Primary thromboprophylaxis is feasible and worth considering for high-risk ambulatory patients with cancer who are initiating systemic chemotherapy, according to Marc Carrier, MD.
Risk scores can identify patients at high risk for venous thromboembolism (VTE), and treatments that are effective and associated with low bleeding risk are available, Dr. Carrier explained at the biennial summit of the Thrombosis & Hemostasis Societies of North America.
However, caution is advised in patients with certain types of cancer, including some gastrointestinal and genitourinary cancers, because of the possibility of increased major and clinically relevant nonmajor bleeding risk, he said.
VTE and cancer
VTE is relatively rare in the general population, occurring in about 1 or 2 per 1,000 people annually. The risk increases 4.1-fold in patients with cancer, and 6.5-fold in patients with cancer receiving chemotherapy.
“So just putting these numbers together, we’re no longer talking about 1 in 1,000, but 1 in 200, so [this is] something that is very common among cancer patients,” said Dr. Carrier, a professor at the University of Ottawa and chief of the division of hematology at The Ottawa Hospital.
The mortality rate associated with cancer-associated thrombosis is about 9%, comparable to that associated with infection in the cancer outpatient setting, which underscores the importance of educating patients about the signs and symptoms of VTE so they can seek medical treatment quickly if necessary, he added.
It may also be useful to discuss prophylaxis or other ways to prevent venous thromboembolic complications with certain patients, he said, noting that in an observational cohort study of nearly 600 patients at the University of Ottawa, 25% of those initiating chemotherapy were identified as intermediate or high risk using the validated Khorana risk score, and thus would likely benefit from thromboprophylaxis.
Risk assessment
The Khorana risk score assesses VTE risk based on cancer site, blood counts, and body mass index. It is simple to use and has been validated in more than 20,000 people in multiple countries, Dr. Carrier said.
In a well-known validation study, Ay et al. showed a VTE complication rate of 10% in patients with a Khorana risk score of 2 or higher who were followed up to 6 months.
“This is huge,” Dr. Carrier stressed. “This is much higher than what we tolerate for all sorts of different populations for which we would recommend anticoagulation or thromboprophylaxis.”
The question is whether the risk score can be helpful in a real-world clinic setting, he said, adding: “I’d like to think the answer to that is yes.”
In the University of Ottawa cohort study, 11% of high-risk patients experienced a VTE complication, compared with 4% of those with lower risk, suggesting that the validation data for the Khorana risk score is not only accurate, it is “actually applicable in real-world practice, and you can use it in your own center,” he said.
Further, recent studies have demonstrated that treatment based on Khorana risk score assessment reduces VTE complications.
Prophylaxis options
Low-molecular-weight heparin (LMWH) has been shown in several studies to be associated with a significant relative VTE risk reduction in patients with cancer initiating chemotherapy – with only a slight, nonsignificant increase in the risk of major bleeding.
However, the absolute benefit was small, and LMWH is “parenteral, relatively costly, and, based on that, although we showed relatively good risk-benefit ratio, it never really got translated to clinical practice,” Dr. Carrier said.
In fact, a 2015 American Society of Clinical Oncology guidelines update recommended against routine thromboprophylaxis in this setting, but stated that it could be considered in select high-risk patients identified using a validated risk-assessment tool.
The guidelines noted that “individual risk factors such as biomarkers and cancer site don’t reliably identify high-risk patients.”
More recent data provide additional support for risk assessment and treatment based on Khorana risk score of 2 or higher.
The AVERT trial, for which Dr. Carrier was the first author, showed that the direct-acting oral anticoagulant (DOAC) apixaban reduced VTE incidence, compared with placebo, in patients with Khorana score of 2 or higher (4.2% vs. 10.2%; hazard ratio, 0.41 overall, and 1.0 vs. 7.3; HR, 0.14 on treatment), and the CASSINI trial showed that another DOAC, rivaroxaban, reduced VTE incidence, compared with placebo, in those with Khorana score of 2 or higher (5.9 vs. 6.7; HR, 0.6 overall, and 2.6 vs. 6.4; HR, 0.40 on treatment). The differences in the on-treatment populations were statistically significant.
The two trials, which included a variety of tumor types, showed similar rates of major bleeding, with an absolute difference of about 1% between treatment and placebo, which was not statistically significant in the on-treatment analyses (HR, 1.89 in AVERT and HR, 1.96 in CASSINI).
A systematic review of these trials showed an overall significant decrease in VTE complication risk with treatment in high-risk patients, and a nonstatistically significant major bleeding risk increase.
Based on these findings, ASCO guidelines were updated in 2020 to state that “routine thromboprophylaxis should not be offered to all patients with cancer. ... However, high-risk outpatients with cancer may be offered thromboprophylaxis with apixaban, rivaroxaban or LMWH, providing there are no significant risk factors for bleeding or drug-drug interactions, and after having a full discussion with patients ... to make sure they understand the risk-benefit ratio and the rationale for that particular recommendation,” he said.
Real-world implementation
Implementing this approach in the clinic setting requires a practical model, such as the Venous Thromboembolism Prevention in the Ambulatory Cancer Clinic (VTEPACC) program, a prospective quality improvement research initiative developed in collaboration with the Jeffords Institute for Quality at the University of Vermont Medical Center and described in a recent report, Dr. Carrier said.
The “Vermont model” is “really a comprehensive model that includes identifying patients with the electronic medical records, gathering the formal education and insight from other health care providers like pharmacists and nurses in order to really come up with personalized care for your patients,” he explained.
In 918 outpatients with cancer who were included in the program, VTE awareness increased from less than 5% before VTEPACC to nearly 82% during the implementation phase and 94.7% after 2 years, with nearly 94% of high-risk patients receiving VTE prophylaxis at that time.
“So we can certainly do that in our own center.” he said. “It’s a matter of coming up with the model and making sure that the patients are seen at the right time.”
Given the high frequency of VTE in patients with cancer initiating chemotherapy, the usefulness of risk scores such as the Khorana risk score for identifying those at high risk, and the availability of safe and effective interventions for reducing risk, “we should probably use the data and incorporate them into clinical practice by implementation of programs for primary prevention,” he said.