ALDH is broadly used as a functional marker in various tumor types. ALDH is a family of detoxifying enzymes responsible for the oxidation of intracellular aldehydes whose activity was initially found to be increased in hematopoietic and neural stem and progenitor cells. Increased ALDH activity in CSCs was first reported by Ginestier et al., which showed that ALDH+ breast cancer cells had increased tumor-initiating ability in immunocompromised mice compared to ALDH− cells. ALDH activity can be detected in live cells through an enzymatic assay (Aldefluor) that was first developed by Jones and colleagues to isolate viable hematopoietic stem cells.
