CD44 and cancer: In this study, we sorted EpCAM+/CD44+/CD166+ (CSC-enriched) and EpCAM+/CD44neg/CD166neg (CSC-depleted) cancer cells from a patient-derived xenograft (PDX) line representative of a moderately differentiated human CRC, following in vivo treatment with either a placebo (saline solution) or irinotecan (CPT-11), an anti-tumor agent that stands at the backbone of systemic chemotherapy for metastatic CRCs [16, 17] and that is known to display only limited activity against human colon CSCs [12].