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Introduction: Among Therapy-Related Myeloid Neoplasms (t-MNs), there are two large groups depending on the cytotoxic trigger. A first group arises after exposure to alkylating agents and / or radiation in the previous 5-10 years and it is associated with unbalanced chromosomal abnormalities, frequently with alterations in Cr 5, 7, complex karyotype and mutated TP53. The second arises after exposure to topoisomerase II inhibitors in the previous 1-5 years, and it is characterized by frequent balanced translocations and KMT2A rearrangement. In those cases with a latency time from cytotoxic exposure to T-MNs diagnosis greater than 10 years, there is doubt about whether they should be considered T-MNs or de novo leukemias. Material and methods: We performed a retrospective analysis of 34 patients with diagnosis of T-MNs treated in our center between 2013 and 2019. We have reviewed the cytogenetic alterations at diagnosis and alterations in TP53 and / or 17p and rearrangements in KMT2A. We divided the cohort into two groups based on the latency time of ≤10 years or> 10 years. The comparison between both groups was carried out using the chi2 test for qualitative variables and the t-student for quantitative variables. The Kaplan Meier method has been used for the calculation of Overall Survival (OS) and Event Free Survival (EFS) and the Cox regression model for the univariate and multivariate analysis. Results: The median follow-up of the global cohort was 8.5 months (0-74). The median OS of the global cohort was 10 months and the EFS was 8 months. In patients with a latency time ≤10 years the median OS was 12 months vs 9 months in those with latency >10 years, with a Hazard Ratio (HR) of 0.6 [95% CI (0.2-1.7), p = 0.3] and the EFS was 7 months vs 9 months respectively [HR 0.3, 95% CI (0.3-1.8), p = 0.7]. The baseline characteristics of the population are reflected in Table 1. A similar percentage of patients with complex or monosomal karyotype at diagnosis is observed in both groups, as well as alterations in TP53 and/or 17p. In the >10-year latency subgroup, there were no patients with prior exposure to Topoisomerase II Inhibitors. Within the Conclusions: Patients with a latency time from exposure to cytotoxic therapy to the diagnosis of T-MNs > 10 years, presented cytogenetic and molecular characteristics similar to those with an exposure time ≤10 years, as well as a similar OS and EFS. Regarding the cytogenetic characteristics at diagnosis of the general cohort, patients with monosomic karyotype and especially those with TP53 and/or 17p alterations had a worse prognosis. Disclosures Garcia-Gutiérrez: Incyte:Consultancy, Other: Travel, Accommodation, Expenses, Research Funding;Novartis:Consultancy, Other: Travel, Accommodation, Expenses, Research Funding;Bristol-Myers Squibb:Consultancy, Other: Travel, Accommodation, Expenses, Research Funding;Pfizer:Consultancy, Other: Travel, Accommodation, Expenses, Research Funding.

Introduction: Cytogenetic and molecular landscape at diagnosis and the depth of response to induction therapy are the most powerful prognostic tools available in patients with Acute Myeloid Leukemia (AML). Among the tests to measure Minimal Residual Disease (MRD), one of the most commonly used is flow cytometry. Nowadays, there is no consensus about optimal time for measurement and the threshold above which has greater prognostic value in AML, as well as its involvement in therapeutic management. Material and methods: We performed a single-center retrospective analysis of 62 patients diagnosed with AML between 2015 and 2019 that reached complete remission after first induction. Patients were stratified according to the European Leukemia Net (ELN) risk classification. MRD measurement was made in bone marrow samples with an 8-color flow cytometer (sensitivity 10-5), cut-off 0.1%. We divided our cohort in two groups according to MRD after induction: negative MRD (MRD-) and positive MRD (MRD+). The baseline characteristics of each group were compared using the Chi2 test. The survival analysis was performed through Kaplan-Meier method and the risk was calculated with Cox regression. The Overall Survival (OS) was defined as the period of time from diagnosis to death and the leukemia-free state (LFS) as the period of time from CR to either relapse or death. Statistical analysis were carried out using SPSS version 19.0. P Results: Baseline characteristics of the sample are represented in Table 1. The median follow-up was 15 months (1-45). The 3-year LFS for MRD- and MRD+ was 50% and 29% respectively (figure 1A) showing a hazard ratio (HR) of 2.02 (CI 95% 0.98-4.6, p=0.05). The 3-year OS was 50% and 36% for MRD- and MRD+ respectively (figure 1B) and HR was 1.3 (CI 95% 0.6-2.8, p=0.4). In MRD+ group according to ELN risk classification, the 3-year LFS was 100% vs 21% vs 19% for favorable, intermediate and adverse risk, respectively (p=0.01) with a HR of 2.1 (CI 95% 1.1-3.9, p=0.01) in the univariate analysis. The 3-year OS was 100% vs 24% vs 18% for each subgroup (p=0.03) with a HR of 2.1 (CI 95% 1.06-4.4, p= 0.03). Thirty-eight patients received consolidation with hematopoietic stem cell transplantation (HSCT), and MRD prior to HSCT was measured in 32 of 38, being positive in 10 patients. All cases with MRD+ before HSCT belonged to MRD+ after induction group (10/20) (p=0.03). In MRD+ group, the 3-year LFS was 36% among those who received HSCT vs 18% in those who did not (log rank p=0.02, HR 3.1 CI 95% 1.3-7.8 p=0.01). Conclusions: The persistence of MRD > 0.1% after first induction by flow cytometry has shown in our population the identification of a AML subgroup of high risk, specially relevant in the intermediate risk group of ELN classification. MRD+ leads to higher risk of relapse, and these patients benefit from more aggressive therapeutic strategies, including allogeneic HSCT. However, MRD+ group has more risk of MRD persistence prior to HSCT, the last being a knowing factor of relapse after allogeneic HSCT, what would justify more aggressive strategies after HSCT in these patients. Disclosures Piris-Villaespesa: Novartis: Honoraria, Other: Advisory Boards. García Gutiérrez:BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Incyte: Honoraria, Research Funding.

Background: Bone marrow (BM) examination is essential in the staging of diffuse large B-cell lymphoma (DLBCL). The assessment of BM involvement includes both histology (gold-standard) and flow cytometry (FC), but few studies have compared BM biopsy (BMB) histologic findings with results of FC analysis of BM aspirate. Discordance between both techniques generates debate about the staging and the prognostic significance in these cases. Methods: We performed a retrospective single-center analysis of patients with DLBCL, not otherwise specified (NOS) diagnosed during a 4-year period (2014-2017). Patients were divided in three groups according to BM findings of BMB and FC at diagnosis. Standard FC was performed by 4-color flow panel until 2016 and by 8-color FC since then. We described main characteristics of each group at diagnosis and analyzed survival outcomes. We applied means of descriptive statistics and Pearson's chi-squared test, and analyzed survival outcomes according to Kaplan-Meier, using Cox regression for comparisons. Results: We analyzed 59 cases, which were divided in three groups: 40 cases (67.8%) presented both negative histology and FC (BMB-/FC-), 10 (16.9%) showed BM involvement using both histology and FC (BMB+/FC+) and 9 cases (15.3%) presented discordant results, all of them with negative histology and positive FC (BMB-/FC+). Clinical and biological characteristics of each group at diagnosis are presented in Table 1. Median infiltration by FC analysis of the BMB-/FC+ group was 0.8% (0.1-2.9) and 3/9 patients presented discordant immunophenotype of lymphoma cells between BM and node biopsy. If we considered BM infiltration as positive in all BMB-/FC+ cases, 4/9 (6.8% of all patients) would be upstaged. First-line treatment was homogeneous in all patients. With a median observation time of 18 months, progression-free survival (PFS) after 2 years was 67%, 22% and 22% with BMB-/FC-, BMB-/FC+ and BMB+/FC+, respectively (Figure 1A), with a multivariate hazard ratio (HR) of 1.9 (95% CI 1.2-2.9, p=0.004) and an univariate HR for FC+ (BMB-/FC+ and BMB+/FC+) vs FC- (BMB-/FC-) of 3.3 (95% CI 1.5-7.3, p=0.003). Two-year overall survival (OS) was 68%, 41% and 33% with BMB-/FC-, BMB-/FC+ and BMB+/FC+, respectively (Figure 1B); multivariate HR was 1.6 (95% CI 1.1-2.6, p=0.042) and univariate HR for FC+ vs FC- was 2.5 (95% CI 1.1-5.9, p=0.035). We found no significant difference between BMB-/FC+ and BMB+/FC+ in survival outcomes. Conclusions: In our series, the group with discordant BM infiltration (BMB-/FC+) presented worsen survival outcomes than BMB-/FC-. Such results should be validated in prospective studies because published series are retrospective and not focused specifically on DLBCL. BM infiltration detected by FC analysis but not by BMB could be considered as extranodal involvement at DLBCL NOS diagnosis. Disclosures García Gutiérrez: Novartis: Consultancy, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Research Funding, Speakers Bureau; Incyte: Consultancy, Research Funding, Speakers Bureau.