20-year trends in socioeconomic disparities in breast cancer care for patients aged < 65 years old.

1559 Background: Socioeconomic disparities (SES) in cancer care have been well described, especially for younger patients with limited financial reserve and insurance vulnerability. It remains unclear, however, whether innovations in breast oncology have mitigated or exacerbated these gaps over time. We evaluated nearly 20-year trends across key breast cancer treatment and diagnostic modalities and sought to determine whether advances in care promote, or further undermine, health equity. Methods: Using the National Cancer Database, we identified working-aged individuals (18-64 yo) diagnosed with breast cancer from 2004–2022. As surrogates for improvements in breast cancer care, we examined: (i) Oncotype DX testing for stage I–II ER/PR-positive, HER2-negative disease; (ii) immediate breast reconstruction (IBR) after mastectomy; (iii) receipt of neoadjuvant chemotherapy (NACT) for stage II HER2-positive (HER2+) and triple-negative breast cancer (TNBC); and, (iv) immunotherapy by subtype and stage (2018–2022). We used multivariable logistic regression to generate adjusted predicted probabilities by median income quartile (MIQ) and year (or year group). Median Income Disparities (MID) were measured as the difference between the highest and lowest MIQ. Results: The final sample included 1,349,691 patients with mean age 51.8 (SD 8.64). Patient population included 7.7% Hispanic, 72.3% Non-Hispanic White, 13.2% Black, 5.9% Asian, and 0.9% unknown race/ethnicity. 76.7% of patients were privately insured, 10.8% Medicaid-covered, 6.2% Medicare-covered, 1.5% other, 1.8% unknown, and 3.1% uninsured. During the study period, overall adoption of treatment increased substantially over time, with SES disparities differing across modality. Oncotype DX testing demonstrated persistent income-related disparities across the study period (MID: 4.2–5.5%, p<0.05 for all). The largest and most durable inequities were seen in post-mastectomy IBR (17.60% in 2004-2008, narrowing to 11.70% in 2018-2022, p<0.05 for all). Receipt of NACT was associated with modest income-based differences that were greatest during years of rapid uptake for stage II HER2+ (4.9% in 2014–2017, p<0.05) and TNBC (4.8% in 2018–2022, p<0.05) breast cancer. Adoption of immunotherapy rose sharply from 2018–2022 across all incomes, with modest but narrowing gaps for stage III–IV disease (MID: 4.9% in 2019, p<0.05 to 1.1% in 2022,NS). Adjustment for insurance status did not significantly change socioeconomic gradients. Conclusions: Socioeconomic disparities in breast cancer care for women <65 years old vary markedly by treatment modality and adoption phase. Advancing equitable access to best-practice breast cancer care will require interventions at the health system, societal guidelines, and policy levels.