ecently SF2/ASF was shown to be a proto-oncogene [19]. It is expressed at high levels in a number of cancers including breast, prostate and cervical cancers [19–21] and is up-regulated in breast cancer through amplification of its gene, SFRS1, which is found on chromosome 17q23 [19]. Evidence for its oncogenic function came from studies in which overexpression in NIH 3T3 cells caused colony formation in soft agar, whereas overexpression of other splicing factors, such as SC35, did not yield colony formation to the same extent.