The goal of this study is to investigate the hemostatic balance in children with acute lymphoblastic leukaemia (ALL) treated according to the ALLTogether1 protocol with focus on the early treatment period including concomitant use of steroids and asparaginase.

The investigators aim to determine if complement proteins or microparticles can be used as clinically relevant predictive or diagnostic biomarkers for thrombosis and if global hemostatic assays can predict bleeding or thrombosis. Characterization of proteins connected to hemostasis before and during ALL treatment may provide pathophysiological insights regarding ALL- and treatment related coagulopathy. The ultimate goal of the study is to minimize the morbidity and mortality related to thrombosis and bleeding complications in children with ALL.

Several pediatric oncology centers in Sweden will be participating in this study, which will enroll approximately 100 pediatric patients.

Inclusion Criteria:

• Diagnosis of Acute Lymphoblastic Leukaemia (ALL) in Sweden
• Age 1-17.99 years at diagnosis
• Planned/Initiated treatment for ALL according to the ALLTogether1 protocol
• Signed informed consent from parents and patients (from 12 years - voluntary if <15 years)

Exclusion Criteria:

• Other underlying diseases which according to examiner's clinical assessment may increase the risk of bleeding or thrombosis and which are expected to lead to adaption of the therapy protocol for ALL (e g APS, moderate/severe v Willebrand disease, haemophilia)
• Patient not treated according to the ALLTogether1 protocol (including patients with BCR::ABL1, mixed phenotype acute leukaemia - MPAL)

Patients fulfilling inclusion criteria and without exclusion criteria diagnosed at participating centres (Stockholm, Uppsala, Linköping, Lund).

When study has been completed and published, IPD may be shared with other researchers on collaborative basis, provided that data protection for study subjects can be ensured and that no violation of data-protection legislation will occur.