Esagian, Stepan M.

e16535 Background: RMC is a rare and highly aggressive malignancy that predominantly affects young individuals with sickle hemoglobinopathies. Due to its rarity, no validated prognostic models exist to guide clinical decision-making. We aimed to develop and internally validate a prognostic model for patients with RMC using routinely available clinical and laboratory variables. Methods: We analyzed a single-institution cohort of patients with RMC. Candidate variables were identified based on biological plausibility and represented in a directed acyclic graph. Missing data were handled via multiple imputation by chained equations ( m = 50). Variables were ranked using elastic net Cox regression ( α = 0.5, λ = λ min ) with stability selection derived from 100 bootstrap resamples per imputed dataset. Predictors achieving > 60% selection frequency were retained for a nested parsimony analysis. Bootstrap internal validation ( B = 2000) estimated optimism-corrected discrimination and calibration performance, with the calibration slope applied as global shrinkage to penalize final coefficients for overfitting. Clinical utility was evaluated via decision curve analysis (DCA) at 18- and 24-month horizons. Results: Among 180 patients (median age 29; IQR 23–37), 142 deaths occurred with a median follow-up of 12.4 months. The final model included four predictors (Table). The optimism-corrected c-index was 0.667 (optimism = 0.009), and the calibration slope was 0.964, indicating minimal overfitting. Calibration plots showed excellent predicted-observed agreement at 12, 18, 24, and 36 months. DCA showed net benefit across threshold probabilities of 10%–75% at 18 months and 10%–80% at 24 months compared to default strategies. In sensitivity analysis, inclusion of TP53 mutation status improved discrimination ( c -index 0.686) and model fit ( ΔAIC −10.6). An interactive web-based risk calculator was developed to facilitate clinical implementation. Conclusions: This study presents the first internally validated prognostic model for RMC, demonstrating acceptable discrimination and excellent calibration using routinely available variables. By stratifying patients into distinct risk groups, this model may inform treatment intensity—guiding escalation to multi-agent regimens or sequential chemotherapy cycling in high-risk patients, while identifying lower-risk patients who may benefit from de-escalation strategies such as metastasis-directed therapy for oligometastatic disease or consideration of cytoreductive nephrectomy. External validation is warranted. Variable Time Ratio 95% CI p value ECOG performance status 0.64 0.53–0.77 <0.001 Distal (non-retroperitoneal) lymph node metastases 0.69 0.52–0.92 0.011 Neutrophil-to-lymphocyte ratio 0.98 0.94–1.02 0.25 Corrected calcium (mg/dL) 0.77 0.56–1.06 0.10 Sensitivity Analysis Only TP53 Mutation 0.63 0.36-1-10 0.10

e16510 Background: Early-onset RCC may reflect distinct biology and hereditary predisposition, yet data on stage-specific clinical features and outcomes remain limited. We comprehensively evaluated age-stratified, stage-specific clinical features and survival outcomes using the National Cancer Database. Methods: Adults with histologically confirmed RCC diagnosed between 2004 and 2022 were analyzed. Patients were categorized into three groups by age at diagnosis: early-onset ( < 40 years), middle-aged (40–50 years), and late-onset ( > = 50 years). The sociodemographic and clinical characteristics, comorbidities, histology, and treatment patterns were compared using descriptive statistics. Overall survival (OS) was evaluated using Cox proportional hazards models, adjusting for the aforementioned variables. Stage-specific analyses were conducted, including a metastatic disease cohort. Results: Among 742,114 patients, 4.3% were classified as early-onset, 10.9% as middle-aged, and 84.8% as late-onset. Overall, 12.6% presented with metastatic disease. Compared with late-onset, early-onset patients were more likely to be from racial minority populations (non-White: 16.9 % vs. 20.2 % in late-onset), uninsured, and had fewer comorbidities (Charlson–Deyo score 0: 85.2% vs. 65.2%). Early-onset RCC was characterized by a lower proportion of papillary RCC (8.9% vs. 12.5%) and higher proportions of clear cell (54.9% vs. 50.8%) and chromophobe RCC (9.3% vs. 4.5%) than late-onset RCC and more likely to undergo partial nephrectomy (50.4% vs. 30.2%). They also presented with earlier-stage disease, with lower rates of stage III (7.4% vs. 10.2% vs. 13.4%) and stage IV disease (5.4% vs. 8.9% vs. 13.5%) compared with middle-aged and late-onset groups. Among patients with metastatic disease, early-onset RCC demonstrated higher minority representation (30.8% vs. 14.1%) and a higher prevalence of non-clear cell histology (70.6% vs. 58.1%). In multivariable analysis, compared with early-onset RCC, middle-aged (HR 1.44, 95% CI 1.39–1.50; P < 0.001) and late-onset patients (HR 2.83, 95% CI 2.74–2.93; P < 0.001) experienced significantly worse OS. However, among metastatic disease, this survival advantage was attenuated. Early-onset patients had similar OS to middle-aged patients (HR 0.99, 95% CI 0.93–1.05, p = 0.69) and late-onset patients only had a modestly worse OS than the early-onset group (HR 1.09, 95% CI 1.03–1.15 p = 0.003). Conclusions: Early-onset RCC was associated with more favorable baseline characteristics, earlier stage at diagnosis, and higher utilization of nephron-sparing nephrectomy, corresponding to improved OS. However, this survival advantage diminishes in metastatic disease despite better baseline health, highlighting stage-dependent differences in outcomes and suggesting distinct histologic patterns in advanced early-onset RCC.