CD9 and cancer: In astrocytes, genes related to the tetraspanin-enriched microdomain, Tspan9 and Pdpn (cancer-related gene directly interacting with tetraspanin CD9 [32]), had significantly higher expression levels in male cells; hyaluronic acid binding-related genes also showed significant sex-biased expression, including Bcan which was more expressed in males and Ncan which was more expressed in females.