Furthermore, several other exosome membrane proteins, such as the transmembrane protein platelet-derived growth factor receptor (PDGFR), the tetraspanin superfamily members, CD63, CD9, and CD81 (with their two extracellular loops), and lactadherin (with its C1C2 domain) can also be engineered to confer cancer cell targeting specificity [155, 156]. This evidence concerns the gene MFGE8 and cancer.