Circulating Blasts Are Associated with High Levels of vWF and Thrombin Activation in Children with Newly Diagnosed ALL.

Background: Children with acute lymphoblastic leukemia (ALL) are known to have thrombin activation at diagnosis. However, the pathophysiology of thrombin generation and the impact of therapy on thrombin activation are so far unknown. Steroids are shown to induce prothrombotic state by increasing prothrombotic factors and reducing fibrinolytic potential. The investigational window on DFCI 05-01 protocol offered an unique opportunity to study the haemostatic effects of prednisone, independent of previous or concurrent therapy, in children with newly diagnosed ALL.

Aims: In children with newly diagnosed ALL, To evaluate the effects of methyleprednisone monotherapy (PMT) (32 mg/m²/day IV for 3 days) on the parameters of thrombin generation [prothrombin fragments 1.2 (F1.2), thrombin-antithrombin complex (TAT), and D-Dimer], fibrinolytic potential [plasminogen, tissue plasminogen activator (tPA), alpha-2 antiplasmin, alpha-2 macroglobulin, plasminogen activator inhibitor-1 (PAI-1), ratio of tPA/PAI-1], and coagulation factors [FVIII:C, von Willebrand factor (vWF) and fibrinogen] To study the effect age at diagnosis (< 10 Vs ³ 10 years), gender, risk categorization of ALL [standard (SR) Vs high risk (HR)], presence or absence of circulating blasts, presenting white cell and platelet count on the above hemostatic factors pre and post steroid therapy

Methods: Children (> 1 to £ 18 years of age) enrolled on DFCI ALL 05-01 protocol, without prior steroid therapy or presence of clot, were eligible for study. Overnight fasting blood samples was collected prior to and after PMT, and analyzed for hemostatic factors. The change in the level of each of the hemostatic parameters following PMT was expressed as percent increase or decrease from the baseline. The effect of steroids was tested using “paired t test”. To assess the effects of patient and disease variable student’s t-test was used.

Results: Of 30 patients (13 females) enrolled, 8 (27%) had HR ALL. The mean age was 6.33 years (SD 4.35); 24 patients were < 10 years. At baseline the levels of F1.2 (mean 1.54 nmol/L; SD 0.90), TAT (mean 10.90 microgram/L; SD 14.93) and D-dimers (2,766.03ng/mL; SD 2385.82) were increased indicating endogenous thrombin activation. Patients with circulating blasts (n=17) had significantly higher mean levels of vWF [1.89 (0.61) vs. 1.14 (0.48) p=0.001], TAT [15.39 (18.62) vs. 5.02 (3.29) p=0.038] and D-dimer [3640 (2499) vs. 1623 (1711) p=0.019] compared to those without circulating blasts. For children with circulating blasts at diagnosis, following steroid therapy the blast count decreased significantly from 24.2% to 3.5% (P<0.001)) with reduction in level of vWF, TAT and D-dimer (Table1).

Conclusions: Patients with circulating blasts had significantly higher baseline level of vWF, TAT, and D-dimer compared to those without circulating blasts. Following steroid therapy there was reduction in circulating blast count and significant reduction in vWF (despite increase in VIII:C levels), TAT and D-dimer whereas children without circulating blasts had increased levels of vWF, FVIII:C, TAT and D-dimer. We postulate that circulating blasts lead to endothelial activation (with vWF production) which in turn activates the coagulation system with resultant thrombin generation. In children with newly diagnosed ALL, PMT has two-fold hemostatic effects, a direct effect inducing procoagulant state and an indirect effect through reduction of blasts.

Table 1. Effect of PMT on hemostatic factors in patients with and without circulating blasts