2021 Update on MRD in acute myeloid leukemia: a consensus document from the European LeukemiaNet MRD Working Party.

Measurable residual disease (MRD) is an important biomarker in acute myeloid leukemia (AML) that is used for prognostic, predictive, monitoring, and efficacy-response assessments. The European LeukemiaNet (ELN) MRD Working Party evaluated standardization and harmonization of MRD in an ongoing manner and has updated the 2018 ELN MRD recommendations based on significant developments in the field. New and revised recommendations were established during in-person and online meetings, and a 2-stage Delphi poll was conducted to optimize consensus. All recommendations are graded by levels of evidence and agreement. Major changes include technical specifications for next-generation sequencing-based MRD testing and integrative assessments of MRD irrespective of technology. Other topics include use of MRD as a prognostic and surrogate end point for drug testing; selection of the technique, material, and appropriate time points for MRD assessment; and clinical implications of MRD assessment. In addition to technical recommendations for flow- and molecular-MRD analysis, we provide MRD thresholds and define MRD response, and detail how MRD results should be reported and combined if several techniques are used. MRD assessment in AML is complex and clinically relevant, and standardized approaches to application, interpretation, technical conduct, and reporting are of critical importance.

Reliability of flow-cytometry in diagnosis and prognostic stratification of myelodysplastic syndromes: correlations with morphology and mutational profile.

Diagnosis and prognostic stratification of myelodysplastic syndromes (MDS) have been complemented by new techniques, including flow cytometry and NGS. To analyze the relationship between molecular and cytofluorimetric data, we enrolled in this retrospective study, 145 patients, including 106 diagnosed with MDS and 39 controls. At disease onset, immunophenotypic (IF), cytogenetic tests, and cytomorphological (CM) examination on bone marrow were carried out in all patients, while NGS was performed in 58 cases. Ogata score presented a specificity of 100% and a sensitivity of 59%. The detection of at least two phenotypic aberrancies in Ogata negative patients increased the sensitivity to 83% and specificity to 87%. Correlations were identified between IF aberrancies and mutations, including positive Ogata>2 and mutations in SRSF2 (p=0.035), CD15 and U2AF1 (0.032), CD56 and DNMT3A (p=0.042), and CD38 and TP53 (p=0.026). In multivariate analysis, U2AF1 mutations, associated with del(20q) and/or abnormalities of chromosome 7 (group 4 as defined by the EuroMDS score), significantly correlated with an inferior overall survival (p=0.019). These parameters and Ogata score>2 also showed a significant correlation with inferior event-free survival (p=0.023 and p=0.041, respectively). Both CM and FC features correlated with prognosis and mutational patterns. In an integrated MDS work-up, these tools may guide indications for mutational screening for optimal risk stratification.

Measurable residual disease monitoring in patients with acute myeloid leukemia treated with lower-intensity therapy: Roadmap from an ELN-DAVID expert panel.

With the availability of effective targeted agents, significant changes have occurred in the management of patients with acute myeloid leukemia (AML) over the past several years, particularly for those considered unfit for intensive chemotherapy. While testing for measurable residual disease (MRD) is now routinely performed in patients treated with intensive chemotherapy to refine prognosis and, possibly, inform treatment decision-making, its value in the context of lower-intensity regimens is unclear. As such regimens have gained in popularity and can be associated with higher response rates, the need to better define the role of MRD assessment and the appropriate time points and assays used for this purpose has increased. This report outlines a roadmap for MRD testing in patients with AML treated with lower-intensity regimens. Experts from the European LeukemiaNet (ELN)-DAVID AML MRD working group reviewed all available data to propose a framework for MRD testing in future trials and clinical practice. A Delphi poll served to optimize consensus. Establishment of uniform standards for MRD assessments in lower-intensity regimens used in treating patients with AML is clinically relevant and important for optimizing testing and, ultimately, improving treatment outcomes of these patients.

Measurable Residual Disease (MRD) as a Surrogate Efficacy-Response Biomarker in AML.

In acute myeloid leukemia (AML) many patients experience relapse, despite the achievement of morphological complete remission; therefore, conventional morphologic criteria are currently considered inadequate for assessing the quality of the response after treatment. Quantification of measurable residual disease (MRD) has been established as a strong prognostic marker in AML and patients that test MRD negative have lower relapse rates and better survival than those who test positive. Different techniques, varying in their sensitivity and applicability to patients, are available for the measurement of MRD and their use as a guide for selecting the most optimal post-remission therapy is an area of active investigation. Although still controversial, MRD prognostic value promises to support drug development serving as a surrogate biomarker, potentially useful for accelerating the regulatory approval of new agents. In this review, we will critically examine the methods used to detect MRD and its potential role as a study endpoint.

Clinical relevance of an objective flow cytometry approach based on limit of detection and limit of quantification for measurable residual disease assessment in acute myeloid leukemia. A post-hoc analysis of the GIMEMA AML1310 trial.

Using a multiparametric flow cytometry assay, we assessed the predictive power of a threshold calculated applying the criteria of limit of detection (LOD) and limit of quantitation (LOQ) in adult patients with acute myeloid leukemia. This was a post-hoc analysis of 261 patients enrolled in the GIMEMA AML1310 prospective trial. According to the protocol design, using the predefined measurable residual disease (MRD) threshold of 0.035% bone marrow residual leukemic cells (RLC) calculated on mononuclear cells, 154 (59%) of the 261 patients were negative (MRD <0.035%) and 107 (41%) were positive (MRD ≥0.035%). Using LOD and LOQ, we selected the following categories of patients: (i) LODneg if RLC were below the LOD (74; 28.4%); (ii) LODpos-LOQneg if RLC were between the LOD and LOQ (43; 16.5%); and (iii) LOQpos if RLC were above the LOQ (144; 54.4%). Two-year overall survival of these three categories of patients was 75.4%, 79.8% and 66.4%, respectively (P=0.1197). Given their superimposable outcomes, the LODneg and LODpos-LOQneg categories were combined. Two-year overall survival of LODneg/LODpos-LOQneg patients was 77.0% versus 66.4% of LOQpos individuals (P=0.043). This figure was challenged in univariate analysis (P=0.046, hazard ratio=1.6, 95% confidence interval: 1.01-2.54) which confirmed the independent role of the LOD-LOQ approach in determining overall survival. In the AML1310 protocol, using the threshold of 0.035%, 2-year overall survival of patients with MRD <0.035% and MRD ≥0.035% was 74.5% versus 66.4%, respectively (P=0.3521). In conclusion, the use of the LOD-LOQ method results in more sensitive detection of MRD that, in turn, translates into a more accurate recognition of patients with different outcomes.

Refractory primary immune thrombocytopenia (ITP): current clinical challenges and therapeutic perspectives.

Chronic primary immune thrombocytopenia (ITP) can today benefit from multiple therapeutic approaches with proven clinical efficacy, including rituximab, thrombopoietin receptor agonists (TPO-RA), and splenectomy. However, some ITP patients are unresponsive to multiple lines of therapy with prolonged and severe thrombocytopenia. The diagnosis of refractory ITP is mainly performed by exclusion of other disorders and is based on the clinician's expertise. However, it significantly increases the risk of drug-related toxicity and of bleedings, including life-threatening events. The management of refractory ITP remains a major clinical challenge. Here, we provide an overview of the currently available treatment options, and we discuss the emerging rationale of new therapeutic approaches and their strategic combination. Particularly, combination strategies may target multiple pathogenetic mechanisms and trigger additive or synergistic effects. A series of best practices arising both from published studies and from real-life clinical experience is also included, aiming to optimize the management of refractory ITP.

Pneumocystis jirovecii pneumonia in patients with previously untreated acute myeloid leukaemia.

BACKGROUND: Several studies in immunocompromised patients, such as those with HIV infection, undergoing cancer chemotherapy or organ transplant, have led to the development of guidelines on the use of prophylaxis to prevent Pneumocystis jirovecii pneumonia (PJP), in these specific conditions. Instead, since the association between PJP and acute myeloid leukaemia (AML) is not clearly defined, the role of prophylaxis in patients with AML is not yet established. METHODS: We retrospectively analysed 251 consecutive patients with newly diagnosed non-M3-AML, admitted at the Hematology Unit of University Tor Vergata in Rome, during the period 2010-2020. The aim of the study was to evaluate the incidence of PJP among AML patients during their first hospital admission, and to identify subjects at a high risk to develop PJP. RESULTS: Among 251 consecutive patients with non-M3-AML, 67 bronchoalveolar lavages (BAL) were performed. PJP was proven in 11/67 (16.7%) subjects undergoing BAL (11 males, median age 71 years), with an incidence of 4.3%. The most common reason for BAL execution were radiological findings such as ground-glass opacities (6/11, 55%) and atypical patterns like consolidations and nodules (5/11, 45%). One patient died because of PJP after 11 days of trimethoprim/sulfamethoxazole therapy. In multivariate analysis older age and smoking habit were independent factors significantly associated with PJP (p = .021 and 0.017 respectively). CONCLUSION: We conclude that PJP infection is not uncommon among patients with AML. If intensive chemotherapy is planned, physicians should be aware of this risk and prophylaxis should be considered, particularly in older patients.

GIMEMA AML1310 trial of risk-adapted, MRD-directed therapy for young adults with newly diagnosed acute myeloid leukemia.

We designed a trial in which postremission therapy of young patients with de novo acute myeloid leukemia (AML) was decided combining cytogenetics/genetics and postconsolidation levels of minimal residual disease (MRD). After induction and consolidation, favorable-risk patients (FR) were to receive autologous stem cell transplant (AuSCT) and poor-risk patients (PR) allogeneic stem cell transplant (AlloSCT). Intermediate-risk patients (IR) were to receive AuSCT or AlloSCT depending on the postconsolidation levels of MRD. Three hundred sixty-one of 500 patients (72%) achieved a complete remission, 342/361 completed the consolidation phase and were treatment allocated: 165 (48%) to AlloSCT (122 PR, 43 IR MRD-positive) plus 23 rescued after salvage therapy, for a total of 188 candidates; 150 (44%) to AuSCT (115 FR, 35 IR MRD-negative) plus 27 IR patients (8%) with no leukemia-associated phenotype, for a total of 177 candidates. Overall, 110/177 (62%) and 130/188 (71%) AuSCT or AlloSCT candidates received it, respectively. Two-year overall (OS) and disease-free survival (DFS) of the whole series was 56% and 54%, respectively. Two-year OS and DFS were 74% and 61% in the FR category, 42% and 45% in the PR category, 79% and 61% in the IR MRD-negative category, and 70% and 67% in the IR MRD-positive category. In conclusion, AuSCT may still have a role in FR and IR MRD-negative categories. In the IR MRD-positive category, AlloSCT prolongs OS and DFS to equal those of the FR category. Using all the available sources of stem cells, AlloSCT was delivered to 71% of the candidates.This trial was registered at www.clinicaltrials.gov as #NCT01452646 and EudraCT as #2010-023809-36.

AMELIORATE: early intensification in FLT3-mutated acute myeloid leukemia based on peripheral blast clearance - MYNERVA-GIMEMA AML1919 trial.

AMELIORATE is a Phase III, randomized trial aiming to personalize treatment intensity in FLT3-mutated acute myeloid leukemia. The current study provides an early appraisal of chemosensitivity based on peripheral blasts clearance, as assessed by multiparameter flow cytometry, from baseline to day 4 of induction. This biomarker was previously demonstrated to predict complete remission achievement and measurable residual disease status. For patients experiencing low peripheral blast cells (i.e., ≤2.0 logs), two major adjustments of treatment as compared with current standard of care are envisioned in the experimental arm: the immediate switch to intensified induction with high-doses cytarabine (1500 mg/m2 b.i.d. on days 5-7 of induction); and the early allocation of the patient to high-risk disease category, to be further refined later based on postinduction measurable residual disease status.

Lay abstract The initial treatment of acute myeloid leukemia is called induction and aims to reduce significantly the number of leukemic cells in the bone marrow. In young adults, this phase comprises several agents, including conventional chemotherapy, monoclonal antibodies, and targeted drugs. Conventionally, induction is delivered as a single block of therapy, the response to which can be appreciated 3­4 weeks after its completion. The authors previously showed that the response to induction can be anticipated by the speed of disappearance of leukemic cells from peripheral blood after four days of therapy. In the AMELIORATE study, the authors aim to personalize the intensity of treatment based on this biomarker, by early intensification of treatment in patients who are predicted to have a poor response.

Applicability and reproducibility of acute myeloid leukaemia stem cell assessment in a multi-centre setting.

Leukaemic stem cells (LSC) have been experimentally defined as the leukaemia-propagating population and are thought to be the cellular reservoir of relapse in acute myeloid leukaemia (AML). Therefore, LSC measurements are warranted to facilitate accurate risk stratification. Previously, we published the composition of a one-tube flow cytometric assay, characterised by the presence of 13 important membrane markers for LSC detection. Here we present the validation experiments of the assay in several large AML research centres, both in Europe and the United States. Variability within instruments and sample processing showed high correlations between different instruments (Rpearson  > 0·91, P < 0·001). Multi-centre testing introduced variation in reported LSC percentages but was found to be below the clinical relevant threshold. Clear gating protocols resulted in all laboratories being able to perform LSC assessment of the validation set. Participating centres were nearly unanimously able to distinguish LSChigh (>0·03% LSC) from LSClow (<0·03% LSC) despite inter-laboratory variation in reported LSC percentages. This study proves that the LSC assay is highly reproducible. These results together with the high prognostic impact of LSC load at diagnosis in AML patients render the one-tube LSC assessment a good marker for future risk classification.

Minimal/measurable residual disease in AML: a consensus document from the European LeukemiaNet MRD Working Party.

Measurable residual disease (MRD; previously termed minimal residual disease) is an independent, postdiagnosis, prognostic indicator in acute myeloid leukemia (AML) that is important for risk stratification and treatment planning, in conjunction with other well-established clinical, cytogenetic, and molecular data assessed at diagnosis. MRD can be evaluated using a variety of multiparameter flow cytometry and molecular protocols, but, to date, these approaches have not been qualitatively or quantitatively standardized, making their use in clinical practice challenging. The objective of this work was to identify key clinical and scientific issues in the measurement and application of MRD in AML, to achieve consensus on these issues, and to provide guidelines for the current and future use of MRD in clinical practice. The work was accomplished over 2 years, during 4 meetings by a specially designated MRD Working Party of the European LeukemiaNet. The group included 24 faculty with expertise in AML hematopathology, molecular diagnostics, clinical trials, and clinical medicine, from 19 institutions in Europe and the United States.

Pulmonary infections in patients with myelodysplastic syndromes receiving frontline azacytidine treatment.

Pulmonary infections (PIs) are a major complication of patients with myelodysplastic syndromes (MDS). We retrospectively evaluated 234 MDS patients treated with azacytidine (AZA). The total number of AZA cycles was 2886 (median 8 cycles per patient). There were 111 episodes of PI (3.8% of AZA cycles) in 81 patients (34.6%). PIs were considered of fungal origin in 27 cases (24.3%), associated to bacteremia in 11 cases (9.9%), to influenza infection in two cases (1.8%) and of unknown origin in the remaining 71 cases (64.0%). Forty-five PI episodes were documented in cycles 1 to 4 of AZA (5.1% of 875 cycles) and the remaining 66 episodes beyond the fourth cycle (3.2% of 2011 cycles) (P = .017). Overall, a fungal PI was documented in 13/875 (1.5%) cycles 1 to 4 and in 13/2011 (0.6%) cycles beyond the fourth cycle (P = .001). A baseline chronic pulmonary disease was significantly associated to a higher risk of severe PIs. In the survival analysis, cases of PI in patients who progressed to acute leukemia (PAL) were excluded, in view of the predominant influence of PAL on the outcome of the patients. A PI unrelated to PAL documented during the first 4 AZA cycles was an independent factor predicting lower survival (OR, 2.13; 95% CI, 1.37-3.33; P = .001). In conclusion, PIs are common in MDS patients receiving AZA, in particular during the first cycles of treatment and are associated with an unfavorable outcome. The results of our study raise the issue of the need of a tailored infection prevention strategy.

Features, reason for testing, and changes with time of 583 paroxysmal nocturnal hemoglobinuria clones from 529 patients: a multicenter Italian study.

In this study, we aimed at disclosing the main features of paroxysmal nocturnal hemoglobinuria (PNH) clones, their association with presentation syndromes, and their changes during follow-up. A large-scale, cooperative collection (583 clones from 529 patients) of flow cytometric and clinical data was entered into a national repository. Reason for testing guidelines were provided to the 41 participating laboratories, which followed the 2010 technical recommendations for PNH testing by Borowitz. Subsequently, the 30 second-level laboratories adopted the 2012 guidelines for high-resolution PNH testing, both upon order by the local clinicians and as an independent laboratory initiative in selected cases. Type3 and Type2 PNH clones (total and partial absence of glycosyl-phosphatidyl-inositol-anchor, respectively) were simultaneously present in 54 patients. In these patients, Type3 component was sevenfold larger than Type2 (p < 0.001). Frequency distribution analysis of solitary Type3 clone size (N = 442) evidenced two discrete patterns: small (20% of peripheral neutrophils) and large (> 70%) clones. The first pattern was significantly associated with bone marrow failure and myelodysplastic syndromes, the second one with hemolysis, hemoglobinuria, and thrombosis. Pediatric patients (N = 34) showed significant preponderance of small clones and bone marrow failure. The majority of PNH clones involved neutrophils, monocytes, and erythrocytes. Nevertheless, we found clones made exclusively by white cells (N = 13) or erythrocytes (N = 3). Rare cases showed clonal white cells restricted only to monocytes (6 cases) or neutrophils (3 cases). Retesting over 1-year follow-up in 151 cases showed a marked clone size increase in 4 cases and a decrease in 13, demonstrating that early breaking-down of PNH clones is not a rare event (8.6% of cases). This collaborative nationwide study demonstrates a clear-cut difference in size between Type2 and Type3 clones, emphasizes the existence of just two classes of PNH presentations based on Type3 clone size, depicts an asymmetric cellular composition of PNH clones, and documents the possible occurrence of changes in clone size during the follow-up.

Efficacy and safety of ruxolitinib in intermediate-1 IPSS risk myelofibrosis patients: Results from an independent study.

Patients with myelofibrosis at intermediate-1 risk according to the International Prognostic Score System are projected to a relatively long survival; nonetheless, they may carry significant splenomegaly and/or systemic constitutional symptoms that hamper quality of life and require treatment. Since registrative COMFORT studies included only patients at intermediate-2/high International Prognostic Score System risk, safety and efficacy data in intermediate-1 patients are limited. We report on 70 intermediate-1 patients treated with ruxolitinib according to standard clinical practice that were evaluated for response using the 2013 IWG-MRT criteria. At 6 months, rates of spleen and symptoms response were 54.7% and 80% in 64 and 65 evaluable patients, respectively. At 3 months, ruxolitinib-induced grade 3 anemia and thrombocytopenia occurred in 40.6% and 2.9% of evaluable patients, respectively. Notably, 11 (15.9%) patients experienced at least one infectious event ≥grade 2. Most (82.6%) patients were still on therapy after a median follow-up of 27 months. These data support the need for standardized guidelines that may guide the decision to initiate ruxolitinib therapy in this risk category, balancing benefit expectations and potential adverse effects.

Comparative analysis of azacitidine and intensive chemotherapy as front-line treatment of elderly patients with acute myeloid leukemia.

The present observational study aimed to compare the efficacy of azacitidine (AZA) and intensive chemotherapy (IC) in elderly patients with untreated acute myeloid leukemia (AML), diagnosed according to WHO criteria. In the two groups, we evaluated complete remission (CR), overall survival (OS), and disease-free survival (DFS). The AZA group included 89 patients; median age was 73 years (range 61-80) and median white blood cell count (WBCc) 2.5 × 109/L (range 0.27-83), 45% of the patients had BM blasts ≥ 30%, and 44 (49%) had a secondary AML (sAML). Karyotype was evaluable in 69 patients: 51 (74%) had intermediate-risk abnormalities and 18 (26%) an unfavorable risk karyotype. IC group consisted of 110 patients who received an induction course with mitoxantrone, cytarabine, and etoposide, followed by two consolidation cycles including idarubicin, cytarabine, and etoposide. Median age was 67 years (range 61-78) and median WBCc 8.0 × 109/L (range 0.69-258); 44 (40%) had a sAML. Karyotype was evaluable in 88 patients, 71 (81%) had intermediate risk, and 17 (19%) unfavorable risk karyotype. To minimize the effects of treatment selection bias, adjustments were made using the propensity-score matching method, which yielded 74 patient pairs. CR rate was significantly higher in IC vs AZA group (73 vs 25%, respectively) (p < 0.0001), but the 3-year OS rates and median OS were not significantly different (21.6 vs 11% and 15.8 vs 13 months, respectively). Our analysis suggests similar outcomes with AZA compared to IC. Controlled, randomized clinical trials are warranted to confirm this conclusion.

Should patients with acute myeloid leukemia and measurable residual disease be transplanted in first complete remission?

PURPOSE OF REVIEW: Measurable ('minimal') residual disease in acute myeloid leukemia during first complete morphologic remission (MRD CR1) identifies patients with particularly high relapse risk and short survival. Here, we examine the evidence regarding optimal postremission treatment strategy for such patients. RECENT FINDINGS: With chemotherapy alone or chemotherapy/autologous hematopoietic cell transplantation (HCT), disease recurrence appears inevitable in patients with MRD CR1. Nonrandomized studies indicate that allogeneic HCT improves outcomes over chemotherapy and/or autologous HCT, although relapse risks remain substantial. Emerging data suggest that myeloablative cord blood HCT may overcome the negative impact of MRD to a greater degree than other transplants, but the relative contributions of intensified conditioning and stem cell source to this effect are unknown. SUMMARY: Available evidence supports the recommendation to consider allogeneic HCT for all acute myeloid leukemia patients in MRD CR1. Whether cord blood transplants should be prioritized deserves further investigation. To what degree outcomes of MRD CR1 patients could be improved by treatment intensification during induction, postremission therapy and/or before transplantation to revert the patient into an MRD state is currently unknown, as is the value of post-transplant preemptive therapies. These remain areas worthy of investigation, preferably in the setting of controlled clinical trials.

Minimal residual disease prior to allogeneic hematopoietic cell transplantation in acute myeloid leukemia: a meta-analysis.

Minimal residual disease prior to allogeneic hematopoietic cell transplantation has been associated with increased risk of relapse and death in patients with acute myeloid leukemia, but detection methodologies and results vary widely. We performed a systematic review and meta-analysis evaluating the prognostic role of minimal residual disease detected by polymerase chain reaction or multiparametric flow cytometry before transplant. We identified 19 articles published between January 2005 and June 2016 and extracted hazard ratios for leukemia-free survival, overall survival, and cumulative incidences of relapse and non-relapse mortality. Pre-transplant minimal residual disease was associated with worse leukemia-free survival (hazard ratio=2.76 [1.90-4.00]), overall survival (hazard ratio=2.36 [1.73-3.22]), and cumulative incidence of relapse (hazard ratio=3.65 [2.53-5.27]), but not non-relapse mortality (hazard ratio=1.12 [0.81-1.55]). These associations held regardless of detection method, conditioning intensity, and patient age. Adverse cytogenetics was not an independent risk factor for death or relapse. There was more heterogeneity among studies using flow cytometry-based than WT1 polymerase chain reaction-based detection (I2=75.1% vs. <0.1% for leukemia-free survival, 67.8% vs. <0.1% for overall survival, and 22.1% vs. <0.1% for cumulative incidence of relapse). These results demonstrate a strong relationship between pre-transplant minimal residual disease and post-transplant relapse and survival. Outcome heterogeneity among studies using flow-based methods may underscore site-specific methodological differences or differences in test performance and interpretation.

Ruxolitinib in clinical practice for primary and secondary myelofibrosis: an analysis of safety and efficacy of Gruppo Laziale of Ph-negative MPN.

Ruxolitinib, a JAK1 and JAK2 inhibitor, has been tested and approved for the treatment of primary and secondary myelofibrosis (MF). Aim of our study is to report safety and efficacy of ruxolitinib in 98 patients affected by MF treated outside clinical trials and collected and treated consecutively by the Lazio Cooperative Group for Ph negative myeloproliferative diseases.There were 45 males and 53 females; median age was 61.8 years (range 35.3-88). Forty-five patients were diagnosed as primary MF and 53 as secondary MF. Seventy-seven patients (78.5%) experienced constitutional symptoms at baseline, and out of 94 patients tested, 66 (70%) were JAK2V617F mutated. Overall, 40 patients received hydroxyurea as firstline treatment, 30 patients received other chemotherapeutic approaches, whereas 28 were treated with ruxolitinib frontline. Median time from diagnosis to start of ruxolitinib in the whole cohort was 34.6 months. Fifty-eight patients (59%) required a dose reduction during the first 3 months due to hematological toxicity in the majority of cases. At 48 weeks, 52% of patients obtained a clinical benefit: of them 7 patients (7%) had a CR, 10 (10%) a PR, 6 patients (6%) a CI, and 28 patients (28.5%) a spleen response. Overall, 66% of patients had disappearance of baseline symptoms burden. After 1 year, of 72 evaluable patients, 52% achieved and maintained a clinical benefit. Adverse events of special interest at any grade included anemia (39.7%), thrombocytopenia (25.5%), infections (16.3%, of which 10 were bronchopneumonia), fluid retention (3%), diarrhea (2%) and abdominal pain (2%). After a median follow-up of 16 months from start of ruxolitinib, median daily dose decreased to 10 mg BID and 21 patients (21%) discontinued the drug. The results of this retrospective multicentric analysis confirmed the efficacy of ruxolitinib outside clinical trials with more than half of treated patients achieving and maintaining a clinical benefit and most of them reporting relief from symptoms.