Julia Riedl

Platelets in cancer and thrombosis.

Platelets are the smallest circulating blood cells and their major function is the maintenance of haemostasis. They do not have a nucleus, but instead a multitude of granules that contain molecules important for several physiological processes. These granules can be released after platelet activation and thereby platelets take part in haemostasis, wound repair or immunological processes. Furthermore, platelets are also involved in the pathophysiology of several diseases, including cancer. Platelets can support various steps of cancer development and progression by promoting tumour growth, angiogenesis and metastasis. Moreover, platelets contribute to the hypercoagulable state frequently observed in cancer patients, leading to an increased risk of venous thromboembolism (VTE). In previous studies a high platelet count was repeatedly found to be associated with an elevated risk of VTE and a worse prognosis in patients with cancer. The aim of this review is to give an overview of the most important alterations of platelet physiology in cancer patients and how these alterations may influence cancer disease and contribute to cancer-associated VTE.

Association of mean platelet volume with risk of venous thromboembolism and mortality in patients with cancer. Results from the Vienna Cancer and Thrombosis Study (CATS).

Venous thromboembolism (VTE) is a frequent complication in cancer patients. Mean platelet volume (MPV) has been associated with arterial and venous thrombosis in patients without cancer. We analysed MPV in cancer patients and investigated the association of MPV with risk of VTE and mortality. MPV was routinely determined in the Vienna Cancer and Thrombosis Study, a prospective, observational cohort study of patients with newly diagnosed or progressive cancer after remission. Study endpoints were occurrence of symptomatic VTE or death during a maximum follow-up of two years. Out of 1,544 included patients, 114 (7.4%) developed VTE and 573 (37.1%) died during a median observation time of 576 days. High MPV ≥75th percentile of the study population; ≥10.8 fL) was associated with decreased risk of VTE compared to MPV below the 75th percentile (HR [95% CI]: 0.59 [0.37-0.95], p=0.031). In multivariable analysis, including age, sex, cancer groups, newly diagnosed vs recurrent disease, platelet count and soluble P-selectin, this association remained statistically significant (0.65 [0.37-0.98], p=0.041). Mortality of patients with MPV (≥75th percentile was significantly decreased compared to those with lower MPV (0.72 [0.59-0.88], p=0.001). Two-year probability of VTE and overall survival was 5.5% and 64.7% in patients with high MPV compared to 9% and 55.7% in those with lower MPV. In conclusion, high MPV is associated with decreased VTE risk and improved survival in cancer patients. This finding is contrary to results observed in patients without cancer. Further studies are needed to confirm our results and elucidate underlying mechanisms.

Red Cell Distribution Width and Other Red Blood Cell Parameters in Patients with Cancer: Association with Risk of Venous Thromboembolism and Mortality

Background Cancer patients are at high risk of developing venous thromboembolism (VTE). Red cell distribution width (RDW) has been reported to be associated with arterial and venous thrombosis and mortality in several diseases. Here, we analyzed the association between RDW and other red blood cell (RBC) parameters with risk of VTE and mortality in patients with cancer. Methods RBC parameters were measured in 1840 patients with cancers of the brain, breast, lung, stomach, colon, pancreas, prostate, kidney; lymphoma, multiple myeloma and other tumor sites, that were included in the Vienna Cancer and Thrombosis Study (CATS), which is an ongoing prospective, observational cohort study of patients with newly diagnosed or progressive cancer after remission. Primary study outcome is occurrence of symptomatic VTE and secondary outcome is death during a maximum follow-up of 2 years. Results During a median follow-up of 706 days, 131 (7.1%) patients developed VTE and 702 (38.2%) died. High RDW (>16%) was not associated with a higher risk of VTE in the total study cohort; in competing risk analysis accounting for death as competing variable the univariable subhazard ratio (SHR) was 1.34 (95% confidence interval [CI]: 0.80–2.23, p = 0.269). There was also no significant association between other RBC parameters and risk of VTE. High RDW was associated with an increased risk of mortality in the total study population (hazard ratio [HR, 95% CI]: 1.72 [1.39–2.12], p<0.001), and this association prevailed after adjustment for age, sex, hemoglobin, leukocyte and platelet count (HR [95% CI]: 1.34 [1.06–1.70], p = 0.016). Conclusions RDW and other RBC parameters were not independently associated with risk of VTE in patients with cancer and might therefore not be of added value for estimating risk of VTE in patients with cancer. We could confirm that high RDW is an independent predictor of poor overall survival in cancer.

Podoplanin expression in primary brain tumors induces platelet aggregation and increases risk of venous thromboembolism

Venous thromboembolism (VTE) is common in patients with brain tumors, and underlying mechanisms are unclear. We hypothesized that podoplanin, a sialomucin-like glycoprotein, increases the risk of VTE in primary brain tumors via its ability to induce platelet aggregation. Immunohistochemical staining against podoplanin and intratumoral platelet aggregates was performed in brain tumor specimens of 213 patients (mostly high-grade gliomas [89%]) included in the Vienna Cancer and Thrombosis Study, a prospective observational cohort study of patients with newly diagnosed cancer or progressive disease aimed at identifying patients at risk of VTE. Platelet aggregation in response to primary human glioblastoma cells was investigated in vitro. During 2-year follow-up, 29 (13.6%) patients developed VTE. One-hundred fifty-one tumor specimens stained positive for podoplanin (33 high expression, 47 medium expression, 71 low expression). Patients with podoplanin-positive tumors had lower peripheral blood platelet counts (P < .001) and higher D-dimer levels (P < .001). Podoplanin staining intensity was associated with increasing levels of intravascular platelet aggregates in tumor specimens (P < .001). High podoplanin expression was associated with an increased risk of VTE (hazard ratio for high vs no podoplanin expression: 5.71; 95% confidence interval, 1.52-21.26; P =010), independent of age, sex, and tumor type. Podoplanin-positive primary glioblastoma cells induced aggregation of human platelets in vitro, which could be abrogated by an antipodoplanin antibody. In conclusion, high podoplanin expression in primary brain tumors induces platelet aggregation, correlates with hypercoagulability, and is associated with increased risk of VTE. Our data indicate novel insights into the pathogenesis of VTE in primary brain tumors.

Hypercoagulabilty, venous thromboembolism, and death in patients with cancer

Venous thromboembolism (VTE) is a frequent complication of malignancy. The aim of this study was to investigate whether multi-state modelling may be a useful quantitative approach to dissect the complex epidemiological relationship between hypercoagulability, VTE, and death in cancer patients. We implemented a three-state/three-transition unidirectional illness-death model of cancer-associated VTE in data of 1,685 cancer patients included in a prospective cohort study, the Vienna Cancer and Thrombosis Study (CATS). During the two-year follow-up period, 145 (8.6 %) patients developed VTE, 79 (54.5 %) died after developing VTE, and 647 (38.4 %) died without developing VTE, respectively. VTE events during follow-up were associated with a three-fold increase in the risk of death (Transition Hazard ratio (HR)=2.98, 95 % confidence interval [CI]: 2.36-3.77, p< 0.001). This observation was independent of cancer stage. VTE events that occurred later during follow-up exerted a stronger impact on the risk of death than VTE events that occurred at earlier time points (HR for VTE occurrence one year after baseline vs at baseline=2.30, 95 % CI: 1.28-4.15, p=0.005). Elevated baseline D-dimer levels emerged as a VTE-independent risk factor for mortality (HR=1.07, 95 % CI: 1.05-1.08, p< 0.001), and also predicted mortality risk in patients who developed VTE. A higher Khorana Score predicted both the risk for VTE and death, but did not predict mortality after cancer-associated VTE. In conclusion, multi-state modeling represents a very potent approach to time-to-VTE cohort data in the cancer population, and should be used for both observational and interventional studies on cancer-associated VTE.

Association Between Decreased Serum Albumin With Risk of Venous Thromboembolism and Mortality in Cancer Patients

BACKGROUND In cancer patients, reduced serum albumin has been described as a marker for global declining health and poor prognosis. Our aim was to investigate the association of albumin concentrations with the occurrence of venous thromboembolism (VTE) and mortality in patients with cancer. METHODS This investigation was performed in the framework of the Vienna Cancer and Thrombosis Study (CATS), a prospective observational cohort study. We included 1,070 patients with active cancer and assayed serum albumin from venous blood taken at study inclusion. Risk for occurrence of VTE was calculated in a proportional subdistribution hazard regression model with respect to competing risk of death and adjusted for cancer site, leukocyte count, estimated glomerular filtration rate, and cholinesterase. RESULTS Patients (630 males [58.9%] and 440 females [41.1%]) were observed for a median of 723 days. During follow-up, 90 VTE events (8.4%) and 396 deaths (37.0%) occurred. The median albumin was 41.3 g/L (25th-75th percentile, 37.6-44.2). Patients with albumin levels below the 75th percentile had a 2.2-fold increased risk of VTE (95% confidence interval [CI] 1.09-4.32), as well as a 2.3-fold increased risk of death (95% CI 1.68-3.20) compared with patients with albumin above the 75th percentile. CONCLUSION Decreased serum albumin levels in cancer patients were significantly associated with increased risk of VTE and mortality. Serum albumin, a marker of a cancer patients overall prognosis, could be considered for risk assessment of important clinical outcomes such as VTE and mortality. IMPLICATIONS FOR PRACTICE Cancer patients are at increased risk of venous thromboembolism (VTE). In this prospective cohort study of 1,070 cancer patients, decreased serum albumin was a marker for risk of VTE and mortality, independent of kidney or liver function and inflammation markers. The study identified a group of patients with high risk of cancer-associated VTE and a reduced prognosis who may benefit from supportive therapy such as primary VTE prophylaxis.

Association of platelet activation markers with cancer-associated venous thromboembolism

Abstract Venous thromboembolism (VTE) is a frequent complication in cancer patients. Platelet activation is thought to be involved in cancer-associated VTE. Here, we determined the association between evolving markers of platelet activation (soluble P-selectin [sP-selectin], soluble CD40 ligand [sCD40L], thrombospondin-1 [TSP-1] and platelet factor-4 [PF-4]) and the development of cancer-associated VTE. A nested matched case–control study was applied within a cohort of 1779 patients with different types of cancer that had been included in the Vienna Cancer and Thrombosis Study (CATS), a prospective, observational study on patients with newly diagnosed or progressive cancer after remission. Primary endpoint is symptomatic VTE during a maximum follow-up of 2 years. Cases (patients who developed VTE during follow-up) were matched in a 1:2 ratio to controls without VTE during follow-up with respect to tumor type, stage and time of observation in the study. In total, 131 VTE cases were compared to 262 controls. In logistic regression analysis, only sP-selectin was associated with risk of VTE. The odds ratios (OR) per double increase of sP-selectin, sCD40L, TSP-1 and PF-4 were 1.66 (95% confidence interval: 1.17–2.35, p = 0.005), 1.04 (0.89–1.21, p = 0.635), 1.09 (0.90–1.32, p = 0.360) and 1.03 (0.87–1.21, p = 0.737), respectively. In conclusion, sP-selectin, but not sCD40L, TSP-1 or PF-4 were associated with risk of VTE in cancer patients in this nested case–control study.

Platelet-specific markers are associated with monocyte-platelet aggregate formation and thrombin generation potential in advanced atherosclerosis

Platelet activation and thrombin generation are crucial steps in primary and secondary haemostasis. However, both also play major roles in intravascular thrombus formation and therefore in the development of adverse cardiovascular events. In the current study, we first sought to investigate the associations of the platelet biomarkers platelet factor (PF)-4, thrombospondin (TSP)-1, soluble CD40 ligand (sCD40L), and soluble P-selectin (sP-selectin) with each other and with monocyte-platelet aggregate (MPA) formation in 316 patients undergoing angioplasty and stenting. To better understand the interplay between platelet activation and thrombin generation, we subsequently investigated the associations of the platelet biomarkers with thrombin generation potential. The mostly platelet-specific markers PF-4, TSP-1 and sCD40L correlated strongly with each other (all p < 0.001), and the best correlation was observed between PF-4 and TSP-1 (r=0.91). In contrast, sP-selectin, which derives from platelets and endothelial cells, correlated rather poorly with TSP-1 (r=0.12, p=0.04), and did not correlate with PF-4 and sCD40L. While PF-4, TSP-1 and sP-selectin correlated significantly with in vivo MPA formation (all p< 0.001), no such association was found between sCD40L and MPA formation. PF-4, TSP-1 and sCD40L correlated strongly with peak thrombin generation (all p< 0.001) with the best correlation between PF-4 and peak thrombin generation (r=0.55), whereas sP-selectin did not correlate with peak thrombin generation. Likewise, PF-4, TSP-1 and sCD40L correlated significantly with the area under the thrombin generation curve (AUC; all p< 0.01), whereas sP-selectin did not correlate with the AUC. In conclusion, platelet-specific markers are associated with MPA formation and thrombin generation potential in patients with advanced atherosclerosis.

Decreased platelet reactivity in patients with cancer is associated with high risk of venous thromboembolism and poor prognosis

Platelets are suggested to play a crucial role in cancer progression and the prothrombotic state of cancer patients. Here, we aimed to examine the activation status of platelets in cancer patients and investigate their association with risk of death and occurrence of venous thromboembolism (VTE) in a prospective observational cohort study. We measured platelet surface P-selectin, activated glycoprotein (GP) IIb/IIIa and monocyte-platelet aggregate (MPA) formation in vivo and platelet response to ex vivo stimulation with agonists of protease-activated receptor (PAR) -1, -4, and GPVI, by whole blood flow cytometry, before beginning of chemotherapy and repeatedly during the first six months thereafter (total number of samples analysed: 230). Endpoints of the study were occurrence of death or VTE during a two-year follow-up, respectively. Of 62 patients (median age [interquartile range, IQR]: 63 [54-70] years, 48 % female), 32 (51.6 %) died and nine (14.5 %) developed VTE. Association with a higher risk of death was found for lower platelet surface expression of P-selectin and activated GPIIb/IIIa in vivo and in response to PAR-1, -4 and GPVI activation, but not for MPA formation. Furthermore, reduced platelet responsiveness to PAR-1 and GPVI agonists was associated with higher risk of VTE (hazard ratio per decile increase of percentage P-selectin positive platelets: 0.73 [0.56-0.92, p=0.007] and 0.77 [0.59-0.98, p=0.034], respectively). In conclusion, cancer patients with a poor prognosis showed decreased platelet reactivity, presumably as a consequence of continuous activation. Our data suggest that decreased platelet reactivity is associated with increased mortality and VTE in cancer.

A clinical prediction model for cancer-associated venous thromboembolism: a development and validation study in two independent prospective cohorts

BACKGROUND Venous thromboembolism is a common complication of cancer, but the risk of developing venous thromboembolism varies greatly among individuals and depends on numerous factors, including type of cancer. We aimed to develop and externally validate a clinical prediction model for cancer-associated venous thromboembolism. METHODS We used data from the prospective Vienna Cancer and Thrombosis Study (CATS) cohort (n=1423) to select prognostic variables for inclusion in the model. We then validated the model in the prospective Multinational Cohort Study to Identify Cancer Patients at High Risk of Venous Thromboembolism (MICA) cohort (n=832). We calculated c-indices to show how the predicted incidence of objectively confirmed venous thromboembolism at 6 months compared with the cumulative 6-month incidences observed in both cohorts. FINDINGS Two variables were selected for inclusion in the final clinical prediction model: tumour-site risk category (low or intermediate vs high vs very high) and continuous D-dimer concentrations. The multivariable subdistribution hazard ratios were 1·96 (95% CI 1·41-2·72; p=0·0001) for high or very high versus low or intermediate and 1·32 (95% CI 1·12-1·56; p=0·001) per doubling of D-dimer concentration. The cross-validated c-indices of the final model were 0·66 (95% CI 0·63-0·67) in CATS and 0·68 (0·62-0·74) in MICA. The clinical prediction model was adequately calibrated in both cohorts. INTERPRETATION An externally validated clinical prediction model incorporating only one clinical factor (tumour-site category) and one biomarker (D-dimer) predicted the risk of venous thromboembolism in ambulatory patients with solid cancers. This simple model is a considerable improvement on previous models for predicting cancer-associated venous thromboembolism, and could aid physicians in selection of patients who will likely benefit from thromboprophylaxis. FUNDING Austrian Science Fund, Austrian National Bank Memorial Fund, and participating hospitals.