KRAS and neoplasm: In our previous studies, we observed that KRAS tumour propagating cells (TPCs) were present in both Sca1+ and Sca1- compartments, and a purely squamous model generated by bialleleic inactivation of Lkb1 and Pten (Lkb1/Pten) harboured Sca1+ and NGFR+ TPCs37.