Long Term Follow-up of an Investigator-Initiated Phase 2 Study of Ruxolitinib in MPN-Associated Splancnic Vein Thrombosis (SVT-RUXO)

Background. Splanchnic vein thrombosis (SVT) is a frequent onset manifestation of an underlying myeloproliferative neoplasm (MPN), or can appear during the disease course. We reported primary results of an investigator-initiated Phase 2 study (SVT-RUXO: Eudract 2012-002253-30) with ruxolitinib (RUX) in 21 patients (pts) with MPN-associated SVT (Pieri L, AJH 2017; 92:187). The treatment proved safe and effective in reducing spleen volume by >35% by NMR at the planned primary analysis at 24 weeks (w) in 29% of the pts, and a >50% spleen length reduction by palpation at any time to 24w was obtained by 62% of the pts. Pts who completed the 24w core study and well tolerated the drug and had evidence of clinically-significant improvement were allowed to enter an extension phase up to w72, then entered a long-term FU (see below for pt disposition).

Aim. Herein we present long-term follow up (FU) of the SVT-RUXO study after a median of 104 months, range 6.2-9.8y.

Study details. The promoter of the study was the AGIMM group of Italian investigators supported by Assoc Italiana per la Ricerca sul Cancro-AIRC. The drug was provided free by Novartis, that had no role in trial design and data analysis. Safety data were reported as cumulative incidence of adverse events (CTCAE v4.03). Clinical responses were defined according to ELN and IWG-MRT criteria. After primary endpoint at 24w, spleen response was assigned by >50% reduction of spleen length by palpation.

Results. Patients disposition. A total of 21 pts (38% PMF, 24% PV, 19% ET, 14% PPV-MF, PET-MF 5%) were enrolled and completed the 24w core study for primary end point. Eighteen pts (86%) were still on study at the 72w extension phase time point, and entered a long-term FU until loss of benefit and/or toxicity, or until shift to commercial RUX. The latter pts were continued to be followed under routine care, and data were collected. One pt died at w252 (sepsis), 1 pt entered another trial after 101 mo and 1 received stem cell transplant after 66 mo for loss of response. As by June 30^th 2022, 15 (71%) pts are still receiving ruxo, 7 ongoing in the study and 8 receiving commercial drug.

Safety. In the post-72w period, the number of AE ranged 0-20/pt. G3 events were thrombocytopenia (n=2), increase of CPK (n=1). All other events were G<2 and included anemia (56%), thrombocytopenia (44%), leukopenia (39%). Four pts (26%) had G2 H. zoster reactivation. SAE included second cancer (1 pheochromocytoma and 1 prostate adenocarcinoma), and one each pneumonia, pleural effusion, encefalopathy, inguinal ernial repair, abdominal pain, sepsis, INR increase in a pt receiving coumadin. Two pts developed COVID-19, with full resolution and under continued ruxo administration.

Efficacy. At latest FU, 11 pts (73%) had a maintained spleen response (defined according to IWG-MRT criteria), the remaining 4 had stable spleen volume, in no pt splenomegaly progressed. No pt had disease-related symptoms. Median Hb was 12.7 g/dL (10.0-14.3), Hct 39.8% (31.3-42.4%), platelet count 136x10⁹/L (46-349), leukocyte count 6.5 x10⁹/L (2.2-43.0), neutrophil count 4.43 x10⁹/L (1.3-38.0). Five pts (33%) were in clinical CR (no spleen/liver, no symptom), 12 pts (80%) had hematologic CR. There was no gastrointestinal or other site bleeding episodes and no thrombotic event. One pt required positioning of a TIP for increased portal hypertension with ascites.

Exploratory endpoint. Fourteen of 15 pts were JAK2V617F mutated, and serial measurements of JAK2VAF VAF in granulocytes were available in 10 pts up to latest cutoff date. Mean JAK2V617F at baseline was 51.7% (+21.1) and 36.5% (+34.5) at 8+1y. According to IWG-MRT response criteria, 4 pts achieved partial molecular response (PMR; ie, >50% reduction from baseline), 5 pts were not responders; one pt had a deep molecular response (DMR) from VAF 15% to <2%, stable since 5+y. A spleen response was present in all pts with PMR+DMR, 4 had hematologic response, while the remaining one pt with PMR had 63x10⁹/L platelets with normal Hb and leukocyte count.

Conclusions. After a median follow-up of 8.6 years, 71% of pts enrolled in the SVT-RUXO study continue to be on drug with substantial efficacy on symptoms and splenomegaly, and no recurrent thrombosis nor GI bleeding events. There was no novel safety signal. Molecular responses were noted in half of pts with serial measurements of JAK2V617F VAF and were associated with hematologic and clinical improvement.

Guglielmelli:Novartis, Abbvie: Other: Other member of advisory board, speaker at meeting. Mannelli:Blueprint: Speakers Bureau; Novartis: Speakers Bureau. Rumi:Novartis: Consultancy, Speakers Bureau. Barbui:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Rambaldi:Celgene-BMS: Honoraria; Janssen: Honoraria; Roche: Honoraria; Incyte: Honoraria; Novartis: Honoraria; Kite-Gilead: Honoraria; Jazz: Honoraria; ABBVIE: Honoraria; Astellas: Honoraria; Pfizer: Honoraria; Amgen: Honoraria; Omeros: Honoraria. Vannucchi:Roche: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Morphosys: Membership on an entity's Board of Directors or advisory committees; Geron: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Blueprint: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Ruxolitinib is not approved for patients with essential thrombocythemia