The Assessment of the European Leukemianet Criteria for Clinicohematologic Resistance and Intolerance to Hydroxyurea in Polycythemia Vera Is Not Easily Applicable in Daily Practice
Authors: Fogliatto Laura , Breunig Raquel , Costa Tito Vanelli , Contin Luis Carlos Zanandrea , Silveira Juarez Fontoura , Silveira Cinara , Daudt Liane Esteves , Silla Lucia 
Published: October 2019

Abstract
Background
Polycythemia vera (PV) is a subgroup of myeloproliferative neoplasm (MPN) BCL-ABL1 negative. The current therapy of PV should be aimed at preventing vascular complications and avoid increasing the risk of leukemic transformation. The therapy response monitoring is based in the European LeukemiaNet (ELN) unified definition of clinical resistance and intolerance to hydroxycarbamide in polycythaemia vera consensus process, published by Barbui T et al in Br J Haematol 2010;148(6):961-963.
Objectives
We conducted a study to assess in our clinical practice the aplicability of the standard criteria for resistance and intolerance proposed by ELN in patients (pts) with PV that have been treated with hydroxycarbamida (HU).
Methods
This is a retrospective study in a cohort of pts with PV enrolled in a single Hematology University center in South Brazil. All pts were treated according to PV guidelines, and the response monitoring was based on clinical practice. All database was compared to standard criteria proposed by ELN. Intolerance /resistance was defined by: a) need for phlebotomy to keep hematocrit < 45% after 3 months of at least 2 g/d of HU or b) uncontrolled myeloproliferation (ie, platelet count > 400 x109/L and white blood count (WBC) > 10 x109/L) after 3 months of at least 2g/d of HU or c) failure to reduce massive splenomegaly by 50% as measured by palpation or failure to completely relieve symptoms related to splenomegaly after 3 months of at least 2 g/d of HU or d) absolute neutrophil count < 1.0 x109/L or platelet count < 100 x109/L or hemoglobin < 10 g/dL at the lowest dose of HU required to achieve a complete or partial clinicohematologic response or e) presence of leg ulcers or other unacceptable HU related nonhematologic toxicities, such as mucocutaneous manifestations, GI symptoms, pneumonitis or fever at any dose of HU.
Results
We analyzed data from 33 patients with PV assisted in the last five years in our outpatient clinical data. The ELN criteria for resistance and intolerance were accessed in these patients. At diagnosis, 42,4% of pts were younger than 61yo, and 54,5 were male. Arterial hypertension, diabetes mellitus and dyslipidemia were identified on 21, 2 and 7 pts, respectively. Only one patient was tobacco smoker at diagnosis. Total of 5 pts showed WBC > 15 x109/L, and 7 pts showed platelets > 450 x109/L. Massive splenomegaly is a rare PV manifestation in our series, occurring in 2 pts. Five patients complained of symptoms related to PV as pruritus and vasomotor phenomena at diagnosis. Less than 5% of patients had been treated with 2 g of HU for more than 3 months. In daily practice, when the patient presented hematologic toxicity, the HU was decreased and, if the hematocrit was over 45%, an occasional phlebotomy was performed. In relation to platelets (less than 400 x 109/L) and leucocyte (less than 10 x109/L) counts, these targets were not used exclusively in the clinical practice to change treatment. The intolerance was easily discriminated in patients with leg ulcers and other non-hematological events.
Conclusion
These criteria were done based on an expertise consensus for international criteria standardization for clinical studies. Its application in a retrospective study, using clinical daily practice data is not adequate. The reason is that in the last years the main target to treat patients was the hematocrit above 45%, the exact number of platelets and leucocytes is still not a consensus to define resistance, so different counts had been used to guide treatment, we rarely used HU doses above 1500 mg/daily to treat our patients and massive splenomegaly was observed in very few patients. These criteria should be used most for prospective studies.

Disclosures
No relevant conflicts of interest to declare.