In addition, 5 of 6 pts (83%) with Grade 2 collagen fibrosis at baseline had a 1-grade reduction, with 2 of 6 pts (33%) improving to Grade 0. Of the pts with Grade 3 BMF at baseline, 2 of 9 pts (22%) had a 2-grade reduction (Table). Improvement in BM reticulin grade was observed in 5 of 7 pts (71%) with Grade 2 BMF at baseline, and in 4 of 9 pts (44%) with Grade 3 BMF at baseline. Complete data on hematology parameters will be available at the time of presentation. Pts in the PRM-151 monotherapy group showed similar improvements in MPN-SAF TSS and splenomegaly as those receiving PRM-151 + RUX (Figure). The mean best percent improvement in MPN-SAF TSS was −54%, with a median percent reduction of TSS of −64%. The mean best percent change (by palpation) in spleen size from baseline was −37%, with a median percent reduction of −26.1% (Figure). ![]() No unexpected AEs were observed, and no deaths were reported during the study period. All pts experienced at least 1 adverse event (AE), with 8 pts (44%) reporting a possible study drug-related AE. Median time on study for these 18 pts was 30.9 months (15.9-47.2 months). Baseline characteristics included median age of 66 years (51-78) 8 pts were DIPSS Int-1, 9 Int-2, and 1 high-risk 6 (33%) had Hgb < 100 g/L, 12 (67%) had PLT < 100 x 10 9/L 7 (39%) had PLT <50 x 10 9/L 8 pts had PMF, 10 had post-ET/PV MF 13 pts (72%) had a palpable spleen, and 9 (50%) had Grade 3 BMF. Results: Of the 18 pts enrolled in the OLE, 9 received PRM-151 as single agent, and 9 in conjunction with RUX. The primary objective of the OLE was to assess safety and efficacy of long-term administration of PRM-151. Immunostaining for fibrocytes was performed on available biopsies. These were evaluated centrally by two independent, blinded hematopathologists for the degree of reticulin and collagen fibrosis. BM biopsies were obtained at baseline, end of main study, and at physician discretion in the OLE. Safety and hematology parameters were assessed monthly, and MPN-SAF TSS Q3 months. Pts receiving PRM-151 alone or in combination with RUX in the main study continued with their respective drugs. Methods: All pts in the OLE received a monthly infusion of PRM-151 10 mg/kg IV. ![]() Here, we report interim efficacy and safety data for 18 pts enrolled in the OLE, who had been treated for up to 35 cycles (140 weeks). ![]() Pts experiencing clinical benefit were allowed to continue beyond 24 weeks in an open label extension (OLE) study. A reduction in BMF, decrease in symptoms (MPN-SAF Total Symptom Score ), and a reduction of palpable splenomegaly were observed, along with a favorable safety profile. In the first stage of a two-stage trial, 27 patients (pts) with primary myelofibrosis (PMF), post-essential thrombocythemia/polycythemia vera (post-ET/PV) MF, and Grade 2 or 3 bone marrow fibrosis (BMF) received PRM-151 10 mg/kg IV ± ruxolitinib (RUX) for 6 cycles (24 weeks). Introduction: PRM-151, a recombinant human pentraxin-2 molecule, has been shown to prevent and reverse fibrosis in animal models of myelofibrosis (MF) by postulated targeting differentiation of fibrocytes (essential cells in fibrotic process) from monocytes.
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