Alterations in the quaternary structure of PP2A also appears to have a crucial function in cells transformation and tumour development, as different B subunits have been found either aberrantly expressed in human cancers or displaced by the interaction of PR65/A with the SV40 small-t antigen, and by mutations of the PP2A A subunits (Janssens et al, 2005). This evidence concerns the gene PTPA and neoplasm.