PENELOPE Observational Study: Prophylaxis and Treatment of Arterial and Venous Thromboembolism

Inclusion Criteria: Potential subjects must satisfy all of the following criteria to be enrolled in the study: * diagnosis of hematologic neoplasm (acute leukemia, myelodysplastic syndrome, lymphoma, multiple myeloma, chronic myeloid leukemia, Ph-negative chronic myeloproliferative neoplasms) independently of the stage of disease or treatment (including transplant procedures); * platelet count \<50 x109/L at the time of starting antithrombotic prophylaxis or * platelet count \<50 x109/L at the time of diagnosis of arterial or venous thromboembolism objectively proven or * platelet count \>50 x109/L at time of thrombosis but subsequent thrombocytopenia \<50 x109/L while receiving antithrombotic treatment; * diagnosis of arterial thrombosis include acute coronary syndrome, ischemic stroke (including major and minor stroke), peripheral arterial thrombosis, retinal arterial thrombosis; * diagnosis of venous thrombosis include thrombosis of deep veins of the limbs and the abdomen, superficial veins of limbs, cerebral and splanchnic veins, retinal vein, and pulmonary embolism. Splanchnic venous thrombosis include occlusion of hepatic, portal, mesenteric, and splenic veins. Exclusion Criteria: The following situations will not be criteria of inclusion neither outcomes of interest: * transient ischemic attack without CT and/or NMR signs; * superficial vein thrombosis without Doppler ultrasound examination showing evidence of thrombosis; * antithrombotic prophylaxis only local fo…