CDKN1A and cancer: Although p21, the protein encoded by CDKN1A, acts downstream of p53, we found one cancer (#1992) from our full set of 50 tumours to have both CDKN1A (p.Tyr77del) and TP53 (p.Arg213Pro) mutations (details not shown) and another (#745) to have CDKN1A mutation (p.Trp65Arg) and low-level MDM2 amplification (Supplementary Table 4).