However, a beneficial effect of the MTHFR TT genotype on the risk of lung cancer was observed in those with heavy smokers; Suzuki et al. [15] in Japan found that MTHFR 677T alleles were associated with reduced risk of squamous/small cell carcinomas, especially among heavy smokers with the MTHFR 677T allele. Here, MTHFR is linked to lung cancer.