CDKN1A and leiomyosarcoma: Others have suggested that loss of myocardin function may account for the differentiation defects of human leiomyosarcoma cells during malignant transformation30: downregulation of myocardin resulted in lower expression of cyclin-dependent kinase inhibitor 1 A (CDKN1A; also known as p21), a mediator of cell cycle G1 phase arrest, which facilitated cell cycle progression.