PTEN and neoplasm: As for TP, HIF-1α protein levels can be raised in tumours due to stimuli other than hypoxia: activation of oncogenes HER2 (Laughner et al, 2001), v-src (Jiang et al, 1997) and H-ras (Chen et al, 2001); loss of tumour suppressor gene function such as PTEN (Zundel et al, 2000) and signalling abnormalities such as MAPK (Richard et al, 1999).