Abstract: Introduction Hyperphosphatemia could be a finding in renal failure, tumor lysis syndrome, hypoparathyroidism, and ingestion of exogenous phosphate. We present the case of a woman with hyperphosphatemia in which we finally diagnosed multiple myeloma, serum phosphate level achieved normal range after chemotherapy started. Although hyperphosphatemia in multiple myeloma is a very rare finding, there are some reports. The proposed mechanisms include a large amount of paraproteins that interferes with phosphorus level determination showing a false increased level. When samples have been deproteinated before analysis, serum phosphorus level can decrease obtaining a true level. This case reminds clinicians the importance of seeking additional causes for abnormal phosphorus levels before starting treatments that could lead to hypophosphatemia. Case report An hispanic woman at the 7th decade of life that only suffered from controlled hypothyroidism, who assisted with complaints of axial pain mainly in thoracic and lumbar segments. She denied neurological and B symptoms. She had a CT scan performed and was referred to the hematology service.On clinical examination we didn't find any neurological signs, no megalies and no palpable nodes. The patient brought a CT spine scan showing thoracic images suggestive of mets with collapse of 50% in T12-L1 and a mass in S2.With these findings we decided to start intrahospitalary studies for excluding malignancy.Her relevant laboratories were: creatinine 0,7, BUN 25, Hemoglobin 9 gr/dl VCM 102 WBC 3330 Granulocytes 55% Platelet 222.000, UN 10,7, albumin 2.8, Lactate dehydrogenase 425. A series of labs seeking secondary causes of malignancy was made including plasmatic cell neoplasie.The hepatic function was normal but an unusually high Phosphorus level was detected (19,6) with normal calcemia (8.98), the tumoral biomarkers were in normal range (CEA, CA 19-9, Ca 125, AFP) and an elevated B2 microglobulin (8) was found. Additional labs included bence jones protein and PTH, both in normal range. A new Thoracic CT described mosaic infiltrates and an extensive bone involvement suggestive of lytic metastatic changes. The abdomen CT showed multiple lytic lesions in lumbo-sacral spine and pelvis, The skull radiography had lytic lesions too. The nephrology service was required by the Hyperphosphatemia and they asked about external intake of phosphorus finding that she was taking "hydrolyzed collagen", so they started iv fluid and chelators (aluminium hydroxide and no calcium chelators).Because of unresponsive hyperphosphatemia, nephrology started hemodialysis.Hematology found high IgG levels (5500) concluding the need for bone marrow studies . Finally a the bone marrow study was performed and prescribed steroids on suspicion of Multiple myeloma. Until this day the Phosphorus level still remained in high levels (17,7) despite hemodialysis sessions. The bone marrow study revealed a plasmatic cell population of 28,9% with big and abundant cytoplasm, some of them with binucleations suggestive of infiltration by plasmatic cell neoplasie. The seric electrophoresis revealed a paraprotein (seric protein of 9,3 with a monoclonal peak of gamma region of 3,4 gr/dl), the seric immunofixation was positive for a monoclonal IgG lambda component. With this report we began chemotherapy treatment for Myeloma with CyBorD regimen (Cyclophosphamide, Bortezomib, dexamethasone). After treatment was initiated, phosphorus level began to lower and achieved normal range (4.28) in the first two weeks. Then she was discharged to continue outpatient management. Nowadays she is receiving her 3rd chemotherapy cycle without complications, her phosphorus level still remains within normality. Conclusions Spurious hyperphosphatemia in patients with paraproteinemias like multiple myeloma can occur. The IgG monoclonal can interfere with the phosphomolybdate principle used in the assay of serum phosphate on most automated chemistry analysers. For labs which do not have a multilayered film technology based system, a serial dilution analysis of the suspected analyte could be performed. Disclosures No relevant conflicts of interest to declare.

Abstract: Introduction: The BCL-2 inhibitor venetoclax (Ven) has been approved on monotherapy or combined with rituximab in relapsed/refractory CLL patients (pts) and combined with obinutuzumab in previously untreated CLL pts. However, evidence from clinical trials can be difficult to generalize to real-world patient populations. The VENARES study assesses the real-world use of Ven following approval to inform of subpopulations underrepresented in clinical trials. Methods: This is Spanish non-interventional retrospective, multicenter post-marketing observational study. The main objective was to evaluate the effectiveness of Ven in adult CLL pts by the overall response rate (ORR) at 9 months (mo) after the first Ven dose administration. Secondary objective was to evaluate the effectiveness for the Ven monotherapy and the Ven combined with rituximab subpopulations. Consecutive adult pts with diagnosis of CLL who have initiated Ven at least 9 mo before the inclusion in the study were included. Data of pts are retrospectively reviewed until the date of last follow-up or death. Results: 125 pts diagnosed with CLL and who met the eligibility criteria were analyzed. The median age was 72 years (67 - 77) with 76.8% being older than 65 years. Most patients were male (68.8%), had a concurrent disease (65.6%). ECOG PS was recorded in 76 pts: 40 pts (32%) had PS 0, 30 pts (24%) PS 1 and 6 pts (4.8%) PS 2. Pts had received a median of 4 prior lines of therapy (range 1-13 lines). At baseline, among the 92 pts with known Binet stage, 31 (33.7%) had stage C and 38 (41.3%) had stage B; bulky nodes ≥ 5 cm were present in 20 of 87 pts; 49 pts (39.2%) had an absolute lymphocyte count ≥ 25 x 10 9/L and 33 of 54 pts (61%) baseline beta-2 microglobulin value above of 3500 ng/mL. In total, 29 of 90 patients (32%) assessed had Cr 17p deletion, 28 of 86 patients (32%) tested had TP53 mutations, and 46 of 56 patients (82%) who were tested had unmutated immunoglobulin heavy-chain variable (IGHV) status. Ven was administered as monotherapy in 71 pts (57.6%), combined with rituximab in 36 pts (28.8%), combined with obinutuzumab in 5 pts (4%) and combined with other drugs in 13 pts (10.4%). 83 of 125 patients included were evaluable for the primary objective of the study: the ORR at 9 mo was 84.3% (70 patients): CR/CRi in 44 (53%) pts, PR/nPR in 26 pts (31.3%), SD in 9 pts (10.8%) and PD in 4 pts (4.8%). By treatment, in the evaluable patients, ORR at 9 months were 79.2% (38 of 48 patients) in the Ven monotherapy group, with 45% of CR/CRi, and 92.3% (24 of 26 patients) in the Ven combined with rituximab, with 61% CR/Cri. The median duration of PFS was not reached at the time of the analysis (1-June-2021). Kaplan-Meier estimates of the probability of PFS at 24 mo was 75.4% (95% CI, 58.2 - 86.3). Disease progression occurred in 21 pts. Assessment of minimal residual disease (MRD) was available for 32 patients (25.6%) on the basis of peripheral-blood samples, bone marrow or both. Best undetectable MRD was reached in fourteen patients (43.8%). uMRD was more common in pts treated with Ven combined with R (83.3%, 5 of 6 pts) than in pts treated with Ven monotherapy (33.3%, 7 of 21 pts). Adverse events (AEs) were reported during Ven therapy in all 125 patients, 93 of these pts reported AEs related to Ven. Related to Ven, 67 patients (53.6%) experienced at least one AE: 52 pts (41.6%) had neutropenia being grade 3 and 4 in 22 (42.3%) and 9 (17.3%) pts, respectively. 9 pts (7.2%) had febrile neutropenia. Thrombocytopenia and anemia were less common occurring in 5.6% and 2.4%, respectively. Tumor lysis syndrome (TLS) occurred in 4 of 125 pts during ramp-up (3 laboratory and 1 clinical), 2 of them were related to Ven both lab TLS. None of the pts discontinued therapy due to TLS. Richter transformation was observed in 6 pts (4.8%). Other common AEs was diarrhea (10.4%), but most cases were mild. Conclusions: Our first real-world data show that Ven monotherapy or combined with rituximab is effective in highly pre-treated CLL patients, ORR at 9 mo was 84.3% in all population and PFS estimate at 24 mo was 75.4% with similar outcomes to those in the pivotal clinical trials. The safety profile of Ven was consistent with prior experience of Ven in monotherapy or combined with rituximab and no new safety signals were detected. Disclosures Baltasar: Janssen, Abbvie: Consultancy. Terol: Roche: Membership on an entity's Board of Directors or advisory committees, Other: Travel; BMS: Consultancy; Roche: Consultancy; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Research Funding; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Other: Travel; Hospital Clinico Valencia: Current Employment. Moreno: Janssen, Abbvie: Research Funding; Abbvie, Janssen, AstraZeneca: Speakers Bureau; Abbvie, Janssen, AstraZeneca, Beigene: Membership on an entity's Board of Directors or advisory committees. Osorio: Janssen, Abbvie, Roche: Consultancy. De la Cruz: Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Beigene: Membership on an entity's Board of Directors or advisory committees; EUSA Pharma: Membership on an entity's Board of Directors or advisory committees; JANSSEN: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Kyowa Kirkin: Membership on an entity's Board of Directors or advisory committees; Roche: 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, Speakers Bureau. de la Serna: AbbVie, AstraZeneca, Roche: Speakers Bureau; ABBVIE, ASTRAZENECA,ROCHE: Research Funding; AbbVie, AstraZeneca, Beigene, Gilead, GSK, Janssen, Jazzpharma, Novartis, Roche: Consultancy. Arguiñano: Takeda, Sanofi, Janssen, BMS-Celgene, Abbvie: Speakers Bureau; Takeda, Sanofi, Janssen, BMS-Celgene, Abbvie: Consultancy. Loscertales: Janssen, Abbvie, Roche, Gilead: Speakers Bureau; Janssen, Abbvie, Astra-Zeneca, Beigene, Roche, Gilead: Consultancy. García: Janssen, Roche, Gilead, Celgene: Consultancy; Janssen, AbbVie: Research Funding; Janssen, Roche, Gilead, AbbVie, Celgene: Other: medical meetings funding. Pérez Persona: BMS/Celgene: Consultancy, Other: Support for attending meetings and/or travel, Speakers Bureau; Amgen: Consultancy, Other: Support for attending meetings and/or travel, Speakers Bureau; Takeda: Speakers Bureau; AbbVie: Other: Support for attending meetings and/or travel, Speakers Bureau; Sanofi: Consultancy, Speakers Bureau; AstraZeneca: Speakers Bureau; GSK: Consultancy; Incyte: Consultancy. Pérez-Encinas: Janssen: Consultancy. Caballero: Celgene, Janssen, Novartis, Abbvie: Speakers Bureau; Celgene, Janssen, Amgen: Consultancy. Ruiz-Zorrilla: Abbvie: Current Employment. Moreno: abbvie: Current Employment. Ferrà: Janssen, Roche, Gilead, Takeda, Abbvie: Consultancy; Janssen, Roche, Gilead, AbbVie: Other: medical meetings funding.

Abstract: Introduction. Ibrutinib is a first-in-class, oral, once-a-day Bruton's tyrosine kinase inhibitor that achieves high overall response rates and durable remissions in patients with chronic lymphocytic leukemia (CLL) including those with high-risk features (unmutated IGHV, TP53 abnormalities, 11q deletion). Survival with continuous single-agent ibrutinib in previously-untreated CLL patients is comparable to an age-matched general population (Figure 1). IBRORS is an observational, retrospective, multicentre study to describe the characteristics and clinical outcomes of patients with CLL treated with single-agent ibrutinib in routine clinical practice in Spain. This present analysis reviews the subset of patients in IBRORS who received ibrutinib as the first-line of treatment. This series includes a significant number of patients with high risk cytogenetic/molecular alterations (del17p/TP53 M), which corresponds with the approved indication for first-line CLL patients in Spain at the time. Methods. Adult patients diagnosed with CLL treated with single-agent ibrutinib in first-line, or at first or second relapse since its commercialization in Spain (between January 2016 to January 2019) were included in the IBRORS study. Clinical characteristics of patients, efficacy and tolerability of ibrutinib as first-line treatment were analyzed here. A Kaplan-Meier analysis was performed for overall survival (OS) and progression-free survival (PFS). Results. 84 patients, from a total of 269 included in IBRORS, received single-agent ibrutinib as first-line treatment. The median age was 71.3 years (range 63-77) at the time of ibrutinib initiation. 56.3% of patients presented with an intermediate/high-risk Rai-Binet stage, and the majority of patients (98.6%) had an ECOG PS of 0-1. 91.7% of patients had at least 1 high risk molecular cytogenetic factor (unmutated IGHV, TP53 abnormalities, 11q deletion or complex karyotype) described in table 1. Baseline comorbidities of patients are described in table 2. Concomitant medication included anticoagulants (9.5% patients; vitamin K antagonist [n=4], Apixaban [n=1] and LMWH [n=3] patients), antiplatelet agents (11.9% patients), and antihypertensives (50% patients). The overall response rate (ORR) was 79.5%; 14/84 (16.6%) achieved a complete response (CR), 14/84 (16.6%) achieved CR unconfirmed, 27/84 (32.14%) achieved a partial response (PR) and 12/84 (14.2%) a PR + lymphocytosis. The median PFS and OS were not reached, and the estimated PFS at 24 months was 84.5% (73.4-95.6%). OS and PFS curves are represented in figure 2. The PFS of each patient subgroup with high-risk cytogenetic characteristics was similar to that of all patients in the first-line cohort: del17p/TP53 mutation (HR = 0.963 [95% CI 0.188-4.928]; p = 0.964), del11q (HR = 0.042 [95% CI 0.000-682.736] ; p=0.521), unmutated IGHV (HR = 0.391 [95% CI 0.110-1.394]; p = 0.148). The median duration of exposure to ibrutinib was 17.3 (11.9-25.6) months. Dose reduction of ibrutinib occurred in 17/84 (20.2%) patients, 8/84 (9.52%) due to toxicity (4 hematologic toxicity and 4 non-hematologic toxicity). 27/84 (32.1%) patients had temporary interruption of treatment. 15/84 (17.8%) patients permanently discontinued ibrutinib including 6 (7.14%) patients due to progression, 4 (4.76%) due to toxicity and 5 for other reasons. Safety: 49/84 (58.3%) patients developed at least one adverse event (AE), while 12/84 (14.2%) patients developed at least one serious adverse event (SAE). Twelve (14.3%) patients reported at least one haematological toxicity while 53 patients (63.1%) recorded at least one non-haematological toxicity. Only 1 patient experienced grade 3 atrial fibrillation, which did not lead to discontinuation. The most common AEs are described in table 3. Conclusion. This population of previously-untreated CLL patients, enriched for high-risk genomic features, reflects the initial approval of ibrutinib for the treatment of first-line patients with del17p in Spain. Single-agent Ibrutinib as the first-line treatment in this real world population was effective regardless of risk factors and well tolerated, with a low rate of discontinuation due to toxicity. Findings are consistent with those reported in clinical trials. Disclosures Loscertales: AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria. Arguiñano:AbbVie: Honoraria; Janssen: Honoraria; BMS-Celgene: Honoraria; Novartis: Honoraria. Hernandez-Rivas:Janssen: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees; Rovi: Membership on an entity's Board of Directors or advisory committees. Pérez Persona:Amgen: Consultancy; Celgene: Consultancy, Speakers Bureau; Roche: Consultancy, Speakers Bureau; Jannsen: Consultancy, Speakers Bureau; Abbvie: Consultancy, Speakers Bureau; Takeda: Consultancy. Loriente:Janssen Cilag: Current Employment. Villanueva:Janssen Cilag: Current Employment.

Abstract: Introduction: Acute myeloblastic leukaemia (AML) is an heterogeneous disease with different molecular and prognostic characteristics. According to the comorbidities and the revised 2017 European Leukaemia genetic risk stratification (ELN17), allogeneic hematopoietic cell transplantation (HCT) is the best therapeutic option for many patients with AML (Grimm, Blood Adv 2020). However, relapse remains the main cause of mortality after transplantation. Impact of MRD on the outcome of patients is well recognized and ELN2017 introduced the new response category complete remission (CR) without MRD (Döhner H, Blood 2017). Detection of measurable residual disease (MRD) by multiparameter flow cytometry (MFC) in AML before allogeneic HCT could be a powerful predictor of outcome and decisive when establishing strategies that modify the prognosis of these patients. Methods: Retrospective multicentre analysis of MRD by MFC of patients undergoing transplantation allogeneic in 4 centres during the period from 2012 to 2020. Both Leukaemia Associated Aberrant Immunophenotype (LAIP) and different from normal (DFN) approach were used to analyse the MRD. The MRD was carried out with 8-color panels based on Euroflow protocols. The samples were acquired in 8-color digital cytometers (FACSCanto II) calibrated and compensated according to Euroflow protocols. Results: 295 of 318 patients were evaluated. Table 1 shows the characteristics of the patients. 285 (96.7%) were in complete remission (CR), 207 had negative MRD, in 21 MRD was less than 0.1% (MRD-low) and in 57 greater than or equal to 0.1% (MRD-high). At 2 years, the overall survival (OS) and leukaemia-free survival (LFS) in the whole group were 69% (95% CI 63.18-74.18) and 58.4% (95% CI 52.4-63.9) respectively. In CR patients, MRD levels significantly influenced on outcomes, with OS and LFS of 76.7% and 67.6% for negative MRD, 68.5% and 49.7% MRD-low and 50 % and 36.6% in MRD-high, p & lt;0.001) (Figure 1). Considering only MRD-high as positive, according to ELN17, cumulative incidence of relapse (CIR) at 2 and 5 years were significantly lower among those with positive MRD: 22% (95% CI 17-28.1%) and 27% (95% CI 21%-33.5%) for negative MRD vs 46,5% (95% CI 32.4%-59.5%) and 50% (95% CI 34.8%-63.2%) in positive MRD, p 0.0005. No differences were observed in terms of non relapse mortality (p 0.2).. Likewise, positive MRD also identified different prognostic subgroups within the ELN2017 subgroups: OS and LFS among high-risk ELN2017 patients of 63.6% and 52.3% in negative MRD vs 35.7% and 18.2% in positive MRD patients, p = 0.0085 and p = 0.0094, respectively; for intermediate risk: 77% and 67.6% in negative MRD vs 67% and 50.5% in positive MRD patients, p = 0.23 and p = 0.056; and for favourable: 84% and 77.7% in negative MRD vs 48% and 39.2% in patients with positive MRD, p = 0.0051 and p = 0.0341. Considering the conditioning regimen, patients with MRD negative before transplant had better OS and LFS at 2 years (82% and 71.4% among those received myeloablative conditioning and 65% and 57.6% among those who received reduced intensity, respectively) than those who had positive MRD prior to transplant (56% and 44.4% in myeloablative and 43% and 25.5% in reduced intensity) (p & lt;0.001) (Figure 2). In multivariate time-dependent analysis, age (HR 1.019 p = 0.024-95% CI 1.001-1,038), adverse risk group according to ELN17 (HR 2.13 p = 0.033 CI95 1.54-3.93 ) and MRD before transplant (HR 3.8 p & lt;0.001 95 CI 1.55-3.93) significantly influenced survival. Conclusions: Detection of MRD prior to transplant by MFC identifies a group of patients with a worse prognosis and could be key when selecting the most appropriate therapeutic strategy. Figure 1 Figure 1. Disclosures Caballero: Celgene: Consultancy. Belén Vidriales: Roche: Consultancy; Novartis: Speakers Bureau; Jazz: Consultancy, Speakers Bureau; Astellas: Consultancy, Speakers Bureau. Montesinos: Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Stemline/Menarini: Consultancy; Tolero Pharmaceutical: Consultancy; Agios: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: 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, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Forma Therapeutics: Consultancy; Glycomimetics: Consultancy; Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau. Perez-Simon: JANSSEN, TAKEDA, PFIZER, JAZZ, BMS, AMGEN, GILEAD: Other: honorarium or budget for research projects and/or participation in advisory boards and / or learning activities and / or conferences.

Abstract: Introduction. There are different scoring systems to differentiate risk groups in patients with DLBCL treated with chemoimmunotherapy. Those systems have used the same 5 variables (age, performance status, LDH, stage, extranodal involvement) for 27 years. However, LATAM data have not been included in the development of previous scoring systems. It is important to mention that novel biological variables, such as albumin, beta-2-microglobulin (B2M) and platelet/lymphocyte ratio (PLR), have been reported and could improve discrimination (Villela et al. Blood 2019; 134Suppl_1: 1613). Therefore, we carried out a large, multinational study to develop and validate a LATAM-IPI score. Methods. This is a retrospective cohort of 1030 patients with a diagnosis of DLBCL treated with standard chemoimmunotherapy with curative intent between 2010 and 2018. Data were obtained from 8 LATAM countries: Argentina, Colombia, Chile, Guatemala, Mexico, Paraguay, Peru, and Venezuela. The five classic IPI variables (age, ECOG, extranodal involvement, LDH, stage) were analyzed and albumin and PLR were added (Villela et al. Blood 2019; 134Suppl_1: 1613). B2M was not included because it was not requested regularly in all countries. Development of LATAM-IPI: The training set consisted of 85% of the sample, randomly selected, and the remaining 15% was reserved for internal validation. Using the training set, the univariate and multivariate association between clinical prognostic factors and OS was analyzed fitting Cox proportional-hazard models. Outcomes. Clinical characteristics of the training (n=878) and internal validation (n=151) cohorts are shown in Table 1. There were no statistical differences in baseline characteristics between the cohorts. The median follow-up for the whole cohort was 36 months (IQR: 11-57). When exploring the classic IPI variables on the training set, all variables were associated with high risk of mortality [age 65-74, Hazard Ratio (HR) 1.24, 95% CI 0.96 to 1.58, p=0.08; age ≥75, HR 1.71, 95% CI 1.28 to 2.28, p=0.0003), ECOG (≥ 2, HR=2, 95% CI 1.61 to 2.53; p & lt;0.0001), EN (≥2, HR=1.53, 95% CI 1.18 to 1.97; p=0.0012), stage (III/IV, HR=2.1, 95% CI 1.64 to 2.69; p & lt;0.0001) and LDH (ratio 1.1-2.9, HR=1.55, 95% CI 1.22 to 1.97; p=0.0003; ratio ≥3, HR= 2.68, 95% CI 1.93 to 3.7, p & lt;0.0001). Similarly, the biological variables Albumin (≤3.5 mg/dL, HR 2.37, 95% CI 1.9 to 2.95, p & lt;0.0001) and PLR (≥273, HR= 1.52, 95% CI 1.23 to 1.87; p=0.0001) were associated with high risk of death. Next, these variables were evaluated by multivariate analysis. The independent variables were albumin ( & lt;3.5 mg/dL, HR 1.84, 95% CI 1.45 to 2.3, p & lt;0.0001, 1 point), LDH (ratio 1.1 to 2.9, HR 1.30, 95% CI 1.02 to 1.67, p=0.03, 1 point; ratio ≥3, HR=1.84, 95% CI 1.31 to 2.5, p=0.0004, 2 points), advanced stage (HR 1.65, 95% CI 1.27 to 2.13, p=0.0001, 1 point), age (≥75, HR= 1.51, 95% CI 1.15 to 1.98, p=0.003, 1 point), and ECOG (≥2, HR 1.40, 95% CI 1.10 to 1.77, p=0.005). Now, for the development of LATAM-IPI, the groups were distributed as follows: 0 points, low; 1-3 points, intermediate; 4-6 points, high risk. There were no differences in the distribution of the risk groups between training and validation sets (Table 2). In the learning cohort, the 5-year OS rates for low, intermediate and high risk were 81%, 63% and 33%, respectively (p & lt;0.0001). In the validation cohort, the 5-year OS rates for low, intermediate and high risk were 81%, 63% and 44%, respectively (p=0.02) (Figure 1). Conclusions: Using multinational learning and validation cohorts including over 1,000 DLBCL patients treated with standard chemoimmunotherapy in LATAM, we developed a novel LATAM-IPI score using age ≥75 years, ECOG ≥2, advanced stage, LDH ratio (1.1-29 and ≥3) and albumin & lt;3.5 mg/dl. Next steps are to disseminate our results with other involved researchers in LATAM to prospectively assess and reproduce our results. We expect this score will help to further define the prognosis of DLBCL patients in LATAM. Disclosures Villela: amgen: Speakers Bureau; Roche: Other: advisory board, Speakers Bureau. Idrobo:Janssen: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Abbvie: Honoraria, Speakers Bureau; Tecnofarma: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau. Gomez-Almaguer:Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: 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; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: 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. Castillo:Janssen: Consultancy, Research Funding; TG Therapeutics: Research Funding; Kymera: Consultancy; Abbvie: Research Funding; Beigene: Consultancy, Research Funding; Pharmacyclics: Consultancy, Research Funding.

Abstract: We evaluated the safety of adding rituximab 375 mg/m2 only on days +1 and +8 following allo-HCT in 18 patients (M=12, F=6), median age 56 (41–66) years, with advanced CD20+ lymphoid malignancies [CLL=9 (CR2=3, PR2=3; ≥PR3=3); Mantle cell lymphoma (MCL)= 5 (CR1=1, PR2=2, ≥PR3=2); follicular (FL)=3 (CR3=2, ≥PR3=1); DLBC NHL=1 (≥PR3=1). Source of stem cells consisted of matched-related (MRD)=11 (61%), matched-unrelated (MUD)=5 (28%), or mismatched-unrelated (MMUD)=2 (11%) donors. Conditioning regimens consisted of fludarabine plus targeted doses of IV busulfan (FLU-BU) (N=11) or 200 cGy TBI (N=4), or cyclophosphamide (FLU-CY) (N=1). ATG was administered on days −3 and −1 in 2 MMUD cases (FLU-BU-ATG). Fifteen patients received rituximab on day +1 (±3) and all on day +8 (±3). GVHD prophylaxis was tacrolimus plus mycophenolate mofetil (N=11) or methotrexate (N=7). Non-relapse mortality at 100 days was 6%. Median time to neutrophils and platelets engraftment was 15 (6–27) days and 12.5 (9–18) days, respectively. Eight patients never dropped platelets below 20,000/uL. Median CD3 and CD33 chimerisms at day +90 (±10) were 89% (50%–100%) and 100% (15%–100%), respectively. DLI was required in 2 patients (FLU-BU=1, FLU-TBI=1) due to poor CD3 engraftment. Response rates after 90 days post allo-HCT, according to diagnosis, were as follows: CLL (evaluable=8/9; CR=7/8; PR=1/8); MCL (evaluable=4/5; CR=4/4); FL (CR=3/3); DLBC (PD=1/1). Twelve (67%) patients remain alive in remission at a median follow up of 9.4 (2.3–42.3) months. The incidence of grade 0,I, II, and III–IV acute GVHD (aGVHD) was 6%, 33%, 50%, and 11%, respectively. Time to onset of aGVHD was 29 (16–77) days. The incidence of chronic GVHD (cGVHD), per NIH consensus criteria, was as follows in 15 evaluable patients: no cGVHD= 27%, mild= 33%, moderate= 13%, and severe=27%. These findings suggest that administration of rituximab 375 mg/m2 only on days +1 and +8 is safe. Response rates are encouraging; but controlled studies will be needed to conclusively determine the effect of post-transplant rituximab on efficacy.