PTGS2 and lip and oral cavity carcinoma: Three single-nucleotide polymorphisms (SNPs) in the COX-2 gene, −1195 G > A (reference SNP ID, rs689466), +837 T > C (rs5275), and −765 G > C (rs20417) have received considerable attention for their close links to oral cancers, compared to the other SNPs of COX-2 gene [16].