CD9 and cancer: Stabilization of EVs on epoxy beads or microplate wells by means of VHH-dependent immunocapture leads to increased stability of the material and consequently less material needs to be used for screening procedures The lack of ability to select VHHs that specifically recognize cancer-derived EVs might stem from the lack of truly tumor-exclusive surface antigens or by their limited expression with respect to common tetraspanins such as CD9, CD63, and CD81, which are present on both normal and malignant cells, making selective targeting difficult [53].