Extremely Rare Prostate Metastasis From Rectal Carcinoma Detected on ⁶⁸Ga-FAPI PET/CT

Metastatic involvement of the prostate from colorectal adenocarcinoma is uncommon and usually results from direct local extension rather than true distant metastatic spread. We report the case of a 52-year-old man with a prior history of rectal adenocarcinoma treated with multimodality therapy. He presented with lower urinary tract symptoms accompanied by progressively rising serum creatinine levels. PSA levels were within normal limits, and colonoscopy revealed no evidence of local recurrence; however, CEA levels were elevated. Whole-body ⁶⁸Ga-FAPI PET/CT revealed diffuse, homogeneous tracer uptake involving the entire prostate gland. Subsequent prostate biopsy confirmed metastatic adenocarcinoma from a rectal primary.