96 Background: Intensified treatment beyond androgen deprivation therapy (ADT) has been shown to improve survival in patients with metastatic castrate-sensitive prostate cancer (mCSPC). However, real-world utilization remains inadequate. To assess potential differential access to such life-prolonging treatments, we assessed the association between sociodemographic marginalization and receipt of intensified treatment in patients newly diagnosed with mCSPC within a universal healthcare system. Methods: We performed a population-based cohort study of men aged 66 years or older diagnosed with de novo mCSPC in Ontario, Canada from Jan 2014-Nov 2021. Hierarchical regression models adjusting for patient, tumor, and physician characteristics were used to estimate odds ratios (OR) and 95% confidence intervals (CI) for the association between patient marginalization, measured by the Ontario Marginalization Index (ON-MARG), and receipt of intensified treatment, within 6 months of diagnosis. ON-MARG, a validated measure created using Canadian census data, provides area-level measures of marginalization in four domains: (1) households and dwellings; (2) material resources; (3) age and labour force; and (4) racialized and newcomer populations. Results: Among 6,051 patients, 1,465 (24%) received intensified treatment. Higher levels of composite marginalization were associated with a lower likelihood of receiving intensified treatment (OR 0.91, 95% CI 0.83–0.99, p=0.03). When examining individual domains of marginalization (Table 1), the racialized and newcomer populations domain showed the strongest negative association with the receipt of intensified treatment (OR 0.89, 95% CI 0.81–0.97, p=0.01). Conclusions: Sociodemographic marginalization, particularly among racialized and newcomer populations, is associated with lower rates of intensified treatment in patients with de novo mCSPC, even within a universal healthcare system, further contributing to known disparities in prostate cancer outcomes. Association between ON-MARG domains and treatment intensification among patients with de novo mCSPC in adjusted models.* ON-MARG Domain Effect Estimate (95% CI) Households & Dwellings OR 0.92 (0.85-0.98), p=0.02 Material Resources OR 0.93, (0.86-0.99), p=0.03 Age & Labour Force OR 0.99, (0.94-1.04), p=0.65 Racialized & Newcomer Populations OR 0.89, (0.81-0.97), p=0.01 *Each ON-MARG Domain was modelled in separate multivariable models adjusting for patient characteristics including age at diagnosis, Charlson comorbidity category, and area; tumor characteristics including Gleason score at diagnosis; as well as physician age, sex, years in practice, specialty, and group volume.