FAN1 and familial colorectal cancer type X: Our findings suggest that several cancer-associated genes may have a role in FCCTX, such as the known hereditary cancer gene CHEK2, the previously FCCTX candidate genes OGG1 and FAN1 and, other cancer-related genes such as ATR, ASXL1, PARK2, SLX4 and TREX1, bringing novel insights into the genetic risk factors for familial colorectal cancer type X. Nevertheless, more studies (in vitro and/or in vivo), such as functional assays, segregation, and loss of heterozygosity, are necessary to ascertain more conclusive hypotheses about their role in FCCTX predisposition.