PIWIL1 and central nervous system cancer: High PIWIL1 expression was associated with higher histological grade and advanced tumor stage in different types of tumors, such as esophageal cancer (He et al., 2009), glioma (Sun et al., 2011), breast cancer (Wang D.W. et al., 2014), and renal cell carcinoma (Stöhr et al., 2019), linking its expression to de-differentiation and the progression of the tumor phenotypes.