Characterization of Philadelphia-Negative Myeloproliferative Neoplasms in the Chilean Public Health System: Multicentric Study

Background: Philadelphia-negative Myeloproliferative Neoplasms (Ph-MPN) are chronic hematological disorders characterized by the overproduction of one or more mature myeloid blood cell lineages. Classical Ph-MPN are Polycythemia Vera (PV), Essential Thrombocytopenia (ET) and Myelofibrosis (MF). The diagnosis includes clinical, histological and molecular features. There are not data from Chile. The aim of this study is to determinate epidemiological, clinical, diagnostic and therapeutic characteristics of Ph-MPN in our country.

Methods: Descriptive and retrospective study. We reviewed the database of the Molecular Biology Laboratory at the Hospital del Salvador, a national reference laboratory, from 2012 to 2017. All patients referred as Ph-MPN were included. We reviewed the clinical records to obtain clinical information.

Results: Clinical data was obtained from 468 cases from 12 public hospitals in Chile. Median age at diagnosis was 70 years. Female to Male ratio= 1,15:1, without significant differences between Ph-MPNs. ET was the most frequently Ph-MNP found, accounting for 49,4% of all Ph-MPN, followed by PV (37%) and MF (10,4%). A 66,2% of ET was JAK2 V617F+. Bone marrow biopsy was performed in 35% of ET cases. Only 7,8% had cytogenetic study. Splenomegaly was found in 8%. Thrombosis was observed in 23,8%. The median platelet count was 842x10⁹/L. All patients received hydrea +/- aspirin or oral anticoagulation. Of the total of PV, 86,6% was JAK2+. Bone marrow biopsy was performed in a quarter of the cases. Thrombosis frequency was 14,5%. A 29% had splenomegaly. Median hemoglobin level was 18 gr/dl. All patients were treated with aspirin +/- phlebotomy and about half of them required cytoreduction. Two patients were refractory to hydrea and used ruxolitinib as second line treatment. A 63,3% of the MF were JAK-2+. Bone marrow biopsy was performed in 59% and 20% had a cytogenetic study. Only one fifth of patients had LDH measurement at diagnosis. Splenomegaly was observed in 75,5% of cases. Thrombosis frequency was 13%. Anemia was the most frequent finding in complete blood count. The treatments were heterogeneous, including hydrea, EPO, thalidomide/prednisone, danazol and ruxolitinib.

Discussion: TE was the most common Ph-MPN. The epidemiological and blood count findings were similar to the data reported in the literature. It is important to note that with the 2016 WHO classification new criteria, some of patients diagnosed with ET, now will be in PV cathegory (21 patients in our serie). The distribution of JAK2V617F+ in Ph-MPN was similar to the published data, except for PV, in which we found a lower percentage of JAK2+. Thrombosis were lower than the data reported for PV. It is worrisome that bone marrow biopsy and cytogenetic study were performed only in a low percentage of the patients. The treatment strategies were heterogeneous and not standardized among the participating centers.

These findings reveal a lack in the use of the diagnostic tools for Ph-MPN. It is important to improve clinical and molecular characterization of these patients in order to guide available therapeutic alternatives in our country.