PTGS2 and rheumatoid arthritis: Studies have found that certain polymorphisms of the cyclooxygenase-2 gene promoter are associated with an increased risk of breast cancer and a decreased risk of RA.25 26 Also, polymorphisms in the DRB1 gene, the major genetic susceptibility locus for RA,27 have recently been linked to a decreased risk of breast cancer.28 However, because of the complex inheritance, it is difficult to estimate the net effect of such singular genetic factors.