We focused on ALDH1A1, ALDH2 and ALDH3A1 expression among the various isoforms because ALDH1A1 and ALDH3A1 have been shown to be markers of resistance to cyclophosphamide in breast and lung cancer cells [26, 27, 30] and because ALDH2 is a major detoxifying enzyme for reactive aldehydes [15]. The gene discussed is ALDH2; the disease is lung cancer.