ALDH1A1 and breast cancer: ALDH1A1, a marker of tumour stem cells in breast, prostate, colon, and lung cancers, is a cytoplasmic enzyme that is upregulated in tumour cells; ALDH1A1 is associated with poor prognosis of many tumours (breast cancer, melanoma, etc.)and has an important role in promoting tumour angiogenesis and metastasis and in acquiring resistance to anticancer drugs.146–148