MTHFR and leukemia: To date, folate and other major factors involved in one-carbon metabolism including vitamin B6, vitamin B12, homocysteine, and MTHFR (a major folate metabolic enzyme) have been associated with several cancer sites including colon, breast, pancreas, cervix, bronchus, and leukaemia [35]; the evidence of an association with colorectal cancer is most compelling in both animal and human studies [36].