To further validate the potential role of these four RPs in ESCC metastasis, we measured their expression levels in two highly metastatic esophageal cancer cell lines, 30-D-4 and K450LM2 cells.26–28 Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) results showed that RPS15 significantly upregulated in metastatic cells compared with that in the parental cells (Fig. 1e). Here, RPS15 is linked to esophageal squamous cell carcinoma.