Prospective observational study in Japanese patients with metastatic castration-sensitive prostate cancer (mCSPC) with or without intraductal carcinoma of the prostate (IDC-P).

87 Background: Intraductal carcinoma of the prostate (IDC-P) is a high-grade, high-volume, invasive form of prostate cancer (PCa) associated with poor clinical outcomes. The International Society of Urological Pathologists (ISUP) recommends incorporating IDC-P into the Gleason scoring system. However, existing data on survival outcomes for prostate cancer patients with IDC-P are primarily based on retrospective analyses. This study aims to prospectively evaluate the survival outcomes of Japanese patients with metastatic castration-sensitive prostate cancer (mCSPC), with and without IDC-P, using real-world data from a multi-institutional observational study. Methods: Between 2018 and 2021, we prospectively enrolled 102 de novo mCSPC patients from affiliated healthcare institutions. Eligible patients were those diagnosed with mCSPC via prostate needle biopsy and classified as high-risk according to the LATITUDE criteria. All participants underwent a standard extended biopsy (≥10 cores) to diagnose IDC-P, ensuring minimal sampling error. A single genitourinary pathologist reviewed all biopsy slides based on the 2019 ISUP grading system. Patients received treatment with androgen receptor signaling inhibitors (ARSI) with or without docetaxel. Results: The median age of the patients was 72 years (range 57–92), and the median serum PSA level was 441 ng/mL (range 3.9–9807 ng/mL). The median follow-up period was 38.3 months (range 8.2–67.4 months). All patients had a Gleason grade ≥ 3, with 66 (64.7%) exhibiting a Gleason pattern 5. Lymph node metastasis was present in 67 patients (65.7%), visceral metastasis in 23, and bone metastasis in all patients. IDC-P was identified in 86 patients (84%). Multivariate analysis revealed that elevated lactate dehydrogenase (LDH) levels and the presence of IDC-P were independent predictors of poor castration-resistant prostate cancer (CRPC)-free survival (HR 4.387, p<0.001; HR 2.009, p=0.01) and progression-free survival (PFS2) (HR 6.801, p<0.001; HR 1.796, p=0.016). Conclusions: This prospective observational study demonstrated that higher LDH levels and the presence of IDC-P in biopsy samples were significantly associated with poorer survival outcomes in Japanese patients with mCSPC. These findings underscore the prognostic importance of IDC-P in mCSPC management.