We describe a patient with bone metastases occurring shortly after radical prostatectomy for organ-confined prostate cancer. The medical history and immunohistochemical findings suggested prostate cancer recurrence to the skeleton. Undetectable serum prostate-specific antigen levels, however, raised doubts about this diagnosis. A whole body ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography scan was obtained and revealed a right-sided breast cancer as the primary site of metastatic spread.