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. This evidence concerns the gene ALDH1A1 and lung cancer.