Abstract: This observational, retrospective study investigates the frequency and reasons for ruxolitinib rechallenge, its therapeutic effects, and its impact on overall survival in a cohort of 219 patients with myelofibrosis discontinuing ruxolitinib for ≥14 days and surviving for ≥30 days. In comparison with 159 patients discontinuing ruxolitinib permanently, discontinuation due to a lack/loss of spleen response is lower ( P = .004) in 60 patients in whom ruxolitinib is rechallenged for ≥14 days (RUX‐again patients): there is a significant increase in the number of patients with large splenomegaly and a high Total Symptom Score ( P 〈 .001) between the first ruxolitinib stop and restart, and there is a significant increase in the number of patients with a Total Symptom Score reduction ( P = .01) during the rechallenge. The use of a ruxolitinib dose 〉 10 mg twice daily is associated with spleen improvements ( P = .05) and symptom improvements ( P = .02), and overall survival is significantly longer in RUX‐again patients ( P = .004).

Abstract: Introduction . Ruxolitinib (RUX) is the only targeted therapy available for the treatment of myelofibrosis (MF)-related splenomegaly and symptoms. Significant clinical responses may be achieved in around 50% of patients (pts). However, half of responding pts lose the response over time. Aims . To report the outcome of a large cohort of MF pts after RUX failure, in terms of disease status, treatment strategies and survival. Methods . A clinical database was created in 23 European Hematology Centers including retrospective data of 537 MF pts treated with RUX from Jan 2011 to July 2018. Updated information at the date of July 15th 2018 was available in 442 pts who were included in the present analysis. Spleen and symptoms response (SR & SyR) to RUX were evaluated according to the 2013 IWG-MRT criteria. RUX-related toxicity and infections were graded according to the WHO scale. Overall (OS) was estimated from the date of RUX discontinuation to the date of death or last contact, using the Kaplan-Meyer method (log-rank test). Results . After a median follow-up of 30.5 months (1.7-84.3), 214 out of 442 evaluable (48.4%) pts had discontinued RUX. 43 (20.1%) died while on therapy because of: MF progression (34.9%), infections (25.6%), heart disease (16.3%), second neoplasia (7%), hemorrhages (7%), other (9.2%). The median follow-up after RUX discontinuation for the remaining 171 pts was 11.3 months (0.5-66.7). Causes of RUX discontinuation were: drug-related toxicity (28.6%), loss/lack of response (23.4%), MF progression (12.3%), acute leukemia (AL) (13.4%), allogeneic stem cell transplantation (ASCT) (11.1%), second solid neoplasia (4.1%), other unrelated causes (i.e. pts decision; 7.1%). After stopping RUX, 68 pts received 1 line of therapy, 21 received 2 lines and 9 received 〉 2 treatments; 73 pts did not receive any therapy. Treatments received after RUX discontinuation, alone or in combination, included hydroxyurea (HU) (n. 61, 62.2%), ASCT (n. 20, 20.4%), second-generation JAK2 inhibitors (momelotinib/fedratinib/pacritinib) (n. 11, 11.2%), splenectomy (n. 7, 7.1%), azacytidine/decitabine (n. 5, 5.1%), chemotherapy (n. 4, 4.1%), investigational agents (imetelstat/PRM151: n. 4), danazole (n. 4), erythropoietin-stimulating agents (ESA) (n. 4). A total of 95 pts (55.6%) died after RUX discontinuation, because of: MF progression (30.5%), AL (25.4%), infections (14.7%), second neoplasia (9.5%), hemorrhages (4.2%), heart disease (4.2%), ASCT (4.2%), thrombosis (2.1%), other (5.2). Median survival time from RUX stop of the 171 evaluable pts was 22.6 mos (95% CI, 13.2-30.7). Among baseline features, survival after discontinuation was significantly influenced by the dynamic international prognostic score (DIPSS) category (p 〈 0.001), transfusion dependency (p 〈 0.001) and driver mutation status (with triple-negative pts having the worst survival compared to JAK2V617F and CALR-mutated pts, p=0.01). During therapy, 45 out of 153 (29.4%) and 123 out of 161 (76.4%) evaluable pts achieved a SR and a SyR at any time. Survival was not affected by the previous response to RUX at any time-point. Conversely, survival significantly differed according to the reason for stopping RUX, with pts discontinuing because of AL evolution/second solid neoplasia having the worst outcome (Figure 1a, p 〈 0.001). In pts who discontinued RUX in chronic phase, the use of second generation TKIs and other investigational agents tended to prolong survival compared to the administration of conventional medical treatments (i.e. HU, danazole, ESA) (Figure 1b, p=0.07) Discussion . After RUX failure, very limited therapeutic options are available and the prognosis of MF pts is dismal, particularly for those pts starting RUX with advanced stage disease (i.e. high DIPSS category and transfusion dependency). Also, disease evolution into AL and occurrence of a second solid neoplasia significantly reduced life expectancy. In chronic phase pts, survival probability may be improved by the use of medical therapies that are still in the experimental phase. Novel investigational agents are needed. Disclosures Palandri: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Abruzzese:BMS: Consultancy; Ariad: Consultancy; Novartis: Consultancy; Pfizer: Consultancy. Vitolo:Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Gilead: Speakers Bureau; Takeda: Speakers Bureau; Sandoz: Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Aversa:Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Basilea: Honoraria, Membership on an entity's Board of Directors or advisory committees; Merck: Honoraria; Astellas: Honoraria; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees. Cuneo:Gilead: Other: advisory board, Speakers Bureau; Roche: Other: advisory board, Speakers Bureau; Abbvie: Other: advisory board, Speakers Bureau; janssen: Other: advisory board, Speakers Bureau. Foà:ROCHE: Other: ADVISORY BOARD, Speakers Bureau; AMGEN: Other: ADVISORY BOARD; JANSSEN: Other: ADVISORY BOARD, Speakers Bureau; GILEAD: Speakers Bureau; NOVARTIS: Speakers Bureau; CELTRION: Other: ADVISORY BOARD; ABBVIE: Other: ADVISORY BOARD, Speakers Bureau; INCYTE: Other: ADVISORY BOARD; CELGENE: Other: ADVISORY BOARD, Speakers Bureau. Di Raimondo:Celgene: Honoraria; Takeda: Honoraria, Research Funding. Cavo:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Breccia:Pfizer: Honoraria; Incyte: Honoraria; BMS: Honoraria; Novartis: Honoraria. Palumbo:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract: Introduction: The outcome of patients (pts) with myelofibrosis (MF) who discontinue ruxolitinib (RUX) is poor with scarce therapeutic possibilities (Palandri et al, 2020). However, some evidences suggest that pts may respond to a rechallenge of RUX after drug stop (Gerds et al, 2018). Aims: To investigate in a real-world context: 1) frequency and reasons for rechallenge; 2) therapeutic effects of rechallenge; 3) impact of rechallenge on overall survival (OS) Methods: After IRB approval, a clinical database was created in 20 European Hematology Centers including now retrospective data of 703 MF pts who started RUX from Jan 2011 to Nov 2019. Only chronic phase (CP) pts who stopped RUX for ≥14 days and survived ≥30 days after discontinuation were included. A specific survey collected clinical/laboratory data at RUX stop and at rechallenge, reasons for discontinuation and treatments before rechallenge. OS was estimated from the date of the first/only RUX discontinuation to last contact (log-rank test). Results: A total of 219 CP pts was evaluable for this study. In 60 (27.4%) pts, RUX was re-challenged for ≥14 days after the first discontinuation (RUX-again), while 159 (72.6%) pts discontinued RUX permanently (RUX-stop). The median time from RUX start to stop was of 16.5 and 12.3 mos for RUX-again and RUX-stop pts, respectively (p=0.41). At RUX start, characteristics of RUX-again were: median age 67y (24-88); males 61.7%; PMF 53.3%; median Hb 10.2 g/dl; median PLT/WBC: 249/12.6 x109/l; median RUX starting dose: 15mg BID. Baseline characteristics of RUX-again and RUX-stop pts were comparable. In the 60 RUX-again pts, reasons for discontinuation included loss of/inadequate response (18 pts, 30%) and toxicity (42 pts, 70%). Toxicity included G3-4 thrombocytopenia (38.1%), anemia (26.2%), infections (21.4%), other (14.3%). Conversely, RUX-stop pts discontinued RUX mainly due to loss of/inadequate response (75 pts, 47.2%), while intolerable toxicity occurred in 69 pts (43.4%) (p=0.004) and other causes in 9.4%. At first RUX discontinuation, 35.7% of RUX-again pts presented with large ( & gt;10 cm) splenomegaly; median Total Symptoms Score (TSS) was 10 (TSS & gt;20 in 30.4% of pts). The median duration of temporary RUX discontinuation was 2 mos (range 0.5-71.1). During RUX stop, 65% of RUX-again pts did not receive any therapy, 15% received only palliation (steroids, hydroxyurea), while 11.7% switched to investigational agents, 3.3% underwent splenectomy and 5% allogeneic transplantation. Compared to disease status at first RUX stop, at RUX restart there was a significant increase of pts with large splenomegaly and high TSS, while the PLT count was higher and RUX dose significantly lower (Table 1). The median duration of RUX rechallenge was 7.5 mos (0.5-72.7). During the rechallenge, 44.6% and 48.3% pts improved spleen and symptoms, and there was a significant increase in pts with TSS reduction (p=0.01); 8 pts (13.3%) continued RUX with stable/worsening spleen size and improvement in TSS. Conversely, 26.8% and 20% of pts had increase in spleen size and in symptoms, respectively. While Hb levels remained stable, PLT count significantly decreased during rechallenge (p & lt;0.001). At last contact, 51.7% of RUX-again pts had permanently discontinued RUX. The reasons for temporary discontinuation had no impact on the reduction of spleen/symptoms during rechallenge and on OS. However, comparing RUX-again and RUX-stop pts, RUX-again pts showed a better OS, with a median survival of 41.1 mos and 23.7, respectively in the 2 cohorts (Fig. 1). Conclusions: This real-world study highlights that RUX rechallenge is quite common in CP-MF pts, involving almost 30% of treated pts, particularly when the discontinuation is due to toxicity. The temporary discontinuation, while improving PLT count, generally caused a significant increase in disease burden. After rechallenge, almost 50% of pts achieved clinical responses regardless of reason of first discontinuation. This residual disease control activity, that correlated with improved OS, should be weighed up also given the new therapeutic possibilities available in these pts. Disclosures Palandri: Novartis: Consultancy, Honoraria. Breccia:Abbvie: Consultancy; Bristol-Myers Squibb/Celgene: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Incyte: Consultancy, Honoraria. Benevolo:Amgen: Honoraria; Celgene: Honoraria; Novartis: Honoraria. Cavazzini:Incyte: Honoraria; Pfize: Honoraria; Novartis: Honoraria. Crugnola:Janssen: Honoraria; BMS: Honoraria; Novartis: Honoraria; Celgene: Honoraria. Heidel:CTI: Consultancy; Celgene: Consultancy; Novartis: Consultancy, Research Funding. Pane:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Other: travel expenses, Speakers Bureau; Daiichi Sankyo: Consultancy, Other: Travel Expenses; Novartis pharma SAS: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Other: Travel Expenses; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Other: Travel Expenses, Speakers Bureau; AbbVie: Consultancy, Other: Travel Expenses, Speakers Bureau. Cuneo:janssen: 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; Gilead: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Krampera:Janssen: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Semenzato:Takeda: Honoraria; Roche: Honoraria; Abbvie: Honoraria. Lemoli:AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; BerGenBio ASA: Research Funding. Cavo:Jannsen, BMS, Celgene, Sanofi, GlaxoSmithKline, Takeda, Amgen, Oncopeptides, AbbVie, Karyopharm, Adaptive: Consultancy, Honoraria. Palumbo:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Abstract: Introduction. Blast phase (BP) is the terminal and most incurable phase of myelofibrosis (MF) and occurs in a not negligible fraction of patients (pts). In the pre-ruxolitinib (RUX) era, peripheral blasts, thrombocytopenia, unfavorable cytogenetics, and high risk category were identified as predictors of BP. RUX is the standard of care for symptomatic MF; however, information on clinical/laboratory correlates of BP in RUX-treated pts is not available. Aims. The primary objective of the study is to assess real-world data on incidence, risk factors and outcome of BP in RUX-treated MF pts. Methods. A multicentre observational retrospective study on RUX-treated MF pts was conducted in 20 European Hematology Centers. Data were extracted from an electronic database that included consecutive pts treated with RUX from June 2011. Data cut-off was June 2019. Risk category was assessed at RUX start according to the Dynamic International Prognostic Score System (DIPSS) or the Myelofibrosis Secondary to PV and ET Collaboration Prognostic Model (MYSEC-PM) in pts with post-Polycythemia Vera (PV)/post-Essential Thrombocythemia (ET) MF (secondary MF, SMF). A time-to-event (BP) analysis was conducted with Fine & Gray model with death/time of stem cell transplant as competing risks. Variables tested for association with BP were: age≥65yr, sex, transfusion-dependency, PLT 〈 150x109/l, peripheral blasts ≥3%, marrow fibrosis grade, CALR-unmutated genotype, unfavorable karyotype, spleen length (≥10 cm), total symptoms score (≥20), previous hydroxyurea (HU), alkylating agents, and interferon (IFN) use, time from MF diagnosis to RUX start, and PV/ET duration. Cumulative Incidence Function among risk categories for DIPSS and MYSEC-PM was calculated applying the Gray's model. Results . Overall, 589 MF pts were included and observed for 1833 pt-yrs from RUX start (median, 35.4 mos). Diagnosis was PMF in 304 pts (51.6%), PPV-MF in 164 pts (27.8%) or PET-MF in 121 (20.6%); 58.4% males. Molecular status was: JAK2V617F (82.5%), CALR (11.3%) and MPLW515K/L (1.1%); 5.1% were triple negatives. Overall, 368 (62.5%) pts received ≥1 cytoreductive therapy before RUX, specifically: HU, n. 357; alkylating agents, n. 47; anagrelide, n. 33; and IFN, n. 29. Median time from MF diagnosis to RUX start was 1.3 yrs. DIPSS for the whole cohort was: INT-1 (52.9%), INT-2 (40.1%), and HIGH (7%). DIPSS distribution in PMF pts was: INT-1 (47.8%), INT-2 (45.7%), and HIGH (6.5%), while SMF pts were categorized at LOW (11.1%), INT-1 (43.1%), INT-2 (31.2%) and HIGH (14.6%) risk according to the MYSEC-PM. Overall, 65 (11%) developed BP. In 61 pts, BP caused RUX withdrawal after a median time of 1.2 yrs (0.7-6.2); in 4 pts BP occurred after RUX stop (median time: 2.4 yrs). BP incidence rate was 3.6 x100 pt-yrs and was comparable in PMF and SMF (p=0.1). In univariate analysis, the probability of BP evolution for the PMF cohort was significantly reduced by previous IFN use (p=0.001). In SMF, predictors for BP in univariate analysis were PLT 〈 150 x109/l (p=0.001), blasts ≥3% (p=0.002), grade 3 marrow fibrosis (p=0.03) and PV/ET duration ≥ 10 yrs (p=0.02); previous IFN significantly reduced the risk of BP (p=0.02). In multivariable analysis, PLT 〈 150 x109/l (HR 2.4, 95% CI 1.1-5.4, p=0.03), blasts ≥3% (HR 3.3, 95% CI 1.4-7.5, p=0.004) and previous IFN (HR 0.1, 95% CI 0.02-0.8, p=0.04) remained significant. High DIPSS risk significantly predicted BP in PMF (p=0.04, HR [95% CI]: 2.6 [1.1-6.5] ) but not in SMF (p=0.40). In this latter cohort, only the MYSEC-PM was associated with BP (p=0.02, HR 1.7 [95% CI]: [1.1-2.8] ) (Fig.1). Estimated HRs, in reference to the lower score category, were: 1.10 for INT-1, 1.82 for INT-2, and 4.04 for HIGH risk. HR for HIGH risk, comparing to all lower risk groups, was 3.53 (95% CI: 1.53-8.11). Overall, 54 (81.8%) BP pts died and median survival was 2.8 mos. Survival after BP was not influenced by type of MF, previous response to RUX, and type of salvage treatment. Conclusions. Thrombocytopenia and peripheral blasts at RUX start identified pts at higher risk of BP in SMF, while previous IFN use was associated with reduced BP evolution in both PMF and SMF, suggesting a possible disease-modifying action of this agent. Also, this analysis supports the ability of MYSEC-PM in predicting BP in pts with SMF. Despite RUX use, outcome after BP remained dismal, confirming the need for newer treatment strategies. Disclosures Palandri: Novartis: Consultancy, Honoraria. Breccia:Incyte: Honoraria; Celgene: Honoraria; Novartis: Honoraria; Pfizer: Honoraria; BMS: Honoraria. Tiribelli:Incyte: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees. Benevolo:Novartis Pharmaceuticals: Consultancy. Bonifacio:Novartis: Honoraria; Amgen: Honoraria; Pfizer: Honoraria; Incyte: Honoraria; BMS: Honoraria. Iurlo:Pfizer: Honoraria; BMS: Honoraria; Incyte: Honoraria; Novartis: Honoraria. Elli:Novartis: Membership on an entity's Board of Directors or advisory committees. Abruzzese:BMS: Consultancy; Incyte: Consultancy; Novartis: Consultancy; Pfizer: Consultancy. Sgherza:Novartis: Honoraria; BMS: Honoraria; Pfizer: Honoraria; Incyte: Honoraria. Cavazzini:Pfize: Honoraria; Incyte: Honoraria; Novartis: Honoraria. Crugnola:Novartis: Honoraria; Incyte: Honoraria. Isidori:Janssen: Honoraria; Novartis: Honoraria; Gilead: Honoraria. Heidel:Novartis: Consultancy, Research Funding; Celgene: Consultancy; CTI: Consultancy. Latagliata:Janssen: Honoraria; Novartis: Honoraria; Pfizer: Honoraria; Celgene: Honoraria. Trawinska:Novartis: Consultancy, Honoraria. Krampera:Janssen: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Cuneo:Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Honoraria, Speakers Bureau; Abbvie: Honoraria, Speakers Bureau; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Cavo:takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; novartis: Honoraria. Palumbo:Novartis: Honoraria; Janssen: Honoraria; Celgene: Honoraria; Amgen: Honoraria; Hospira: Honoraria; Teva: Honoraria.

Abstract: The impact of ruxolitinib therapy on evolution to blast phase (BP) in patients with myelofibrosis (MF) is still uncertain. In 589 MF patients treated with ruxolitinib, we investigated incidence and risk factors for BP and we described outcome according to disease characteristics and treatment strategy. After a median follow‐up from ruxolitinib start of 3 years (range 0.1‐7.6), 65 (11%) patients transformed to BP during (93.8%) or after treatment. BP incidence rate was 3.7 per 100 patient‐years, comparably in primary and secondary MF (PMF/SMF) but significantly lower in intermediate‐1 risk patients (2.3 vs 5.6 per 100 patient‐years in intermediate‐2/high‐risk patients, P   〈  .001). In PMF and SMF cohorts, previous interferon therapy seemed to correlate with a lower probability of BP (HR 0.13, P = .001 and HR 0.22, P = .02, respectively). In SMF, also platelet count 〈 150 × 10 9 /l (HR 2.4, P = .03) and peripheral blasts ≥3% (HR 3.3, P = .004) were significantly associated with higher risk of BP. High‐risk category according to dynamic International Prognostic Score System (DIPSS) and myelofibrosis secondary to PV and ET Collaboration Prognostic Model (MYSEC‐PM predicted BP in patients with PMF and SMF, respectively. Median survival after BP was 0.2 (95% CI: 0.1‐0.3) years. Therapy for BP included hypomethylating agents (12.3%), induction chemotherapy (9.2%), allogeneic transplant (6.2%) or supportive care (72.3%). Patients treated with supportive therapy had a median survival of 6 weeks, while 73% of the few transplanted patients were alive at a median follow‐up of 2 years. Progression to BP occurs in a significant fraction of ruxolitinib‐treated patients and is associated with DIPSS and MYSEC‐PM risk in PMF and SMF, respectively.

Abstract: The 2016 WHO criteria identified early primary myelofibrosis (PMF) as an individual entity with milder clinical features and better outcome compared with overt PMF. Here, we compared early and overt PMF patients treated with ruxolitinib in terms of baseline clinical/laboratory characteristics, response, and toxicity to treatment. We observed that early‐PMF patients achieve better and more stable spleen and symptoms responses, with significantly lower rates of hematological toxicities. No differences in overall and leukemia‐free survival were detected between the two cohorts. The application of 2016 WHO criteria is crucial to identify those PMF patients who deserve a stricter monitoring during treatment.

Abstract: In real‐world data from 524 patients who received ruxolitinib for myelofibrosis, the incidence of and risk factors associated with drug discontinuation were investigated along with how reasons for discontinuation, disease phase at discontinuation, and salvage therapies may influence outcomes. At 3 years, higher risk category, lower platelet count, unfavorable karyotype, and transfusion dependency at the start of ruxolitinib were associated with a greater probability of drug discontinuation; and outcomes were significantly better in patients who discontinued in chronic phase versus blast phase and in those who received investigational agents and/or ruxolitinib rechallenge.

Abstract: Introduction . The 2016 WHO criteria identified early primary myelofibrosis (early-PMF) as an individual entity with different clinical/laboratory presentations and a significantly better outcome compared to overt PMF. No information is available on the therapeutic effects of ruxolitinib (RUX) in the context of each disease separately. Aims . To report the differences between early and overt PMF patients (pts) treated with RUX in terms of baseline clinical/laboratory characteristics, response to treatment and toxicity. Methods . A clinical database was created in 23 European Hematology Centers including retrospective data of 537 MF pts treated with RUX from Jan 2011 to July 2018. Spleen and symptoms response (SR & SyR) to RUX were evaluated according to the 2013 IWG-MRT criteria. Hematologic toxicity and infections were graded according to the WHO scale. Overall survival (OS) and progression-free survival (PFS) were estimated from diagnosis using the Cox proportional hazards regression model, with adjustment for the dynamic international prognostic score system (DIPSS) and left-truncation. Results . A total of 199 pts had a diagnosis of early (n. 59, 29.7%) or overt (n. 140, 70.3%) PMF confirmed by bone marrow biopsy at RUX start and were included in this analysis. At RUX start, median age was 68.4 yrs (26.5-88.9) and 66.3% of pts had a spleen palpable at ≥10 cm below the left costal margin (LCM) (median spleen length: 12 cm). Median hemoglobin value and total symptoms score (TSS) were 10.5 g/dL and 20 (0-80), respectively. DIPSS distribution was: intermediate-1 (50.5%), intermediate-2 (42.1%), high (7.4%). Molecular status was: JAK2V617F 72.3%, CALR 13.7%, MPLW515K/L 3.1%, triple-negative 5%. Median time from diagnosis to RUX start was 22.4 mos (0.1-394). Compared to overt PMF pts, pts with early PMF started RUX with higher hemoglobin levels (median, 11.6 vs 10.4 g/dl, p=0.01) and lower circulating blast counts (p 〈 0.001), and were more frequently at intermediate-1 DIPSS risk (69.6% vs 42.5%, p 〈 0.001). RUX starting and 12-weeks titrated doses were comparable in the two groups. At 3 and 6 months, 43.1% and 48.9% of early-PMF pts achieved a SR, compared to 27.9% and 31.3% of overt-MF pts (p=0.04 and p=0.04, respectively). The rate of SyR was also higher in early-PMF pts at 3 months (82.5% vs 68.8%, p=0.05) and at 6 months (90.0 vs 73.7, p=0.02). In the first 12 months from RUX start, anemia/thrombocytopenia of all grades occurred in 75.6%/43.1% and 86.3%/60.0% of early and overt PMF pts, respectively (p=0.11 and p=0.03). At 3 months, anemia was more frequent in overt PMF pts (94.7% vs 80.0%, p=0.01), with 32.6% of pts having a grade 3-4 anemia compared to 17.8% in early PMF (p=0.02). The incidence of thrombocytopenia was also higher in overt PMF at 3 (51.5% vs 36.2%, p=0.05) and 6 (52.9% vs 35.8%, p=0.04) months, with only 2.2% and 2.5% of pts having a grade 3-4 thrombocytopenia, respectively. Seventy-five pts had at least one grade ≥2 infectious episode during RUX therapy. Considering death as competing risk, the cumulative risk of infections grade ≥2 was comparable in the two cohorts (p=0.4). Overall, 108 pts discontinued RUX (52.5% and 55.0% of early and overt PMF pts, p=0.7). Evolution into acute leukemia (AL) occurred in 21 pts. After a median follow-up of 23 months, 69 pts died (19 early), specifically because of progression of myelofibrosis (38%), AL (16.9%), infections (11.3%), hemorrhage/thrombosis (12.6%), second neoplasias (8.5%) or transplant-associated toxicity (2.8%), other causes (9.9%). OS (p=0.88) and PFS (p=0.86) were comparable in early and overt PMF pts. Conclusions . This study indicates for the first time that early PMF represents a category of pts that is projected to have better responses and lower toxicities from RUX treatmemt. In the setting of RUX therapy, a WHO-defined diagnosis may contribute to better identify pts who may deserve a strict monitoring during treatment. Disclosures Palandri: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Palumbo:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Abruzzese:BMS: Consultancy; Pfizer: Consultancy; Novartis: Consultancy; Ariad: Consultancy. Foà:INCYTE: Other: ADVISORY BOARD; GILEAD: Speakers Bureau; JANSSEN: Other: ADVISORY BOARD, Speakers Bureau; ROCHE: Other: ADVISORY BOARD, Speakers Bureau; CELTRION: Other: ADVISORY BOARD; ABBVIE: Other: ADVISORY BOARD, Speakers Bureau; AMGEN: Other: ADVISORY BOARD; NOVARTIS: Speakers Bureau; CELGENE: Other: ADVISORY BOARD, Speakers Bureau. Vitolo:Takeda: Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Gilead: Speakers Bureau; Sandoz: Speakers Bureau. Aversa:Basilea: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Honoraria; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Merck: Honoraria; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees. Cuneo:Roche: Other: advisory board, Speakers Bureau; Abbvie: Other: advisory board, Speakers Bureau; Gilead: Other: advisory board, Speakers Bureau; janssen: Other: advisory board, Speakers Bureau. Di Raimondo:Celgene: Honoraria; Takeda: Honoraria, Research Funding. Cavo:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Breccia:Incyte: Honoraria; Pfizer: Honoraria; Novartis: Honoraria; BMS: Honoraria.