PKP4 and cancer: The lack of these cancer stem cell markers, specifically SEMA5A (semaphorin 5A), KITL (KIT ligand, stem cell factor), CAV2 (caveolin 2), EPS8 (epidermal growth factor receptor pathway substrate 8) and PKP4 (plakophilin 4), was associated with acquired resistance to radiation in this study (Fig. 3E).