RB1 and retinoblastoma: Nonheritable retinoblastoma presents as unilateral disease (mean age at diagnosis, 24 months), and heritable retinoblastoma primarily presents as bilateral and/or multifocal disease (mean age at diagnosis, 15 months).6 Up to 14% of unilaterally affected patients with retinoblastoma without a family history carry an RB1 germ-line variant.1,6 Patients with heritable retinoblastoma have a lifelong increased risk of developing second primary cancers (SPCs).7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22 This risk may be increased further in patients treated with radiotherapy.10,11,12,19,22