Using the tumor DNAs from spontaneous tumor model mice such as BXH2, AKXD and SL/Kh, inverse PCR was performed,26, 42, 43 which involves digestion of the host cell DNA with a restriction enzyme such as SacII, which recognizes CpG islands near gene-coding regions, followed by a ligation reaction using T4-ligase.36 The development of inverse PCR-dependent cloning has allowed the identification of numerous integration sites that have in turn been used for the identification of novel oncogenes26 such as Stat5a,43Hipk2, Fiz144 and Zfp521,45 which are frequent integration loci. Here, STAT5A is linked to neoplasm.