This finding is probably due to a strong association of stage and MYCN amplification (43% of patients with stage 4 harboured MYCN amplification in their tumours versus only 22% of patients with earlier stages; p = 0.001 by Fisher's exact test) and a strong association between stage and age <18 months (25% of patients with stage 4 were under 18 months versus 72% of patients with earlier stages; p = 0.006 by Fisher's exact test). The gene discussed is MYCN; the disease is neoplasm.