Bone scintigraphy and serum phosphatases in the detection and follow-up of bone metastases in prostatic cancer.

Bone scintigraphy, serum acid phosphatase activity (ACP), prostatic acid phosphatase by radioimmunoassay (PAP) and alkaline phosphatase activity (ALP) were studied in 117 consecutive patients with prostatic cancer. Serum PAP was more sensitive than ACP in indicating prostatic cancer in the 63 patients with normal bone scans: 28% had positive PAP tests and 15% positive ACP tests. In the 54 patients with bone metastases no difference in the frequency of positive PAP (84%) and ACP (85%) test was observed. Serum PAP and ACP, but not ALP, were useful for the assessment of the response to therapy particularly in patients without bone metastases. In the follow-up of patients with bone metastases the scan was more informative than any of the phosphatase assays studied.