People with cancer are at increased risk of blood clots. The blood thinner (anticoagulant) administered in the first few days after identifying a blood clot can consist of unfractionated heparin (infused through a vein),low molecular weight heparin (injected under the skin once or twice per day; dalteparin, and tinzaparin are two different types of low molecular weight heparin), or fondparinux (injected under the skin once daily). These blood thinners may have different effectiveness and safety profiles.
We searched scientific databases for clinical trials comparing different blood thinners in people with cancer with a confirmed diagnosis of deep vein thrombosis (a blood clot in the limbs) or pulmonary thrombosis (a blood clot in the lungs). We included trials of adults and children with either solid tumors or blood cancer irrespective of the type of cancer treatment. The trials looked at death, recurrent blood clots, and bleeding. The evidence is current to January 2018. We included 15 trials.
In this systematic review, data from five studies with 422 participants suggested that the effect of low molecular weight heparin on death compared with unfractionated heparin was uncertain, but if anything of small size. There was not enough evidence to prove superiority in reducing recurrence of blood clots or risk of bleeding. We found no data to compare the safety profile of these two medications. Also, fondaparinux did not prove or exclude any important effect compared to heparins, on death, blood clots, or bleeding. Similarly,the available evidence did not show any difference between dalteparin and tinzaparin for all tested outcomes.
Certainty of the evidence
We judged the certainty of evidence for low molecular weight heparin versus unfractionated heparin to be moderate for all assessed outcomes.
We judged the certainty of evidence for fondaparinux versus heparin to be moderate for all tested outcomes.
We judged the certainty of evidence for tinzaparin versus dalteparin to be low for all tested outcomes.