SAT-716 Metastatic Prostate Cancer Masquerading as Paget's Disease of Bone: A Case Report

Abstract Disclosure: V. Florova: None. R.H. Nguyen: None. S.K. Devineni: None. M.F. Siddiqui: None. Background: Paget's disease of bone (PDB) is a chronic metabolic bone disorder characterized by abnormal bone remodeling. PDB and metastatic prostate cancer can present with overlapping clinical and imaging features, making differential diagnosis challenging, especially in complex cases. Case Presentation: A 72-year-old man nursing home resident with medical history of dementia, hypertension, hyperlipidemia and asthma presented after a fall, which led to inability to ambulate for two days and concurrent bilateral hip pain. The patient reported progressive right lower extremity pain, ambulatory difficulties, and systemic symptoms, including cachexia and weight loss for the past three months. Physical examination revealed bilateral lower extremity tenderness and mild hearing impairment. Laboratory studies demonstrated markedly elevated alkaline phosphatase 814 U/L [34-104 U/L] with slightly low corrected serum calcium of 8.3 mg/dl [8.6-10.3 mg/dl]. Xray revealed sclerosis in the right acetabulum, pubic bones, and sacroiliac joint, raising suspicion for Polyostotic PDB. A radionuclide bone scan showed multiple foci of increased uptake in the bilateral ribs, pelvis, and right femur, suggesting polyostotic PDB or metastatic disease. The markedly elevated PSA level 1015 ng/mL [0-4.4 ng/ml] heightened concern for metastatic prostate cancer. Subsequently, CT-guided biopsy of the right iliac bone was performed with pathology showing PSA-positive staining, thus confirming diagnosis of metastatic prostate cancer. Antiandrogen therapy (Bicalutamide) and gonadotropin-releasing hormone agonist (Leuprolide acetate) treatment for metastatic prostate cancer was initiated with biochemical improvement in PSA level. Discussion: This case illustrates the diagnostic challenges in differentiating Polyostotic PDB from metastatic bone disease, in an elderly man with overlapping clinical and radiological findings. Despite initial suspicion of PDB, the elevated PSA levels and histopathological findings established metastatic prostate cancer as the underlying etiology. While prostate cancer bone metastases are typically osteoblastic, they can also present as osteolytic or mixed osteoblastic-osteolytic lesions that resemble the radiographic appearance of Paget disease of bone. Both conditions can show increased uptake on bone scintigraphy. Misdiagnosis can lead to inappropriate treatmentConclusion: It is crucial for physicians, to consider metastatic prostate cancer in the differential diagnosis when encountering bone lesion that could be mistaken for Paget’s disease of bone.Biopsy and histological examination are often necessary to distinguish between these conditions definitely. Multidisciplinary care and close coordination among specialties are vital to ensure accurate diagnosis and optimal patient management. Presentation: Saturday, July 12, 2025