While this feature has come to be regarded mainly as an unwanted complication for the use of retroviral vectors in gene therapy [3,4], it has long been a valuable asset in cancer research, as the integration sites of retroviruses in naturally occurring or experimentally induced cancers from birds, mice and cats have provided a rich harvest of cancer driver genes and families including Myc, Myb, Pim, Runx, Bmi1, Gfi1 and Notch [1]. The gene discussed is BMI1; the disease is cancer.