ALDH2 and breast cancer: The expression and activity of formaldehyde generating enzymes, such as lysine-specific demethylase 1 (LSD1) [25], [26], semicarbazide-sensitive amine oxidase (SSAO) [27], [28] and cytochrome P-450 [29], [30], formaldehyde degrading enzymes, such as aldehyde dehydrogenase 2 (ALDH2) and class III alcohol dehydrogenase (ADH3) [31], [32], are considered to have critical roles in the pathogenesis of breast cancer.