inferior Relapse-free Survival Research Articles

Expression and prognostic value of transcription-associated cyclin-dependent kinases in human breast cancer.

The expression and prognostic significance of transcription-associated cyclin-dependent kinases (TA-CDKs) in breast cancer have not been systematically investigated. Using Oncomine, GEPIA2, the Human Protein Atlas, the Kaplan-Meier Plotter, cBioPortal, Metascape, and DAVID 6.8, we profiled the expression of TA-CDKs in breast cancer, inferred their biological functions, and assessed their effect on prognosis. The expression of CDK7/10/13/19 mRNAs in breast cancer tissues was significantly higher than in normal breast tissues. Survival analysis of breast cancer patients revealed that increased CDK8 expression was associated with inferior overall survival (OS), higher expression of CDK7 or CDK8 was associated with inferior relapse-free survival (RFS), but higher expression of CDK13 was associated with favorable RFS and OS. In addition, a high genetic alteration rate (56%) in TA-CDKs was associated with shorter OS. On functional enrichment analysis, top GO enrichment items for TA-CDKs and their neighboring genes included cyclin-dependent protein serine/threonine kinase activity and transferase complex. The top KEGG pathways included cell cycle and mismatch repair. These results suggest that CDK7/8/13 are potential prognostic biomarkers for breast cancer patients and provide novel insight for future studies examining their usefulness as therapeutic targets.

Outcomes of pediatric mixed phenotype acute leukemia treated with lymphoid directed therapy: Analysis of an institutional series from India

There is limited data regarding pediatric mixed phenotype acute leukemia (MPAL) and there is no global consensus on its management yet. In this retrospective study, we analyzed the outcomes of children diagnosed with MPAL at our institute. This study included children ≤ 14 years with MPAL who presented to a tertiary cancer center in India from January 1st 2009 to December 31st 2015. Over a seven-year period, 1390 patients with leukemia presented to our institute of which 22 patients (1.5%) had MPAL. Sixteen patients (72.7%) had B/myeloid leukemia, while 4 (18.1%) and 2 (9%) patients had T/myeloid and B/T leukemia respectively. Twenty-one patients were treated with a modified BFM ALL 95 protocol. 76.1% (n = 16) of patients had a good prednisolone response (GPR) on day 8 and end-of-induction (EOI) marrow was in remission in 90.5% (n = 19). A poor prednisolone response (PPR) on day 8 correlated with an inferior relapse-free survival (25% vs 79.5%, P=.025). The 4-year event-free survival (EFS) and overall survival (OS) for the entire group was 60.8% and 64.9% respectively while the EFS for patients who had a GPR and remission at the EOI (n = 15) was 80% as compared to 16.7% in patients with PPR or induction failure. Lymphoid directed chemotherapy is seen to have good survival outcomes in pediatric MPAL. However, a PPR on day 8 or a positive EOI marrow may be an indication for more aggressive treatment.

Grade 3–4 cytokine release syndrome is associated with poor survival in haploidentical peripheral blood stem cell transplantation

The information on the impact of cytokine release syndrome (CRS) on haploidentical donor peripheral blood stem cell transplant (haploPBSCT) outcomes is limited. We retrospectively evaluated 98 patients who underwent haploPBSCT between June 2012 and June 2019 for the onset and severity of CRS per the ASTCT guidelines. The incidence of CRS was 93% (91/98). Outcomes were compared between grade 1–2 and 3–4 CRS. Eighty-one patients developed grade 1–2 CRS (89%) and 10 (11%) developed grade 3–4 CRS. Compared to grade 1–2 CRS, grade 3–4 CRS experienced adverse survival (73.7% vs. 30%, p<.001), inferior relapse-free survival (64.0% vs. 20%, p<.001), and higher non-relapse mortality (NRM) (16.4% vs. 60%, p<.001) at 1-year. Propensity score-based multivariable analyses revealed worse survival (HR 2.71, p=.04), and higher NRM (SHR 4.51, p=.006) with grade 3–4 CRS. Our study shows that grade 3–4 CRS was adversely associated with survival. Therefore, early identification and preventive strategies are warranted.

Allogeneic Hematopoietic Cell Transplantation for Relapsed and Refractory Philadelphia Negative B Cell ALL in the Era of Novel Salvage Therapies

Introduction of novel salvage therapies and expansion of the donor pool within the past decade have allowed more patients with relapsed/refractory (r/r) B cell acute lymphoblastic leukemia (B-ALL) to receive allogeneic hematopoietic cell transplantation (alloHCT). The impact of each salvage therapy on transplant outcomes have not been compared. Our primary objective was to determine post-HCT relapse-free survival (RFS) in adult patients with r/r Philadelphia-chromosome negative (Phneg) B-ALL. We retrospectively studied alloHCT outcomes in 108 adult patients with r/r Phneg B-ALL transplanted in morphological remission achieved by salvage therapy. Salvage therapies were chemotherapy-based combination (n=45, 42%), blinatumomab (n=43, 40%), inotuzumab (n=14, 13%), or CAR T cells (n=6, 6%). The 2-year RFS and overall survival (OS) were 44% and 50%, respectively. In multivariable analysis, conditioning with reduced-intensity or non-myeloablative regimens (hazard ratio [HR]=2.23, 95% confidence interval [CI], 1.31-3.80; P=.003), having received ≥3 lines of therapies prior to transplant (HR=2.66, 95% CI, 1.56-4.54; P < .001), and inotuzumab (HR=2.42, 95% CI, 1.14-5.12; Wald P value=.021) were independently associated with lower RFS. Blinatumomab (HR=1.10, 95% CI, 0.62-1.96) had comparable RFS to chemotherapy. Incidence of hepatic sinusoidal syndrome was highest with inotuzumab (P < .001); however, 30-day mortality and intensive care unit admissions were not different per salvage therapy. The alloHCT in r/r Phneg B-ALL after remission induction with blinatumomab or chemotherapy led to encouraging outcomes if morphologic CR was achieved. In contrast, pretransplantation inotuzumab therapy was associated with inferior RFS. Larger studies are warranted to confirm our observations. Early transplantation after relapse and the utilization of myeloablative conditioning, when feasible, were key factors associated with improved outcomes after alloHCT in these patients.

Allogeneic Stem Cell Transplantation for Mantle Cell Lymphoma Can Achieve Durable Remission and Myeloablative Conditioning Is Associated with Inferior Survival: An Australasian Bone Marrow Transplant Recipient Registry Study

Introduction Mantle cell lymphoma (MCL) is a mature B lymphoproliferative disorder with a frequently aggressive clinical course. Although the response rates in patients eligible for conventional chemoimmunotherapy are high, relapses are virtually inevitable, with a median overall survival (OS) of three to five years. For some patients allogeneic stem haematopoietic cell transplantation (alloHCT) is a potential therapeutic option. AlloHCT for MCL has been associated with long term overall survival (OS) of around 40%, with high rates of non-relapse mortality (NRM) of 20-40% and relapse rates of 20-30% (Urbano-Ispizua et al., Biol Blood Marrow Transplant 2015;21:1746, Robinson et al., Leukemia 2015;29:464). Whilst there is evidence of a graft-versus-lymphoma effect in MCL, it has not been shown to translate into improved OS. We performed a retrospective national registry study to examine alloHCT practice and outcomes for MCL in Australia and New Zealand in the modern era. Methods Data was collected through the Australasian Bone Marrow Transplant Recipient Registry (ABMTRR) for patients receiving an alloHCT for MCL between January 2009 and December 2019. This time range was chosen to capture the era of widespread rituximab use. Survival, relapse and toxicities of alloHCT were investigated, as well as transplant trends over time. Survival was analysed using the Kaplan-Meier method, with comparisons between the transplant periods 2009-2014 and 2015-2019 performed using the log-rank test. Cox proportional hazards regression was performed to determine significant risk factors for transplant outcome. The following risk factors were analysed for impact on outcomes: age, transplant before 2015, previous autologous HCT (autoHCT), remission status at transplant, use of myeloablative conditioning (MAC), haploidentical donor and use of T cell depletion (TCD). Results A total of 86 patients were included in the analysis. The median age was 56 (range 39-71). There was a male predominance with only 12% female patients. At the time of transplant, 51% were in complete remission, 26% had a partial response and 20% had stable or progressive disease (data missing in 3%). Sixty-seven percent had undergone previous autoHCT. The majority of donors were HLA-matched siblings (51%), followed by HLA-matched-unrelated (42%) and haploidentical (7%). Myeloablative conditioning was utilised in 14%, and T-cell depletion (TCD) in 24%. The median times to neutrophil engraftment (&amp;gt;0.5x109/L) and platelet engraftment (&amp;gt;20x109/L) were 16 and 20 days respectively. NRM at 1 and 5 years was 23% (95% confidence interval [95%CI] 10-39%) and 30% (95%CI 15-48%) respectively. The 100-day cumulative incidence of grade II to IV acute GVHD was 29%. The 3-year cumulative incidence of chronic GVHD was 27%. The median duration of follow up was 4.17 years (range 0-9.6 years). Median OS was 4.2 years, with an estimated 5-year OS of 47% (95%CI 35-58%) and 10-year OS of 23% (95%CI 8-43%) (figure 1). Five-year relapse free survival (RFS) was 38% (95%CI 26-50%) (figure 2). The cumulative incidence of relapse (CIR) was 20% at 1 year and 33% at 4 years, with a flattening of the curve after this point (figure 3). On multivariate analysis (MVA), the use of myeloablative conditioning (MAC) was associated with inferior RFS (hazard ratio 2.33; 95%CI 1.05-5.17; p=0.038) and OS (hazard ratio 3.11; 95%CI 1.39-7.00; p=0.006) (figure 4). No risk factors on MVA impacted NRM or CIR. Chronic GVHD was not associated with RFS or CIR. An average of nine alloHCTs were performed each year. There was an increase in the proportion of haploidentical transplants between 2009-2014 and 2015-2019 (4% to 10%). There was no significant change over time in OS, RFS or NRM, or in the use of MAC or TCD. Conclusion There has been no significant change in the rates of alloHCT for MCL in Australia and New Zealand over the past decade. Trends show an increasing utilisation of haploidentical donors. Overall outcomes were comparable to those previously published with favourable OS and durable remissions seen in a subset of patients. MAC was associated with inferior OS and RFS, however the cause for this is unclear given the lack of association with NRM or CIR. Ongoing reporting of alloHCT outcomes in MCL is important given the emerging role of novel therapies, such as Bruton tyrosine kinase inhibitors, bispecific T cells and CAR-T cell therapy. Figure 1 Disclosures Di Ciaccio: Jansen: Honoraria, Other: travel and accomodation grant. Greenwood:MSD: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Servier: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hamad:Novartis: Honoraria; Abbvie: Honoraria.

Allogeneic Blood or Marrow Transplantation (BMT) with Post-Transplantation Cyclophosphamide (PTCy) Based Graft Versus Host Disease (GVHD) Prophylaxis for Myelodysplastic Syndrome/ Myeloproliferative Neoplasm-Overlap Syndromes (MDS/MPN)

INTRODUCTION: MDS/MPN are a group of clonal hematopoietic disorders with overlapping features of MDS and MPN, and include chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia (aCML), MDS/MPN-unclassifiable along with juvenile myelomonocytic leukemia and MDS/MPN with ring sideroblast and thrombocytosis. Therapeutic options for MDS/MPN remain limited and BMT remains the only modality with curative potential. However, the overall survival of these patients following BMT remains poor marked by a high incidence of non-relapse mortality (NRM) and relapse. Moreover, most of the published cohorts consisted of patients receiving matched related donor grafts, with limited data on the outcomes of patients receiving grafts from alternative donors. In the current study, we aim to describe outcomes of BMT for MDS/MPN using PTCy as the GVHD prophylaxis platform and primarily haploidentical related (haplo) donors. PATIENTS AND METHODS: We performed a retrospective analysis of patients with MDS/MPN who underwent BMT with PTCy at Johns Hopkins between 1/2011-1/2019. Kaplan-Meier analysis was used to evaluate overall survival (OS), relapse-free survival (RFS), and GVHD/relapse-free survival (GRFS). Cumulative incidence of relapse and non-relapse mortality (NRM) were estimated non-parametrically in presence of competing events where NRM was a competing event of relapse, and vice versa. Univariate analysis was used to evaluate the impact of donor type, HCT-CI, and karyotype on these clinical outcomes via Cox proportional hazard models for OS/RFS/GRFS, and Fine-Gray's sub-distribution (s) hazard models for relapse/NRM/GVHD. RESULTS: Thirty-four consecutive patients (11 women and 23 men) with a median age of 63 years (range 51-74) at the time of BMT were identified. Of these, 21 (61.8%) had haplo donors and 31 (91%) received non-myeloablative conditioning with fludarabine, cyclophosphamide and total body irradiation. Median follow up was 3.9 years (range: 24 days - 8.4 years) based on reverse Kaplan-Meier approach. Other patient, disease and BMT related details are shown in Table 1. Time to neutrophil and platelet recovery was 22 days (range 19 - 28 days) and 31 days (range 22 - 67 days), respectively. Two (6%) patients had primary graft failure, both had received a marrow graft. At 3-years, probability of OS was 46% (95% CI: 31% - 68%), 3 RFS was 30% (17% - 51%), GRFS was 26% (14%-48%), cumulative incidence of relapse was 59% (95% CI: 41% - 77%) and incidence of NRM was 12% (95% CI: 1% - 23%). The incidence of grade 2-4 acute GVHD at 1 year following HCT was 24% but no patients had grade 3-4 acute GVHD. The cumulative incidence of any chronic GVHD at 3 years was 20% with 3 (9%) patients requiring systemic therapy. Univariate analysis showed that HCT-CI score at the time of HSCT was associated with higher incidence of relapse (sHR 5.22, 95% CI 2.26-12.08) and inferior RFS (HR 3.09, 95% CI 1.16-8.2). Other patient-, disease- and HCT-related factors were not statistically significantly associated with these clinical outcomes. The outcomes of patients with haplo donors (n=21) were also estimated at 3 years and estimates of OS were 56% (95% CI 38% - 82%), RFS 42% (95% CI 26% - 70%), GRFS 37% (21% - 66%), cumulative incidence of relapse 43% (95% CI 21% - 66%), NRM 14% (95% CI 1% - 30%), chronic GVHD 21% (95% CI 2% - 40%). No patients developed grade 3-4 acute GVHD. While the sample size is limited, comparison of K-M estimates for RFS and relapse with haplo donor (n=21) and matched related/unrelated donor (n=12), is shown in Figure 1. CONCLUSIONS: We report, for the first time, clinical outcomes of BMT for MDS/MPN with the PTCy based GVHD platform, and outcomes appear comparable with those previously described in other retrospective studies using conventional approach. Although limited by sample size for a statistical analysis, the outcomes with haplo donor BMT appear promising. The relatively high incidence of relapse in these patients appears to be the major factor contributing adversely to outcomes, while NRM and GVHD incidence with our non-myeloablative conditioning PTCy platform are low. We are currently exploring strategies to decrease relapse rates to further improve BMT outcomes in these patients. Disclosures Levis: Amgen: Honoraria; FujiFilm: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria; Menarini: Honoraria; Astellas: Honoraria, Research Funding. DeZern:MEI: Consultancy; Astex: Research Funding; Abbvie: Consultancy; Celgene: Consultancy, Honoraria. Gojo:BMS: Membership on an entity's Board of Directors or advisory committees; Genentech: Research Funding; Amgen: Research Funding; Merck: Research Funding; Amphivena: Research Funding. Jain:Takeda: Consultancy, Honoraria; CareDx: Other: Advisory Board; Bristol Myer Squibb: Other: for advisory board participation.

BCOR Mutations in Acute Myeloid Leukemia: Clonal Evolution and Prognosis

Background BCOR gene is a transcription repressor that may influence normal hematopoiesis and is associated with poor prognosis in acute myeloid leukemia (AML) with normal karyotype. However, due to the rare mutation frequency in AML (3.8%-5%), clinical characteristics and prognosis of AML patients with BCOR mutation including abnormal karyotype are still unknown. In addition, the clonal evolution of AML patients with BCOR mutation has not been fully investigated. Methods By means of next generation of sequencing, we performed sequencing of 114 genes related to hematological diseases including BCOR on 509 newly diagnosed AML patients (except for acute promyelocytic leukemia) from March 2017 to April 2019. The 2017 European Leukemia Net (ELN) genetic risk stratification was used to evaluate prognosis. Overall survival (OS) was defined as the time from diagnosis to death or last follow-up. Relapse-free survival (RFS) was measured from remission to relapse or death. Clonal evolution was investigated through analyzing bone marrow samples at diagnosis, complete remission (CR) and relapse from the same patient. Result Among 509 AML patients, we found BCOR mutations in 23 patients (4.5%). BCOR mutations were enriched in patients with mutations of RUNX1 (p = 0.008) and BCORL1 (p = 0.0003). Patients with BCOR mutation were more at adverse ELN risk category compared to patients without BCOR mutation (p = 0.007). Besides, there was a larger proportion of patients with normal karyotype in BCOR mutation group but it had not reached statistical difference (62.5% vs 45.5%, p = 0.064). The abnormal karyotype in patients with BCOR mutations included trisomy 8, t(9;11), inv(3), -7 and complex karyotype.There were no significant differences in age, sex, white blood cell count, hemoglobin or platelet count between the two groups. More patients died during induction (13.0% vs 3.5%, p = 0.56) and fewer patients achieved CR after 2 cycles of chemotherapy when patients had BCOR mutations (69.6% vs 82.5%, p = 0.115) but the difference had not reached statistical difference . Patients with BCOR mutations had inferior 2-year OS (52.1% vs 70.7%, p = 0.0094) and 2-year RFS (29.8% vs 61.1%, p = 0.0090). After adjustment for ELN risk stratification, BCOR mutation was still remain a poor prognostic factor. However, the adverse prognostic impact of BCOR mutation is overcome by hematopoietic stem cell transplantation (HSCT), in which there was no difference between BCOR mutation group and wild type group (p = 0.474) (Figure 1). Through analysis of paired bone marrow sample at diagnosis, remission and relapse, we revealed the clonal evolution that BCOR mutation was only detected at diagnosis sample as a subclone and diminished at CR and relapse while TP53 mutation was only detected at relapse with a variant allele frequency (VAF) of 25.5%. We also found BCOR mutation at another patient's diagnosis and relapse sample while TP53 mutation was detected at relapse with VAF of 11.8%. Conclusion BCOR is associated with RUNX1 mutation and higher ELN risk. AML patients with BCOR mutation including normal and abnormal karyotype conferred a worse impact on OS that can be overcome by HSCT. BCOR mutation is a subclone at diagnosis or relapse in some patients, in which TP53 mutation clone occurred at relapse. Disclosures No relevant conflicts of interest to declare.

Low expression of CTBP2 and CASP8AP2 predicts risk of relapse in childhood B-cell precursor acute lymphoblastic leukemia: a retrospective cohort study

CtBP is a known corepressor abundantly expressed in cancer and regulates genes involved in cancer initiation, progression, and metastasis. This study aimed to investigate the prognostic significance of CTBP2 expression in a cohort of pediatric patients with B cell precursor acute lymphoblastic leukemia (BCP-ALL). It further evaluated the role of combined CTBP2 and CASP8AP2 expression in risk of relapse of BCP-ALL. The expression of CTBP2 mRNA was retrospectively detected by a qRT-PCR approach in bone marrow samples from 104 children with newly diagnosed BCP-ALL. CASP8AP2 was assessed simultaneously in the 100 patients included in this study. The receiver operating characteristic (ROC) curve analysis determined the cut off levels for CTBP2 and CASP8AP2 expression with good predictive significance for relapse of BCP-ALL. Patients with low CTBP2 expression had inferior relapse-free survival (RFS) and event-free survival (EFS) when compared to patients with high-CTBP2 expression. The expression level of CTBP2 was significantly associated with CASP8AP2 expression (r = 0.449, P < 0.001). Patients were stratified into three groups according to the combined evaluation of the two gene expression, and patients with simultaneous low-expression had the worst outcome (6-year RFS: 64.6%±12.8%, P < 0.001). Multivariate analysis demonstrated the expression of CTBP2 and CASP8AP2, minimal residual disease (MRD) at day 33 remained as independent prognostic factors for RFS. Based on the final Cox hazards model, we proposed an algorithm to calculate the risk index, which was more precise for predicting relapse. In conclusion, low expression of CTBP2 and CASP8AP2 correlated with poor outcome and predicted risk of relapse in pediatric BCP-ALL.

Prognostic Impact of Extramedullary Infiltration in Pediatric Low-risk Acute Myeloid Leukemia: A Retrospective Single-center Study Over 10 Years

BackgroundThe impact of extramedullary infiltration (EMI) on the clinical outcomes of pediatric patients with acute myeloid leukemia (AML) are controversial. Patients and MethodsA total of 214 pediatric patients with low-risk AML were classified as having EMI (central nervous leukemia [CNSL] and/or myeloid sarcoma [MS]) and not having EMI. Patients with isolated MS before AML diagnosis by bone marrow examination were confirmed with histopathologic examination. For patients diagnosed with AML by bone marrow examination, a thorough physical examination and radiologic imaging were used to confirm MS. ResultsMale gender, a high white blood cell count, the FAB-M5 subtype, t(8;21) and t(1;11) abnormalities, and c-KIT mutations were associated with EMI. The presence of MS was associated with a low complete remission rate (63.6% vs. 79.4%; P = .000) and poor 3-year relapse-free survival (RFS) (62.6% ± 7.5% vs. 87.0% ± 2.8%; P = .000) and 3-year overall survival (73.5% ± 7% vs. 88.8% ± 2.6%; P = .011). Multivariate analysis revealed that MS was a poor prognostic factor for RFS and overall survival. Bone infiltration was an independent risk factor for inferior RFS with MS. Patients with CNSL had a low complete remission rate (58.3% vs. 77.2%; P = .045); however, CNSL did not significantly affect the survival of low-risk patients with AML. ConclusionMS should be considered an independent risk factor to guide stratified treatment.

Breast cancer: The Indian scenario.

e12567 Background: This study was undertaken to evaluate the clinic-pathological characteristics and outcome of patients with female breast cancer at I.R.C.H, AIIMS, New Delhi, one of the largest tertiary-care cancer center in India. Methods: This ambispective study included patients with breast cancer in females, registered at our institute from January 1st, 2014 to December 31st, 2018.We retrieved data from prospectively maintained clinical case records. Results: We included 997 patients with median age of 47.5 years (21–90) The TNM (AJCC-7th edition) stage distribution was stage I, 40 (4.01%); stage II, 326 (32.70%); stage III, 419 (42.02%); and stage IV, 212 (21.26%). The median tumour diameter was 5 cm. Infiltrating ductal carcinoma (96%) was the most common histologic subtype. Fifty eight percent of cases were positive for ER or/ and PR whereas 30.89% patients were HER2/neu positive. Triple negativity was found in 29.88 % of cases. Patients underwent breast conserving surgery in 28.2% of cases, 41.7% were received neo-adjuvant chemotherapy and 9.5 % of patients offered palliative chemotherapy. The pathological complete response was seen in 20.5% of cases. Loco-regional recurrence occurred in 2.8%, and 23.2% of patients developed distant metastases. The discordance of receptor was present in 20.5% for ER, 25.1% for PR, and 15 % for HER2/neu on re-biopsy at the time of relapse . Only 37.83% of the eligible patients received trastuzumab upfront. For non- metastatic group, the median time of relapse was 36 months, 3 year relapse free survival (RFS) was 73.5% and overall survival (OS) was 82.1% . Clinical stage(stage III), triple negativity and HER2 neu positivity were associated inferior RFS however pathological node involvement (HR 1.4, 95% CI 1.01–2.18, p = 0.01) and triple negativity (HR 1.9, 95% CI 1.36–2.90, p = 0.001) were associated with poor OS . For metastatic group, the median time of progression was 18 months and 3 year progression free survival (PFS) was 35% and OS was 20%. More than 2 sites of metastasis, upfront brain metastasis, triple negativity, and poor performance status (ECOG III/IV) were associated with inferior survival. Conclusions: This is one of the largest comprehensive data from a single center. Majority of our patients are younger in age, advance in stage, aggressive in biology and unaffordability of targeted therapy on eligible patients might lead to poor overall outcome. Triple negativity is found in around 30% of cases and associated with poor survival.

Post-transplant lymphoproliferative disorder (PTLD) after solid organ transplant (SOT): A multicenter real world analysis (RWA) of 877 patients (pts) treated in the modern era.

e20026 Background: Historically, SOT PTLD have modest outcomes in part due to heterogeneous treatment approaches. Additionally, there remains an absence of a large data repository in PTLD to help delineate contemporary pt outcomes &amp; prognostic factors. We conducted a large, multicenter RWA to study outcomes &amp; prognostication of SOT PTLD in the modern era. Methods: Retrospective data on 877 untreated SOT PTLD pts ages ≥18 years (yrs) (2000-2018) were analyzed from 15 academic centers. Prognostic factors for relapse free survival (RFS) &amp; overall survival (OS) were assessed by Cox model. Results: The median age at diagnosis was 54 yrs (range 18-84). The majority of pts were white (78%) &amp; male (67%). Median time from SOT to PTLD diagnosis was 57 months (range 0.23-470). SOT types: kidney (41%) liver (19%), lung (16%), and heart (11%); 11% multi-organ. Tumor was EBV+ in 52%. Graft involvement (18%) and rejection (21%) were seen in a proportion of pts. Most pts had reduction in immunosuppression (79%) and rituximab (R)-containing regimen (61%) as part of 1st line therapy (Tx). Most common Tx: R monotherapy (34%), R+chemotherapy (29%) &amp; chemotherapy without R (8%). Maintenance R use was infrequent (6%). Overall response rate was 63% [51% complete response (CR) and 12% partial response (PR)] and 19% of pts had primary refractory disease. With 44-month median follow-up (0.1-304), 62% of pts were alive. Median OS &amp; RFS for all pts were 12 &amp; 9 yrs, respectively, while differential survival rates were identified for several pt subsets (Table). On univariate analysis, lung SOT was associated with borderline RFS (HR 0.68 [95% CI 0.44-1.03], P= 0.07) and inferior OS (HR 0.67 [95% CI 0.49-0.91], P= 0.012), while EBV negative PTLD was associated with poorer RFS (HR 1.51 [95% CI 1.12-2.04, P= 0.006). In addition, achievement of PR to 1st line Tx vs CR was strongly prognostic for inferior RFS (HR 2.58 [95% CI 1.88-3.54], P&lt; .0001) and OS (HR 2.30 [95% CI 1.60-3.29], P&lt; .0001). Conclusions: In this large, multicenter PTLD RWA, type of SOT was strongly associated with long-term RFS and OS and EBV status predicted RFS. Furthermore, depth of response to 1st line Tx was a critical determinant for long-term pt survival. [Table: see text]

Oral arsenic trioxide, all-trans retinoic acid, and ascorbic acid maintenance after first complete remission in acute promyelocytic leukemia: Long-term results and unique prognostic indicators.

The role of arsenic trioxide (As2 O3 ) in the maintenance of first complete remission (CR1) in acute promyelocytic leukemia (APL) is unclear. A total of 129 consecutive adult patients with APL of all risk categories who achieved CR1 with conventional induction (all-trans retinoic acid [ATRA]/daunorubicin) and consolidation (daunorubicin/cytarabine [induction daunorubicin and consolidation omitted for age ≥70 years]) underwent maintenance comprising ATRA (45 mg/m2 /day), oral As2 O3 (10 mg/day), and ascorbic acid (1 g/day) (AAA) for 2 weeks every 2 months for 2 years. Over a 17-year period from August 1, 2002, to July 31, 2019, 63 men and 66 women (median age, 46 years [range, 18-82 years]) received AAA maintenance, which was alreadycompleted in 117 patients. At a median follow-up of 100 months (range, 8-215 months), 17 patients (13%) developed first relapse (R1) (hematologic, n=14; molecular, n=3) after a median of 19 months (range, 7-96 months) from CR1. Two R1 patients had concomitant central nervous system (CNS) involvement. All patients achieved CR2 with oral As2 O3 -based salvage. Five patients had a subsequent relapse and died. Eight patients died of unrelated causes while still in CR1. The 5-year and 10-year rates of relapse-free survival (RFS) were 89% and 85%, respectively. The 5-year and 10-year rates of overall survival (OS) were 94% and 87%, respectively. Multivariate analysis showed that inferior RFS was associated with FLT3-ITD (P=.005) and CNS involvement on presentation (P=.004), and inferior OS was associated with therapy-related APL (P=.03), FLT3-ITD (P=.03), and relapse (P=.03). The safety profile was favorable, with no grade 3/4 organ toxicities. CR1 maintenance with AAA is safe and results in favorable long-term survival in patients with APL.

Clinical presentation and differential splicing of SRSF2, U2AF1 and SF3B1 mutations in patients with acute myeloid leukemia.

Previous studies demonstrated that splicing factor mutations are recurrent events in hematopoietic malignancies with both clinical and functional implications. However, their aberrant splicing patterns in acute myeloid leukemia remain largely unexplored. In this study, we characterized mutations in SRSF2, U2AF1, and SF3B1, the most commonly mutated splicing factors. In our clinical analysis of 2678 patients, splicing factor mutations showed inferior relapse-free and overall survival, however, these mutations did not represent independent prognostic markers. RNA-sequencing of 246 and independent validation in 177 patients revealed an isoform expression profile which is highly characteristic for each individual mutation, with several isoforms showing a strong dysregulation. By establishing a custom differential splice junction usage pipeline, we accurately detected aberrant splicing in splicing factor mutated samples. A large proportion of differentially used junctions were novel, including several junctions in leukemia-associated genes. In SRSF2(P95H) mutants, we further explored the possibility of a cascading effect through the dysregulation of the splicing pathway. Furthermore, we observed a validated impact on overall survival for two junctions overused in SRSF2(P95H) mutants. We conclude that splicing factor mutations do not represent independent prognostic markers. However, they do have genome-wide consequences on gene splicing leading to dysregulated isoform expression of several genes.

Post-induction Measurable Residual Disease Using Multicolor Flow Cytometry Is Strongly Predictive of Inferior Clinical Outcome in the Real-Life Management of Childhood T-Cell Acute Lymphoblastic Leukemia: A Study of 256 Patients.

Background: Measurable/minimal residual disease (MRD) status is suggested as a powerful indicator of clinical-outcome in T-cell lymphoblastic leukemia/lymphoma (T-ALL). Contrary to B-cell ALL, reports on T-ALL MRD are limited and mostly based on molecular methods, mainly from developed countries. Multicolor flow cytometry (MFC)-based T-ALL studies are very few. Clinically relevant cut-off levels and ideal time-point for MRD assessment are still inconclusive. In view of lack of T-ALL MRD data from the developing world, we evaluated the prognostic value of MFC-based post-induction (PI)-MRD assessment in T-ALL in the context of standard practice.Methods: We included 256 childhood-T-ALL patients (age < 15 years) treated with a modified-MCP841 protocol, which uses high-dose cytarabine during consolidation, as a part of standard hospital practice. MRD was studied using 10-color 11-antibody MFC with any level of detectable disease being considered positive. Post-induction (PI)-MRD was available in all patients, and post-consolidation (PC) MRD was available mostly in PI-MRD-positive patients (n = 88).Results: Three years cumulative-incidence-of-relapse (3years-CIR) in PI-MRD-positive patients was inferior to negative patients (46.3% vs. 18.4%). The median relapse-free-survival (RFS), event-free-survival (EFS) and overall-survival (OS) with hazard ratio (HR) of PI-MRD-positive patients were 21.4 months vs not reached (p < 0.0001, HR-4.7), 21.6 months vs. not-reached (p = 0.0003, HR-2.01) and 37.3 months vs. not reached (p = 0.026, HR-1.64) respectively. RFS, EFS and OS of patients with PI-MRD<0.01% (n = 17) were as inferior as PI-MRD ≥ 0.01% in comparison with MRD-negative patients with HR of 4.7 (p < 0.0001), 2.45 (p = 0.0003), and 2.5 (p = 0.029), respectively. Three-years-CIR of patients with hyperleukocytosis (≥100 × 109/L) was also higher (50.5 vs. 27.6%) with inferior RFS, EFS, and OS. Among PI-MRD-positive patients, 3years-CIR, RFS, EFS, and OS of PC-MRD-positive were also inferior to that of negative patients. On multivariate analysis any-level detectable PI-MRD and hyperleukocytosis remained independently associated with inferior RFS, EFS, and OS. A combination of PI-MRD-positive status and hyperleukocytosis identified the patients with the worst clinical outcomes.Conclusion: Detectable PI-MRD using MFC was found to be the strong predictive factor of inferior clinical outcome in T-ALL patients. The combination of PI-MRD status and hyperleukocytosis provides the most influential tool for the management of T-ALL in resource constrained settings from developing world.

Pathogenic variants in PTEN to predict for increased risk of relapse and death in patients with limited stage small cell bladder cancer.

526 Background: Small cell bladder cancer (SCBC) is a rare histologic subtype with insufficient genomic characterization. Patients with limited stage (LS) SCBC have a poor prognosis, and no biomarker exists to optimize treatment selection. We sought to identify genomic aberrations in patients with LS-SCBC using a comprehensive next generation sequencing (NGS) platform. Mutations in the PTEN/AKT pathway are important in urothelial tumor biology but have an undefined role in SCBC. Methods: 23 LS-SCBC cases were identified. NGS was performed on diagnostic transurethral bladder tumor resection or cystectomy specimens containing SCBC. Detected variants were filtered by in silico algorithms predicting for a deleterious impact on protein function. Variant allele frequencies (VAF) greater than 2% were permitted in this analysis. Variants in the PTEN gene were assessed for association with relapse-free survival (RFS) and overall survival (OS) using Kaplan-Meier techniques and Cox proportional hazards models. Results: Median follow up for the cohort was 4.02 years. 14/23 (60.9%) patients have died. Six unique deleterious PTEN mutations were observed in 9/23 (39.1%) patients. p.W274C was the most common PTEN variant and was detected in 5 (21.7%) patients. Three variants were detected at &gt; 10% VAF. All 9 patients with a deleterious PTEN variant died. The presence of deleterious PTEN variants [HR = 4.68 [(1.54, 14.27), p = 0.003]] predicted for inferior OS. In the 19 patients with known relapse history, 6/7 (85.7%) with and 3/12 (25%) without any deleterious PTEN mutation relapsed. The presence of deleterious PTEN variants [HR = 9.41 [(2.32, 38.23), p &lt; 0.001]] also predicted for inferior RFS. Conclusions: Pathogenic variants in tumor suppressor PTEN were associated with inferior RFS and OS in this pilot cohort of patients with LS-SCBC, suggesting that disruption of PTEN function may be a critical genomic event underlying the progression of small cell bladder cancer. Our findings also support prior reports that pathogenic gene variants detected at low allele frequencies may be clinically important.

Abstract P2-18-05: Delayed chemotherapy in HER2 positive breast cancer

Abstract Introduction: It is always a great concern when breast cancer treatment is delayed for a variety of reasons such as patient personal situation, medical conditions, insurance issues and scheduling difficulties. Most studies regarding delayed cancer treatment focus on chemotherapy and the findings are conflicting. This study aimed to determine the rate of delayed neoadjuvant or post-operative adjuvant chemotherapy/targeted treatment in HER2 amplified breast cancer at a single institution and examine its effects on survival outcomes including relapse free survival (RFS), overall survival (OS), breast cancer specific survival (BCSS) and distant metastatic free survival (DMFS). Methods: Patients with a tissue diagnosis proven HER2 amplified breast cancer who were surgically treated at the Revlon/UCLA Breast Center between 2002 and 2018 were included. Patients with a previous history of breast cancer, metastasis and no follow-up were excluded. Patients without clear dates of diagnosis, surgery, beginning and end of chemotherapy and radiation were excluded for further analysis. Delayed neoadjuvant chemotherapy with target treatment was defined as greater than 2 months from the time of tissue diagnosis and delayed adjuvant treatment was defined as greater than 2 months from the last cancer surgery. Chi-squared test was used to compare the differences of clinicopathologic characteristics between the two groups: delayed and non-delayed. Kaplan-Meier curve and log-rank test was used to identify candidate prognosticators and Cox-regression analysis was used to identify independent prognosticators for survival outcomes. Results: Of the 322 cases surgically treated at the Revlon/UCLA Breast Center, 101 had neoadjuvant, 168 had adjuvant, 5 were unknown and 48 had no chemotherapy/target treatment. Median follow-up was 74.5 months. In the entire studied population, OS was significantly better in the groups who received either neoadjuvant or adjuvant chemotherapy/target treatment than those who did not (HR 0.0248; 95% CI, 0.086-0.711). In the neoadjuvant group, 11 (11.5%) had delayed start. Breast conserving surgery was more frequent in the delayed group (63.6%) and mastectomy was more frequent in the non-delayed group (72.6%). In addition, clinically positive node was more frequent in the non-delayed group (p=0.001). Residual cancer in the breast was associated with worse RFS (p=0.027). Residual nodal metastasis was associated with inferior RFS (p=0.012), OS (p=0.012), BCSS (p=0.037) and DMFS (p=0.011). In multivariate analysis, pCR was associated with better OS (HR 6.329, 95% CI, 1.354-29.586). In the adjuvant group, 38 (22.6%) had delayed chemotherapy/target treatment which was found to be negatively associated with RFS (HR 6.707; 95% CI, 1.224-36.769). Conclusion: Delayed chemotherapy/target treatment in HER2 positive breast cancer appeared to occur more frequently in the adjuvant group than the neoadjuvant group. In the adjuvant group, delayed start of chemotherapy/target treatment negatively impacted survival. In the entire cohort and surgery first group, those who did not receive adjuvant chemotherapy/target treatment had worse survival than those who did. Taken together, chemotherapy/target treatment should be considered in all patients with HER2 positive breast cancer and neoadjuvant treatment is preferred to minimize any possible delay in starting chemotherapy/target treatment. Citation Format: Ho Hur, Amy Le, Helena R Chang. Delayed chemotherapy in HER2 positive breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-18-05.

Objective quantification of BCL2 protein by multiplex immunofluorescence in routine biopsy samples of diffuse large B-cell lymphoma demonstrates associations with survival and BCL2 gene alterations

Up-regulation of BCL2 in cases of diffuse large B-cell lymphoma (DLBCL) can confer treatment resistance. Quantitative immunofluorescence (QIF) histology allows objective quantification of protein-based biomarkers. We investigated the utility of QIF for evaluating BCL2 as a biomarker in DLBCL by quantifying BCL2 selectively in CD20-expressing lymphoma cells in biopsy samples from 116 cases of DLBCL in two cohorts one of which consisted of relapsed/refractory cases from a clinical trial. BCL2 protein by QIF correlated with BCL2 mRNA abundance and was associated with both translocation and copy number gain of the BCL2 gene. Elevated BCL2 protein expression by QIF, but not immunohistochemistry or mRNA quantification, was associated with inferior overall and relapse-free survival in the relapsed/refractory cohort. QIF is an effective means of quantifying BCL2 protein objectively in routine cancer biopsy specimens and shows promise for identifying relapsed/refractory DLBCL patients at risk of inferior outcomes after salvage therapy.

Interactions between Donor Activating Killer Immunoglobulin-like Receptors (KIRs) and Somatic Mutations and Their Association with Outcomes after Allogeneic Hematopoietic Cell Transplant for Acute Myeloid Leukemia (AML)

Background: Graft-versus-leukemia (GVL) responses after allogeneic hematopoietic cell transplantation (alloHCT) for AML are mediated by alloreactive donor-derived immune effector cells including T lymphocytes and natural killer (NK) cells. The function of NK cells is regulated by inhibitory and activating signals mediated through cell-surface receptors, including KIRs. Various models of NK cell alloreactivity have been associated with post-transplant outcomes, including leukemia relapse. However, these results have varied widely between different investigators employing similar models of NK cell alloreactivity. Assessment of somatic mutations in AML on post-transplant outcomes has not been investigated in the context of KIR profiles. Methods: In this single-institution retrospective cohort study, we investigated KIR haplotypes (haplotype AA vs. Bx [associated with multiple activating KIRs]; Cooley S., et al. Blood. 113:726-732. 2009) in the context of somatic mutations. We included 34 adult patients with AML who underwent alloHCT from a matched related donor from 2006 to 2013. A targeted multi-amplicon deep NGS panel of 79 commonly mutated genes in myeloid neoplasia was performed. Post-HCT outcomes were assessed based on mutational status and KIR haplotype with Kaplan-Meier method and log-rank test. Results: Median age at transplant was 54 (range 31-73). Cytogenetic risk groups were 9% favorable, 56% intermediate, and 35% poor based on 2017 ELN classification. HCT-CI scores included 26% low, 32% intermediate, and 41% high. Disease risk group defined by ASTCT included 71% low, 26% intermediate, and 3% high. Disease status at HCT included 74% CR1 and 26% CR2. Frequencies of somatic mutations prior to HCT were: 21% DNMT3A, 18% IDH2, 9% each for STAG2 and NRAS, 6% each for ASXL1, JAK2, PHF6, RUNX1, TET2, and 3% each for CBL, FLT3, NPM1, and U2AF1. Overall, 53% of patients had at least 1 mutation: 24%, 18%, 9%, and 3% of patients had 1, 2, 3, and 4 mutations, respectively. 41% were carriers of KIR haplotype AA, and 59% were haplotype Bx. Relapse (p=0.40), relapse-free (p=0.33), and overall survival (p=0.30) between haplotypes AA and Bx were not statistically different. However, when considering somatic mutations in the context of KIR haplotypes, those with any somatic mutation (n= 18) present had inferior relapse-free (p=0.002) and overall survival (p=0.002; figures A-B) as compared to those with none. Further assessment of outcomes was then considered for those who had the following poor prognostic mutations (n=12): ASXL1, DNMT3A, FLT3, NRAS, RUNX1, and TET2. KIR haplotype AA with one or more of these mutations was associated with inferior relapse-free (p=0.05) and overall survival (p=0.008). At median follow-up of 83 (range 66-137) months, 38% were alive. Non-relapse mortality rates were 21% (9-36) at 1 year and 29% (15-39) at 3 years. The most common causes of death for all patients were relapse (48%) followed by infection (33%). Conclusion: In presence of somatic mutations, carrying KIR haplotypes Bx was associated with better survival in AML post-alloHCT. The presence of multiple activating KIRs may also help mitigate the worse prognosis associated with some of the more deleterious somatic mutations in AML. These observations may have implications for improving patient risk stratification prior to transplant and optimizing donor selection. Future investigation with larger cohorts interrogating KIR haplotypes in the context of pre-transplant AML somatic mutations on post-transplant outcomes may further elucidate which patients may benefit most from transplant. Disclosures Nazha: Tolero, Karyopharma: Honoraria; Abbvie: Consultancy; Daiichi Sankyo: Consultancy; Novartis: Speakers Bureau; Jazz Pharmacutical: Research Funding; Incyte: Speakers Bureau; MEI: Other: Data monitoring Committee. Mukherjee:Bristol-Myers Squibb: Speakers Bureau; Projects in Knowledge: Honoraria; Celgene Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Partnership for Health Analytic Research, LLC (PHAR, LLC): Consultancy; McGraw Hill Hematology Oncology Board Review: Other: Editor; Pfizer: Honoraria; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees. Advani:Pfizer: Honoraria, Research Funding; Macrogenics: Research Funding; Glycomimetics: Consultancy, Research Funding; Kite Pharmaceuticals: Consultancy; Amgen: Research Funding; Abbvie: Research Funding. Gerds:Sierra Oncology: Research Funding; Incyte: Consultancy, Research Funding; CTI Biopharma: Consultancy, Research Funding; Imago Biosciences: Research Funding; Celgene Corporation: Consultancy, Research Funding; Roche: Research Funding; Pfizer: Consultancy. Sekeres:Celgene: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Millenium: Membership on an entity's Board of Directors or advisory committees. Majhail:Mallinckrodt: Honoraria; Atara Bio: Consultancy; Anthem, Inc.: Consultancy; Nkarta: Consultancy; Incyte: Consultancy. Maciejewski:Novartis: Consultancy; Alexion: Consultancy.

MAPK-ERK Pathway Activation: The Achilles' Heel of IL-7R‒Induced Steroid Resistance

INTRODUCTION. Mutations in the IL-7R signaling pathway (e.g.IL7Ra, JAK1/3, PTPN11, NF1, STAT5B, N/KRAS or AKT) are associated with steroid resistance and inferior relapse-free survival. These mutant molecules drive strong activation of the JAK-STAT, MAPK-ERK and/or PI3K-AKT signaling pathways. Also, activation of wild type RAS or AKT-reflecting physiological IL7-induced signaling-drives steroid resistance. These observations extend the findings in preB-ALL where RAS mutations were related to steroid resistance. Impaired transcription of pro-apoptotic BIM-an essential direct transcriptional target gene of the glucocorticoid receptor NR3C1 that mediates steroid-induced apoptosis-is observed in various steroid resistant PDX models. AIM. Given the central role of BIM in steroid-induced apoptosis, we investigated how mutations in IL7R or downstream signaling components would affect the function of BIM and other BCL2 protein family members (BCL2, BCLXL and MCL1) in steroid-exposed T-ALL. RESULTS. We generated doxycycline-inducible SUP-T1 and P12 Ichikawa cell line models that can overexpress specific IL-7R signaling mutants. Expression of mutant JAK1, NRAS or IL7Ra molecules results in robust activation of the MAPK-ERK pathway that confers steroid resistance. As a target of NR3C1, BIM transcription was not impaired in these steroid treated cell lines. Therefore, we investigated post-transcriptional mechanisms of steroid resistance. We observed strong phosphorylation of BIM downstream of MAPK-ERK activation under steroid treated and untreated conditions. Exposure to each of three MEK-inhibitors CI1040, Selumetinib or Trametinib abolished not only phospho-ERK but also phosphorylation of BIM. To study the consequences of BIM phosphorylation in relation to binding and inactivation of anti-apoptotic proteins, we immunoprecipitated BIM. Increased BIM levels following steroid exposure was related to increased binding to BCL2, BCLXL and MCL1 in steroid-sensitive control cells. In contrast, activation of mutant JAK1 and NRAS molecules resulted in phosphorylated BIM and reduced binding of BIM to these anti-apoptotic BCL2 family members. This indicates that preventing ERK-mediated phosphorylation of BIM enhances steroid responsiveness. T-ALL patients with activating IL-7R signaling mutations may therefore benefit from treatment combining steroids and MEK inhibitors. Indeed we observed strong synergy between MEK inhibitors and steroids in primary T-ALL patient samples. CONCLUSIONS AND FUTURE PERSPECTIVES. Treatment with MEK-inhibitors Selumetinib or Trametinib was shown effective in reversing steroid resistance, and therefore strongly synergize with steroid treatment. Our data highlights the importance of the dynamic interplay between BIM and anti-apoptotic BCL2 family members in MAPK-ERK-driven steroid resistance. Therefore, we are exploring whether MEK inhibitors (that prevent phosphorylation and inactivation of BIM) combined with BH3-mimetics (that block anti-apoptotic family members) will further enhance restoration of steroid responsiveness in IL-7R signaling mutant T-ALL patients. As physiological IL7-induced signaling is sufficient to raise cellular steroid resistance, these inhibitors could be applied for all IL-7R signaling-dependent T-ALL patients, also in the absence of IL-7R signaling mutations. Refractory/relapse T-ALL patients are now eligible for the current phase 1/2 MEK-inhibitor‒dexamethasone (SeluDex) trial. We are using mass-spectrometry to determine the exact phospho-sites in BIM that drives steroid resistance that can serve as a valuable biomarker. Disclosures No relevant conflicts of interest to declare.

Flowsom: An R-Based Evaluation Strategy for Flow Cytometry-Based Measurable Residual Disease (MRD) Diagnostics in Acute Myeloid Leukemia (AML)

Patients with Acute Myeloid Leukemia (AML) frequently relapse due to chemorefractory AML cells persisting after intensive chemotherapy at levels below the 5% morphological detection threshold (measurable residual disease, MRD). MRD has been established as an important prognostic factor for relapse-free and overall survival, making it highly relevant for post-remission treatment stratification. In contrast to MRD assessment by molecular techniques, multiparameter flow cytometry (MFC)-based MRD measurements are applicable in more than 95% of AML patients, while still offering a sensitivity of 10-4 to 10-5. Current MFC MRD assessment strategies measure 8-10 fluorochromes in parallel, resulting in a high-dimensional data set. However, evaluation of this data is usually performed by scatterplot-based manual, two-dimensional analysis. This leads to loss of information and significant inter-observer variability in MRD diagnostics. We therefore established a computational data analysis strategy for MFC MRD diagnostics, based on the unsupervised FlowSOM algorithm. By comparison with healthy bone marrow (HBM) data, FlowSOM analysis can identify aberrant (sub-)populations of cells, clustered in nodes (according to similarity of their antigen profile). These nodes can be denoted as "nodes of interest" (NOI) to simplify MRD analysis after clustering. Aim of the project was to establish FlowSOM analysis protocols and retrospectively evaluate their prognostic significance in a cohort of 46 patients with known outcomes. Bone marrow samples of these patients were analyzed at aplasia (day 16 after initiation of induction chemotherapy). Only patients with morphological blast clearance at aplasia were included. Healthy reference FlowSOM trees were established by merging flow data of 17 HBM. Analysis protocols were developed to report individual ("any node" approach) and cumulative ("sum node" approach) differences in NOI percentages when comparing HBM and MRD samples. We then performed FlowSOM MRD analyses in a patient subcohort of 19 AML patients. Importantly, for these analyses, we excluded patients who underwent allogeneic stem cell transplantation in first remission (non-HSCT subcohort). Median follow-up time was 8.3 (range 2-40) months for this subcohort. Receiver operating characteristic (ROC) analyses were used to determine optimal threshold values to differentiate relapse (n=5) and non-relapse (n=14) patients within the cohort. For "sum node" analysis strategies (defining MRD levels as cumulative difference of NOI percentages) a threshold of -2.44% was identified, optimized for Youden (Y) index and diagnostic odds ratio (DOR). For the "any node" strategy (defining MRD levels by the maximum difference of any NOI), a threshold of 0.04%, also optimized for the Y-index and DOR, discriminated best between relapse and non-relapse patients. Relapse-free survival (RFS) was significantly shorter for MRD-positive (MRDpos) patients identified by "sum node" analysis (median 8 months vs. not reached, p=0.016) and tended to be shorter for MRDpos patients by "any node" analysis (median 8 months vs. not reached, p=0.1). When applying the thresholds identified in the non-HSCT cohort to the full set of 46 patients (median follow-up interval 10.6 months, range 2-40), median RFS was not reached for the MRD-negative group (both for "sum node" and "any node" analysis), and was 14 ("sum node", p=0.098) and 14 months ("any node", p=0.360) for the MRDpos patients. Median overall survival for MRDpos patients by "sum node" analysis was 27 months, whereas it was not reached for MRD-negative patients. However, this difference did not reach statistical significance (p=0.335), probably due to the small sample size. Taken together, FlowSOM-based analysis strategies seem well suited to identify patients with MRD positivity after intensive induction chemotherapy. MFC MRD positivity at aplasia, defined by FlowSOM-based analysis, is associated with inferior RFS in retrospective analyses of small patient cohorts. Due to the underlying computational, unsupervised data analysis, FlowSOM-based assessment can be a means to harmonize MFC MRD evaluation. These promising results need to be verified in larger cohorts, with inclusion of post-induction assessments, and should be followed by prospective analyses to delineate the diagnostic validity of FlowSOM for AML MRD diagnostics in clinical trials. Disclosures Subklewe: Janssen: Consultancy; Morphosys: Research Funding; Celgene: Consultancy, Honoraria; Gilead: Consultancy, Honoraria, Research Funding; Miltenyi: Research Funding; Oxford Biotherapeutics: Research Funding; Pfizer: Consultancy, Honoraria; AMGEN: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Research Funding.