PB0987 - Performance of the CHAP Score in Patients with Cancer on Primary Thromboprophylaxis

Background: Despite demonstrated efficacy, there is limited uptake of primary thromboprophylaxis in patients with cancer at high risk of VTE. This apprehension is, in part, due to concerns about bleeding risk.

Aims: We aimed to determine the predictive performance of the CHAP score for anticoagulant-related bleeding in cancer patients randomized to thromboprophylaxis during participation in the AVERT randomized trial.

Methods: We used the 288 patients in the modified intent-to-treat analysis in the AVERT randomized to apixaban. The primary outcome of interest was development of a MB or clinically relevant non-major bleed (CRNMB). The CHAP score was applied to the cohort with clinical point assignments as in the original paper [chap=0.032*exp(0.0017*iserum - 0.0127*q3val + 0.0251*iage + 0.8995*useantiplat)].

Using a Fine and Gray competing risk model, we tested the association between the CHAP score and development of first bleed following anticoagulant prescription. The performance of each model was evaluated using time-dependent ROC (model discrimination) and Brier score (model calibration/discrimination).

Results: In patients receiving apixaban, there were 10 MBs and 18 CRNMBs when censoring patients at the time of first bleed. Of the 18 CRNMB events, 6 required a medical intervention. For each point increase in CHAP score, there was an 88% (sHR 1.88, p = 0.047) increase in risk of MB+CRNMB. When limiting analysis to MB+CRNMB that required medical intervention, results remained consistent (sHR 2.74, p = 0.01). Discrimination of the score at 183 days was 0.60 and calibration. Results of calibration slope 1.47 (p=0.35).

Conclusion(s): While an increasing CHAP score is associated with risk of anticoagulant-related bleeding in this cohort, discrimination of the model was moderate. Of our work to date, the modified RIETE score remains the score with the highest discrimination in this population. Work is underway to improve discrimination by modifying the score.