The Impact of Edition Differences in the International Retinoblastoma Classification (IIRC vs. ICRB) on Staging and Globe Salvage Prognosis: Analysis of 642 Eyes.

Purpose: The objectives of this study were to compare the prognostic performance, staging concordance, and eye salvage prediction of the International Intraocular Retinoblastoma Classification (IIRC) and the International Classification of Retinoblastoma (ICRB), and to assess the clinical impact of definitional discrepancies between the two systems. Design: This study used retrospective, observational case series. Participants: A total of 642 eyes with intraocular retinoblastoma (Rb) that received conservative management with intent for globe salvage (2003-2024) were assessed. Methods: Clinical records and imaging were reviewed for tumor characteristics. Each eye was staged according to both IIRC and ICRB criteria. Prognostic performance for eye salvage was analyzed using odds ratios (OR), the concordance index (C-index), and likelihood ratio χ2 tests. Main Outcome Measures: The eye salvage rate and concordance between IIRC and ICRB staging were assessed. Results: The overall eye salvage rate was 73% (471/642), decreasing significantly with larger tumor size, subretinal fluid (SRF) extent, and more seeding (p < 0.0001). The globe salvage was 24% for tumors occupying >50% of the globe compared to 77% for smaller tumors, and 47% for tumors with SRF > 1 quadrant compared to 62% for tumors with SRF ≤ 1 quadrant. Under the IIRC, the salvage rates by group were 98%, 94%, 92%, 51%, and 14% (A-E); under the ICRB, 98%, 94%, 94%, 60%, and 24%. Failure odds (ORs) increased across stages from 2.8 in Group B to 276 in Group E (IIRC) and 145.2 (ICRB). Eighty-seven (14%) eyes were upstaged under the ICRB. Of these, 72 (11%) with tumors > 50% of globe volume shifted from IIRC Group D to ICRB Group E (25% salvage), and 15 (2.3%) with SRF > 3 mm shifted from IIRC Groups B/C to ICRB Group D. The ICRB showed superior discrimination (C-index = 0.824; 95% CI, 0.80250-0.84937) compared with IIRC (C-index = 0.790; 95% CI, 0.768-0.814). Conclusions: Both systems accurately predict eye salvage, but definitional variations significantly affect staging and outcome interpretation. The ICRB improves discrimination for advanced tumors by including large tumors in Group E, while the IIRC provides finer stratification in intermediate disease through SRF extent. Integrating these criteria could yield a unified, more prognostically precise classification for Rb.