Thrombin Generation Test During Asparaginase Treatment In Children With Acute Lymphoblastic Leukemia
Authors: Rozen Laurence , Noubouossie Denis F , Dedeken Laurence , Huybrechts Sophie , Le Phu-Quoc , Ferster Alina , Demulder Anne 
Published: October 2019

Abstract
Asparaginase (Aase) and corticosteroid (CS) used to treat acute lymphoblastic leukemia (ALL) in children during the Induction and Late Intensification phases have adverse effects on coagulation and increase the incidence of thrombotic events. Aase and CS reduce both pro- and antithrombotic factors and most studies have evaluated the individual components of the coagulation system to infer the prothrombotic profile. However, global haemostatic potential of these children and its changes during treatment are poorly reported.
We aimed to characterize the global haemostatic phenotype of ALL patients during native Aase therapy, using a global haemostatic assay, the Calibrated Automated Thrombogram® (CAT) method of thrombin generation (TG) in B lineage ALL children treated according to the latest CLG-EORTC first-line protocol (a BFM derived protocol). CAT method was performed on platelets-poor plasma (PPP) at diagnosis (day 1), before each Aase infusion (8 during Induction and 4 during Late Intensification), and at distance of Aase infusion (during and after Interval Therapy and at start of Maintenance). TG was triggered using 1pM tissue factor (TF) and 4µM phospholipids (PL), with and without addition of thrombomodulin (TM). Endogenous Thrombin Potential (ETP) and Peak were monitored and the interquartile range was compared to the [2,5 – 97,5] percentile range of normal controls (NC) of the same range of age (n=28). Protein C activity (PC), free Protein S (PS), antithrombin (AT) and fibrinogen levels were also measured.

Results
Thirty six children were included (20 boys and 16 girls). Their median age at diagnosis was 3.7 years (range 1-14). Twenty had pre-B ALL and 16 common ALL. Elevated ETP and Peak of TG in ALL patients above the 97,5 percentile of NC were noted at diagnosis and persisted during all the Induction phase. During Interval Therapy and later at start of Maintenance, ETP and Peak returned to values below 97.5 percentile of NC. During Late Intensification, ETP and Peak levels increased above the 97.5 percentile of NC. At all time points studied the variation of ETP and Peak levels were similar in the presence and absence of TM. PC, PS, AT and fibrinogen levels decreased during Induction phase with median PS level remaining within the 2.5-97.5 percentile of NC and median AT and PC levels reaching a value lower than the 2.5 percentile of NC at the time of the 7th and 8th Aase infusion respectively (day 32 and 35). Fibrinogen levels were below the 2.5 percentile of NC during Induction from day 15 to day 29. Among the 36 analyzed patients, 2 experienced 3 symptomatic thromboses. One sub-clavian thrombosis occurred during Induction on day 22 and 1 jugular vein thrombosis occurred in a second child after completion of Induction on day 50 (13 days after the 8thAase infusion). These 2 events were concurrent with a central venous catheter infection. The second patient also developed during Late Intensification a cerebral thrombosis in the longitudinal sinus. Concomitant to these three events, ETP and Peak values of these patients were above the P75 value of ALL patients sampled at the same time points compatible with a marked prothrombotic profile and a higher risk of thrombosis.
This study suggests that TG is a promising global assay to evaluate the hypercoagulable state in ALL children under treatment. TG reveals an increased thrombin potential which is present early at diagnosis, persists during Induction and reappears during Late Intensification. This observation is consistent with the high incidence of thrombotic events previously described during Induction and until 10 days after the last Aase infusion. TG profiles observed in patients who experienced thrombotic events suggest that this assay could be used as a predictive tool since their TG parameters were above P75 value of the ALL children tested. Further investigations are needed to address this issue.

Disclosures:
No relevant conflicts of interest to declare.