USP4 and neoplasm: The occurrence of tumour metastasis consists of a series of critical steps, among which the epithelial‐mesenchymal transition (EMT) is of great importance in enhancing tumour cell metastatic ability, and is generally characterized by the up‐regulation of N‐cadherin expression and meanwhile down‐regulation of E‐cadherin expression.25 Therefore, we turned to see whether USP4 exerted its impact on melanoma metastasis via EMT.