Objective: To determine the time course and extent of tumor reduction associated with systemic chemotherapy or external beam radiotherapy (EBRT) in the treatment of advanced intraocular retinoblastoma. Methods: Retrospective review of children with Reese-Ellsworth stages IV and V retinoblastoma undergoing primary globe-conserving therapy with either systemic chemoreduction or EBRT. Study variables were recorded at baseline, at monthly intervals for the first 6 months, and at 12 months after the initiation of treatment. Tumor volumes were calculated using basal area and height values determined by ultrasonography, physical examination, and fundus photographic review. Main Outcome Measures: Outcome measures included tumor volume, tumor reduction, regression pattern, treatment-related complications, metastases, and survival. Results: Twenty-six eyes of 26 patients were evaluated for tumor response; 18 patients were treated with systemic chemotherapy and 8 patients were treated with EBRT. Median follow-up was 36 months. A mean 68% reduction in tumor volume occurred after 1 cycle of chemotherapy compared with a 12% reduction at a similar time point (1 month) after initiation of EBRT (P<.004). There was no statistically significant difference in tumor volume reduction between treatment modalities at the 12-month follow-up visit. Both systemic chemoreduction and EBRT achieved 100% globe conservation and 100% patient survival in this series. Conclusions: Retinoblastoma reduction exhibits a differential time course based on the applied primary treatment. Systemic chemotherapy is associated with earlier tumor reduction than EBRT.
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