Social determinants of health and disparities in cancer care for patients with metastatic breast cancer in Mexico.

223 Background: Patients diagnosed with metastatic breast cancer (MBC) in low- and middle-income countries (LMICs) face poorer outcomes than their counterparts in high-income countries. Social determinants of health (SDH)—including housing, food security, employment, and education—have been increasingly recognized as critical non-medical factors influencing access to care and cancer-related outcomes. We aimed to describe SDH among Mexican patients with MBC and examine their association with treatment adherence, receipt of standard therapy, and survival. Methods: This was a prospective multicenter cohort study including patients from three public cancer centers in Mexico City. Eligible participants were adults with MBC receiving first- or second-line systemic therapy. A trained patient navigator conducted structured interviews at baseline and every three months over one year using validated questionnaires (SDH needs, SEAMS, FACT-G, and BPI). Treatments were categorized as standard or non-standard based on NCCN guidelines. Associations between SDH and clinical outcomes were explored using chi-square tests. Linear mixed models were used to assess longitudinal changes in health-related quality of life. Survival was estimated using the Kaplan-Meier method and compared with the log-rank test. Results: A total of 324 patients were included (mean age 58.1 years; 99.7% female). At baseline, 92% reported at least one SDH-related need, most commonly employment (77.5%), housing (55.2%), and food (45.7%). The mean number of SDH needs at baseline was 3.1±1.8, remaining consistent across timepoints. Receipt of standard treatment was lower among those with needs in utilities (47.6% vs. 69.1%, p = 0.001) and education (58.0% vs. 69.0%, p = 0.046). Median SEAMS scores improved slightly over time (35 to 37). Median follow-up was 12.1 months (95% CI, 12.05-12.15). One-year overall survival was 85.0% (95% CI, 81.0–89.0), with no differences based on presence (p = 0.61) or number of SDH needs (p = 0.51) at baseline. The presence of any SDH need was significantly associated with FACT-G scores (p = 0.002) throughout the follow-up period. FACT-G scores were consistently lower in patients with any SDH need, and no significant interaction was observed between time and presence of any SDH need (p = 0.481). Conclusions: SDH needs were highly prevalent and persistent among patients with MBC in Mexico and were associated with lower likelihood of receiving guideline-concordant care and lower quality of life. Addressing these social barriers through targeted interventions may be critical to improving treatment equity and clinical outcomes in LMIC settings.