The association with age may indicate a role of highly penetrant RB1 mutations in the risk of SMN, although at present time there is only preliminary evidence for an association between mutation penetrance and SMN,21,22 while the calendar year findings may reflect decreases in radiation dose over time.7,10,20 For melanoma, only a family history of retinoblastoma appeared to be associated with risk. This evidence concerns the gene RB1 and retinoblastoma.