KRAS and cancer: In a wide panel of human cancer cell lines, KRAS4B was on average significantly more expressed than KRAS4A, although different ratios were observed across tissues.43 Consequently, KRAS4B has been the most studied isoform, but KRAS4A transcriptional activity is also widespread in cancer.44 Both isoforms exhibit distinct subcellular trafficking and isoform-dependent effector specificity, which may explain their non-overlapping functions in cancer.45,46