Collectively, these studies using K5.Cre  ×  Stat3flox/flox mice indicated that Stat3 is required for survival of keratinocytes that have accumulated DNA damage during initiation with DMBA and that initiated keratinocytes harboring Ha-ras mutations require Stat3 for proliferation and clonal expansion during tumor promotion with TPA. This evidence concerns the gene STAT3 and neoplasm.