Urinary calcium excretion in the monitoring of bone metastases from prostatic carcinoma

BACKGROUND: One of the greatest problems in treating advanced prostate carcinoma is monitoring the therapeutic response of bone metastases. As these metastases are mainly osteosclerotic and lead to a markedly increased bone calcium requirement that may give rise to an imbalance in calcium homeostasis, the authors investigated whether changes in calcium balance may be useful for evaluating the response of bone metastases to treatment. METHODS: The study involved 268 prostate carcinoma patients: 142 in Stage A-C2 (International Union Against Cancer [UICC] staging system, 1998) and 126 with bone metastases who had failed to respond to hormone therapy and were receiving chemotherapy. Prostate-specific antigen (PSA), calcium and phosphate metabolism, and the main bone formation and resorption markers were all assayed before and after chemotherapy. RESULTS: Of the 126 patients on chemotherapy, 109 were evaluable for response: according to standard criteria, 25 (23%) had improved, 43 (39.5%) were unchanged, and 41 (37.5%) had worsened. All of the improved and 16 unchanged patients had decreased PSA and bone marker levels and an increased urinary calcium/creatinine ratio (UCa/Cr); the worsened patients had increased PSA and bone marker levels, and their UCa/Cr decreased after only six treatment cycles. PSA and UCa/Cr were the biochemical markers whose changes showed the best agreement with treatment response. CONCLUSION: The UCa/Cr ratio was the most useful marker of clinical response, mainly because it allowed an early decision to continue or to stop chemotherapy. Furthermore, UCa/Cr and PSA together identified a percentage of patients classified as unchanged on the basis of standard criteria but whose condition had actually improved.