Cancer-related thromboembolic disease in patients with solid tumours: a retrospective analysis

Low-Molecular-Weight Heparin and Calcium Heparin in Thrombosis Prophylaxis in Patients with Percutaneous Arterial and Venous Ports for Colorectal Liver Metastases

Study Objective

The evaluation of low-molecular-weight heparin use to prevent arterial and venous thrombosis in patients with indwelling arterial Port-a-Cath implants.

Methods

From 1996 to March 2003 we placed 370 indwelling hepatic arterial catheters with a minimally invasive approach. The left distal subclavian artery was approached from beneath the left clavicle, then an angiographic study of the tumoral vascular district was performed and the gastroduodenal artery was occluded by an embolus. A polyurethane catheter was introduced distally into the hepatic artery and connected to a reservoir through a 3-4 cm long subcutaneous tunnel. In 90 patients a venous Port-a-Cath was placed for concurrent systemic chemotherapy. All 370 patients received regional chemotherapy and were treated with calcium heparin at a dose of 5000 IU twice a day and with low-molecular-weight heparin at prophylactic doses (dalteparin 2500 IU or nadroparin 3000 IU) during catheter permanence to prevent hepatic artery thrombosis. Intra-arterial trans-port radionuclide scans using technetium-99m-labeled micro-aggregated albumin were performed monthly to check the infusion distribution and hepatic artery patency. In the presence of anomalous patterns, thrombosis, pulmonary embolism or other complications, angiography and/or other diagnostic studies were performed to determine the cause of the vascular event and the local or systemic symptoms. The mean arterial and venous Port-a-Cath permanence times were 6 and 8 months, respectively.

Results

We observed episodes of hepatic artery thrombosis in 4.3% of patients. Three of these 17 patients were successfully treated by intra-arterial thrombolysis using urokinase. No venous thrombosis occurred as a consequence of regional and/or systemic chemotherapy, no episodes of arterial thrombosis were registered during arterial catheter permanence, nor did any hemorrhagic complications related to anti-coagulant therapy occur. Five patients treated with low-molecular-weight heparin required treatment suspension due to a platelet count of <40,000/dL.

Conclusion

Our experience suggests that low-molecular-weight heparin and/or calcium heparin at prophylactic doses could be useful in the prevention of arterial and venous thrombosis in patients with indwelling arterial catheters or venous Port-a-Cath treated with regional or systemic chemotherapy for hepatic metastases from colorectal cancer. The homogeneity of the patient group and the use of analogous chemotherapeutic drugs (fluoropyrimidines) avoided statistical contamination related to differences between kinds of cancer and between the chemotherapeutic agents used.

A case report of acute pulmonary hypertension after hyperthermic intraperitoneal chemotherapy (HIPEC) and review of the literature

BACKGROUND

Hyperthermic intraperitoneal chemotherapy (HIPEC) poses a widely used and accepted treatment option for patients with peritoneal carcinomatosis of gastrointestinal tumors. In contrast to the well-described risks and complications of intravenous cytostatic drugs, literature offers only scarce information of serious complications following HIPEC. To our knowledge no other description of rapid progressive pulmonary hypertension (PH) and consecutive respiratory failure following HIPEC have been described in current literature.

CASE PRESENTATION

A 48-year-old female suffering from a recurrent appendix-carcinoma developed progressive dyspnea and fatigue six weeks after multivisceral abdominal resection and HIPEC. Medical examinations included laboratory-checks, non-invasive imaging, scintigraphy as well as invasive examinations (left-/right-heart-catheterization) and confirmed PH of unknown origin to be the cause of dyspnea. The patient died nine days after admission of respiratory failure and rapid deterioration as a result of aggravating PH.

CONCLUSION

Rapid progressive respiratory insufficiency due to PH following HIPEC procedure might represent a rare complication, but must be considered because of the high clinical impact. Further studies are necessary to investigate the correlation between HIPEC and PH.

Cancer associated thrombosis: risk factors and outcomes

Deep vein thrombosis of the leg and pulmonary embolism are frequent diseases and cancer is one of their most important risk factors. Patients with cancer also have a higher prevalence of venous thrombosis located in other parts than in the legs and/or in unusual sites including upper extremity, splanchnic or cerebral veins. Cancer also affects the risk of arterial thrombotic events particularly in patients with myeloproliferative neoplasms and in vascular endothelial growth factor receptor inhibitor recipients. Several risk factors need to interact to trigger thrombosis. In addition to common risk factors such as surgery, hospitalisation, infection and genetic coagulation disorders, the thrombotic risk is also driven and modified by cancer-specific factors including type, histology, and stage of the malignancy, cancer treatment and certain biomarkers. A venous thrombotic event in a cancer patient has serious consequences as the risk of recurrent thrombosis, the risk of bleeding during anticoagulation and hospitalisation rates are all increased. Survival of cancer patients with thrombosis is worse compared to that of cancer patients without thrombosis, and thrombosis is a leading direct cause of death in cancer patients.

Direct Medical Costs Attributable to Cancer-Associated Venous Thromboembolism: A Population-Based Longitudinal Study

PURPOSE

The purpose of this study is to estimate medical costs attributable to venous thromboembolism among patients with active cancer.

METHODS

In a population-based cohort study, we used Rochester Epidemiology Project (REP) resources to identify all Olmsted County, Minn. residents with incident venous thromboembolism and active cancer over the 18-year period, 1988-2005 (n = 374). One Olmsted County resident with active cancer without venous thromboembolism was matched to each case on age, sex, cancer diagnosis date, and duration of prior medical history. Subjects were followed forward in REP provider-linked billing data for standardized, inflation-adjusted direct medical costs from 1 year prior to index (venous thromboembolism event date or control-matched date) to the earliest of death, emigration from Olmsted County, or December 31, 2011, with censoring on the shortest follow-up to ensure a similar follow-up duration for each case-control pair. We used generalized linear modeling to predict costs for cases and controls and bootstrapping methods to assess uncertainty and significance of mean adjusted cost differences. Outpatient drug costs were not included in our estimates.

RESULTS

Adjusted mean predicted costs were 1.9-fold higher for cases ($49,351) than for controls ($26,529) (P < .001) from index to up to 5 years post index. Cost differences between cases and controls were greatest within the first 3 months (mean difference = $13,504) and remained significantly higher from 3 months to 5 years post index (mean difference = $12,939).

CONCLUSIONS

Venous thromboembolism-attributable costs among patients with active cancer contribute a substantial economic burden and are highest from index to 3 months, but may persist for up to 5 years.

Acute Anterior Myocardial Infarction After Chemotherapy for Testicular Seminoma in a Young Patient

Testicular cancer is the most common solid tumor among young men aged 15 to 35 years. Combination chemotherapy with cisplatin, etoposide, and bleomycin remains the mainstay of treatment. We present a 27-year-old man who presented with an acute anterior myocardial infarction during the second course of chemotherapy for seminoma. Because the patient had no significant risk factors for coronary heart disease, the infarction was likely caused by the chemotherapy regimen.

CHADS2 scores as a predictor of ischemic stroke after radical prostatectomy

Patients with prostate cancer have an increased risk of stroke, but their absolute rate of stroke depends on age and comorbid conditions. The Charlson Comorbidity Index Score (CCIS) is a widely accepted measure for risk adjustment in administrative claims data sets. This study assesses the predictive value of CHADS2 scores and CCIS for stroke among patients with prostate cancer. The study was conducted based on data taken from Taiwan's National Health Insurance Research Database (NHIRD). We identified a total of 5414 participants with nonatrial fibrillation (AF) prostate cancer diagnoses who underwent radical prostatectomy between 1997 and 2011. CHADS2 scores and CCIS were used to stratify the 5‐year ischemic stroke risk. All participants were followed from the date of enrollment until ischemic stroke, death, or the end of the 5‐year follow‐up period. The 5‐year risk of ischemic stroke in the present study was 1.7%. Ischemic stroke has a better correlation with CHADS2 (CHADS2 score = 0 to 1: 0.02%, CHADS2 score = 2 to 3: 13.9%, CHADS2 score ≥ 4: 44.4%; AUC = 0.978) than CCIS (CCIS = 0 to 1: 1.6%, CCIS = 2 to 3: 1.7%, CCIS ≥ 4: 3.8%; AUC = 0.520). Our results show that patients with prostate cancer who underwent radical prostatectomy show significantly higher risk of ischemic stroke in high CHADS2 score patients, and the CHADS2 score could be applied for ischemic stroke prediction. Cardiovascular risks evaluation and management are suggested for prostate cancer patients with higher CHADS2 score.

Venous thromboembolism in lymphoma: how effectively are we treating patients?

INTRODUCTION

Patients with solid tumors and venous thromboembolic episodes (VTE) have a high risk of recurrence and bleeding during oral anticoagulant treatment. However, we are unaware of studies expressly evaluating such risks in patients with lymphoma. Therefore, we conducted a retrospective study to determine the frequency of such complications during treatment of lymphoma patients who develop VTE.

METHODS

Charts of patients with histologically proven non-Hodgkin lymphoma and Hodgkin lymphoma were retrospectively reviewed and patients with their first acute symptomatic VTE episode were identified (49 non-Hodgkin lymphoma, 8 Hodgkin lymphoma). Recurrence of VTE episodes and major and minor bleeding during treatment with warfarin or low molecular weight heparin (LMWH) were recorded.

RESULTS

All 57 patients were initially treated with high-dose-adjusted intravenous heparin or body-weight-adjusted LMWH. Forty-six patients were started on oral warfarin and 11 patients continued LMWH. Recurrent VTE episodes occurred in 14 of 46 patients on warfarin therapy, whereas major bleeding was documented in 6 of 46 patients, and minor bleeding in 9 of 46 patients. Recurrent VTE episodes occurred in 1 of 11 patients treated with LMWH, whereas major bleeding occurred in 0 of 11 and minor bleeding in 3 of 11 patients.

CONCLUSIONS

Lymphoma patients treated with warfarin experienced a 30.4% rate of recurrent thrombosis and 13% major bleeding. During this treatment most (65%), but not all, bleeding and thrombotic complications occurred with an international normalized ratio within the therapeutic range. The percentage of serious complications (recurrent VTE and major bleeding) during warfarin use was 44.5%, and the death rate was 6.5%, compared with 9% and 0%, respectively, during use of LMWH.

Health care costs associated with venous thromboembolism in selected high-risk ambulatory patients with solid tumors undergoing chemotherapy in the United States

BACKGROUND

This study examines venous thromboembolism (VTE)-associated resource utilization and real-world costs in ambulatory patients initiating chemotherapy for selected common high-risk solid tumors.

METHODS

Health care claims data (2004-2009) from the IMS/PharMetrics(®) Patient-Centric database were collected for propensity score-matched adult cancer (lung, colorectal, pancreatic, gastric, bladder, or ovarian) patients initiating chemotherapy with VTE (n = 912) and without VTE (n = 2736). Health care resource utilization (inpatient, outpatient, and outpatient prescription drug claims) and costs were compared between the two cohorts during the 12-month follow-up period after the index VTE event. Incremental costs were adjusted for demographic and clinical covariates.

RESULTS

Cancer patients with VTE had approximately three times as many all-cause hospitalizations (mean 1.38 versus 0.55 per patient) and days in hospital (10.19 versus 3.37), and more outpatient claims (331 versus 206) than cancer patients without VTE (all P < 0.0001). Cancer patients with VTE incurred higher overall all-cause inpatient costs (mean USD 21,299 versus USD 7459 per patient), outpatient costs (USD 53,660 versus USD 34,232 per patient), and total health care costs (USD 74,959 versus USD 41,691 per patient) than cancer patients without VTE (all P < 0.0001). Total mean VTE-related health care costs were USD 9247 per patient over 12 months. Adjusted mean incremental all-cause health care costs of VTE were USD 30,538 per patient for cancer overall, ranging from USD 11,946 for gastric to USD 38,983 for pancreatic cancer.

CONCLUSION

VTE is associated with significant inpatient and outpatient resource utilization, and increased all-cause (in addition to VTE-related) health care costs among ambulatory cancer patients. Measures to prevent outpatient cancer-associated VTE may reduce health care utilization and costs in this population.

International clinical practice guidelines for the treatment and prophylaxis of venous thromboembolism in patients with cancer

BACKGROUND

 Guidelines addressing the management of venous thromboembolism (VTE) in cancer patients are heterogeneous and their implementation has been suboptimal worldwide.

OBJECTIVES

To establish a common international consensus addressing practical, clinically relevant questions in this setting.

METHODS

An international consensus working group of experts was set up to develop guidelines according to an evidence-based medicine approach, using the GRADE system.

RESULTS

For the initial treatment of established VTE: low-molecular-weight heparin (LMWH) is recommended [1B]; fondaparinux and unfractionated heparin (UFH) can be also used [2D]; thrombolysis may only be considered on a case-by-case basis [Best clinical practice (Guidance)]; vena cava filters (VCF) may be considered if contraindication to anticoagulation or pulmonary embolism recurrence under optimal anticoagulation; periodic reassessment of contraindications to anticoagulation is recommended and anticoagulation should be resumed when safe; VCF are not recommended for primary VTE prophylaxis in cancer patients [Guidance]. For the early maintenance (10 days to 3 months) and long-term (beyond 3 months) treatment of established VTE, LMWH for a minimum of 3 months is preferred over vitamin K antagonists (VKA) [1A]; idraparinux is not recommended [2C]; after 3-6 months, LMWH or VKA continuation should be based on individual evaluation of the benefit-risk ratio, tolerability, patient preference and cancer activity [Guidance]. For the treatment of VTE recurrence in cancer patients under anticoagulation, three options can be considered: (i) switch from VKA to LMWH when treated with VKA; (ii) increase in LMWH dose when treated with LMWH, and (iii) VCF insertion [Guidance]. For the prophylaxis of postoperative VTE in surgical cancer patients, use of LMWH o.d. or low dose of UFH t.i.d. is recommended; pharmacological prophylaxis should be started 12-2 h preoperatively and continued for at least 7-10 days; there are no data allowing conclusion that one type of LMWH is superior to another [1A]; there is no evidence to support fondaparinux as an alternative to LMWH [2C]; use of the highest prophylactic dose of LMWH is recommended [1A]; extended prophylaxis (4 weeks) after major laparotomy may be indicated in cancer patients with a high risk of VTE and low risk of bleeding [2B]; the use of LMWH for VTE prevention in cancer patients undergoing laparoscopic surgery may be recommended as for laparotomy [Guidance]; mechanical methods are not recommended as monotherapy except when pharmacological methods are contraindicated [2C]. For the prophylaxis of VTE in hospitalized medical patients with cancer and reduced mobility, we recommend prophylaxis with LMWH, UFH or fondaparinux [1B]; for children and adults with acute lymphocytic leukemia treated with l-asparaginase, depending on local policy and patient characteristics, prophylaxis may be considered in some patients [Guidance]; in patients receiving chemotherapy, prophylaxis is not recommended routinely [1B]; primary pharmacological prophylaxis of VTE may be indicated in patients with locally advanced or metastatic pancreatic [1B] or lung [2B] cancer treated with chemotherapy and having a low risk of bleeding; in patients treated with thalidomide or lenalidomide combined with steroids and/or chemotherapy, VTE prophylaxis is recommended; in this setting, VKA at low or therapeutic doses, LMWH at prophylactic doses and low-dose aspirin have shown similar effects; however, the efficacy of these regimens remains unclear [2C]. Special situations include brain tumors, severe renal failure (CrCl<30 mL min(-1) ), thrombocytopenia and pregnancy. Guidances are provided in these contexts.

CONCLUSIONS

Dissemination and implementation of good clinical practice for the management of VTE, the second cause of death in cancer patients, is a major public health priority.

Splanchnic vein thrombosis in the mediterranean area in children

Abdominal venous thrombosis may present as splanchnic venous thrombosis (SVT) (occlusion of portal, splenic, superior or inferior mesenteric veins) or Budd- Chiari Syndrome (BCS) (thrombosis of inferior vena cava and/or hepatic veins). The aim of this review is to report the scanty data available for SVT in the South Mediterranean area. In one Egyptian study, the possible circumstantial risk factors for portal vein thrombosis (PVT) were found in 30% of cases: 19% neonatal sepsis, 8.7% umbilical catheterization, 6% severe gastroenteritis and dehydration. Another Egyptian study concluded that hereditary thrombophilia was common in children with PVT (62.5%), the commonest being factor V Leiden mutation (FVL) (30%). Concurrence of more than one hereditary thrombophilia was not uncommon (12.5%). The first international publication on hepatic veno-occlusive disease (VOD) in Egypt was in 1965 in children who rapidly develop abdominal distention with ascites and hepatomegaly. This disease was more frequent in malnourished children coming from rural areas; infusions given at home may contain noxious substances that were hepatotoxic and infections might play a role. VOD of childhood is rarely seen nowadays. Data from South Mediterranean area are deficient and this may be attributable to reporting in local medical journals that are difficult to access. Medical societies concerned with this topic could help distribute this information.

Diagnostic laparoscopy of patient with deep vein thrombosis before diagnosis of ovarian cancer: a case report

Venous thromboembolism (VTE) is a common complication in patients with malignant disease. Epidemiological studies have demonstrated an increased risk of subsequent cancer in the patients who are diagnosed with idiopathic venous thrombosis. Cancers of the breast, lung and ovary in women and adenocarcinomas of an unknown primary cancer are most strongly associated with thrombosis. Mucin-producing cancers are most often associated with VTE and the highest rates of VTE were found for cases of ovarian cancer, but the absolute risk of cancer after thrombosis is relatively low (about 2% over the first year) and so the benefit of screening for cancer in thrombosis patients seems limited. But as this case, the association between thrombosis and occult cancer shows the importance of this association for patients who have thrombosis that is unresponsive to anticoagulant therapy. Especially, we should recognize that such patients can undergo investigation for an underlying malignancy. Diagnostic laparoscopy of an adnexal mass for confirming cancer in the acute setting of deep vein thrombosis (DVT) was performed for our patient. We report here on a case of a patient with DVT in the upper and lower extremities before the diagnosis of ovarian cancer, and we briefly review of the relevant literature.

Management of venous thromboembolism in patients with advanced cancer: a systematic review and meta-analysis

Venous thromboembolism is common in patients with cancer. However, no management guidelines exist for venous thromboembolism specific to patients with advanced progressive cancer. To help develop recommendations for practice, we have done a comprehensive review of anticoagulation treatment in patients with cancer, with particular focus on studies that included patients with advanced disease. Data from 19 publications, including randomised, prospective, and retrospective studies suggest that: long-term full-dose low-molecular-weight heparin (LMWH) is more effective than warfarin in the secondary prophylaxis of venous thromboembolism in patients with cancer of any stage, performance status, or prognosis; warfarin should not be used in patients with advancing progressive disease; and in patients at high risk of bleeding, full-dose LMWH for 7 days followed by a long-term decreased fixed dose long term can be considered. The optimum treatment duration is unclear, but because the prothrombotic tendency will persist in patients with advanced cancer, indefinite treatment is generally recommended. For patients with contraindications to anticoagulation, inferior-vena-caval filters can be considered, but their use needs careful patient selection. Ultimately, the decision to initiate, continue, and stop anticoagulation will need to be made on an individual basis, guided by the available evidence, the patient's circumstances, and their informed preferences.

Etiology and consequences of thrombosis in abdominal vessels

The thrombophilia which can be either congenital or acquired in adult life has major implications in the abdominal vessels. The resulting portal vein thrombosis, Budd-Chiari syndrome and mesenteric vein thrombosis have a variety of consequences ranging from acute abdomen to chronic hepatomegaly and even totally asymptomatic patient in whom the only finding is pancytopenia. The complications like esophageal varices, portal gastropathy, ascites, severe hypersplenism, liver failure requiring liver transplantation are well known. Interesting features of collateral venous circulation showing itself as pseudocholangiocarcinoma sign and its possible clinical reflection as cholestasis are also known from a long time. The management strategies for these complications of intraabdominal vessel thrombosis are not different from their counterpart which is cirrhotic portal hypertension, but the prognosis is unquestionably better in former cases. In this review we presented and discussed the abdominal venous thrombosis, etiology and the resulting clinical pictures. There are controversial issues both in nomenclature, and management including anticoagulation problems and follow up strategies. In light of the current knowledge, we discussed some controversial issues in literature and presented our experience and our proposals about this group of patients.

Venous thromboembolism syndrome in gynecological cancer

Venous thromboembolism (VTE) could be presented as an initial clinical feature in some cancer patients or a complication followed by various cancer treatments, which all indicates a poor outcome. This review focuses on elucidating the relationship of VTE and the main gynecological cancers including ovarian, endometrial, and cervical cancers. First, the general VTE information about gynecological cancer are introduced; second, the risk factors of VTE developing in gynecological cancer were discussed; third, we do a retrospective analysis on a novel treatment targeting coagulation cascade; and last, we analyze VTE as a remarkable complication followed by recombinant human erythropoietin and anti-vascular endothelial growth factor treatment in gynecological cancer patients. In summary, the interaction between the coagulation system and cancer progression is a novel promising area to be explored in the study of VTE in patients with gynecological cancer.

Pulmonary embolism and cardiac enzymes

BACKGROUND

Pulmonary embolism (PE) is often associated with chest pain, electrocardiographic changes, and right ventricular (RV) dysfunction on echocardiogram. There have been reports of elevated troponin levels with PE. RV dysfunction and elevated troponin levels have prognostic implications in acute PE. The purpose of this retrospective analysis was to determine whether PE was associated with elevated cardiac enzymes and whether there was any difference among patients who presented with or without chest pain.

METHODS

Records of 93 consecutive patients with high-probability ventilation/perfusion lung scan results for PE were analyzed for the presence or absence of chest pain on presentation, abnormalities in cardiac enzymes, and evidence of RV dysfunction on echocardiogram.

RESULTS

A total of 56 of 93 patients had cardiac enzymes evaluated; 24 of these 56 patients had chest pains, and 32 did not. Only 1 patient of the 56 had abnormal cardiac enzymes. This patient had a known history of coronary artery disease (CAD) and had experienced an acute anterior myocardial infarction. Echocardiograms were performed in 36 of 93 patients. Evidence of RV dysfunction on echocardiograms was found in 22 of these patients. No significant relationship was found between RV dysfunction and chest pains (P > .10).

CONCLUSION

We found no significant relationship between high-probability ventilation/perfusion scan results and abnormalities in cardiac enzymes irrespective of the presence or absence of chest pain. Patients with a history of CAD or RV dysfunction did not have a higher incidence of chest pain when compared with those with no known history of CAD or RV dysfunction.

Inhibitors of the vascular endothelial growth factor receptor

The inhibitors of VEGF-mediated signaling continue to wind their way through extensive preclinical and clinical development paths. Whereas the first phase III trial did not meet its endpoints, one hopes that the others will. As we learn more about the VEGF pathways in the laboratory and the clinic, we can interpret with greater certainty what role these drugs or their successors will have in the treatment of human cancers.

The clinical course of deep vein thrombosis in patients with gynecologic cancer

OBJECTIVE

The aim of this study was to evaluate the survival of gynecologic cancer patients diagnosed with deep vein thrombosis.

METHODS

We retrospectively reviewed the charts of patients admitted to our institution with gynecologic malignancy who were diagnosed with deep vein thrombosis (DVT) between 1984 and 1995. Data were collected regarding site, stage, histology, treatment, and proximity of DVT to treatment with surgery, chemotherapy, and radiotherapy. This study was limited to cases of ovarian, uterine, and cervical cancer. Descriptive statistics were generated and the survival of patients from the time of DVT was calculated using the Kaplan and Meier method. Cases were then matched by site, stage, histology, and age to controls without DVT to evaluate the effect of DVT on survival. A Cox regression model was used to assess the effect of multiple variables on survival.

RESULTS

A total of 74 cases were identified. Ovarian, uterine, and cervical cancer accounted for 45, 27, and 28% of cases, respectively. Approximately 64% of patients had stage III or greater disease. The median survival of all patients from the time of DVT diagnosis was 7.8 months, with only about 20% of patients surviving at 5 years. Patients with cervical cancer or patients who had radiation therapy within 3 months of DVT diagnosis had significantly lessened survival (P < 0.01) than other patients with DVT. The survival of patients from the time of cancer diagnosis with venous thrombosis was significantly worse than a matched control group without DVT (P < 0.001). On multivariate analysis, there was a twofold greater risk of dying in those patients with gynecologic cancer and DVT.

CONCLUSION

The development of DVT in conjunction with a gynecologic malignancy connotes a poor prognosis, especially in patients with cervical cancer. It is possible that this poor prognosis is related to the pathophysiology that results in venous thrombosis and not just the presence of cancer.

Acquired thrombophilic syndromes

As the biochemical mechanisms of hypercoagulable states are revealed, the syndromes of venous thromboembolism have been increasingly associated with specific aberrations. Most of these changes involve an increase in procoagulant potential, for example, by activation of the coagulation cascade, or by a defect or decrease in natural inhibitors of clotting. Similar abnormalities of the fibrinolytic pathways may contribute, as can loss of inhibitory mechanisms of endothelial cells, as well as changes in vascular anatomy and rheologic patterns of blood flow. All of these factors can directly influence thrombus formation and/or the physiologic response to the thrombus.(1)