To get an insight into various aspects of DSBs repair mechanisms, we first characterized the presence of DSBs in three cancer cell lines before and after 48 h of treatment with a known DSB-inducer (doxorubicin), with or without DDR inhibitors (B02, NU7026 or olaparib, respectively inhibiting RAD51, DNA-PK or PARP1) through the immunofluorescent quantification of 53BP1 foci, 48 h after treatment, using automated quantification (CellInsight CX5, ThermoFisher Scientific, USA). This evidence concerns the gene PARP1 and cancer.