 When p53 build-up triggers cell cycle arrest the levels of downstream proteins p21 and WAF1 are increased which prevents cyclinB/CDK1 complex activation and therefore progression through the cell cycle.It has also been observed that decreasing cyclin B levels in cells increases the levels of functional p53.Therefore, siRNAs for cyclin B may be an effective treatment against cancers where p53 function is inhibited but the gene has not been deleted.