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Predicting cancer-associated venous thromboembolism
dence in the group with a score of 2 points or higher was 8.3% (95%CI: 6.4-10.7). The relative risk of patients with a score of 3 or higher compared to those with a lower score was 1.9 (95%CI: 1.5-2.3).
Discussion
This systematic review and meta-analysis examined the performance of the Khorana score in predicting VTE in over 34,000 patient ambulatory patients with various types of cancer. To minimize between-study heterogene- ity and obtain clinically relevant estimates, the main analysis was restricted to the first six months of follow up. During this period, the summary estimate of the risk of VTE in patients with a high-risk Khorana score was 11.0%, which was significantly higher than in those with a low-risk (5.0%) or intermediate-risk (6.6%) score. These findings indicate that the Khorana score may help clini- cians in selecting patients at high risk of VTE for thrombo- prophylaxis, which is in support of the suggestions pre- sented in current guidelines.
The analyses also highlight several limitations of the score. Within the high-risk group, the estimated risk of
VTE was considerably lower for patients with lung cancer and hematologic malignancies than for those with other cancer types (Figure 2C). Hence, the Khorana score appears to be less informative for these two large groups of patients. Furthermore, the VTE incidence in patients with a low-to-intermediate risk score was 5-7%, which indi- cates that the residual risk in this group is still substantial. Therefore, the Khorana score is of limited use in ruling out a future venous thromboembolic event. Lastly, the Khorana score is designed to select patients in the high-risk group for thromboprophylaxis. However, about one in four (23.4%, 95%CI: 18.4-29.4) of the venous thromboem- bolic events occur in patients with a high-risk Khorana score. This means that a substantial amount of cancer patients with subsequent venous thromboembolic events will not be identified with this form of risk stratification, and will, therefore, not benefit from thromboprophylaxis.
A major strength of this study is the additional data obtained from 34 studies on the 6-month incidence of VTE after starting chemotherapy, representing 81% of cancer patients in the available relevant literature. This approach minimized between-study heterogeneity related to the broad range of reported median follow-up dura- tions. We considered this 6-month period to be clinically
Figure 1. PRISMA flow chart. ASH: American Society of Hematology; ISTH: International Society on Thrombosis and Haemostasis.
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