SHMT1 and lung cancer: The associations between both well-known, functional polymorphisms: the MTHFR c.665C>T [11–23], MTHFR c.1286A>C [11, 14–20, 22, 23], MTR c.2756A>G (14–18), MTRR c.66A [14, 15, 17, 19], SHMT1 c.1420C>T [14, 24], TYMS 6bp ins/del polymorphism within the 3’UTR (untranslated region) [25], TYMS 5’UTR 2R/3R [15, 25] and other variants within the MTHFR [18, 26], TYMS [18], MTHFD1 [18], CBS [19], SLC19A1 [19], SHMT1 [24] and MTRR gene [26] and lung cancer risk have been evaluated.