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Predicting cancer-associated venous thromboembolism
C
Figure 2. Venous thromboembolism incidence in the low-, intermediate-, and high-risk group over six months. Venous thromboembolism incidence in the low-risk (A), intermediate-risk (B), and high-risk (C) groups according to the Khorana score, over six months follow up.
most relevant. Prediction of VTE only for the first few months of chemotherapy may be too short, since the risk remains elevated throughout the first six months. On the other hand, the Khorana score calculated with pre- chemotherapy laboratory data likely predicts less well for longer term (>6 months) than for shorter term intervals. The inclusion of more than 50 studies enabled the meta- analysis for various subgroups of cancer patients, showing that the performance of the Khorana score varies across tumor types. A potential limitation is the substantial pro- portion of studies judged to be at high risk of bias (Online Supplementary Table S4). However, the sensitivity analyses restricted to studies at low risk of bias did not materially alter the results (Table 3). When the analysis was restricted to studies with a prospective design or to studies without systematic VTE screening preceding study, results were comparable (data not shown). Additional data for the first
six months could not be obtained for eleven studies, pos- sibly introducing sampling bias. We believe, however, that the magnitude of this risk of bias is at best modest since 6- month data were available in the final analyses for 81% of all patients. Some studies included more types of venous thromboembolic events than specified in our primary out- come. However, these types of venous thromboembolic events occur infrequently. A large proportion of the stud- ies (n=32, 60%) included incidentally detected VTE, unlike the outcome in the derivation study of the Khorana score.7 However, we believe these events should also be considered since clinical outcomes in patients with inci- dental VTE are similar to those with symptomatic events.14-16 Consequently, international guidelines regard incidental VTE events as clinically relevant and recom- mend anticoagulant treatment, as for patients with symp- tomatic VTE.6,17 Despite minimizing bias due to differ-
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