Health-related quality of life.

1109 Background: Trials typically pool patient-reported outcomes across demographics, assuming baseline differences reflect normal variation. When adequate enrollment permits disaggregation, nuanced patterns emerge across quality-of-life domains. Methods: Individual participant data meta-analysis of 15 breast cancer trials (N=12,656). HRQoL domains (Physical, Emotional, Social, Role, Cognitive) and breast symptoms assessed via EORTC QLQ-C30/FACT-B at baseline, treatment, and post-treatment. Comparisons: Hispanic vs Not-Hispanic; White vs Asian vs Black vs Other. Dual approach: 1) direct between-group comparisons, 2) pooled within-group trajectories revealing between-group mean differences and absolute changes. Results: Population: 2.3% Black, 9.6% Hispanic, 19.9% Asian. Baseline disparities were substantial and domain-specific. Hispanic demonstrated higher cognitive functioning (MD 2.72, p<0.05). Black had superior role functioning versus White (84.11 vs 67.19, MD -7.80, p<0.001); all minority groups scored lower on emotional functioning (Black MD -4.76, Asian MD -3.34, Other MD -1.88, all p<0.001). During treatment, Hispanic maintained physical (MD 1.99, p<0.05) and role functioning (MD 3.67, p<0.05); Asian showed less role decline (MD 2.61, p<0.01). All groups experienced similar symptom improvement and cognitive decline. Post-treatment divergence: Black patients' breast symptoms worsened (change +1.27) while Asian showed highest improvement (change -2.09, p<0.05). Hispanic cognitive advantage eroded (MD -1.77, p<0.05), and treatment resilience disappeared. Uniform 60% attrition across all groups. Conclusions: Equal treatment response does not equal equity when groups enter with disparate baselines and experience differential post-treatment trajectories. Post-treatment divergence was striking: Black patients' symptoms worsened while Asian improved most—invisible in binary White vs Not-White comparisons. Hispanic treatment resilience disappeared in survivorship and cognitive advantages eroded. Uniform 60% attrition demonstrates recruitment, not retention, is the barrier requiring redirection of diversity initiatives. Even pooling 15 trials, Black and Hispanic representation remained inadequate. Equal treatment perpetuates existing disparities from unequal starting points or creates new disparities through differential recovery. Trial equity requires adequate diverse enrollment and interventions addressing pre-enrollment disparities and post-treatment survivorship needs.