In this study, the pooled results of meta-analysis showed that DOACs significantly reduced the occurrence of recurrent VTE and DVT, but not PE or fatal PE, compared with LMWHs in patients with cancer. Subgroup analyses revealed an important role of rivaroxaban in decreasing the VTE and DVT recurrence. In addition, DOACs did not increase the risk of major bleeding events, but the risk of CRNMBs were increased. Subgroup analyses confirmed the role of rivaroxaban in increasing the risk of major bleeding events and CRNMBs.
Anticoagulant therapy is a complex clinical issue in cancer patients because it should balance between anticoagulation and bleeding. Traditionally, LMWHs are the preferred drugs for anticoagulant therapy in the prophylaxis and treatment of VTE, which were recommended by many guidelines(4). It has been well established that LMWHs was effective in reducing the VTE and overall mortality(28), though the risk of bleeding was still in debate(4). In recent years, the role of DOACs in the treatment of cancer-associated VTE has been increasingly recognized. A series of reviews and meta-analyses showed that DOACs was better than the LMWHs in preventing the recurrent VTE in cancer patients(29, 30). Similarly, DOACs were effective in reducing the DVT recurrence(9, 31), but not PE recurrence(31). In consistent with these results, we confirmed in our meta-analysis that the risk of VTE recurrence, as well as DVT recurrence, was significantly lower in patients treated with DOACs than that of LMWHs. But there was no significant difference in the risk of recurrent PE or fatal PE between the two groups.
Since DOACs include rivaroxaban, edoxaban, apixaban, etc., we further analyzed the risk effects of different kinds of DOACs in cancer patients by subgroup analyses. One RCT compared the efficacy of edoxaban with LMWH(22), but no significant difference in VTE recurrence was detected. Ten studies(1, 9, 12–16, 18, 19) including one RCT (11) investigated the risk of recurrent VTE in patients receiving rivaroxaban compared with that of LMWH. The occurrence of VTE recurrence was significantly lower in rivaroxaban group, suggesting a role of rivaroxaban in reducing the recurrent VTE compared with that of LMWH. After excluding the RCT in meta-analysis, the difference in VTE recurrence between the two groups was still significant, further confirming the association between lower VTE risk and rivaroxaban treatment. Two RCTs(20, 21) and one retrospective study(19) compared the effect of apixaban with LMWH, and the results did not reveal significant OR for apixaban in VTE risk. However, when we excluded the retrospective study, pooled analysis of the two RCTs did demonstrate lower VTE risk in patients with apixaban. So, more RCTs are needed to further confirm the role of apixaban in preventing the VTE recurrence in cancer patients.
DVT events and PE events are the main manifestations of VTE in patients with cancer. Our study found that DOACs was superior than LMWHs in preventing recurrent DVT, which was consistent with previous studies(9, 31). Subgroup analyses were performed in edoxaban, rivaroxaban and apixaban groups based on the available data. Only one RCT(22) investigated the DVT recurrence between edoxaban group and LMWH group and results showed a lower risk of recurrent DVT in patients receiving edoxaban. One RCT(11) and two retrospective studies(12, 14) compared the efficacy of rivaroxaban and LMWHs, and results demonstrated that riaroxaban significantly reduced the DVT recurrence in cancer patients. Two RCTs(20, 21) on apixaban found that it had no effect on reducing the DVT recurrence compared with that of LMWHs. Moreover, pooled analysis, as well as subgroup analyses, of the included studied did not show a superior effect of DOACs, including edoxaban, rivaroxaban and apixaban, upon LMWHs to reduce the risk of recurrent PE and fatal PE. According to the limited data, these results indicated that rivaroxaban was particularly important in reducing the risk of VTE recurrence in cancer patients. Further studies are still needed to clarify the role of other DOACs in the treatment of patients with cancer.
Currently, there is inconsistency about the effect of DOACs on major bleeding events in cancer patients. Some studies revealed that DOACs would increase the risk of major bleeding(9) but other studies did not find such an elevated risk(31). In our pooled analysis, regardless of RCTs or retrospective studies, there was no significant difference in the occurrence of major bleeding events between DOACs and LMWHs. However, subgroup analyses showed that rivaroxaban did increase the major bleeding events in cancer patients while edoxaban and apixaban did not induce elevated risk of major bleeding events. Thus, it is important for clinicians to consider the characteristics of different DOACs in patients with cancer. Consistent with previous studies(9, 31), our analysis confirmed that DOACs increased the risk of CRNMBs, suggesting a tendency of promoting bleeding of DOACs. However, one RCT about edoxaban found that the CRNMBs risk was not increased after treatment(22). Two RCTs(20, 21) and one retrospective study(19) consistently showed that apixaban did not increase the risk of CRNMB events in patients with cancer. Therefore, edoxaban and apixaban may be safer than the rivaroxaban in the treatment of VTE in cancer patients.
This study has some limitations. First, due to the limited data on different kinds of DOACs, the studies comparing the edoxaban, apixaban and LMWHs are rare. So, the conclusions in this study still needed be further confirmed. Second, the number of RCTs for different DOACs are somewhat small, which is only one or two RCTs in meta-analysis. Multi-center RCTs with large sample size are needed to further investigate the efficacy and safety of specific DOAC. Third, the subgroups of different kinds of cancers were not analyzed, which may influence the efficacy and safety of DOACs(31). Future studies should focus on the effects of different DOACs on specific cancers so as to help clinicians better determine the treatment strategy for VTE in patients with different cancers.