CASS4 and cancer: Roles in cancer and tumor metastasis are well established for the two paralogous scaffolding proteins NEDD9 (neural precursor cell expressed, developmentally down-regulated 9; also known as HEF1 or Cas-L) and CASS4 (Cas scaffolding protein family member 4; also known as HEPL), and for their interacting partner, the kinase PTK2B (protein tyrosine kinase type 2 beta; also known as PYK2, Cak2β, or RAFTK) [1-4].