Indeed, as shown in Fig. 4B, the decrease of 53BP1 foci after ionizing irradiation was significantly retarded in TL+ cell lines compared with the normal control, and the rate in decline of 53BP1 foci was lower than in MMR-deficient lines, which may suggest that the NHEJ pathway is less active in TL+ Ewing sarcoma cells, although the abnormalities in the NHEJ genes are currently not known in these TL+ cell lines and, on the contrary, compromised HR has also been reported in Ewing sarcoma cells44. Here, MRC1 is linked to Ewing sarcoma.