PAK1 and esophageal squamous cell carcinoma: We found that inhibition of PAK1 by using shRNA and a small-molecule inhibitor (IPA-3) remarkably suppressed ESCC cell proliferation, colony formation, migration and invasion in vitro, and tumor growth and lung metastasis in vivo, at least in part, via down-regulating the Raf1/MEK1/ERK signaling pathway.