Relationship of thrombin generation to peripheral blast cell count in patients with acute myeloblastic leukemia (AML)

Phosphatidylserine index as a marker of the procoagulant phenotype of acute myelogenous leukemia cells

Patients with acute myelogenous leukemia (AML) are at risk for thrombotic complications. Risk to develop thrombosis is closely tied to leukemia subtype, and studies have shown an association between leukocytosis and thrombosis in AML M3. We evaluated the relative roles of cell count and the surface expression of tissue factor (TF) and phosphatidylserine (PS) in the procoagulant phenotype of AML cell lines. The TF-positive AML M3 cell lines, NB4 and HL60, and AML M2 cell line, AML14, exhibited both extrinsic tenase and prothrombinase activity in a purified system and promoted experimental thrombus formation. In contrast, the TF-negative AML cell line, HEL, exhibited only prothrombinase activity and did not affect the rate of occlusive thrombus formation. In plasma, NB4, HL60 and AML14 shortened clotting times in a cell-count, PS- and TF-dependent manner. Exposure of cultured NB4, HL60, and AML14 cells to the chemotherapeutic agent daunorubicin increased their extrinsic tenase activity and PS expression. Clot initiation time inversely correlated with logarithm of PS index, defined as the product of multiplying leukocyte count with cell surface PS exposure. We propose that leukemia cell PS index may serve as a biomarker for procoagulant activity.

Hematologic malignancies and thrombosis

Patients with hematologic malignancies have an increased risk of venous thromboembolism (VTE), particularly at diagnosis and during the treatment with chemotherapy, asparaginase or immunomodulatory drugs (IMiDs). A disease-dependent hypercoagulable condition associated with other risk factors like drugs, central venous catheter (CVC), immobility and infections are responsible for this high VTE rate. Thrombotic complications have a significant impact on morbidity and in some cases also on mortality of patients with onco-hematologic diseases, therefore thromboprophylaxis to prevent VTE in this setting is needed. However, thrombocytopenia and hemorrhagic complications pone many difficulties in the management of an anticoagulant or antiaggregant treatment in these patients. Recommendations from current guidelines are limited to multiple myeloma patients treated with thalidomide or lenalidomide associated with dexamethasone or chemotherapy, but hematological clinical departments should implement a policy for prevention and treatment of thromboembolic complications in hematologic malignancies.

Bleeding complications and coagulopathy in acute leukaemia

Factors and inhibitors of coagulation and fibrinolysis were investigated on admission in 57 patients with acute leukaemia and they were correlated to the occurrence of haemorrhage. Coagulation disturbances were found in 98%. Seventeen of the patients with haemorrhagic symptoms had major bleeding. Severe thrombocytopenia (< 20 x 10(9)/l) was found in 16%. Patients with major bleedings had significantly lower concentrations of prothrombin complex, fibrinogen, protein C and platelets. Low levels of antiplasmin and fibrinogen were characteristic of 'bleeders' with promyelocytic and lymphoblastic leukaemia. We found a positive correlation between vWF:Ag and leukaemic cell count especially in lymphoblastic leukaemia (ks = 0.72). Reduced levels of antithrombin indicated a poorer prognosis.