HIF1A and neoplasm: Double staining for HIF-1α and RNApII-S2P revealed that a significant number of HIF-1α+ RNApII-S2P-/low tumor cells existed in the rather broad area around large ischemic necroses (blue nuclei in Fig 5A), in striking contrast to a small number of SOX2+ HIF-1α+ RNApII-S2P-/low cells (purple nuclei in Fig 5B).