All exosomes isolated from the four types of PCa cells expressed CD9 and Alix, although the exosomes showed clear differences in the enrichment of the proteins; furthermore, the exosomes from MDA PCa 2b, PC3, and LNCap AI+F cells were positive for Annexin V, whereas C4‐2 exosomes were negative for this marker. Here, CD9 is linked to posterior cortical atrophy.