Primary prophylaxis for venous thromboembolism in ambulatory cancer patients receiving chemotherapy

Background
Venous thromboembolism (VTE) oHen complicates the clinical course of cancer. The risk is further increased by chemotherapy, but the
trade-oJ between safety and eJicacy of primary thromboprophylaxis in cancer patients treated with chemotherapy is uncertain. This is
the third update of a review first published in February 2012.
Objectives
To assess the eJicacy and safety of primary thromboprophylaxis for VTE in ambulatory cancer patients receiving chemotherapy compared
with placebo or no thromboprophylaxis, or an active control intervention.
Search methods
For this update the Cochrane Vascular Information Specialist searched the Cochrane Vascular, CENTRAL, MEDLINE, Embase and CINAHL
databases and World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers to 3 August
2020. We also searched the reference lists of identified studies and contacted content experts and trialists for relevant references.
Selection criteria
Randomised controlled trials comparing any oral or parenteral anticoagulant or mechanical intervention to no thromboprophylaxis or
placebo, or comparing two diJerent anticoagulants.
Data collection and analysis
We extracted data on risk of bias, participant characteristics, interventions, and outcomes including symptomatic VTE and major bleeding
as the primary eJectiveness and safety outcomes, respectively. We applied GRADE to assess the certainty of evidence.
Main results
We identified six additional randomised controlled trials (3326 participants) for this update, bringing the included study total to 32 trials
(15,678 participants), all evaluating pharmacological interventions and performed mainly in people with locally advanced or metastatic
cancer. The certainty of the evidence ranged from high to very low across the diJerent outcomes and comparisons. The main limiting
factors were imprecision and risk of bias.
Thromboprophylaxis with direct oral anticoagulants (direct factor Xa inhibitors apixaban and rivaroxaban) may decrease the incidence of
symptomatic VTE (RR 0.43, 95% confidence interval (CI) 0.18 to 1.06; 1526 participants, 3 studies; low-certainty evidence); and probably
increase the risk of major bleeding compared with placebo (RR 1.74, 95% CI 0.82 to 3.68; 1494 participants, 3 studies; moderate-certainty
evidence).
When compared with no thromboprophylaxis, low molecular weight heparin (LMWH) reduced the incidence of symptomatic VTE (RR 0.62,
95% CI 0.46 to 0.83; 3931 participants, 11 studies; high-certainty evidence); and probably increased the risk of major bleeding events (RR
1.63, 95% CI 1.12 to 2.35; 7282 participants, 15 studies; moderate-certainty evidence).
In participants with multiple myeloma, LMWH resulted in lower symptomatic VTE compared with the vitamin K antagonist warfarin (RR
0.33, 95% CI 0.14 to 0.83; 439 participants, 1 study; high-certainty evidence), while LMWH probably lowers symptomatic VTE more than
aspirin (RR 0.51, 95% CI 0.22 to 1.17; 781 participants, 2 studies; moderate-certainty evidence). Major bleeding was observed in none of the
participants with multiple myeloma treated with LMWH or warfarin and in less than 1% of those treated with aspirin.
Only one study evaluated unfractionated heparin against no thromboprophylaxis, but did not report on VTE nor major bleeding.
When compared with placebo or no thromboprophylaxis, warfarin may importantly reduce symptomatic VTE (RR 0.15, 95% CI 0.02 to 1.20;
311 participants, 1 study; low-certainty evidence) and may result in a large increase in major bleeding (RR 3.82, 95% CI 0.97 to 15.04; 994
participants, 4 studies; low-certainty evidence).
Antithrombin versus no antithrombin was evaluated in one study involving paediatric patients. T