E383: Extended Venous Thromboembolism Prophylaxis After Cancer Surgery is Paradoxically Associated with a Higher Incidence of Venous Thromboembolism

Introduction: The American Society of Clinical Oncology recommends extended venous thromboembolism (VTE) prophylaxis with low-molecular weight heparin (LMWH) or direct oral anticoagulants (DOAC) following cancer surgery. However, these recommendations were based on trials utilizing routine venography that detects asymptomatic VTEs, and real-life efficacy is not well-studied. We aimed to assess the association of extended VTE prophylaxis with the incidence of clinically significant VTE after elective cancer surgery.

Methods: Patients who underwent surgical resection for lung, breast, esophageal, gastric, pancreas, and colon cancer from 2010 to 2017 were identified from the SEER-Medicare linked dataset. Patients who received extended VTE prophylaxis were defined as having filled a prescription for prophylactic doses of LMWH or DOAC within 7 days of postoperative discharge as identified from Medicare Part D files. Multilevel mixed-effects cox regression with landmark analyses were performed to obtain adjusted impact of extended VTE prophylaxis with clinically significant VTE.

Results: A total of 113,739 Medicare beneficiaries were identified, of which 1,570 (1.4%) received extended VTE prophylaxis. There was an increase in the use of extended VTE prophylaxis in every year during the study period, rising from 0.6% in 2010 to 3.3% in 2017. The overall 1-month incidence of VTE was 1.6%, 4.3% at 6 months, 5.7% at 12 months, and differed by cancer types (p< 0.001). However, patients who received extended VTE prophylaxis had a higher 1-year cumulative incidence of postoperative VTE (11.4%) when compared to patients who did not (5.3%, p< 0.001), an association consistent across cancer sites. On adjusted analyses, the utilization of extended VTE prophylaxis was independently associated with increased odds of developing cumulative incidences of VTE (HR 1.6, 95% CI 1.3 – 2.0, p< 0.001). Patients who received extended VTE prophylaxis were also associated with higher 1-year incidence of bleeding events (12.0%) when compared to patients who did not (8.5%, p< 0.001).

Conclusions: The utilization rate of extended VTE prophylaxis after cancer surgery is low, albeit rising every year. Patients who received extended VTE prophylaxis paradoxically had a higher incidence of clinically significant VTE and bleeding events compared to patients who did not. This is likely mediated by patient selection and surveillance bias following cancer surgery. In view of these findings, national guidelines regarding postoperative extended VTE prophylaxis may need to be re-examined.