An old man presented with a pathological fracture. On investigation, his serum calcium and phosphorus are normal but urine calcium is low. Serum alkaline phosphatase and acid phosphatase are elevated. Biopsy of bone shows osteoblastic metastasis. Where could be the primary tumor in this patient?

Types of bone metastases are osteolytic, osteoblastic and mixed. Only myeloma has purely lytic lesions. Other tumors which causes lytic lesions are primary tumor of bronchus, breast, kidney, or thyroid. Metastases from prostate cancer are predominantly osteoblastic. In osteolytic metastases, urine calcium is often increased. Serum calcium and phosphorus may be normal or increased. Serum ALP is usually normal or increased. Serum acid phosphatase is slightly increased. In osteoblastic metastases, serum calcium is normal, it is rarely elevated. Urine calcium is low. Serum ALP is usually increased. Serum acid phosphatase is increased in prostatic carcinoma. Serum phosphorus is variable. Osteoblastic lesions are also accompanied by pathologic fractures because of the poor quality of bone produced by osteoblasts. Ref: Interpretation of Diagnostic Tests, 8e By Jacques Buon Wallach, 2007, Page 350; Textbook of bone metastases - Claude Jasmin, Rodolfo Capanna, Page 41; Differential Diagnosis in Conventional Radiology - Francis A. Burgener, Mati Kormano, Tomi Pudas, Page 110.