PTPA and neoplasm: Coexpression of the SV40 large T antigen, telomerase catalytic subunit, and mutant HRAS in epithelial cells requires an additional step involving the inhibition of at least one PP2A subunit such as Cα, Aα, Aβ, or one of the tumor suppressive B subunits to result in complete transformation, as characterized by the ability to grow in an anchorage-independent manner in vitro and to form tumors in immunocompromised mice (18–20).