We noticed that absence of KLF5 in PCa cells did not significantly change their propagation in vitro but dramatically attenuated their tumor formation (Figs. 2a–d and 3e–h) by affecting both apoptosis and cell proliferation (Figs. 2g, h and 3i–k), which indicates that KLF5 is essential for tumor formation and is consistent with reported functions of KLF5 in stem cell maintenance and embryonic development49,76–78. The gene discussed is KLF5; the disease is neoplasm.