Background In primary central nervous system lymphoma (PCNSL), venous thromboembolism (VTE) can cause significant morbidity and hinder chemotherapy delivery. Objectives To assess VTE incidence, timing and adequacy of inpatient and outpatient VTE prophylaxis in patients with PCNSL receiving chemoimmunotherapy with curative intent. Patients/Methods We reviewed patients diagnosed with PCNSL between 1997 and 2018 who received methotrexate, procarbazine, and vincristine ± Rituximab. Patient demographics, VTE prophylaxis and incidence, adverse events of anticoagulation, and survival outcomes were collected. Results Fifty‐one PCNSL patients were included (median 67 years [range, 32‐87], 30 males [59%]). Thirteen patients (25%, 95% confidence interval [CI], 14‐40) developed VTE at a median of 1.6 months from diagnosis (range, 0‐4). Patients with Khorana Risk Score ≥2 were more likely to have VTE than those with a KRS < 2 (60% vs 15%; P = .01). Eighty‐five percent had deviations from inpatient VTE prophylaxis guidelines, and outpatient prophylaxis was not routinely administered. Three patients required inferior vena cava filters. Hemorrhagic complications of anticoagulation included an intracranial hemorrhage from therapeutic anticoagulation and three cases of major bleeding from prophylactic anticoagulation. No patients died from VTE or its treatment. Conclusions Patients with newly diagnosed PCNSL are at high risk of VTE. Further research is required into optimal VTE prophylaxis in PCNSL.

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Aim Elevated D-dimer post-anticoagulation cessation is a recognised risk factor for recurrent venous thromboembolic events (VTE). In particular, raised D-dimer post cessation has been associated with increased risk of recurrence in unprovoked major VTE. Currently in Australia, D-dimer has not been widely used in practice to stratify the risk of VTE recurrence. This study aims to retrospectively analyse the effect of routine D-dimer testing and it's association with VTE recurrence. Methods A retrospective evaluation was performed on 1024 patients with a diagnosis of VTE at a tertiary hospital in Australia between January 2013 and December 2016. Data collected included demographics, results and timing of D-dimer testing and serial imaging results. Results 1024 patients were reviewed with a total median follow up of 12 months (range 0-59 months). D-dimer was tested in 189 patients (18.5%) within 90 days after cessation of anticoagulation. Of these patients, median age was 58 (18-92) and 55.3% (n=105) were female. 33.3% (n=63) had isolated distal deep vein thrombosis (IDDVT), 66.3% (n=126) had above knee DVT (AKDVT)/pulmonary embolus (PE), 54.5% (n=103) of VTE were provoked. Abnormal post cessation D-dimer (>500) was found in 72 patients (37.9%). Of these, 25 patients were restarted on anticoagulation; one had recurrent VTE whilst on low dose apixaban 2.5mg BD and one had recurrence after cessation of anticoagulation at a later date. Patients with elevated D-dimer post cessation had a higher rate of recurrence with the highest risk in patients with D-dimer >1000 (RR 7.38, p=<0.01) outlined in Table 1. Of the 164 patients with post cessation D-dimer testing who remained off anticoagulation there were a total of 24 (12.6%) episodes of recurrent VTE. Elevated D-dimer post anticoagulation cessation was a significant risk factor for recurrence in both provoked VTE (RR 4.21, p=0.01) and unprovoked VTE cohorts (RR 4.55, p=0.008) outlined in Table 2. When provoked VTE were sub-categorised, raised D-dimer demonstrated the most statistical significance in VTE provoked by travel (RR 13.5 p=0.06). Of the patients with post anticoagulation cessation D-dimer testing 170 patients (89.9%) had repeat imaging to assess for residual thrombus. In the subgroup of patients with no residual thrombus, elevated D-dimer was a significant risk factor for VTE recurrence (RR 6.4, p=<0.01). Patients with normal D-dimer and no residual thrombus had the lowest rate of recurrence 5.4% (n=4) see Table 3. When stratified by type of VTE, elevated D-dimer post anticoagulation cessation was significantly related to risk for recurrence in the overall IDDVT sub-cohort (RR 4.09, p=0.007). This was not significant for the AKDVT/PE sub cohort (RR 3.24, p=0.079). However, for patients with unprovoked AKDVT or PE, having D-dimer tested post anticoagulation, regardless of result, was associated with lower rates of VTE recurrence RR 0.30 (p=0.02) compared to those who had no D-dimer testing as part of follow-up. Conclusion Post treatment D-dimer testing may have a clinical role in stratifying the risk of VTE recurrence along with repeat imaging to detect residual thrombus. Elevated D-dimer post anticoagulation cessation is associated with increased risk of VTE recurrence for both provoked and unprovoked VTE with highest risk in patients with D-dimer >1000. Patients with no residual thrombus and a negative D-dimer post anticoagulation cessation had the lowest rate of recurrence. In the subgroup of patients with provoked VTE and IDDVT a positive D-dimer post cessation was associated with 4.21 and 4.09 relative risk of recurrence respectively, suggesting that the role of D-dimer testing can be extended to these subpopulations. Interestingly, in patients with unprovoked AKDVT or PE, having post-cessation D-dimer testing performed, regardless of result, was associated with a significantly lower rate of VTE recurrence compared to patients without D-dimer testing, which may be related to specialist review and recommencement of anticoagulation in high-risk patients. Disclosures No relevant conflicts of interest to declare.

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