How significant are serial bone scans in monitoring advanced prostatic cancer?

We report a total of 169 serial bone scan studies conducted in 21 patients with histologically proven metastatic cancer of the prostate. Aim of the study was to investigate the concordance of findings on bone scans with serum acid phosphatase (AP) levels and the clinical performance status (CPS) of the patients; and to see how important bone scan is by itself in determining the metastatic progression in the follow-up. Eighty-seven and 86% of scans demonstrated changes concordant with AP and CPS levels subsequently. It was also found that 100% of the progressions on bone scans along with elevated levels of AP had been confirmed as metastatic progression, whereas only 41% of progressions on bone scans solely had been shown to be metastases in the follow-up investigations. Findings on bone scans not in correlation with clinical findings and serum AP levels are mostly misleading. Use of bone scans in conjunction with serum AP levels and most probably with prostate-specific antigen and CPS is the most reliable and therefore treatment modality changes should not be based on bone scans only.