P1036: VOLUMETRIC SPLENOMEGALY IN PATIENTS WITH POLYCYTHEMIA VERA

Abstract

Background: At present, palpable splenomegaly is relatively uncommon in patients with polycythemia vera (PV), possibly because of early diagnosis facilitated by a lowering of the diagnostic thresholds for hemoglobin and hematocrit levels as well as the wide application of driver gene mutation tests. Radiological volumetric analysis of spleen size is now readily available. However, non-palpable splenomegaly in patients with PV has seldom been addressed. Aims: In this retrospective study, we evaluated non-palpable, volumetric splenomegaly defined based on age- and body surface area (BSA)–matched criteria in patients with PV diagnosed according to the 2016 World Health Organization diagnostic criteria. Methods: Patients with PV who underwent abdominal computed tomography (CT) and who had palpable splenomegaly at diagnosis from January 1991 to December 2020 at Chungnam National University Hospital were enrolled in the study. The spleen volume of each patient was determined by volumetric analysis of abdominal CT and adjusted for the patient’s age and BSA. And then the degree of splenomegaly was classified as follows: no splenomegaly, spleen volume less than the mean plus 2 SD of the reference volume based on both age and BSA; overt volumetric splenomegaly, spleen volume greater than the mean plus 3 SD of the reference volume based on both age and BSA; borderline volumetric splenomegaly, a spleen volume between no splenomegaly and overt splenomegaly; or palpable splenomegaly, spleen palpable below the left costal margin. Results: Of the 87 PV patients enrolled in the study, 15 (17.2%) had no splenomegaly, whereas 17 (19.5%), 45 (51.7%), and 10 (11.5%) had borderline volumetric, overt volumetric, and palpable splenomegaly, respectively. Spleen volume was significantly positively correlated with lactate dehydrogenase level (r = 0.227, P = 0.042) and tended to be positively related to white blood cell count (r = 0.209, P = 0.055) and monocyte count (r = 0.210, P = 0.059) at diagnosis. Spleen volume was not correlated with hemoglobin level, platelet count, or JAK2V617F burden at diagnosis. The degree of splenomegaly did not affect the cumulative incidence of thrombotic vascular events (10-year incidence: 7.7%, 0%, 22.3%, and 50.7%, respectively, P = 0.414). By contrast, splenomegaly tended to adversely affect myelofibrotic transformation (10-year cumulative incidence: 0%, 0%, 7.1%, and 30.3%, respectively, P = 0.062). Moreover, the cumulative incidence of myelofibrotic transformation was significantly higher in patients with overt volumetric or palpable splenomegaly than those with no or borderline volumetric splenomegaly (10-year incidence: 0% vs. 10.3%, respectively; 15-year incidence: 0% vs. 26.3%, respectively, P = 0.020). Overall survival (OS) differed among patients with different degrees of splenomegaly (15-year OS: 100%, 78.6%, 71.7%, and 51.9%, respectively, P = 0.021). The degree of splenomegaly was independent risk factor for both myelofibrotic transformation (hazard ratio [HR]: 7.75; 95% confidence interval [CI]: 1.87-21.10; P = 0.005) and OS (HR: 6.70; 95% CI: 1.89-23.72; P = 0.003). Summary/Conclusion: The degree of splenomegaly, including volumetric splenomegaly, based on age- and BSA-matched reference spleen volumes at diagnosis reflects disease progression in PV patients. Therefore, volumetric splenomegaly should be evaluated at the time of PV diagnosis and taken into consideration when predicting the prognosis of patients with this disorder.