MDM4 and cancer: Following those known TP53 phenocopying genes, the gene USP28 was the 4th ranked gene (genes neighboring MDM2/MDM4/PPM1D excluded) in terms of overall statistical significance (p = 5.9e-07, combined across all six tests), and in particular scored highly on CRISPR codependency (pan-cancer score for USP28 = 0.54, compared with -0.72 for MDM2 and -0.53 for MDM4, breakdown by cancer type in Additional file 1: Fig. S4a).