Hypoxic tumour signature is usually monitored by the levels of hypoxia-inducible factor 1α or 2α (HIF-1α or HIF-2α) or by the expression of their target genes (for example, carbonic anhydrase IX (CA9)).15 While the correlation between a hypoxic signature and poor clinical prognosis is accepted for several tumours, including NB,6, 16, 17 the duration and levels of hypoxia responsible for this association remain unknown. The gene discussed is CA9; the disease is neoplasm.