Background: Intensification of androgen deprivation therapy (ADT) with docetaxel (DOC) or novel hormone therapies (NHTs) [abiraterone, enzalutamide, or apalutamide] has shown to improve survival outcomes and is SOC in men with mCSPC.¹ However, recent evidence indicates that most pts still only receive ADT ± first-generation non-steroidal antiandrogens (NSAA).^2-4 This is one of the first studies to assess the real-world utilization of intensified treatments as first-line (1L) therapies for pts with mCSPC by physician specialty. Methods: This retrospective study used the Optum health insurance claims database, which includes pt claims data from commercially insured and Medicare Advantage populations. Adult pts (≥18 years) had ≥2 claims for prostate cancer (PC) and ≥1 claim for metastasis (the first claim was index date) within 90 days (d) prior to, or any time after, the first claim for PC from January 2014– June 2019. 1L treatments included any systemic treatment for mCSPC within 90 d pre-index, plus any other treatment received within 180 d of the first. Physician specialty was determined from medical or pharmacy claims during 1L treatment and categorized as Urologist; Oncologist; urologists and oncologists (Both); or other specialties (Other). Treatment patterns and pt characteristics across specialties were analyzed descriptively. Results: Of 4,675 mCSPC pts identified, 16% received care from Urologists, 20% from Oncologists, 63% from Both, and 1% from Other. Pts seen by Urologists were more likely to be older and have Medicare compared to pts seen by the Oncologists or Both. Treatment intensification with NHT and/or DOC was numerically higher among Oncologists and Both compared with Urologists. However, all specialties prescribed ADT ± first-generation NSAA most frequently for 1L mCSPC treatment, even in patients with visceral metastases (Table). Conclusions: Despite evidence of improved survival with intensified treatment for pts with mCSPC, we observed its underuse by all specialties and even among pts with visceral metastases. Our results highlight a great need to advance the implementation of evidence-based medicine in mCSPC. 1. Sayegh N et al. JCO Oncol Pract 2021; OP2100206. 2. Ryan CJ et al. J Urol 2021; Online ahead of print. 3. Freedland S et al. Ann Oncol 2021; 32: S650-S651. 4. Freedland S et al. J Clin Oncol 2021; 39(Suppl 15): e5073.