CD274 and breast cancer: Among the mechanisms by which tumor cells can regulate PD-L1 expression are oncogenic alterations such as the PTEN/PI3K and the Ras–MAPK pathways, which have been shown to contribute to immune evasion in breast cancer.7, 8 MPBC are enriched for PIK3CA mutations when compared with TNBC,5 and the patient presented here also carries a PIK3CA mutation (H1047R), which may account for tumoral PD-L1 expression.