ALDH1A1 and gastric cancer: Aldehyde dehydrogenase 1 (ALDH1) has been used as a marker for cancer-initiating cells (CICs), and ALDH1 positive cells have been detected in diffuse GC in recent years; this is because ALDH1 positive cells show strong tumorigenicity, self-renewal and the ability to generate tumor hierarchy and heterogeneity in vivo.