# A high eosinophil proportion increases the risk of skin-related adverse events induced by apalutamide in patients with prostate cancer

## TL;DR

High eosinophil levels predict skin side effects in prostate cancer patients taking apalutamide, especially in Japanese patients.

## Contribution

Identifies baseline eosinophil proportion as a novel predictive biomarker for apalutamide-induced skin adverse events.

## Key findings

- Baseline eosinophil proportion was significantly higher in patients with skin AEs.
- An eosinophil proportion ≥1.8% was an independent predictor of skin-related AEs.
- The AUC of 0.768 indicates moderate predictive accuracy of the eosinophil cut-off.

## Abstract

Skin-related adverse events (AEs) induced by apalutamide occur frequently in Japanese patients with prostate cancer. However, biomarkers for predicting these skin-related AEs have not yet been identified. Therefore, this study investigated whether the proportion of eosinophils could serve as a predictive biomarker for skin-related AEs in Japanese patients with prostate cancer treated with apalutamide.

A total of 109 patients were enrolled in this study. Among them, 79 patients with prostate cancer who received apalutamide were categorized into two groups: the skin AE group (n = 45) and the non-skin AE group (n = 34), based on whether they experienced skin-related AEs of any grade. The eosinophil proportions in baseline samples collected before treatment were then analyzed.

The baseline eosinophil proportion was significantly higher in the skin AE group compared with the non-skin AE group (P < 0.05). The optimal cut-off value of the eosinophil proportion for predicting skin-related AEs of any grade was 1.8% (area under the receiver operating characteristic curve [AUC] = 0.768). In multivariate analysis, an eosinophil proportion ≥1.8% was identified as an independent factor associated with skin-related AEs of any grade (odds ratio, 13.3; 95% confidence interval, 3.82–46.4; P < 0.05).

The baseline eosinophil proportion may serve as a predictive biomarker for skin-related AEs of any grade in Japanese patients with prostate cancer treated with apalutamide.