USP4 and breast cancer: The therapeutic effects of DUB inhibitors such as USP1, USP4, USP7, USP14 and USP33 have been confirmed in prostate cancer, lung cancer, breast cancer and hematological malignancies (Ma et al., 2019; Xia et al., 2019a; Guo et al., 2020; Gutierrez-Diaz et al., 2020; Lai et al., 2020).