SUMMARY: The Center for Disease Control and Prevention (CDC) estimates that approximately 1-2 per 1000 individuals develop Deep Vein Thrombosis (DVT)/Pulmonary Embolism (PE) each year in the United States, resulting in 60,000-100,000 deaths. Venous ThromboEmbolism (VTE) is the third leading cause of cardiovascular mortality, after myocardial infarction and stroke.
Clinically, VTE is classified as provoked, occurring after transient risk factors such as surgery, trauma, or immobility, or unprovoked, when no clear trigger is identified. Standard management involves 3 months of anticoagulation for provoked events and extended therapy for unprovoked events because of their higher recurrence risk (6–10% per year after discontinuation). However, many patients present with provoked VTE in the context of enduring risk factors such as obesity, chronic inflammatory disease, atherosclerotic cardiovascular disease or chronic pulmonary conditions, factors that may sustain a prothrombotic milieu even after the transient trigger has resolved. Current guidelines offer limited direction for this increasingly common patient subset.
Venous thromboembolism (VTE) is a frequent and clinically significant complication in patients with cancer, contributing substantially to morbidity, disruptions in systemic cancer therapy, and mortality. Direct oral anticoagulants (DOACs) have reshaped management strategies, offering efficacy comparable to vitamin K antagonists with improved convenience and safety.
Among DOACs, Apixaban (ELIQUIS®) and Rivaroxaban (XARELTO®) are widely used. However, until recently, the absence of direct comparative randomized data has limited evidence-based selection between agents, particularly in patients with elevated bleeding risk, such as those with malignancy.
Study Design and Methods
The COBRRA (Comparison of Bleeding Risk between Rivaroxaban and Apixaban) trial was an international, prospective, randomized, open-label study and represents the first randomized, head-to-head comparison of Apixaban and Rivaroxaban in patients with acute symptomatic Pulmonary Embolism or proximal Deep-Vein Thrombosis.
A total of 2,760 patients with acute symptomatic Pulmonary Embolism or proximal Deep-Vein Thrombosis were randomized 1:1 to:
- Apixaban: 10 mg twice daily for 7 days, followed by 5 mg twice daily
- Rivaroxaban: 15 mg twice daily for 21 days, followed by 20 mg once daily
The Primary endpoint was clinically relevant bleeding (major or clinically relevant nonmajor bleeding) over 3 months. Secondary outcomes included all-cause mortality and recurrent VTE.
Notably, patients with cancer-associated thrombosis were excluded, reflecting historical standards at the time of trial design.
Key Results: Significant Reduction in Bleeding with Apixaban
At 3 months, Apixaban demonstrated a significant reduction in clinically relevant bleeding:
- 3.3% (Apixaban) vs 7.1% (Rivaroxaban)
- Relative Risk (RR): 0.46 (95% CI, 0.33–0.65; P<0.001)
This represents a 54% reduction in bleeding risk with Apixaban.
- Clinically relevant nonmajor bleeding:
- 2.9% (Apixaban) vs 4.9% (Rivaroxaban)
- Major bleeding was also lower with Apixaban (notably rare overall)
Common bleeding events included vaginal and gastrointestinal bleeding, with consistently lower rates observed in the Apixaban arm.
Comparable Efficacy
- Recurrent VTE rates were similar between groups (~1%)
- The improved safety profile of Apixaban did not compromise antithrombotic efficacy
Safety
- No deaths due to bleeding were reported
- Non-bleeding serious adverse events were comparable between groups
Relevance to Oncology Practice
Although cancer patients were not included, the findings have important indirect implications for oncology:
- Bleeding Risk Is Paramount in Cancer
Patients with malignancy often have:
- Tumor-related mucosal bleeding (e.g., GI, GU cancers)
- Treatment-related thrombocytopenia
- Drug–drug interactions with systemic therapies
In this context, the lower bleeding risk observed with Apixaban is highly clinically meaningful, particularly for patients at elevated hemorrhagic risk.
- Alignment with Emerging Oncology Data
Subsequent cancer-specific trials (e.g., CARAVAGGIO) have already demonstrated that Apixaban is effective and relatively safe in cancer-associated thrombosis, with a favorable bleeding profile compared with other DOACs in certain settings.
The COBRRA findings reinforce a growing body of evidence suggesting that Apixaban may be the preferred DOAC when bleeding risk is a major concern.
- Practical Treatment Considerations
- Dosing strategy matters: The extended 21-day high-dose phase with Rivaroxaban may contribute to early bleeding risk
- Pharmacokinetics: Higher peak drug levels with once-daily Rivaroxaban may increase mucosal bleeding, relevant in GI or GU malignancies
- Adherence: Despite slightly lower adherence with Apixaban in the trial, efficacy remained preserved
Limitations and Applicability to Oncology
- Exclusion of cancer-associated thrombosis limits direct generalizability
- Short follow-up (3 months) does not address extended anticoagulation
- Underrepresentation of diverse populations
- Not powered for efficacy differences
Despite these limitations, the biologic and pharmacologic insights are highly translatable to oncology populations
Clinical Takeaways
- Apixaban significantly reduces clinically relevant bleeding compared with Rivaroxaban in acute VTE
- Efficacy remains equivalent, supporting its use as a first-line agent
- For oncology patients, particularly those with high bleeding risk, Apixaban may represent a more favorable therapeutic option
- These findings may help inform DOAC selection in cancer-associated thrombosis, alongside existing oncology-specific trial data and guidelines
Conclusion
The COBRRA trial provides the first randomized evidence demonstrating a clear safety advantage of Apixaban over Rivaroxaban in acute VTE. For oncology clinicians, where balancing thrombosis prevention with bleeding risk is critical, these data support prioritizing Apixaban in appropriate patients, while awaiting further dedicated studies in cancer-associated thrombosis populations.
Bleeding Risk with Apixaban vs. Rivaroxaban in Acute Venous Thromboembolism. Castellucci LA, Chen VM, Kovacs MJ, et al.for the COBRRA Trial Investigators. N Engl J Med 2026;394:1051-1060
