Are bone scans necessary in men with low prostate specific antigen levels following localized therapy?

The prostate specific antigen level at which to recommend a bone scan after treatment of early prostate cancer is controversial. We identified the incidence of bone metastases at varying prostate specific antigen levels in asymptomatic men following radical prostatectomy, radiation therapy and watchful waiting.

Data were obtained from the Early Prostate Cancer trial comparing placebo with bicalutamide in addition to standard care for localized prostate cancer. As part of the trial patients were required to have routine bone scans regardless of prostate specific antigen levels. The prostate specific antigen levels were divided into subgroups and the incidence of positive bone scans was calculated for each group.

The incidence of positive bone scans in patients treated with watchful waiting and given bicalutamide or placebo was low (0.7% to 3.2%) at prostate specific antigen levels less than 20 ng/ml. At greater than this level the sample sizes were smaller but there was a significant increase in the incidence of positive bone scans. In the groups treated with radiation therapy or radical prostatectomy, regardless of the addition of bicalutamide, the incidence of positive bone scans was low (0.2% to 1.4%) at prostate specific antigen levels less than 5 ng/ml. The sample sizes were smaller at prostate specific antigen levels greater than 5 ng/ml so the results are harder to interpret.

Bone scans can be confidently eliminated in the followup of patients with early prostate cancer after standard care of those with prostate specific antigen levels less than 5 ng/ml. This level can be increased to 20 ng/ml with caution in those patients treated with watchful waiting.