Increase in copy number of N-myc in retinoblastomas in comparison with chromosome abnormality

N-myc oncogene amplification was studied in tumor tissue DNA from Japanese retinoblastoma patients, taking into consideration their uni- or bilateral disease form, their family history, and any chromosome abnormalities. Of the 23 cases examined, seven (30%) showed a 1.9- to 2.3-fold amplification of N-myc. No correlation was found between N-myc amplification and either tumor form or family history. Two of three cases having double minute bodies in their tumors showed N-myc amplification. In two tumors with 13q deletions, one produced in the host with constitutional 13q--abnormality showed no N-myc amplification, and the other one produced in the host with normal karyotype showed an N-myc amplification. These results indicate N-myc amplification is independent of the known genetic background in retinoblastoma patients.