OBJECTIVES
Hyperleukocytosis is defined as a white blood cell (WBC) count of >50.000/µL, caused by malignant proliferation of leukemic cells. Possible complications are leukostasis, tumor lysis and disseminated intravascular coagulation. Hyperleukocytosis in newly diagnosed acute myeloid leukemia (AML) has a higher risk for complications than in other underlying disorders due to the risk of rapid increase in WBC count and the size of myeloid precursors. Only 5-20% AML patients present with hyperleukocytosis [1], but it is associated with poor prognosis due to a high risk of early death and increased risk of relapse. Immediate start of cytoreductive treatment (IV chemotherapy, hydroxyurea or leukapheresis or a combination) is essential to improve outcome. Evidence to prefer one therapy over the other is lacking and especially the risk-benefit ratio of leukapheresis has been questioned [2-7]. Therefore, we decided to investigate the current approach of hyperleukocytic AML in Belgian centers.

METHODS
Through a general questionnaire sent to all Belgian intensive hematology centers (defined as centers where they start intensive treatment for AML), we outlined their current approach of newly diagnosed hyperleukocytic AML patients.

RESULTS 
We already received results from 10 centers out of 14. The responding centers have a median of 24.5 beds (15-40) and on average 5.5 hematologists and 2 trainees working in these centers. The number of newly diagnosed patients with AML varies from 10 to 49 per year. 
One center considers hyperleukocytosis as >50.000/µL WBC at time of diagnosis, in contrast to >100.000/µL in four centers, and five centers do not use a threshold (definition based on symptoms instead of WBC count) (figure 1a).
In figure 2, the threshold used in different centers to start leukapheresis in different circumstances is illustrated.
The majority of the centers (n=8) have a protocol to manage AML patients presenting with hyperleukocytosis (figure 1b) and leukapheresis is performed in 8 of the centers (figure 3a/b). 
In most centers, leukapheresis can be started within four hours and is mostly performed at the ICU, prescribed by the hematologist (figure 3c/d).

CONCLUSION
Most of the Belgian intensive hematology centers have a protocol for hyperleukocytic presentation of AML, which includes leukapheresis for the majority of them. The procedure can be rapidly started, mostly at ICU, and is prescribed by the hematologist. With evidence of leukostasis, half of the centers start leukapheresis only when WBC count transcends the threshold of 100.000/µL. We hereby present an overview on current management of hyperleukocytic AML in Belgium.

Current routine and beliefs in management of hyperleukocytic acute myeloid leukemia in multiple Belgian centers based on an electronic survey