ERCC4 and osteosarcoma: In order to reveal the potential genetic mechanism of secondary osteosarcoma occurrence, we analysis the result of whole-exome sequencing and found 8 germline gene variations, which consist of 7 germline genes (including EPAS1, SETD2, MSH3, BMPR1A, ERCC4, CDH1 and AR; shown in Table 1).