Background: Over the past 6 years, intensification of androgen deprivation therapy (ADT) with docetaxel (DOC) and novel hormonal therapies (NHT) [abiraterone, enzalutamide, and apalutamide], has been shown to improve survival outcomes in men with mCSPC. This study assessed the real-world utilization of effective combination therapies as 1L treatment in insured pts in the U.S. with mCSPC. Methods: This retrospective study used the Optum health insurance claims database, which includes pt claims data from both commercially insured and Medicare Advantage populations. Eligible pts were adult men with ≥1 claim with a metastatic International Classification of Diseases diagnostic code (first claim was index date) within 90 days (d) prior to, or any time after, a prostate cancer diagnosis between January 2014 and June 2019. Pts with evidence of systemic anticancer therapy during the 1-year pre-index baseline period were excluded, unless the first drug claim occurred within 90 d prior to the diagnosis of metastatic disease. The 1L treatments were identified as any treatment for mCSPC within 90 d pre-index, plus any other treatment received within 180 d of the first, and were grouped by regimen: ADT only; ADT + first-generation antiandrogens (AA); ADT + DOC; ADT + NHT; and ADT + NHT + DOC. Results: Of 4221 men with mCSPC, 2364 (56.0%) received ADT only; 892 (21.1%) ADT + AA; 577 (13.7%) ADT + NHT; 348 (8.2%) ADT + DOC; and 40 (0.9%) ADT + NHT + DOC. Pts who received ADT + DOC or ADT + DOC + NHT were generally younger than the other treatment groups (Table). By 2019, use of ADT only and ADT + AA had declined, while the use of ADT + NHT and ADT + NHT + DOC had increased (Table). However, in 2018 and 2019, the majority of men with mCSPC still received either ADT alone, or ADT + AA, including those with visceral metastases (Table). Survival analysis across treatment cohorts is ongoing. Conclusions: Despite level 1 evidence demonstrating improved survival with intensified treatment (ADT + DOC or NHT), this study shows its underutilization in pts with mCSPC. This is evident even in those with more aggressive disease (visceral metastases) as recently as 2019. These data highlight that a minority of pts with mCSPC received optimal life-prolonging therapies in a commercially insured and Medicare Advantage U.S. population. Further studies are needed to identify the reasons for this underutilization of intensified treatments.