ImportanceAdjuvant therapy is an important and effective treatment for retinoblastoma. However, there is a lack of head-to-head clinical trials comparing 3 vs 6 cycles of CEV chemotherapy (carboplatin, etoposide, and vincristine) for enucleated unilateral retinoblastoma with high-risk pathological features.ObjectiveTo assess whether 3 cycles of CEV chemotherapy is noninferior to 6 cycles for enucleated unilateral retinoblastoma with high-risk pathological features.Design, Setting, and ParticipantsThis double-center, randomized, open-label, noninferiority trial was conducted at 2 premier eye centers in China and included 187 patients who had undergone enucleation for unilateral retinoblastoma with high-risk pathological features (massive choroidal infiltration, retrolaminar optic nerve invasion, or scleral infiltration) between August 2013 and March 2024. The final date of follow-up was March 21, 2024.InterventionsPatients were randomly assigned to receive either 3 (n = 94) or 6 (n = 93) cycles of CEV chemotherapy regimen after enucleation.Main Outcomes and MeasuresThe primary end point was disease-free survival, with a noninferiority margin of 12%. Secondary end points encompassed overall survival, safety, economic burden, and the quality of life of children.ResultsAll 187 patients (median [IQR] age, 25.0 [20.0-37.0] months; 83 [44.4%] female) completed the trial. Median (IQR) follow-up was 79.0 (65.5-102.5) months. Five-year disease-free survival was 90.4% for the 3-cycle group vs 89.2% for the 6-cycle group (difference, 1.2% [95% CI, −7.5% to 9.8%]), which met the noninferiority criterion (P = .003 for noninferiority). The 6-cycle group experienced a higher frequency of adverse events, greater reduction in quality of life scores, and increased costs compared with the 3-cycle group.Conclusions and RelevanceAmong patients with unilateral pathologic high-risk retinoblastoma, 3 cycles of CEV chemotherapy resulted in 5-year disease-free survival that was noninferior to 6 cycles of CEV chemotherapy.Trial RegistrationClinicalTrials.gov Identifier: NCT01906814
