CDKN1A and neoplasm: Additionally, to further improve the safety profile and achieve a more controllable expression, the promoter driving the expression of IL-12 was switched from a constitutive one to the tumor-specific and genotoxic stress-inducible promoter of the cyclin-dependent kinase inhibitor 1 (CDKN1a) gene, more commonly known as p21 [14,15,16,17,18,19].