This idea first occurred to us when we realized that, upon inhibiting expression of the small GTPase Rab27a in a murine tumour cell line [19], we observed a decreased secretion of some exosome-associated proteins, such as the tetraspanin CD63, TSG101, HSC70 (gene name: Hspa8), as described in a human HeLa cell line [20]), but not of others, which were so far considered also as ‘exosome-markers’, such as another tetraspanin, CD9, or the phosphatidylserine-binding protein Milk Fat Globule-EGF-Factor VIII (MFGE8). Here, RAB27A is linked to neoplasm.