Since the Slit2-ΔE15 splicing form, but not Slit2-WT, is able to inhibit the growth of cancer cells, a higher ratio of Slit2-WT/Slit-ΔE15 expression in the tumor microenvironment is more favorable for the development of lung cancer than a lower ratio of Slit2-WT/Slit-ΔE15 expression. The gene discussed is SLIT2; the disease is neoplasm.