Prognostic value of raised prostatic acid phosphatase and negative skeletal scintigraphy in prostatic cancer

Of 438 consecutive cases of newly diagnosed prostate cancer, 178 (41%) had skeletal metastases (T0-4 M1) at the time of diagnosis according to skeletal scintigraphy; 139 men had serum prostatic acid phosphatase (PAP) greater than twice the upper limit of normal on 2 separate occasions at the time of diagnosis and 65% of them had metastases on bone scan. However, 49 men with normal bone scans were found to have similarly raised serum PAP. (Such patients are defined as having skeletal metastases in the current Medical Research Council immediate versus deferred orchiectomy study and stratified accordingly). The actuarial survival of this group was calculated by life table methods and was compared with that of 2 other subgroups: those patients having metastases demonstrated on bone scan, and those patients having both normal bone scans and normal serum PAP. The survival of the "metastatic by acid phosphatase" group was significantly better than that of the "metastatic by bone scan" group but did not differ from that of patients having both normal scans and PAP. For patients with no scintigraphic evidence of skeletal metastases at diagnosis, those with a raised PAP were at a significantly greater risk of scan conversion, although this was more powerfully predicted by high histological grade.