Effect of New or Worsening Anemia on Clinical Outcomes in 2233 Patients with Myelofibrosis Treated with Ruxolitinib in the Expanded-Access Jump Study

Introduction: Transient dose-dependent anemia is a known consequence of ruxolitinib treatment and can influence decisions regarding initiation, dosing, and discontinuation of therapy. Whether new or worsening anemia following ruxolitinib initiation has an impact on efficacy is unknown. A recent analysis of pooled COMFORT-I/II data indicated that new or worsening anemia did not impact the clinical outcomes of spleen volume response or symptom control (Al-Ali et al., Abstract PB2185, Presented at EHA 2023). The analysis presented here sought to validate this result using data from JUMP, the largest trial of ruxolitinib in patients with myelofibrosis (MF) to date.

Methods: JUMP was a large (N=2233) single-arm, phase 3b, expanded-access trial that enrolled and provided ruxolitinib treatment for patients with MF in a setting similar to routine clinical practice. The study evaluated the safety and efficacy of ruxolitinib in patients aged ≥18 years with diagnosed primary or secondary intermediate (Int)-1, Int-2, or high-risk MF (International Prognostic Scoring System criteria) with baseline platelets ≥50×10⁹ /L. All patients received ruxolitinib twice daily at a starting dose of 5–20 mg based on baseline platelet count. In this post hoc analysis, patients were stratified at baseline based on anemia due to MF (anemia defined as hemoglobin [Hb] <100 g/L) and transfusion status among patients with anemia (transfusion-requiring anemia [TRA; received ≥2 units of red blood cells over 8 weeks before first ruxolitinib dose] or non–transfusion-requiring anemia [NTRA]). Outcomes were stratified by presence or absence of new or worsening anemia following ruxolitinib initiation (defined as a decrease in Hb of ≥15 g/L or new transfusion requirement at Week 4, 8, or 12). Outcomes evaluated included spleen length response (SLR; defined as ≥50% reduction at Week 24 or 48 from baseline assessed with manual palpation), ≥6.5-point increase in Functional Assessment of Cancer Therapy–Lymphoma total score (FACT-Lym TS response) from baseline at Weeks 24 and 48, and overall survival (OS) measured by Kaplan-Meier method.

Results: 2233 patients were included (baseline status: nonanemic, n=1386 [62.1%]; NTRA, n=521 [23.3]; TRA, n=326 [14.6]). Median (range) age of all patients was 67.0 (18–89) years, and 54.5% were men. Baseline characteristics were comparable between patients with vs without new or worsening anemia. Rates of SLR at Week 24 among patients with vs without new or worsening anemia were 31.5% vs 31.2%, respectively, (nonanemic; P=0.93), 24.4% vs 27.9% (NTRA; P=0.49), and 25.0% vs 29.8% (TRA; P=0.48; Table). FACT-Lym TS response at Week 24 for patients with vs without new or worsening anemia was 34.5% vs 34.0% (nonanemic; P=0.86), 32.7% vs 29.6% (NTRA; P=0.52), and 41.7% vs 32.1% (TRA; P=0.13). Similar trends were observed at Week 48 among patients with vs without new or worsening anemia for both SLR (35.6% vs 26.1%; P=0.02 [nonanemic], 29.6% vs 27.2%; P=0.71 [NTRA], and 19.0% vs 33.3%; P=0.10 [TRA]) and FACT-Lym (30.4% vs 23.3%; P=0.02 [nonanemic], 26.4% vs 27.6%; P=0.84 [NTRA], and 34.2% vs 33.3%; P=0.91 [TRA]). For nonanemic patients at baseline, time to median OS was not reached in either cohort; however, better OS was seen in those without vs with new/worsening anemia (hazard ratio: 0.559, [95% CI: 0.357–0.876]; P=0.01; Figure). For patients with baseline anemia (NTRA and TRA), no difference in OS was observed in those with or without new/worsening anemia (P=0.24)

Conclusions: Analysis of 2233 patients in the JUMP trial indicates that onset of new or worsening anemia following ruxolitinib initiation did not diminish clinical benefit of treatment. Ruxolitinib was associated with improvements in spleen size and symptom burden irrespective of baseline anemia and transfusion status. These results are consistent with a recent analysis of pooled COMFORT-I/II data (n=277), which reported similar findings for spleen volume and symptom responses. In contrast to the controlled clinical trial setting of COMFORT-I/II, JUMP reflects a real-world setting and enrolled a broader MF population, including those with platelet count <100×10⁹/L and lower-risk MF. Taken together, these results support real-world use of ruxolitinib in patients with MF, regardless of baseline anemia or development of treatment-related anemia.