Outcome of Splenectomy in JAK2 Inhibitor Treated Patients with Myelofibrosis: A Mayo Clinic Experience in 34 Consecutive Cases
Authors: Carey Patricia , Pardanani Animesh D. , Starlinger Patrick , Tefferi Ayalew , Gangat Naseema 
Published: December 2024

Background: Treatment of symptomatic splenomegaly in myelofibrosis (MF) was revolutionized by JAK2 inhibitors (JAKi), with ruxolitinib inducing a &gt;35% spleen volume reduction in 42% of patients at 24 weeks (N Engl J Med 2012;366). However, the benefit is often transient with a median duration of spleen response of three years (N Engl J Med. 2011;365). Treatment modalities for the management of MF-associated splenomegaly resistant to JAKi treatment includes surgical resection and involved-field radiotherapy. In the current study, we describe our experience with the former.

Methods: Study patients were retrospectively recruited from Mayo Clinic (USA) databases based on the following criteria: i) diagnosis according to the International Consensus Classification (Blood 2022;140:1200); ii) documentation of JAKi therapy exposure followed by splenectomy; iii) availability of information before and after splenectomy. Splenectomy was performed as an open (n=29) or laparoscopic (n=5) surgery. Conventional statistical methods were employed for data analysis (JMP Pro 17.0.0, SAS Institute, Cary, NC, USA).

Results: A total of 34 patients (median age 62.5 years, range 43-79; 59% males) were identified with splenectomies performed between 2011-2024. Mutation distribution included JAK2 62%, CALR 26%, MPL 3%, and triple negative 9%. ASXL1 mutation was present in 37% and SRSF2 mutation was present in 26% of 19 informative cases. Karyotype was very high risk in 15% and unfavorable in 12%.

Median time from diagnosis to JAKi initiation was 7.5 years (0-31). Majority (76%) were treated with one JAKi; 18% had been exposed to 2 different JAKi and 6% with three JAKi. JAKi included ruxolitinib (n=27), momelotinib (n=5), pacritinib (n=3), fedratinib (n=3), and BMS-911543 JAKi (n=5). Two patients underwent allogeneic stem cell transplant (ASCT) three and six months prior to splenectomy. Prior treatment included splenic radiation in 4 patients (median 0.6 years (0.2-1.2)). Pre-operative splenic embolization was performed in 4 patients on same day of splenectomy; one patient had embolization 10 months prior to splenectomy. Median interval from diagnosis to splenectomy was 10.3 years (1.0-35.4) and from initiation of JAKi therapy to splenectomy 1.8 years (0.03-12.1). Most patients had multiple indications for splenectomy including 76% with symptomatic splenomegaly, 50% with significant cytopenia, and 18% in preparation of ASCT. At time of splenectomy, median spleen size on imaging was 25.1 cm (14.7-36) and 55% were red cell transfusion-dependent (Revised international working group criteria).

Postoperative complications were reported in 22 (65%) of patients. Major bleeding occurred in 11 (32%) (of which 7 (64%) required repeat surgical exploration) and thrombosis in 9 (26%); 5 patients experienced both major bleeding and thrombosis. Other complications included infection (n=5), renal injury (n=3), and pneumothorax (n=2).

At a median follow up of 1.7 years (0.01-10.2) post-splenectomy, 12 (35%) ASCT were documented at a median of 2.3 years (1.5-26.4) post-procedure. Median post-splenectomy survival was 4.3 years (5-year survival 44%) and significantly longer in transplanted patients (median not reached vs 2.6 years; 5-year survival 65% vs 22%; p=0.02). Among patients without post-splenectomy ASCT (n=22), 12 (55%) deaths (including 2 from post-operative complications) and 3 leukemic transformations were recorded. Additionally, 13 of the 22 had transfusion-dependent anemia at splenectomy and subsequently 6 (46%) became transfusion-independent (TI) (≥12 weeks without transfusion) with median TI response duration of 2.8 years (0.3-7.1). In addition, among 5 non-transplanted patients with baseline thrombocytopenia (&lt; 50 x 109/L (16-42 x 109/L)), 4 (80%) had platelet count &gt; 100 x 109/L (median; 170 x 109/L, range: 119-279 x 109/L) within 3 months post-procedure.

Conclusions: Splenectomy following JAKi-resistant or intolerant MF is associated with improvement of transfusion-dependent anemia (46% response), resolution of severe thrombocytopenia (80%), and may allow for successful transition to ASCT (35%). However, the procedure is associated with significant perioperative complications occurring in the majority of patients and underscores the need for future collaborative studies to develop selection criteria and evaluate alternative treatment modalities.