CD44 and cancer: In PC, previous work has demonstrated that CD44, CD24, and ESA-expressing PCSCs, represented only by a small percentage of the cancer cell population (∼1%), were associated with high tumorigenic potential, and it is likely that PCSCs at least partially mediate chemoradiotherapy-induced drug resistance, as evident in PCSC enrichment in response to chemoradiotherapy treatment (Du et al., 2011).