STAT1 and triple-negative breast carcinoma: Here, using siRNAs and the S283A-PD-L1 variant, we demonstrate that the cell-autonomous pro-metastatic functions of PD-L1—tumor cell proliferation and invasion, and release of the pro-metastatic chemokine CXCL8—required the activation of STAT3 and STAT1 in luminal A and triple-negative breast cancer cells.