This is the first retrospective cohort study to assess the efficacy and safety of different anticoagulation therapy in Chinese patients with lung cancer-associated VTE by using PSM analysis. Patients treated with rivaroxaban had the decreased risks of composite outcome, VTE recurrence, and major bleeding, and an increased risk of CRNMB without significant differences compared to LMWH users. However, LMWH group had a significantly higher risk of 12-month all-cause mortality compared to rivaroxaban group. The efficacy and safety outcomes after IPTW analysis or competing risk analysis were consistent with primary analysis of PSM-matched population. In subgroup analysis, the primary and secondary outcomes favored rivaroxaban over LMWH in all the subgroups expect for PE location and risk stratification.
For the primary outcomes, rivaroxaban group was 27% less likely to suffer from the composite event of VTE recurrence or major bleeding compared to LMWH group. Unexpectedly, the mortality was significantly higher in LMWH group compared to rivaroxaban group. The trend of all-cause mortality in the present study was similar to an Asian-based retrospective study and two prospective trials, but the other trials with cancer-associated VTE did not show distinct comparisons among vitamin K antagonist, LMWH and DOACs[30–34]. Indeed, LMWH group had high proportion of central PE, intermediate-risk PE, CCI score ≥ 3, and receiving palliative oncotherapy during the study period, which suggested that the more advanced cancer stage and heavier thrombotic burden might contributed to the increased risks of VTE recurrence and mortality. Death mostly occurred in patients with those clinical characteristics who were inclined to be administered to LMWH group, while patients with better prognosis were more likely to be treated with rivaroxaban, increasing the likelihood of lower mortality rate for the cohort.
The efficacy outcome of our study was comparable to those previously reported. SELECT-D trials showed less VTE recurrence with rivaroxaban versus dalteparin (4% vs 11%; HR, 0.43; 95% CI, 0.19–0.99), with a similar trend toward a reduced risk in rivaroxaban group of our study (8.4% vs 10.5%; HR, 0.69; 95% CI, 0.36–1.34)[14]. Hokusai and Caravaggio also reported similar results, with a reduction of VTE recurrence in DOACs group (edoxaban vs dalteparin: HR, 0.71; 95% CI, 0.48–1.06; apixaban vs dalteparin: HR, 0.63; 95% CI, 0.37–1.07)[17, 18]. In a 2022 network meta-analysis, rivaroxaban was also associated with noted numerically lower rate of VTE recurrence (OR, 0.41; 95% CI, 0.16–0.95) and higher rate of CRNMB (OR, 4.09; 95% CI, 1.79–10.59) compared with dalteparin, which also accorded with the findings summarized by Overvad et al[34, 35].
For the safety outcomes, there was no significant difference between DOAC and LMWH in the incidence of major bleeding in our study, which was in accordance with SELECT-D and Caravaggio trials but in contrast to Hokusai trials favoring LMWH (edoxaban vs dalteparin: HR 1.77, 95% CI 1.03–3.04, P = 0.04). SELECT-D trials indicated a significantly increased risk of CRNMB in rivaroxaban (HR, 3.76; 95% CI, 1.63–8.69), which corresponded to our study with a rising tendency of CRNMB in rivaroxaban group with no significant difference (HR, 1.13; 95% CI, 0.62–2.09). It was reported that rivaroxaban was ranked the least safe drug in CRNMB compared with dalteparin (OR, 4.09; 95% CI, 1.79–10.59) and other DOACs (rivaroxaban vs apixaban: OR, 2.73; 95% CI, 1.08–7.71; rivaroxaban vs edoxaban: OR, 2.99; 95% CI, 1.21–8.26)[34]. It reflected a special hemorrhagic vulnerability of cancer tissue to rivaroxaban rather than the specific predilection for specific cancer. Our clinical findings were also consistent with the effect estimates derived from a meta-analysis including more than 35,000 patients in observational studies and more than 2,000 patients in clinical trials[36].
Three additional aspects of our results warranted comment. First, these results consistently demonstrated that rivaroxaban had the improved efficacy, noninferior safety of major bleeding and increased risk of CRNMB compared to LMWH. The enhanced antithrombotic effect of rivaroxaban was associated with its high peak serum anti-Xa activity and a greater perturbation of coagulation through high-selectively inhibiting prothrombinase activity and factor Xa without any cofactors, whereas LMWH only inhibited the antithrombin of activated factor X[37]. Rivaroxaban was ranked the least safe in CRNMB due to its local and systemic effect on gastrointestinal bleeding, as well as its high peak-to-trough ratio with a less favorable safety effect[38]. Other potential reasons for more CRNMB included lower mortality, greater length of time in therapeutic range, more complications with high bleeding risks and more drug interactions that altered the serum level and bioavailability of rivaroxaban. CRNMB might increase the propensity for major bleeding and lead to anticoagulation interruptions which increased VTE recurrence. It suggested further research to reduce CRNMB through risk stratification, refinement of the anticoagulant regimens, and minimizing drug interactions by reviewing concomitant medications. Second, the mortality in rivaroxaban group was significantly lower than LMWH group in the present study and rivaroxaban group in SELECT-D trials. Our study focused on Chinese lung cancer patients, and the mortality rate was comparable to an Asian-based retrospective study[31]. The lower mortality of rivaroxaban compared with other trials might be due to ethnic differences, specific cancer types and risk stratification of PE between populations. Khorana et al reported rivaroxaban had a better overall survival than LMWH without decreased VTE recurrence or major bleeding rates[39]. However, LMWH group in our study was more closely associated with high risk factors of VTE, and patients with more aggressive or extensive cancer were inclined to be administrated to LMWH group due to selection bias by prescribers. It was reported that poorer performance status and higher bleeding risks were associated with higher all-cause mortality, and those residual variables were worthy of investigation[40]. Third, the benefit of rivaroxaban in the efficacy and safety was consistent in all the subgroups except for central PE and intermediate-risk PE. The observed inferior efficacy of rivaroxaban in specific subgroups might be associated with the heavier thrombotic burden, worse performance status and more complications such as cardiovascular diseases. Therefore, it was essential to find who might profit from rivaroxaban in terms of race, clinical characteristics of cancer and PE, relevant drug interactions, and concomitant cancer treatment. These results provided additional arguments for the benefits and risks from broader use of DOACs in lung cancer patients with PE.
Since there were no head-to-head comparative trials between rivaroxaban and LMWH in lung cancer with PE, our study was the first retrospective analysis on the anticoagulation therapy selection for Chinese patients with lung cancer-associated PE. To control confounding bias, we performed PSM to balance baseline differences and stabilized IPTW for sensitivity analysis. The outcomes after stabilized IPTW or adjusting for competing risks remained consistent with PSM analysis, proving the stability of these results among the unmatched, PSM-matched and IPTW-weighted population. Due to indefinite anticoagulation for cancer-associated VTE, the follow-up period of our study (12 months) was longer than that of most trials (3–6 months) leaving uncertainty about the anticoagulant effect beyond this period. Furthermore, we did not exclude the patients with high bleeding risks or poor performance status, making results more accordant to routine clinical practice. Treatment with rivaroxaban yielded superiority of the efficacy and safety over LMWH expect for the subgroups of central PE and intermediate-risk PE, which endorsed caution with use of rivaroxaban in special types of PE patients. Our finding also indicated rivaroxaban could be a more convenient alternative to LMWH as the initial treatment without prior 3–6 months use of LMWH. Considering that cancer patients with VTE was heterogenous and complex, our study focused on lung cancer-specific PE in Chinese patients, and important future directions must include cancer-specific anticoagulation selection for the initial treatment and long-term management.
Our study had some limitations. As a single center retrospective cohort study, our findings focused on Chinese lung cancer patients with nonhigh-risk PE receiving rivaroxaban or LMWH with an absence of generalization. Information on prescribed drugs from database was likely to overestimate patients’ compliance, and the anticoagulant effect was directly influenced by the normalization of treatment, patients’ preference and medication selection bias. Finally, residual confounding variables on clinical characteristics and laboratory values which could not be observed in our study, such as PD-L1 expression, gene mutations, performance status and cancer progression, influenced the survival outcome of mortality and needed further exploration.