BCL2 and cancer: Tumour-specific IS were found more often than expected in exons (Supplementary Fig. 5), although these were mainly non-coding exons (Supplementary Table 5), including the 5′ UTRs of cancer-related genes BCL2, IL6R, KRT13 and TRAF4. To investigate possible retroviral-mediated dysregulation of host genes, we selected the gene closest to each IS as a way to generate an unbiased gene set.