ALDH1A1 and colorectal cancer: While ALDH1 has been used as a CSC marker in several types of solid neoplasms, including breast, lung, prostate, brain, liver, gastric, colorectal cancer and PDAC [40,51,52,53,54,55,56,57], ALDH1 has been shown to mediate cyclophosphamide- as well as gemcitabine-resistance in PDAC [58].