Several studies have found that the expression of IL–9 was higher in peripheral blood of patients with LSCC and small cell lung cancer than that of normal controls, and the expression levels of IL–9 in patients with stages III and IV were higher than those in patients with stages I and II, suggesting that IL–9 expression may correlate with tumour stages [55,56]. The gene discussed is IL9; the disease is small cell lung carcinoma.