XRCC1 and thyroid cancer: Many studies have reported the association of XRCC1 polymorphisms at 194, 280, and 399 (Arg194Trp, Arg280His, and Arg399Gln) with thyroid cancer risk [16]–[25], but the results were inconclusive, some original studies thought that these polymorphisms were associated with thyroid cancer risk, but others had different opinions.