Bleeding Risk in a Cohort of Ambulatory Cancer Patients Receiving Outpatient Prophylactic Anticoagulation for Venous Thrombosis Prevention
Authors: Wilks Andrew B , Douce Daniel , Ades Steven , Cushman Mary , Zakai Neil A. , Holmes Chris E. 
Published: February 2020

Background: Recent clinical trials have evaluated the safety and efficacy of direct oral anticoagulant (DOAC) therapy for venous thromboembolism (VTE) prophylaxis in cancer outpatients at high risk for thrombosis. Bleeding risk in these trials were approximately 2% over the first 6 months of therapy. For individual patients, the utility of prophylactic anticoagulation (AC) depends on an acceptable safety profile between bleeding and thrombosis. We investigated whether ambulatory cancer patients on contemporary cancer-directed therapies and prophylactic AC had an increased risk of major bleeds over the first 6 months of therapy.
Methods: As part of a single-center prospective cohort study, we assessed consecutive ambulatory patients initiating cancer-directed treatment, risk-stratified these patients for VTE using the Khorana score and educated them about VTE. High risk patients (Khorana score ≥3) were offered prophylactic AC. Major bleeding events and minor bleeding events (based on ISTH standard definitions) were prospectively captured via billing code screening and confirmed by physician review of the medical record. Logistic regression was used to compare the odds of developing a major bleed within 6 months in those who received prophylactic AC compared to those that did not.
Results: A total of 1,210 patients were enrolled from October 2015 - June 2018, of which, 640 were women (52.9%). The most common cancers were gastrointestinal 270 (22%), lung 213 (18%), and breast 198 (16%). There were 393 patients (32%) with a Khorana score of 0, 706 (58%) with a Khorana score of 1-2, and 111 (9%) with a score of ≥3. A total of 421 patients received any AC (LMWH or DOAC). Of these, 282 received a prophylactic dose anticoagulant and 139 were receiving a full dose anticoagulant prior to enrolling for other medical reasons. Prophylactic dose anticoagulants prescribed included apixaban in 107 (41%), rivaroxaban in 6 (2.3%), enoxaparin in 119 (45.7%), and other heparin products in 50 (19.2%). A total of 27 (2.33%) major bleeds and 22 (1.81%) minor bleeds occurred within the first 6 months of starting therapy. Of these bleeding events, 8 (2.8%) occurred in those on prophylactic AC, and 6 (4.3%) occurred in those on full dose AC. The odds ratio (OR) of developing a major bleed on any type of AC was 1.78 [CI 0.817-3.88]. The OR of major bleeding on prophylactic AC was 1.49 [CI 0.64-3.479]. The OR of major bleed was highest in lung cancer patients on prophylactic AC (OR 2.81, CI 1.27-6.25). Men, when compared to women, were more likely to bleed on prophylactic AC in the first six month (OR 0.2; CI 0.07-0.52). The OR for major bleed with each 1 year increase in age was 1.02 (CI 0.99, 1.06). The OR of bleeding with a high risk Khorana score (≥3) compared to a lower score was 1.04 (CI 0.73-1.50).
Conclusion: During the first six months of therapy, prophylactic AC was associated with an increased risk of major bleeding events in patients on cancer-directed therapy. In this study, the rate of major bleeding was similar as compared to published clinical trials. Neither age nor higher Khorana score were associated with an increased risk of major bleeds in patients on prophylactic AC. The finding that men, when compared to women, and patients with lung cancer may have an increased risk of major bleeding while on prophylactic AC and cancer-directed chemotherapy suggests these groups may warrant both increased education and monitoring to ensure safety while on prophylactic AC.

Disclosures
No relevant conflicts of interest to declare.