SLIT2 and pneumothorax: As there were no normal lung specimens available for detecting the Slit2-exon15 splicing variants and both the normal lung bronchial epithelial Beas2B cells and 40% of the pneumothorax specimens expressed a higher level of Slit2-ΔE15 than Slit2-WT, we investigated whether lung metastasis affects the Slit2 isoform expression in Balb/c nude mice injected with CL1-5 human lung cancer cells into the tail vein.