PROS1 and posterior cortical atrophy: Extracellular CSC markers that have been implicated in PCa but are not always specific to this cancer type per se include CD117/c-kit, CD133, CD44, α2β1 integrin, α6 integrin, CXCR4, E-cadherin, EpCAM, Cytokeratin 5, PSA, ABCG2, Trop2, AR variant 7, and CD166/ALCAM (Stefano et al., 2018).