Bone marrow metastasis in prostate cancer: Treatment feasibility and survival in a real-world cohort.

e17051 Background: Bone marrow metastasis (BMm) in prostate cancer (PCa) is a rare and life-threatening condition, typically presenting with severe cytopenias and limited therapeutic options. Owing to its rarity, real-world data on clinical presentation, treatment feasibility, and outcomes remain scarce. Methods: We retrospectively evaluated PCa patients with histopathologically confirmed BMm across four tertiary centers in Türkiye. Clinicopathological characteristics, laboratory findings, treatments administered after BMm diagnosis, and overall survival (OS) were analyzed. OS was calculated from the time of BMm diagnosis. Results: Among 3,129 screened patients with PCa, 36 (1.2%) had BMm. Most patients developed BMm during the castration-resistant phase (mCRPC; 77.8%), while 22.2% were in the hormone-sensitive phase (mHSPC). All cases were prostate adenocarcinoma, with no evidence of neuroendocrine differentiation. At BMm diagnosis, cytopenias were highly prevalent, including anemia in 91.4% (median hemoglobin 8.4 g/dL, IQR 7.7–9.4), thrombocytopenia in 83.3% (median platelet count 87×10³/µL, IQR 58–120.5), and leukopenia in 47.2% (median leukocyte count 4.0×10³/µL, IQR 3.0–4.75). Hemoglobin decline was the earliest laboratory abnormality in 69.4% of patients, whereas leukocyte counts were the last to decline in 77.7%. Following BMm diagnosis, 25 patients received systemic treatment, including chemotherapy (n = 16), ARPI (n = 8), or androgen deprivation therapy alone (n = 1), while 11 patients received best supportive care alone. Median overall survival (OS) for the entire cohort was 4.1 months (95% CI 2.4–5.7). Treated patients had significantly longer OS than untreated patients (9.1 vs 0.7 months, p < 0.001). OS was significantly longer in patients who developed BMm during the mHSPC phase compared with the mCRPC phase (10.2 vs 3.8 months, p = 0.038). At the time of BMm diagnosis, concomitant visceral metastases included lung metastases in 10 patients, liver metastases in 5, brain metastases in 4, and adrenal metastases in 2. On univariate analysis, the presence of brain metastasis at the time of BMm diagnosis was associated with a markedly inferior OS (HR 9.5, 95 %CI; 2.7-33.9, p < 0.001), while other visceral sites did not show a similar impact. No survival difference was observed according to the type of systemic therapy administered after BMm diagnosis. Conclusions: BMm defines an extremely high-risk disease state in PCa, characterized by early marrow failure and very limited survival. Although overall prognosis is poor, the marked survival difference between treated and untreated patients suggests that BMm does not uniformly preclude meaningful survival. Early recognition and individualized treatment decisions, particularly in the hormone-sensitive setting, may meaningfully influence outcomes in selected patients.