RB-312 and respective controls were tested in vitro against HER2+ FaDu oropharyngeal cancer cells or triple-negative breast cancer cells MDA-MB-231, both of which were engineered to constitutively express programmed cell death ligand-1 (PD-L1) to stabilize the cancer cell-dependent dynamics of PD-1/PD-L1 interactions (named FaDu and MDA-MB-231 hereafter). This evidence concerns the gene PDCD1 and triple-negative breast carcinoma.