However, because Klf4, the remaining oncogenic factor, or insertional mutagenesis due to retroviral transduction itself might also cause tumor formation, it will be important to investigate the possibility of using recombinant proteins (and small molecules) to reduce the number of genetically transduced factors required for iPS cell induction, or even to entirely obviate the need for viral gene delivery. This evidence concerns the gene KLF4 and neoplasm.