In previous studies, our group identified key molecules essential for the survival of BC cells by CRISPR‐Cas9 screening with lentiviral library targeting factors involved in transcriptional and epigenetic regulation.[3, 12] Among the candidate essential genes identified, SETD8 drew our attention due to its critical role in multiple biological processes and remains uncharacterized in bladder cancer (BC) (Figure S1a, Supporting Information).[13] Consistently, gene effect scores of SETD8 in BC cell lines are all negative (Figure S1b, Supporting Information). This evidence concerns the gene KMT5A and breast cancer.