Background: Patients with cancer receiving chemotherapy are at an increased risk of venous thromboembolism (VTE)(Khorana,2005). In the United Kingdom, the use of primary thromboprophylaxis is not recommended in ambulatory patients with cancer (NICE,2018). Recent data evaluating the directly acting oral anticoagulants for primary prophylaxis of cancer associated thrombosis (CAT) has emerged. There is a requirement to include this within a review.

Aims: This systematic review and meta-analysis examined the efficacy and safety of primary thromboprophylaxis in ambulatory patients with cancer receiving chemotherapy. Hypothesising that primary thromboprophylaxis is associated with a reduction in VTE occurrence and does not increase rates of major bleeding.

Methods:

Ovid’s Medline (R), Embase, Clinicaltrials.gov, Cochrane’s CENTRAL database and the ISCRTN registry were searched using relevant terms, and without restrictions, up to the 2nd June 2020. Randomised control trials meeting pre-defined inclusion criteria were selected (see figure 1). VTE and major bleeding outcome data were extracted alongside methodological and participant characteristics.

A PRSIMA flow diagram detailing the study selection process with reasons for the exclusion of studies given at each stage. Meeting one exclusion criterion excluded a study and the first criterion met was recorded for the reason for exclusion.

Results: Eleven randomised control trials (7375 participants) were included. VTE occurred in 1.94% of participants receiving thromboprophylaxis and 5.71% of controls [OR 0.39 95% CI 0.27, 0.56 I2 41% P=<0.00001] (see figure 2), NNT=27. The enrolment of high risk participants was not associated with an increased treatment effect. Major bleeding events occurred in 1.89% of participants receiving thromboprophylaxis and 1.39% of controls [OR 1.39 95% CI 0.96, 2.04 I2 0% P=0.08] (see figure 2). There was no significant alteration in the probability of major bleeding when studies were grouped by degree of bias, anticoagulant agent or risk score.

Forest plots for the two major outcomes of the review. Inset (a) represents the primary efficacy outcome of VTE occurrence, the overall effect estimate shows a reduction in the odds of VTE for those participants who received thromboprophylaxis (OR 0.39 [95% CI 0.27, 0.56]). Inset (b) represents the primary safety outcome of major bleeding, the overall effect estimate shows a non-significant increase in the odds of major bleeding with confidence intervals spanning one (OR 1.39 [95% CI 0.96, 2.04]).

Conclusions: Primary thromboprophylaxis decreased venous thromboembolic events in patients with cancer receiving chemotherapy, and was not significantly associated with an increase in major bleeding. The inclusion of DOAC data within the review lowered the number needed to treat (Di Nisio,2016), indicating these agents are  a viable option for CAT prophylaxis.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/the-role-of-primary-thromboprophylaxis-in-people-with-cancer-a-systematic-review-and-meta-analysis/