Anticoagulant outcomes in managing tumor thrombus: a systematic review

Background: Tumor thrombus (TT), defined as intravascular extension of malignant tissue, is a distinct manifestation of cancer-associated thrombosis driven by malignant vascular invasion rather than fibrin-rich clot. Despite limited evidence, anticoagulant therapy is frequently prescribed empirically. This systematic review synthesized available data on the effectiveness and safety of anticoagulation in adults with solid tumor-associated TT. Methods: A PRISMA (2020) compliant systematic review (PROSPERO-registered) was conducted using PubMed/MEDLINE, Embase, and CENTRAL through September 2025. Eligible studies included adults with solid tumor-associated TT who received anticoagulation and reported thrombus response, thromboembolic recurrence, survival, or bleeding outcomes. Results were synthesized narratively in accordance with SWiM guidance. Risk of bias was assessed using the Newcastle-Ottawa Scale and the Joanna Briggs Institute tools, and the certainty of evidence was assessed using the GRADE approach. Results: Eight studies met the inclusion criteria, comprising three retrospective cohort studies and five case reports. Anticoagulants evaluated included low-molecular-weight heparin, vitamin K antagonists, direct oral anticoagulants, unfractionated heparin, and parenteral direct thrombin inhibitors. Across all studies, anticoagulation alone was not associated with radiographic regression of TT. Apparent thrombus resolution occurred exclusively following tumor-directed or mechanical interventions, such as surgical thrombectomy or percutaneous aspiration, and could not be attributed to anticoagulation alone. Evidence for a reduction in thromboembolic recurrence was limited, heterogeneous, and inconsistently adjudicated as bland thrombosis versus malignant embolic disease. No survival benefit attributable to anticoagulation was demonstrated. In contrast, anticoagulant therapy was associated with a clinically meaningful risk of major bleeding, particularly among patients with renal cell carcinoma-associated TT. Overall certainty of evidence ranged from very low to moderate. Conclusion: Current evidence does not demonstrate a consistent benefit of routine anticoagulation for isolated TT. Anticoagulation may be appropriate when conventional indications are present (e.g., pulmonary embolism, proximal deep-vein thrombosis, atrial fibrillation, catheter-associated thrombosis). Tumor-directed therapy remains the primary determinant of outcomes. Prospective studies are needed to define optimal management strategies. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/view/CRD420251111117, identifier CRD420251111117.