CD9 and ovarian cancer: Diameters of the collected EVs by nanoparticle tracking analysis indicated that the average sizes between normal ovarian cell-derived EVs and ovarian cancer cell-derived EVs were similar (60–100 nm) (Fig. 1c).Besides, both cell supernatants-derived EVs expressed the classical EV markers, including CD9, CD81and CD63 (Additional file 1: Fig. S1a).