In order to gain insights into the molecular events responsible for thymic tumour development in Tdp2−/−Atm−/− mice, we analysed and compared copy-number variation by comparative genomic hybridization (CGH) in six Tdp2−/−Atm−/− and three Atm−/− thymic tumours (Fig. 3a, Supplementary Fig. 3 and Supplementary Table 1). This evidence concerns the gene ATM and thymus neoplasm.