Up to 14% of unilateral sporadic affected patients may carry an RB1 pathogenic variant.1,6 Some patients classified as having nonheritable retinoblastoma were likely misclassified, causing underestimation of SPC incidence in those with heritable retinoblastoma and overestimation of those with nonheritable retinoblastoma. This evidence concerns the gene RB1 and retinoblastoma.