We first demonstrated the analytical validity and feasibility of RNAscope® for the assessment of PD-L1 mRNA expression in BC FFPE tissue, also in line with the current literature in breast [24,25,26,27] (Table S2) and other cancer types [28,29,30,31], as well as the combined detection of the protein, thus enabling the simultaneous visualization of gene and protein levels in situ. Here, CD274 is linked to breast cancer.