Therefore, the mRNA levels of cancer- and stem cell-related transcription factors (Oct4, Sox2 and Nanog), angiogenesis (VEGF 188), inflammation (COX–2), and keratinocyte differentiation (Keratin 10)-related factors were analyzed in biopsied skin at 9 weeks after irradiation, and HPRT1 was adopted as the most suitable reference gene for the normalization of mRNA levels in radiation-exposed canine dermal tissues [25]. Here, PTGS2 is linked to cancer.