Although exosomes circulate in biological fluids, the CD44 they carry is the membrane-associated form rather than the proteolytically shed soluble CD44, as exosomal CD44 is transferred intact from the cancer cell membrane to recipient cells, similarly to what has been demonstrated in ovarian cancer where exosomal CD44 increases CD44 levels in mesothelial cells and promotes invasion [104]. Here, CD44 is linked to ovarian cancer.