CSF3R-mutated chronic neutrophilic leukemia: A two-center study of 44 consecutive patients

Abstract Introduction: CSF3R mutations (CSF3RMUT), most commonly T618I, represent the defining genomic alteration in chronic neutrophilic leukemia (CNL), present in ~80% of cases. Despite emerging real-world data, information on treatment outcomes and prognostic factors remains limited due to rarity of the disease. In this two-center retrospective study, we examined clinical and molecular predictors of treatment response, overall survival (OS), and blast transformation (BT) and outcome following allogeneic stem cell transplant (ASCT). Methods: The study was approved by the institutional review boards of the Mayo Clinic (USA) and the University of Montreal (Canada). Electronic medical records were reviewed to identify patients with CSF3R mutated CNL at both institutions and extract relevant data. Statistical analyses were conducted using JMP Pro 17.0.0 software (SAS Institute, Cary, NC, USA). Results: Forty-four patients (68% male, median age 68 years [range: 26-93]) were included. At diagnosis, 20 (56%) were asymptomatic, 13 (36%) presented with constitutional/non-specific symptoms, and 20 (50%) had antecedent leukocytosis at a median of 13 months(mo) prior. Splenomegaly (palpable or radiological) was observed in 28 (67%) patients, hepatomegaly in 7 (17%) and lymphadenopathy in 4 (9.8%). Median white blood cell count (WBC) was 52×10⁹/L (range: 17-390). CSF3RMUT/variants included 39 (89%) with T618I (7 of the 39 had additional CSF3RMUT), 2 (5%) with M696T, and 1 (2%) each for I598I, Q739* and T640N. Frequent co-mutations included ASXL1 in 25 (63%) patients, SETBP1 in 14 (36%), and SRSF2 in 8 (31%), with overlapping occurrence; 10 (38%) patients had ≥2 of these 3 mutations. Ten patients (median WBC 29 x10⁹/L [range: 19–58]), were initially observed without treatment for a median of 8.6 mo; 2 remained on observation alone at 46 and 77 mo. Hydroxyurea (HU) alone or in combinations excluding ruxolitinib (Ruxo) was the most common first-line treatment (68%). Second-line therapies included Ruxo (39%), HU (25%), and hypomethylating agents (14%). WBC response (≥50% reduction from baseline) was 78% with HU vs. 60% with Ruxo (p=0.2). WBC response to HU was lower with abnormal karyotype (40% vs. 94%; p=0.02). WBC response to Ruxo was lower with SETBP1MUT (0% vs. 72%; p=0.05) and with male sex (40% vs. 100%; p=0.04). Seven patients underwent ASCT, including 2 after BT; four (57%) of the 7 remain alive, including 2 without evidence of disease (both 45 mo post-ASCT; one harbored ASXL1MUT) and the other 2 with active disease (both harbored ASXL1MUT). Three patients died from veno-occlusive disease (Day+34), CNS relapse with AML (at 105 mo post-ASCT), or unrelated causes (at 44 mo post-ASCT). Median OS was longer in transplanted patients (115 vs 23 mo; p=0.03). At a median follow-up of 44 mo for living patients, disease transformation occurred in 10 patients, including 7 with BT (6 with T618I, 1 T640N) and 3 with chronic myelomonocytic leukemia (2 M696T, 1 T618I). BT rate at 2, 3, and 5 years was 15%, 31%, and 43%, respectively. Univariate analysis (UVA) identified male gender (p<0.01), >5% immature WBCs (p=0.02), platelets <160×10⁹/L (p=0.04), higher WBC (p=0.02), and ASXL1 or SETBP1 mutation (p<0.01) as risk factors for BT. On multivariable analysis (MVA), only the latter remained significant. Median OS was 26 mo (95% CI: 21-43) for the entire cohort; 24 mo for patients with T618I CSF3RMUT vs 53 mo with other CSF3RMUT, p=0.1. In UVA, age >60 years (HR 5.0, p=0.03), platelets <160×10⁹/L (HR 3.4, p=0.006), WBC >50×10⁹/L (HR 2.6, p=0.02), and ASXL1 or SETBP1 mutations (HR 4.2, p=0.01) were associated with shorter OS. In MVA, age >60 (HR 6, p=0.03), WBC >50×10⁹/L (HR 12, p<0.01), and the presence of ASXL1MUT or SETBP1MUT (HR 9.5, p=0.01) remained significant. Based on the HRs on MVA, one adverse point was allocated for age >60 years, and two adverse points each for WBC >50×10⁹/L and presence of ASXL1 or SETBP1 mutations. Patients were accordingly stratified into low (0-2 points), intermediate (3) and high (4-5) risk groups with corresponding median OS of “not reached”, 29 mo, and 16 mo (p<0.01). Causes of death included disease progression (82%), infection/bleeding (9%), and ASCT complications (9%). Conclusion: The current study highlights the prognostic relevance of “SETBP1 or ASXL1” mutation for both overall survival and risk of blast transformation. The study also signifies variable natural history and potential benefit from ASCT.

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