Recent studies have demonstrated that CTU2 is significantly overexpressed in breast cancer (16), drug-resistant melanoma (22), and activated T cells (53), where it drives mcm5s2U-modified tRNAs to decode U34 codons, selectively upregulating the translation efficiency of metastasis-related LEF1, glycolysis-related HIF1α, and stress-responsive transcription factor Atf4, all of which feature gene coding regions rich in U34 codons. This evidence concerns the gene ATF4 and breast cancer.