ARNT and neoplasm: Hypoxia is a common feature of solid tumors and tumor cells often adapt to this stressful condition by activating hypoxia‐inducible factor 1 (HIF‐1) (Semenza, 2001), a heterodimeric transcription factor composed of HIF‐1α, an oxygen sensitive subunit, and HIF‐1β, a constitutively expressed subunit (Wang et al., 1995).