TRAF6 and breast cancer: However, in breast cancer, USP4 was also recognized as a tumour suppressor for its up‐regulatory effect on programmed cell death 4 (PDCD4) to restrain tumour growth.20 Moreover, USP4 was able to target TRAF2 and TRAF6 for deubiquitination and thereafter inhibited TNFα‐induced cancer cell migration.34 In the present study, we proved that USP4 expression was drastically increased in melanoma.