Conditional analysis on new tumor formation with solitary unilateral retinoblastoma in 482 consecutive patients

PURPOSE: The objective of the study was to understand dynamic risk (conditional analysis based on patient age) for new tumor development in patients with solitary unilateral retinoblastoma. METHODS: This was a retrospective analysis. RESULTS: Of 482 patients with solitary unilateral retinoblastoma, 55 new tumors developed in 20 patients (4%). Comparison (new tumor vs. no new tumor development) revealed those with new tumor demonstrated younger mean age at presentation (10 vs. 36 months, P < 0.001), greater likelihood of family history of retinoblastoma (35% vs. 3%, P < 0.001), and greater probability of primary tumor location in the macula (50% vs. 15%, P = 0.003). Conditional risk for new tumors (at age 6, 9, 12, 18, and 24 months) declined for those who presented at 0–3 months old (25%, 15%, 15%, 8%, and 0%), >3–6 months old (17%, 14%, 6%, 6%, and 0%), >6–9 months old (not applicable [na], 6%, 6%, 0%, and 0%), and >9–12 months (na, na, 3%, 3%, and 0%). Younger patients showed greater development of bilateral tumors (P < 0.001). Of patients with new tumors, those that occurred within 1 year from presentation were located in the preequatorial region in 46%, whereas those that occurred more than 1 year from presentation were preequatorial in 78%. Patients ≤24 months at initial presentation demonstrated all new tumors by 24 months of age. Older patients (>24 months at presentation) showed new tumors up to 56 months of age. CONCLUSION: Children (≤24 months) with solitary unilateral retinoblastoma showed decreasing risk for new tumors up to 24 months of life. Later onset of new tumor was more likely located in preequatorial region.