It was further demonstrated that the cytoplasmic localization enabled P21 to inhibit apoptosis through protein–protein interactions with pro-apoptotic proteins, which again highlights that P21 may function as both an oncogene (or in this case contributes to the resistance phenotype) and a tumor suppressor which is most likely determined by many factors including subcellular localization [39,263,273,274]. This evidence concerns the gene CDKN1A and neoplasm.