CD274 and breast carcinoma: By using an elegant genetically engineered mouse model, Ruhland et al. reported that stromal senescence creates an immunosuppressive microenvironment to promote tumour formation.25 In the clinical setting, PD-L1 is detected in the epithelium or stroma in 30–60% of breast cancer and is a predictor of pathological complete response to neoadjuvant chemotherapy and immunotherapy.26,27 How PD-L1 is upregulated in the stroma of breast tumour is unclear.