Background
A central venous catheter (CVC) is a tube that is inserted into a large vein to give fluids or medicines. CVC placement increases the risk of blood clots in people with cancer. This review evaluated the effectiveness and safety of blood thinning agents (anticoagulants) in people with cancer and a CVC.

Study characteristics
We searched the scientific literature for studies of anticoagulants in people with cancer and a CVC. The evidence is current to 14 May 2018.

Key results
We included 13 trials enrolling 3420 people with cancer and a CVC. Most trials included people with various types and stages of cancer. Seven studies compared injectable blood thinners to no anticoagulation, six studies compared blood thinner pills to no anticoagulation, and three studies compared injectable blood thinners to blood thinner pills. When considering people with cancer and a CVC, injectable blood thinners probably reduced the risk of CVC-related blood clots compared to no anticoagulation and probably increased the risk of thrombocytopenia (low levels of platelets in the blood, which causes bleeding into the tissues) compared to blood thinner pills.

Certainty of the evidence
When comparing injectable blood thinners to no anticoagulation, we judged the certainty of the evidence to be moderate for blood clot at the catheter site, low for mortality, for blood clot at the catheter site and minor bleeding and very low for major bleeding.

When comparing blood thinner pills to no anticoagulation, we judged the certainty of the evidence to be low for mortality major and minor bleeding, premature catheter removal and catheter-related infection low, and very low for blood clot at the catheter site.

When comparing injectable blood thinners to blood thinner pills, we judged the certainty of the evidence to be low for mortality and blood clots in the limbs and very low for blood clot at the catheter site, major and minor bleeding.