Our study investigating the origin of agressive bladder cancer (Shin, Beachy NCB 2014) was highlighted in Nature Review Cancer. In original study, using lineage tracing techniques, we have tracked the development of invasive bladder cancer in mice and show that basal stem cells, which express sonic hedgehog (Shh), initiate this disease, but the expression of Shh is lost as the disease progresses. These findings indicate a model in which Shh-expressing basal stem cells are essential for the development of CIS lesions that can progress to invasive carcinoma. Why Shh expression is lost at the stage of invasive growth is not yet clear. These findings also indicate that surgery for invasive bladder cancer might not remove all of the cells with the capacity to generate invasive bladder cancer and might explain the frequent recurrence of disease in these patients and the associated high morbidity.