Exon 3b encodes 19 amino acids that are inserted in‐frame immediately after the Switch‐II domain of RAC1, leading to a conformational change that favors the active GTP‐bound state.[23]RAC1B has been found to be specifically overexpressed in several cancer types, including lung cancer,[21] indicating that RAC1B may have distinct functions compared with RAC1A. This evidence concerns the gene RAC1 and cancer.