PD-L1 copy number loss is associated with lower survival in women with advanced breast cancer in Indonesian cohort

Background The prognostic value of PD-L1 copy number variation (CNV) in advanced breast cancer (BC) patients remains unclear. This study investigated the association between PD-L1 CNV and its prognostic significance in advanced BC.Methods PD-L1 CNV was analyzed using real-time PCR in advanced BC patients (n = 132) who received chemotherapy or hormonal therapy, along with a non-malignant control group (n = 5) obtained from patients with histopathologically confirmed fibroadenoma used as reference controls. The association of PD-L1 CNV with overall survival and clinicopathological features was determined.Results PD-L1 CNVs were identified in 22% (29/132) of advanced BC cases, comprising 9 CN losses and 20 CN gains. PDL-1 CN loss was associated with low overall survival (OS) (HR = 2.61; 95% CI = 1.10-6.21; p = 0.024) and remained significant after multivariate adjustment (HR = 3.13; 95% CI = 1.23-7.94; p = 0.016). The adverse prognostic effect was pronounced in HR-positive (p = 0.004) and HER2-negative patients (p = 0.040). PD-L1 CNVs were more frequent in patients > 40 years (p = 0.027) and HER2-negative tumors (p = 0.019).Conclusions PD-L1 CN loss was associated with lower OS, particularly in HR(+) and HER2(-) patients. This result revealed the prognostic value of PD-L1 CNV in Indonesian advanced BC who received primary systemic therapy.