On the origin of leukocyte procoagulant activity

The pathogenesis of venous thromboembolism in cancer: emerging links with tumour biology

Venous thromboembolism (VTE) is a frequent complication in individuals with cancer and is considered to be a cause of substantial mortality. Epidemiological studies identify malignancy as an independent VTE risk factor and show that cancer patients are at increased risk of both initial and recurrent VTE events. The risk due to cancer is compounded by the effects of chemotherapy and other treatments. The pathogenesis of cancer-associated VTE is complex involving multiple interactions between tumours and various components of haemostasis. The development of a systemic hypercoagulable state is considered a key pathogenetic feature and is attributed to tumour expression of tissue factor and other procoagulants, activation of vascular cells by tumour-derived cytokines and adhesive interactions between tumour cells and host cells. An increasing body of evidence indicates that the activation of haemostasis in malignant disease contributes to tumour growth and progression by stimulation of intracellular signalling pathways. The interaction of tissue factor, thrombin and other coagulation factors with protease activated receptor (PAR) proteins expressed by tumour cells and host vascular cells leads to the induction of genes related to the processes of angiogenesis, cell survival and cell adhesion and migration.

The prothrombotic state in cancer: pathogenic mechanisms

Thrombosis and disseminated intravascular coagulation (DIC) are common complications in cancer. Patients with malignancy have a prothrombotic state due to the ability of almost all type of cancer cells to activate the coagulation system. However, none of the haemostatic markers of coagulation has any predictive value for the occurrence of the thrombotic events in one individual patient. The pathogenesis of the prothrombotic state in cancer is complex and, probably, multifactorial. Prothrombotic factors in malignancy include the tumour production of procoagulants (i.e., tissue factor (TF) and cancer procoagulant (CP)) and inflammatory cytokines, and the interaction between tumour cells and blood (i.e., monocytes/macrophages, platelets) and endothelial cells. Other mechanisms of thrombus promotion include some general responses of the host to the tumour (i.e., acute phase, inflammation, angiogenesis), decreased levels of inhibitors of coagulation, and impaired fibrinolysis. In addition, the prothrombotic tendency of cancer patients is enhanced by anticancer therapy, such as surgery, chemotherapy, hormone therapy and radiotherapy, by indwelling central venous catheter, and by haemodinamic compromise (i.e., stasis). However, not all of the mechanisms allowing the prothrombotic state of cancer are entirely understood. Therefore, it is presently difficult to rank the relative weight of these multiple interactions on the basis of the well-recognised clinical evidences of enhanced thrombotic episodes in patients with cancer. In this review we attempt to describe the current proposed mechanisms for the pathogenesis of the prothrombotic state in cancer patient. A better understanding of these mechanisms could help clinicians in the developments of more targeted treatment to prevent thromboembolic complications in cancer patient.

Hemostasis in malignancy

Hemostatic abnormalities are present in a majority of patients with metastatic cancer. These abnormalities can be categorized as 1) increased platelet aggregation and activation, 2) abnormal activation of coagulation cascade, 3) release of plasminogen activator, and 4) decreased hepatic synthesis of anticoagulant proteins like Protein C and antithrombin III. The abnormal activation of coagulation cascade is mediated through release of Tissue Factor, Factor X activators, and other miscellaneous procoagulants from the plasma membrane vesicles of tumor cells. Macrophages of a tumor-bearing host also produce increased amounts of Tissue Factor. Production of Factor X activators and macrophage Tissue Factor is decreased by warfarin. The ability of the tumor cells to produce platelet-aggregating activity and plasminogen activator parallels their metastatic potential in animal and experimental systems. These studies also show that antiplatelet agents and antibodies against plasminogen activator can suppress the metastatic process. One or more laboratory abnormalities of hemostasis can be shown in up to 95% of patients with metastatic cancer. These abnormalities, however, are unable to predict subsequent development of thromboembolic or hemorrhagic complications. Clinical complications occur in 9-15% of the patients in the form of thrombotic or hemorrhagic disorders. The therapy of tumor-related coagulopathy should be guided by its clinical expression. Subclinical DIC should not be treated. Coumadin is generally ineffective for therapy of thrombosis in cancer patients. There is no consensus regarding the use of heparin in acute promyelocytic leukemia (APL). The defibrination in APL may be from disseminated intravascular coagulation as well as systemic fibrinolysis, as shown by decreased alpha 2 antiplasmin levels. In such cases, epsilon aminocaproic acid plus heparin therapy may be of benefit.

Procoagulant cellular activity (PCA) in the classification of acute leukemia

The procoagulant cellular activity (PCA) of leukemic cells was evaluated, before and after endotoxin stimulation, in 38 patients with acute leukemia at presentation subdivided according to the FAB classification. In the M4 and M5 subgroups the stimulated leukemic cells showed a significant increase in the production of PCA compared with freshly isolated cells. No evident PCA was documented in M1 and M2 AML as well as in the majority of acute lymphoid leukemias tested, both before and after endotoxin stimulation. The myeloid and lymphoid leukemic cells appear to behave similarly to normal leucocytes, within which only monocyte/macrophages are capable of producing PCA following endotoxin stimulation. These findings suggest that in human leukemic cells the endotoxin-induced production of PCA may be considered a indicator of monocyte/macrophage differentiation and thus represent a valuable diagnostic tool in the classification of acute leukemias.

Procoagulant cellular activity and disseminated intravascular coagulation in acute non-lymphoid leukaemia

The procoagulant cellular activity (PCA) of intact and lysed leukaemic cells was evaluated at diagnosis in 23 patients with acute non-lymphoid leukaemia (ANLL). The leukaemic cells of all 13 patients having DIC feature (excess of fibrin monomers, serum FDP and plasma fibrino-peptide A) showed a significant (P less than 0.0001) increase of PCA, while a pattern similar to that of normal granulocytes and lymphomonocytes was observed in the remaining 10 patients without evidence of DIC. When the patients were subdivided according to the FAB cytological classification, features of DIC and increased PCA were demonstrated in 3/3 M3 patients, 5/6 M5 patients and only in 5/14 remaining patients. These findings indicate that in ANLL patients: (1) the increased PCA of leukaemic cells is closely related to the occurrence of DIC; (2) the increased PCA seems related to the differentiation line and maturation level of the leukaemic cells.