PCNA and cancer: USP7 has many reported substrates (≥ 20), and one possibility mechanism of USP7 plays a key role in affecting cancer progression is that USP7 function as a binding protein to regulate the expression and stabilities of genes (N-Myc, PTEN, PCNA, FOXO4, p53 and so on) associated with tumorigenesis and proliferation (Zhou et al. 2018; Yeasmin Khusbu et al. 2018; Schauer et al. 2020).