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Risk stratification of recurrent venous thromboembolism in patients with cancer-associated VTE
    Results
Study selection
The literature search identified 329 article records of which 229 were assessed for eligibility (Figure 1). Nine studies reporting data on 14,963 patients were eligible and were included in the analyses.9,13-19
Study characteristics
Study characteristics are depicted in Table 1. Of the reported studies, six were prospective, six were multicen- ter, and four used the original score. In total, seven studies were validation studies of the Ottawa score. Mean age of the patients was 58-69 years; female gender accounted for 45-59% of the patients.
Risk of bias within studies
Risk of bias is summarized in Online Supplementary Appendix 1. For six studies, at least four out of six potential bias areas were judged satisfied.9,14-16,18 Confounding meas-
A
urement was not accounted for in all studies, and attrition was accounted for in only one study.18 A significant publi- cation bias between the studies was observed (P=0.001) (Online Supplementary Appendix 2A). This bias was only observed in studies reporting on the modified score (Online Supplementary Appendix 2B and C).
Synthesis of results
All nine identified studies were included in the meta- analysis. Data were extracted from original publications for six studies9,13-15,19 or, after that, additional data were pro- vided by corresponding authors.16-18 The overall 6-month rate of recurrent VTE varied from 4.3% to 18.1% in the different studies; the overall 6-month pooled rate was 9.8% (95%CI: 6.4-13.8; I2=96%).
The original Ottawa score was derived in one and vali- dated in three studies.9,14,15,19 The total number of patients included in these studies was 1,558 with an overall pooled 6-month rate of recurrent VTE of 12.7% (95%CI: 8.9-17.2, I2=81%). Overall, 763 (49.3%) patients were classified in
 B
Figure 2. Pooled recurrence rates of venous thromboembolism for the original Ottawa score. (A) Pooled recurrence rates of venous throm- boembolism for the original Ottawa score in high-risk patients. (B) Pooled recurrence rates of venous thromboembolism for the original Ottawa score in low-risk patients
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