ATOH1 and cancer: Regardless of how the Ptc−/−; Kif20afl/− GNPs were produced, our results would indicate that the prolonged survival time in the tamoxifen-induced Atoh1-CreER; Ptcfl/fl; Kif20afl/fl mice (Fig. 3a) might be underestimated, due to the incomplete deletion of the Kif20a gene in some of the cancer-initialing progenitor cells.