Lp-PLA2 activity does not significantly modify dual antiplatelet therapy efficacy in minor stroke/TIA with CYP2C19 loss-of-function alleles

This study presents a prespecified subgroup analysis from the CHANCE-2 randomized controlled trial, investigating whether lipoprotein-associated phospholipase A2 (Lp-PLA2) activity modifies the efficacy of dual antiplatelet therapy in a specific high-risk population. The analysis included 5919 patients from the original CHANCE-2 trial (n=6412) who had experienced a minor ischemic stroke or high-risk transient ischemic attack (TIA) and carried CYP2C19 loss-of-function alleles. The study setting was not reported, but the parent CHANCE-2 trial was conducted in China. All patients received guideline-recommended background therapy, including aspirin, with the intervention determined by their randomized assignment in the parent trial.

The intervention was ticagrelor (90 mg twice daily) plus aspirin (75-100 mg once daily on days 1-21, then aspirin alone), compared to clopidogrel (75 mg once daily after a 300 mg loading dose on day 1) plus aspirin (75-100 mg once daily on days 1-21, then aspirin alone). The dual antiplatelet therapy was administered for 21 days, followed by monotherapy with the assigned P2Y12 inhibitor (ticagrelor or clopidogrel) through 90 days. Patients were stratified based on their baseline Lp-PLA2 activity level, using a prespecified cutoff of 188.4 nmol/min per mL to define low (≤188.4) and high (>188.4) activity groups.

The primary outcome was stroke recurrence within 90 days. In patients with low Lp-PLA2 activity, the stroke recurrence rate was 5.4% in the ticagrelor-aspirin group versus 7.4% in the clopidogrel-aspirin group, yielding an adjusted hazard ratio of 0.72 (95% CI, 0.54-0.97). In patients with high Lp-PLA2 activity, the stroke recurrence rate was 6.9% with ticagrelor-aspirin versus 8.2% with clopidogrel-aspirin, with an adjusted hazard ratio of 0.84 (95% CI, 0.65-1.09). The formal test for interaction between Lp-PLA2 activity level and treatment effect was not statistically significant (p=0.45), indicating that Lp-PLA2 activity did not significantly modify the treatment effect.

No specific secondary outcomes were reported for this subgroup analysis. The parent CHANCE-2 trial's primary outcome was stroke recurrence at 90 days, which showed superiority of ticagrelor-aspirin over clopidogrel-aspirin in the overall population of patients with CYP2C19 loss-of-function alleles.

Detailed safety and tolerability findings specific to this Lp-PLA2 subgroup analysis were not reported. The parent CHANCE-2 trial reported that severe or moderate bleeding events occurred in 0.3% of patients in the ticagrelor-aspirin group versus 0.2% in the clopidogrel-aspirin group, a non-significant difference. Rates of adverse events leading to drug discontinuation and other tolerability metrics were not provided for this specific analysis.

These results should be interpreted in the context of prior landmark studies. The CHANCE-2 trial itself established ticagrelor-aspirin as superior to clopidogrel-aspirin for preventing stroke recurrence in minor stroke/TIA patients with CYP2C19 loss-of-function alleles. The POINT trial demonstrated the benefit of clopidogrel-aspirin over aspirin alone in a broader TIA/minor stroke population. This analysis sought to identify a biomarker (Lp-PLA2 activity) that might further refine treatment selection within the genetically defined CHANCE-2 population, but found no significant effect modification.

Key methodological limitations include its nature as a subgroup analysis of an RCT, which is inherently exploratory and hypothesis-generating rather than confirmatory. The interaction p-value of 0.45 indicates no statistically significant modification of treatment effect by Lp-PLA2 activity. The analysis may be underpowered to detect a true interaction effect. The generalizability is limited to patients with CYP2C19 loss-of-function alleles, predominantly of Chinese ethnicity from the CHANCE-2 trial. The cutoff for Lp-PLA2 activity (188.4 nmol/min per mL) was prespecified but may not represent the optimal threshold for clinical decision-making.

The clinical implications are straightforward: Lp-PLA2 activity should not be used to guide the choice between ticagrelor-aspirin and clopidogrel-aspirin dual antiplatelet therapy in patients with minor stroke/TIA who carry CYP2C19 loss-of-function alleles. The decision to use ticagrelor-aspirin in this population should continue to be based on the overall results of the CHANCE-2 trial, considering bleeding risk and cost, not on Lp-PLA2 activity levels. These findings do not support adding Lp-PLA2 testing to the current workup for antiplatelet selection in this patient subgroup.

Several important questions remain unanswered. Would Lp-PLA2 activity modify treatment effect in patients without CYP2C19 loss-of-function alleles? Is there a different threshold or continuous relationship between Lp-PLA2 activity and treatment response? Does Lp-PLA2 activity predict bleeding risk with either regimen? How do these findings apply to non-Chinese populations? What is the mechanistic relationship, if any, between Lp-PLA2 activity and the pharmacodynamics of P2Y12 inhibitors? Prospective studies specifically designed to test Lp-PLA2 as a treatment effect modifier are needed to provide definitive answers.