CD9 and cancer: When cancer cells from primary and metastatic tumors were compared, seven DEGs were identified: small EDRK-rich factor 2 (SERF2), calmodulin-like protein 5 (CALML5), fatty acid binding protein 7 (FABP7), homeodomain-only protein (HOPX), androgen receptor (AR), CD9, and phospholipase A2 group IIA (PLA2G2A) (Figures 4D,E).