USP21 and lung cancer: A study in lung cancer revealed that USP21 was upregulated in non-small cell lung cancer and promoted cell proliferation, migration, and invasion by stabilizing Yin Ynag-1 (YY1), a well-known oncogene, which further increased USP21 expression level via the positive feedback regulation of YY1/SNHG16/miR-4500 axis [23].