The close association between cancer and thrombosis has been recognized now for more than 150 years.1 Not only is it now known that patients with cancer are at substantially increased risk of developing venous thromboembolism, even prior to the diagnosis of cancer, but the association between coagulation factors and tumor growth and invasion and development of metastases has been unequivocally established.2
Reported rates of venous thromboembolism in patients with cancer have been increasing in recent decades, most likely reflecting improved diagnosis using sophisticated imaging techniques and more aggressive cancer diagnosis, staging, and therapeutic interventions. Indeed, patients with cancer are placed at increased risk of venous thromboembolism by several therapeutic interventions, including surgery, chemotherapy, hormonal therapy, and targeted therapeutic strategies, as well as by the frequent use of indwelling catheters and other invasive procedures.
The increased risk of venous thromboembolism, the multitude of risk factors, and the greater risk of venous thromboembolism recurrence and death among patients with cancer represent considerable real-world challenges for the practicing oncologist. ASCO originally developed guidelines for venous thromboembolism specifically in patients with cancer in 2007.3 Following an extensive systematic review of the literature since publication of the original guidelines, ASCO recently updated clinical practice guidelines on the treatment and prevention of venous thromboembolism in patients with cancer.4
Although several new studies in this area have added to our knowledge since the original guidelines were developed, many questions remain concerning the intimate relationship between venous thromboembolism and cancer. The updated guideline recommendations and the risks and consequences associated with venous thromboembolism in patients with cancer were discussed at a recent Education Session at the 2013 ASCO Annual Meeting and in the Education Book available online at the ASCO website.5
Hospitalized and Surgical Patients
The ASCO Venous Thromboembolism Guidelines address recommended measures for the treatment and prevention of venous thromboembolism in hospitalized medical and surgical patients with cancer, as well as in ambulatory patients receiving cancer therapy. Three recent randomized controlled trials of thromboprophylaxis in medically ill inpatients were identified,6-8 one of which evaluated extended prophylaxis.6
Despite limited cancer-specific data in these trials, the ASCO Guidelines continue to recommend that hospitalized patients with other major medical illnesses or reduced mobility without serious bleeding risk receive prophylactic anticoagulation. Although hospitalized patients with cancer without additional risk factors may also be considered for prophylactic anticoagulation, there are inadequate data supporting routine prophylaxis in patients admitted for minor procedures or infusions of chemotherapy.
The literature review identified three randomized controlled trials evaluating perioperative prophylaxis in patients undergoing major abdominal or pelvic surgery.9-11 The updated guidelines recommend perioperative prophylactic anticoagulation in patients undergoing major cancer surgery, ideally beginning preoperatively and continued for at least 7 to 10 days. Systematic reviews have been conducted of extended prophylaxis for up to 4 weeks.12-14 Based on the available evidence, extended postoperative prophylaxis for up to 4 weeks is recommended in high-risk patients undergoing major cancer surgery, and those with restricted mobility, obesity, or a history of venous thromboembolism.
Nine randomized controlled trials of low–molecular-weight heparin thromboprophylaxis compared to placebo or untreated controls in ambulatory patients with advanced cancer have been reported. A meta-analysis estimated a relative risk for symptomatic venous thromboembolism of 0.47 (95% confidence interval [CI] = 0.36–0.61, P < .001) but with an absolute reduction in venous thromboembolism risk of only 2.8% (95% CI = 1.8%–3.7%, P < .001).15
The most dramatic impact on the absolute risk of venous thromboembolism was observed in patients with advanced pancreatic cancer receiving specific chemotherapy.16-18 Nevertheless, due to the limitations in these trials and the small incremental benefit observed in most trials of ambulatory patients, the ASCO Guideline panel concluded that routine anticoagulation prophylaxis is not warranted. One notable exception to this recommendation relates to patients with multiple myeloma receiving thalidomide (Thalomid) or lenalidomide (Revlimid) along with chemotherapy and/or dexamethasone, where the risk of venous thromboembolism is sufficient to justify routine thromboprophylaxis.
Established and Incidental Venous Thromboembolism
In patients with cancer and established venous thromboembolism, the ASCO Guidelines recommend low–molecular-weight heparins for both the initial 5 to 10 days of anticoagulation as well as for secondary prevention of recurrence for at least 6 months. Extended anticoagulation to prevent venous thromboembolism recurrence is encouraged in high-risk patients with active malignancy continuing on chemotherapy.
Of importance, the risk of recurrence, bleeding, and mortality appears similar between patients with cancer who have symptomatic venous thromboembolism and those who have incidental or unsuspected venous thromboembolism.19 The ASCO Guideline panel recommends that incidental venous thromboembolism be treated the same as symptomatic venous thromboembolism, based on consensus.
Although a meta-analysis of randomized controlled trials has demonstrated a significant reduction in mortality with anticoagulation in patients with cancer without a clear indication for treatment or prevention, anticoagulation for cancer treatment is not currently recommended in the updated guidelines due to the limitations of the trials reported to date and concern over an increased risk for major bleeding complications.4,20
Finally, risk factors for venous thromboembolism in patients with cancer include patient-, disease-, and treatment-related factors. Importantrisk factors include such comorbid conditions as infection, pulmonary or renal disease, and obesity. Elevations in leukocyte and platelet counts, reductions in hemoglobin, and use of the erythroid stimulating factors also increase the risk of venous thromboembolism in patients with cancer.
The primary site of cancer is particularly important, with highest rates of venous thromboembolism observed in patients with brain, pancreas, stomach, kidney, ovary, and lung cancers as well as hematologic malignancies including lymphoma and myeloma. The risk of venous thromboembolism is further increased in patients receiving systemic therapy, including chemotherapy, hormonal therapy, and certain targeted agents. Although the risk of arterial thrombotic events is increased with bevacizumab (Avastin), it remains unclear whether the risk of venous thromboembolism is increased after adjusting for duration on treatment.21
A risk score for cancer-associated venous thromboembolism based on five readily available clinical and laboratory parameters has been developed and validated in multiple studies (see Table).22-24 When the risk model was retrospectively evaluated in large randomized trials, the risk of venous thromboembolism among high-risk patients was significantly reduced in those randomized to thromboprophylaxis.25,26
The updated ASCO Guidelines recommend that patients with cancer be educated about the symptoms and signs of venous thromboembolism and that venous thromboembolism risk be assessed at the time of chemotherapy initiation and periodically thereafter. ■
Dr. Lyman is Professor of Medicine in the Division of Medical Oncology, Duke University School of Medicine and Duke Cancer Institute, Durham, North Carolina.
Disclosure: Dr Lyman is supported by grants from the National Cancer Institute (RC2CA148041-01) and the National Heart, Lung and Blood Institute (R01HL095109).
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ASCO has released a new evidence-based clinical practice guideline for venous thromboembolism prophylaxis and treatment, updating the 2007 practice guideline.1 The update is based on a systematic review of literature published from December 2007 to December 2012. An Update Committee reviewed...
Gary H. Lyman, MD, MPH, FRCP (Edin), Co-Chair, Duke University Medical Center
Anna Falanga, MD, Co-Chair, Ospedali Riuiniti Bergamo, Italy
Daniel Clarke-Pearson, MD, University of North Carolina
Christopher Flowers, MD, MS, Winship Cancer Institute
Charles W. Francis, MD, University of...