Prostate cancer with lytic bone metastases: 18F-fluorodeoxyglucose positron emission tomography-computed tomography for diagnosis and monitoring response to medical castration therapy
A 67-year-old male patient presented with low grade fever of 3 months duration. During routine work-up, multiple lytic lesions were demonstrated on the radiograph of pelvis, suspicious for metastases. The patient underwent 18F-FDG PET-CT for localization of the primary malignancy. 18F-FDG PET-CT images revealed multiple lytic lesions involving almost entire skeleton, showing increased 18F-FDG uptake (highest maximum standardized uptake value-6.9 [SUVmax]) [Figure and ]. The prostate gland was enlarged and showed increased 18F-FDG uptake along the periphery (SUVmax-5.5) []. Also noted were enlarged 18F-FDG avid pelvic (SUVmax-10.6) [] and retroperitoneal (SUVmax-6.4) [] lymph nodes. Based on the 18F-FDG PET-CT findings a diagnosis of carcinoma prostate with nodal and lytic skeletal metastases was made. The diagnosis was confirmed with transrectal ultrasound guided biopsy from prostate, which revealed prostatic adenocarcinoma with perineural invasion (Gleason score-9/10). The serum prostate specific antigen (PSA) was elevated (370 ng/ml; normal: 0-4 ng/ml).\nAs lytic metastases are uncommon in prostate cancer, the patient underwent bone marrow biopsy to rule out any other malignant pathology. Bone marrow biopsy revealed metastatic carcinoma, positive for cytokeratin and PSA but negative for thyroid transcription factor-1, confirming the diagnosis. The patient was advised orchiectomy, which he refused. The patient was then put on medical castration therapy with combined androgen blockade. He was given luteinizing hormone releasing hormone agonist goserelin (10.8 mg subcutaneous injection every 3 months) along with non-steroidal anti-androgen bicalutamide (50 mg once daily orally).\nSix months later the patient was referred for response assessment 18F-FDG PET-CT. 18F-FDG PET-CT revealed that most of the lytic lesions were replaced with sclerotic lesions with no significant 18F-FDG uptake [Figure and ], except for lytic lesions in eighth dorsal vertebra, which showed mild 18F-FDG uptake (SUVmax-3.2). Also noted was a reduction in size of the prostate gland and disappearance of peripheral 18F-FDG uptake (SUVmax-1.1) []. The pelvic and retroperitoneal lymph nodes also have disappeared [Figure and ]. Thus, a diagnosis of minimal residual disease was made on 18F-FDG PET-CT. This correlated with serum PSA levels, which showed drastic reduction (0.14 ng/ml; normal: 0-4 ng/ml).