Whereas endothelial selectin and cancer cell surface-expressed CD44 mediate CTC attachment, Rac1 and cell division control protein 42 (CDC42) promote transendothelial migration via extension of cancer cell protrusions facilitating the whole process of extravasation, for example, invadopodia which expand through the endothelial barrier [118, 124, 125]. The gene discussed is CDC42; the disease is cancer.