Beyond conventional metastatic patterns: a case report of isolated omental metastasis from high-risk prostate adenocarcinoma

Abstract Background Peritoneal and omental metastasis from prostate adenocarcinoma is rare and usually occurs in the setting of widespread disease. Isolated peritoneal involvement without skeletal or nodal disease is uncommon, and the mechanism of spread is not well understood. Case presentation A 64-year-old man presented with lower urinary tract symptoms and was diagnosed with high-risk prostate adenocarcinoma (Gleason 4 + 5=9, WHO Grade Group 5) after transurethral resection of the prostate (TURP); post-operative prostate-specific antigen (PSA) was 7.8 ng/mL, and the pre-operative work-up was not available. Staging with prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) showed locally invasive disease extending into the seminal vesicles and bladder base, without nodal or distant metastasis. He was treated with hormonal therapy and external beam radiotherapy, achieving a PSA nadir of 0.35 ng/mL. Despite a subsequent rise in PSA, a surveillance PSMA PET/CT was negative for recurrence. PSA continued to rise progressively, reaching 59.17 ng/mL, with new lower urinary tract symptoms. Repeat PSMA PET/CT showed ascites and diffuse PSMA-avid omental caking with peritoneal fat stranding, without local recurrence, lymphadenopathy, or osseous metastasis. Image-guided tru-cut biopsy of the omentum confirmed metastatic carcinoma compatible with the known prostatic primary. He was started on docetaxel with continued luteinizing hormone-releasing hormone (LHRH) therapy, abiraterone, and prednisolone, and remains under oncological surveillance. Conclusion Peritoneal and omental recurrence can occur after TURP-diagnosed prostate cancer without involvement of the usual sites of spread, and a TURP-related iatrogenic contribution cannot be excluded. A negative PSMA PET/CT does not exclude progression; in selected patients with a marked, sustained PSA rise and new symptoms, repeat imaging may be considered when it is likely to alter management, and histopathological confirmation is required when an atypical metastatic site is suspected.