Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Alongside the hundreds of Cochrane Reviews of treatments for patients with cancer, there are many of ways to reduce the adverse effects of those treatments. In December 2020, we published the third update of one of these, looking at the effects of drugs to prevent venous thromboembolism in patients receiving chemotherapy. Marcello Di Nisio from the University "G. D'Annunzio" of Chieti-Pescara in Italy tells us about the latest findings in this podcast.

Marcello: Venous thromboembolism often complicates the clinical course of patients with cancer who are receiving chemotherapy. The events include deep vein thrombosis or pulmonary embolism and are associated with high morbidity, often needing the patient to stay in hospital and increasing their risk of recurrent thrombosis or bleeding complications after they are given anticoagulation to treat the thromboembolism. Added to this, venous thromboembolic events often lead to the postponement of the patient's cancer treatment, delaying the course of their chemotherapy, and this can have a negative impact on morbidity and survival, as well as on their quality of life.
Widespread use of preventive medication, called primary thromboprophylaxis, may help prevent venous thromboembolic events, but the benefits need to be weighed against the potential harms of bleeding complications.
Therefore, our updated Cochrane review assesses the efficacy and safety of primary thromboprophylaxis for venous thromboembolism in ambulatory patients with cancer receiving chemotherapy. We included randomized trials comparing primary thromboprophylaxis with placebo, no thromboprophylaxis, or an active control intervention.
For the current update, we added six randomized trials, bringing the total number of studies to 32. These 32 studies included nearly 15,700 participants, most of whom had locally advanced or metastatic cancer. 
Combining the findings suggests that primary thromboprophylaxis with oral direct factor Xa inhibitors may reduce the incidence of symptomatic venous thromboembolism while probably increasing the risk of major bleeding, when compared with placebo. One way to think about this is to consider a population of 1000 cancer patients who are receiving chemotherapy. Without oral direct factor Xa inhibitors, perhaps 80 of them would have a venous thromboembolic event, but with the drug, this number would drop by 46 to 34. On the other hand, major bleeding would probably increase by 13, up from 18 in a 1000 people without the drug to 32 in those who take it.
For another of the prophylactic medications, low-molecular-weight heparin, the evidence showed a decrease in symptomatic venous thromboembolic events compared to no such treatment or placebo, but an increase in the risk of major bleeding. Here, the numbers for 1000 patients would equate to an average of 27 fewer symptomatic venous thromboembolic events, at the cost of seven more major bleeds. 
There were too little data to be sure about the conclusions for other comparisons such low-molecular-weight heparin versus active control, or the effects of antithrombin, unfractionated heparin or vitamin K antagonist; or to determine if the effects are similar or different for people with different types of cancer or who are receiving different types of chemotherapy. 
In conclusion, we hope that this latest update of our review will not only help guideline developers but also patients with cancer who are on chemotherapy and their care-givers when deciding whether or not to take or offer thromboprophylaxis.

Monaz: If you would like to read the full version of this update, including the results for all the comparisons that Marcello mentioned, you can find it at Cochrane Library dot com with a simple search for 'preventing venous thromboembolism from chemotherapy'.