USP21 and cancer: Notably, the results of this study showed that USP21 knockdown promoted anchorage-independent growth of cancer cells, including A549 and MDA-MB-231, which seemed to be inconsistent with several studies indicating the positive role of USP21 in cell proliferation, migration, and invasion of A549 and MDA-MB-231 (Urbe et al., 2012; Peng et al., 2016b; Arceci et al., 2019; Xu et al., 2020).