Can serum prostate-specific antigen replace bone scintigraphy in the follow-up of metastatic prostatic cancer?

Bone scintigraphy is the most sensitive imaging technique for the initial detection of bone metastases and is widely used in the staging of prostatic cancer. This study was performed to assess whether the development of further bone metastases can be detected by serial measurements of the serum glycoprotein prostate-specific antigen (PSA) as an alternative to follow-up scintigraphy. The bone scintigrams and PSA levels of 101 patients with metastatic prostate cancer entered into two therapeutic trials have been reviewed. Serial results of both investigations were available in 59 cases. In three cases new bone deposits were observed without a corresponding rise in PSA. In two other cases the scintigrams were considered to be suspicious of progression with no change in PSA levels; however, further follow-up indicated that these changes were not due to metastases. In 13 cases PSA levels were rising in advance of new deposits on the scintigrams. In the remaining 41 cases the PSA levels and scintigraphic findings paralleled each other. We conclude that serial estimation of PSA levels is a simpler marker for disease progression than bone scintigraphy in metastatic prostatic cancer, but that neither technique in isolation gives complete accuracy.