Phazar: A Phase Ib Study to Assess the Safety and Tolerability of Ruxolitinib in Combination with Azacitidine in Advanced Phase Myeloproliferative Neoplasms (MPN), Including Myelodysplastic Syndromes (MDS) or Acute Myeloid Leukaemia (AML) Arising from MPN [ISRCTN16783472]

Background Treatments for ’accelerated phase’ MPNs (MPN-AP, 10-19% blasts)/post-MPN AML (MPN-BP, ≥20% blasts) are limited. Most patients are precluded from potentially curative haematopoietic stem cell transplantation (HSCT). For HSCT ineligible patients, azacitidine (AZA) is licensed to treat high-risk MDS or AML. Whilst dose and toxicity profile of AZA is well understood, the response of MPNs and post-MPN AML to monotherapy is limited. AZA-based doublet chemotherapy may however result in improved clinical responses. The phase Ib single-arm PHAZAR trial was established to determine maximum tolerated dose (MTD), safety profile and clinical activity of the selective JAK1/2 inhibitor ruxolitinib (RUX) used in combination with AZA to treat MPN-AP and MPN-BP patients. Methods A modified two-stage continual reassessment method with an expansion cohort at the MTD, was used to establish the MTD of RUX in combination with AZA. Successive flexible cohorts of 3-5 patients were enrolled at a fixed AZA dose of 75 mg/m2 s/c for 7 days (excluding weekends, on a 5-2-2 schedule) of a 28-day cycle with continuous administration of an allocated oral RUX dose (dose levels 0, 1, 2 and 3 = 10, 15, 20 and 25 mg BD respectively), and a formal response assessment recorded after 6 cycles. Toxicities were prospectively recorded as per CTCAE v4.0 with dose limiting toxicity (DLT) defined as a grade 3 or 4 non-haematological toxicity during treatment cycle 1. Clinical activity was evaluated over 12 months through assessment of bone marrow response after 3 and 6 treatment cycles, progression free survival (PFS), leukaemia free survival (LFS) and overall survival (OS). Results Thirty four advanced phase MPN patients were recruited from 12 Trials Acceleration Programme sites (19 MPN-AP; 15 MPN-BP). Baseline characteristics are summarized in Table 1. Driver mutation status was available for 25/34(74%) patients. 17/25(68%) carried canonical mutations in JAK2, 4/25 (16%) in CALR, and 4/25(16%) were triple negative. Three patients each received 10 and 15 mg of RUX BD, 4 patients received 20 mg RUX BD, 21 patients received 25 mg RUX BD and 3 did not begin treatment. Median number of cycles received was 3 RUX and 4 AZA. The MTD of RUX in combination with AZA was determined at 25 mg BD, with no DLTs reported during phase 1 of the study. During the expansion phase, 1 DLT at dose level 3 was reported as grade 3 febrile neutropenia; with this patient's RUX dose reduced from 25 to 20 mg BD. Overal