Safety and Effectiveness of Ruxolitinib in Real-World Patients with Myelofibrosis: A 2-Year Observational Study from Taiwan

Introduction Ruxolitinib (RUX) is an approved JAK1/JAK2 inhibitor for the treatment of intermediate or high-risk myelofibrosis, including primary myelofibrosis (PMF), post-polycythemia vera myelofibrosis (PPV-MF), and post-essential thrombocythemia myelofibrosis (PET-MF), but real-world safety and efficacy of RUX in Taiwan are not well understood. This study was conducted to evaluate the safety and efficacy of treatment with RUX with intermediate-2 or high risk PMF, PPV-MF or PET-MF in routine clinical practice.

Method This 2-year, single-arm, multicenter, post-marketing surveillance registry collected data on the safety, tolerability, efficacy, and other clinical information of adult patients (pts) aged ≥20 years with a confirmed diagnosis of intermediate-2 or high-risk PMF, PPV-MF, or PET-MF who either received RUX or starting RUX in accordance with the general clinical practice in Taiwan. Primary endpoint included collection of adverse events (AEs), AE of special interest (AESIs; anemia, thrombocytopenia, leukocytosis, hepatitis B virus (HBV) infection or reactivation, tuberculosis (TB) infection, and other infections), and serious adverse events (SAEs) throughout the study. Key secondary endpoints included treatment duration, discontinuation rates, dosage of prescribed RUX, Myeloproliferative Neoplasm symptom assessment form (MPN-10) score after study entry and change in spleen size, specifically in naïve patients who were eligible for spleen response evaluation.

Results A total of 99 (51% PMF, 22.4% PPV-MF, and 26.5% PET-MF) pts were recruited, of which 38 (38.4%) pts discontinued due to consent withdrawal (n=11), death (n=10), discontinued prescription of RUX for 3 months (n=4), AEs (n = 2), unsatisfactory therapeutic effect (n=2), administrative problems (n=1), disease progression (n=1), required immediate stem cell transplantation (n=1), and others (n=6). Median age was 68.1 (range: 38.3-87.2) years and gender ratio was balanced, with 97 Taiwanese pts (98.0%). Median disease duration was 13.9 months (range: 0-967.6 months) and 70.7% and 28.3% of pts were identified with the risk of intermediate-2 or high using IPSS/DIPSS risk assessment, respectively. Majority of the recruited pts were RUX pre-treated (n=75; 75.8%) and 24.2% (n=24) pts were RUX-naïve at baseline.

During the study, 88 pts (89.8%) had 673 AEs, and 44 (44.9%) experienced 159 SAEs. Half of the pts (55.1%) had moderate or severe SAEs and 39 pts recovered. Over 80% of SAEs (n=131) were not related to RUX. Major AESIs were anemia (29.6%) and thrombocytopenia (20.4%). There were no HBV infection or reactivation reported; 2% of pts had TB while 3% of pts had herpes zoster infections. The major reported infection was pneumonia (20.4%). Key safety data are summarized in Table 1. Most pts had their AEs resolved (77.6%), while 10 deaths occurred due to AEs (10.2%).

Majority of the pts (41.8%) received a daily dose of RUX 20 mg at the enrolment, with an average mean daily dose of 22.7±9.2 mg (Figure 1). For naïve pts, mean initial dose was 18.8 ± 8.50 mg and gradually titrated up to 22.3 ± 8.69 mg at 3 months and to 24.0 ± 9.17 mg at 6 months. Among 98 pts, 13.3% pts whose platelet counts between 100-200×10³/μL and 21.4% pts whose platelet counts were >200×10³/μL were treated with RUX 5-10 mg twice daily.

Among 27 RUX pre-treated patients (mean RUX duration before study entry: 17.0 ± 20.98 months), spleen size by palpation was relatively stable throughout the study period. For the 7 RUX naïve pts, the mean spleen size change from baseline was -15.9 %± 28.72 at 12 weeks, -30.8% ± 31.28 at 24 weeks, -54.2% ± 41.93 at 48 weeks and -52.0% ± 36.41 at 96 weeks. However, it should be interpreted with caution due to the small pt pool. A total of 65 pts (65.7%) had >50% improvement in the symptom response by MPN-10 during 2-year study period. .

Conclusion This is the first real-world study in Taiwan to evaluate safety and efficacy with RUX in patients with MF. It was observed that physicians employed a conservative strategy for a lower starting dose with gradual titration resulting in comparable safety profile, but lower incidences of thrombocytopenia compared to published clinical trials. The majority of pts reported continuous symptomatic improvement and a small number of RUX naïve pts had pronounced spleen size reduction. Further investigations are required to evaluate whether optimal dose of RUX or titration speed would improve spleen response.

Yeh:Abbvie: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Jansen: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Bristol Myer Squibb: Honoraria; Pfizer: Honoraria. Chiang:Novartis: Current Employment. Chung:Novartis: Current Employment. Lee:Novartis: Current Employment. Ku:Novartis: Current Employment. Chang:Novartis: Consultancy, Honoraria.