Positive CTC selection markers have included prostate-specific membrane antigen (PSMA), chemokine receptors, CD133, VCAM-1, MCAM (CD146), ICAM-1, CEA, HER-2, N-cadherin (CDH2)/O-cadherin (CDH11), and MUC1.5–7 Some of these antigens target only a particular cancer (i.e., PSMA) or lack cancer-specificity (CD133, VCAM-1, ICAM-1) as hematopoietic/endothelial/benign cells also expressed these antigens,8–11 producing low CTC purity and confounding clinical interpretations of the data. Here, PROM1 is linked to cancer.