FBXW7 promotes ubiquitination of XRCC4 via lysine 63 linkage to facilitate nonhomologous end-joining, rather than proceeds to XRCC4 degradation [14], while these two pathways of ubiquitination (via K48 and K63 linkage) contribute to the tumor suppressor role of FBXW7 together. Here, XRCC4 is linked to neoplasm.